mri of rectal cancer

Role Of MRI In Assessment Of Rectal
Neoplasms
AnEssay
Submitted for Fulfillment of the Master Degree in
Radio Diagnosis
By
Abd El-Fattah Reda El-Sayeh
M.B. B.Ch.
Under Supervision
Prof. Dr.Medhat Mohammed Refaat
Professor and Head Of Radio-Diagnosis
Faculty Of Medicine, Benha University
Dr. Islam Mahmoud Elshazly
Lecturer of Radio-Diagnosis
Faculty of Medicine, Benha University
2015

Acknowledgement
First and foremost, i would like to express my deepest gratitude
and thanks to Prof.Dr. Medhat Mohammed Refaat
professor &head of radiodiagnosis, Faculty of medicine, Bnha-
University, for his support, guidance and care; he is my very
special and dear professor.
Words could not express my great appreciation and respect to
Dr. Islam Mahmoud Elshazly lecturer of Radiodiagnosis,
Faculty of medicine, Bnha-University, for his assistance and
concern throughout this work, providing this thesis with his
scientificexperience and constructive supervision.
Last, but not least, I would like to express my appreciation and
thanks to my family for their understanding, patience and
encouragement.

List of tables
Table number and title Page No
Table (1) Illustration of modified duke's staging. 15
Table (2) Illustration of TNM staging. 17
Table (3) Comparison between TNM & Dukes staging systems. 18
Table (4)Illustration of T-stage of rectal cancer. 44
Table (5)Illustration of N-stage of rectal cancer. 65

List of Contents
Title page
Introduction and Aim of the Work 1
Anatomy of the Rectum 3
MRI Anatomy 10
Pathology of Rectal Cancer 14
Clinical review of rectal cancer……………………………..19
Imaging Modalities of Rectal Carcinoma …………………23
Techniques of MR Imaging 26
MR Imaging Manifestations of Rectal Cancer 41
Summary and Conclusion 84
References 86
Arabic Summary

List of abbreviations
CRC Colorectal Cancer
CRM Circumferential Resection Margin
CT Computed Tomography
FDG 18F-FluoroDeoxyGlucose
FOV Field Of View
HRT Hormone Replacement Therapy
IMV Inferior Mesenteric Vein
MRI Magnetic Resonant Imaging
MRF Mesorectal Fascia
PET/CT Positron Emission Tomography
TME Total Mesorectal Excision
TNM Tumor, lymph Nodes, distant Metastasis
TRUS Transrectal Ultrasound
US Ultrasound

List of figures
LIST OF FIGURES
1- Coronal illustration of rectum & anal canal anatomy. 3
2- Coronal illustration of arterial supply, venous & lymphatic drainage 6
of the rectum and anal canal.
3- Axial T2-weighted sequence shows normal rectal wall anatomy 10
4- Axial T2 weighted image shows Rectum is surrounded by 11
mesorectal fat within the mesorectal fascia.
5- Coronal turbo spin-echo T2-weighted MR image shows the normal 12
anatomy of the rectum
6- Normal anatomy of the mesorectum 13
7- Diagrammatic illustration of T stage 16
8- Coronal illustration of the rectum with a tumor extending through 22
the rectal wall into the mesorectal fat and with some lymph nodes.
9- Transverse plane of endorectal US exam of rectal 23
carcinomashowing a mass lesion and LN deposit
10- Oblique coronal CT reformatted image perpendicular to the tumor 24
axis shows mesorectal fasciaspeculations extending into the peri-
rectal fat
11- Axial and sagittal fused PET/CT images of the pelvis showed 25
increased FDG uptake of recurrent rectal carcinoma after resection
& chemoradiotherapy
12- Axial T1-weighted image of pelvis at level of sacro-coccygeal 28
junction in patients with (a) and without (b) administered rectal gas.
Measurements from rectal wall to mesorectal fascia are
demonstrated

List of figures
13- Rectal adenocarcinoma. Sagittal turbo spin-echo T2-weighted MR 29
image obtained with a high-resolution phased-array surface coil shows
a stenosing lesion (arrow) of the rectal lumen (*). This lesion is outside
the potential field of view of endorectal US and endorectal coil MR
imaging
14- (a,b) (a) Endorectal coil. (b) T2 weighted image using the 31
endorectal coil. The bowel wall layers are shown but there is
insufficient detail from the surrounding mesorectum to adequately
stage rectal tumors
15- The sagittal T2 weighted scans are used to plan thin-section axial 32
oblique scans. It is important to ensure the scans are obtained in a
plane orthogonal to the tumour to prevent over-estimation of tumour
spread
16- For tumours arising below the origin of the levator muscle, scans are 33
obtained in a coronal or paracoronal plane as shown
17- Scan planes used for assessing mesorectal lymph nodes. The 33
mesorectum can be assessed for lymph nodes by planning a block of
coronal slices that run parallel to the sacrum
18- Overview of the applied sequences on a whole-body magnetic 36
resonance protocol for a 32-receiver channel scanner (Magnetom
Avanto; Siemens Medical Solutions, Erlangen, Germany). Total
scan time is 55minutes
19- Poor coil positioning. The images shown (top left and right) have 37
been obtained with the lower edge of the pelvic coil placed at the
level of the symphysis pubis. Consequently there is poor signal to
noise ratio from the lower rectum and anal sphincter region.
Repositioning the coil restores adequate signal to noise ratio
20- It is important to centre the coil correctly to the whole rectum. Thus 37
the lower edge of the coil needs to be placed so that it lies at least
10cm below the symphysis pubis in order to ensure adequate signal
is obtained from the lower rectum and anorectal junction. The

List of figures
uppermost limit for coil placement is the sacral promontory
21- 38
A T1 weighted image has been obtained with a high spatial
resolution but the bowel wall layers cannot be distinguished
22- 39
T1 fat saturated image with contrast enhancement. The bright fat
signal intensity from perirectal fat (asterisk) has been suppressed
and is of low signal intensity, there is florid enhancement of the
entire bowel wall (arrow) and perirectal vessels (arrowheads) which
would not be readily distinguishable from tumor if it were present
23- 40
Motion artifact. (a) This characteristically produces a series of bands
that degrade the image. (b)This can often be overcome by ensuring
the patient is not in discomfort, by repositioning the patient and
ensuring adequate abdominal compression and repeating the
sequence again after swapping phase and frequency directions
24-
Sagittal turbo spin-echo T2-weighted MR image obtained with a 41
high-resolution phased-array surface coil shows a stenosing lesion
(arrow) of the rectal lumen
25- Rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image 41
shows a stage T1 tumor (*) of the rectum
26- High-resolution T2-weighted image demonstrating a T1 polypoid 43
carcinoma (arrow). There is partial preservation of the submucosal
layer (short arrow) seen as a thin rim of high signal intensity deep
into the tumor. The tumor does not extend into the muscularis
propria layer
27- Axial T2-weighted FSE MR image demonstrating a semiannular 44
plaque of tumor with central ulceration (arrowhead) and raised

List of figures
rolled edges (arrows)
28- Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted 45
MR image shows a huge pedunculated tumor (T) on the left lateral
rectal wall.
29- Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted 46
MR image shows the tumor (T) invading the rectal wall without
infiltrating the perirectal fat (arrow)
30- Stage T1 rectal carcinoma.Axial turbo spin-echo T2-weighted 46
MR image shows a polypoid tumor (T) on the right lateral aspect
of the rectal wall protruding into the rectal lumen.
31- Stage T2 rectal carcinoma. Coronal T2-weighted MR image shows 47
a stenosing neoplastic lesion
32- Stage T2 rectal carcinoma. Unenhanced T2-weighted fast spin- 47
echo image shows mesorectal fascia (arrowheads) as fine linear
hypointense structure enveloping mesorectum.
33- Stage T3 rectal cancer .Transverse contrast material-enhanced T1- 48
weighted turbo spin-echo MR image shows rectal tumor (black
arrow) with transmural stranding (arrowheads) in mesorectal fat.
Mesorectal fascia (white arrows) is clearly depicted
34- T2-w image of a stage T3 rectal tumor ) (a) Axial high-resolution 49
T2-w image showing a tumor with a pushing edge. . (b) Axial T2-
w FSE image showing nodular extension with ill-defined margins.
The tumor is spreading into the perirectal fat at its leading edge
35- Drawing illustrates the relationship between the CRM and rectal 50

List of figures
tumors of various stages
36- CRM is safe if distance of tumor to mesorectal fascia is >6mm 51
37- Transverse T2-w image of the distance of tumor to mesorectal fascia 52
38- .Stage T3 tumor with involvement of the mesorectal fascia. 53
39- Extramural vein invasion 54
40- AxialT2-w image of tumor extending into an extramural vein 54
41- Stage T4 tumor. Axial turbo spin-echoT2-weighted MR image 55
shows a neoplastic rectal lesion (arrow) disrupting the mesorectal
fascia.
42- (a) Paraxial T2-weighted FSE sequence and (b) sagittal T2-weighted 55
FSE sequence of a T4 cancer located in the upper third of the rectum
invading the uterus (arrows)
43- Sagittal T2-w turbo spin-echo MR image in same patient clearly shows 56
that tumor originates from the rectum (black arrows).
44- (a): Transverse gadolinium-enhanced T1-w image of tumor with 57
enhancing spiculations
(b):Transverse gadolinium-enhanced T1-w image in a patient with
enhancing spiculations
(c)Coronal T2-w FSE image of rectal tumor with pattern nodular
infiltration
45- Transverse T2-w image of bulky rectal tumor causing mass effect 58
46- Coronal FSE T2-w image of a tumor of the rectal ampulla infiltrating 59
the sphincteral plane
47- Staget 3 rectal mucinous adenocarcinoma. Transverse T2-weighted 60
turbo spin-echo MR images show hyperintense rectal tumor
(arrowheads) extending to mesorectal excision plane on anterior and

List of figures
left lateral sides (arrow
48- Axial T2-w FSE MR image demonstrating a mucinous tumor 60
characterized by very high signal intensity
49- (a): Axial FSE T2-w image of a mucinous tumor(b): Axial T1-w 61
image (c): Coronal T2-w image
50- (a):Sagittal FSE T2-w image of a false-positive diagnosis of 63
mucinous carcinoma
(b):Coronal FSE T2-w image
51- Axial T2-w image shows lymph node in the region of the middle 64
rectal artery
52- Axial T2-weighted FSE sequence. Inguinal lymph node metastases 64
(arrows) in a patient with low rectal cancer
53- Rectal adenocarcinoma with metastatic lymphadenopathy. Coronal 66
turbo spin-echo T2-weighted MR image demonstrates a rectal
tumor (*) and two enlarged lymph nodes within the mesorectal fat
(arrowhead)
54- False-negative diagnosis of a regional LN 66
55- (a): T2-w FSE transverse MR image through the upper portion of 67
the rectum. A node with an irregular border(b): T2-w FSE transverse
MR image through the middle portion of the rectum. A high-signal-
intensity node with smooth borders
56- Identification of lymph nodes at transverse T2-weighted MR 68
imaging. Axial image shows two intermediate-signal-intensity
lymph nodes
57- Rectal cancer with involved lateral node outside mesorectum. 69
Transverse T2-weighted turbo spin-echo MR image shows enlarged,
round, hyperintense lymph node (arrowheads) in left hypogastric
........................... region in, suggestive of a metastatic node.
58- T2-w FSE transverse MR image shows a node of mixed signal 69

List of figures
intensity with a low-signal intensity rim (arrow head). A focus of
low signal intensity (arrow) is demonstrated within the
predominantly intermediate-signal intensity node
59- (a)Coronal T1 image of the liver in a patient under consideration for 73
metastectomy showing typical hypointense hepatic metastasis
(arrow). (b)Axial T1-w image. (c)Axial T2-w image,
60- (a)T1-w transverse scan with fat suppression. The hepatic 74
metastasis at segment V is hypointense (arrow).
(b)Post-contrast transverse scan at arterial phase shows a
hyperintense ring-like enhancement of the lesion (arrow), which is
centrally hypovascular.
(c)Post-contrast transverse scan at portal venous phase illustrates
washout of the peripheral enhancement of the metastasis
61- (a) Axial T2WI showed slight focal thickening of rectal 75
wall(b)Axial DWI of the same plane demonstrated focal
hyperintense area
62- Sagittal fast spin-echo T2-w image of a T3 rectal cancer (b): 76
Sagittal diffusion-weighted image (c): Fused image superimposing
sagittal T2-w image and color-coded map
63- (a):Sagittal T2-w FSE MR images obtained before administration of 81
chemoradiotherapy to tumor with small volume(b): Sagittal T2-w
FSE MR image obtained after administration of chemoradiotherapy
to tumor
64- (a):: Prechemoradiation image of rectal tumor with invasio MRF and 83
left Seminal vesicle
(b): Postchemoradiation image

INTRODUCTION
Introduction
Colorectal cancer is the third most common cancer worldwide. Around
30-40% of colorectal cancers are located in the rectum, accounting for
5% of malignant tumors, and ranking as the fifth most common cancer in
adults. Murray T.et al. (2005).
Rectal cancer is defined as a tumor whose distal margin measured with
the rigid rectoscope is 16 cm or less from the anocutaneous line.
The prognosis of rectal cancer is influenced by several factors, such as
local tumor extent, involved lymph nodes, and the presence of distant
metastases. Among these, the presence and extent of extramural tumor
spread influence both long-term survival and the risk of local recurrence.
With the more widespread acceptance of neoadjuvant concepts, there is
an increasing need for preoperative imaging methods to aid adequate
management because treatment strategies need to be individualized
according to the depth of tumor invasion and the status of the regional
lymph nodes, while previously patients were considered for surgery
without undergoing preoperative cross-sectional pelvic imaging. Accurate
preoperative assessment is an important first step in assigning patients to
one of the available treatment strategies.Jemal A.et al. (2005).
1

INTRODUCTION
Aim of the work
The aim is to detect the role of MRI in diagnosis and staging of
rectal neoplasms preoperative&postoperatively
2

Anatomy of the Rectum
SURGICALANATOMY
The rectum is the part of the gastrointestinal tract extending from the upper end of
the anal canal to the rectosigmoid junction.Iafrate F. and Laghi A. (2006).
Both proximal and distal limits of the rectum are controversial: the rectosigmoid
junction is considered to be at the level of the third sacral vertebra by anatomists
but at the sacral promontory by surgeons, and likewise, the distal limit is regarded
to be the muscular anorectal ring by surgeons and the dentate line by anatomists.
Herold A. et al. (2008), Beck D.E. and Roberts P. L. (2009).
Fig (1)Coronal illustration of the rectum & anal canal anatomy.Max Lahaye.et al.(2010).
Recognition of the lower limits of the rectum is important because determining the
distance between a neoplastic lesion and the levator ani muscle is vital to surgical
planning. The lower end of the rectum is characterized by the insertion of the
levator ani muscle onto the rectal muscular layer. The rectum forms an acute
anorectal angle with the anal canal as it is pulled forwards by the sling formed by
3

the puborectalis muscle forming a U -shaped sling.Iafrate F. and Laghi A.
(2006),Salerno G.et al. (2006).
The rectum measures approximately 12-15 cm in length. Anatomically, the rectum
can be divided in to three segments: the lower third, the middle third, and the upper
third. These segments correspond (measuring from the anal verge) to the first 7-
10cm, the next 4-5cm, and the last 4-5cm.Klessen C.et al. (2007).
The lower third of the rectum can be considered on anatomical and imaging
features as the area of rectum and mesorectum below the origin of the levator ani
where the mesorectum tapers sharply.Salerno G. et al. (2006).
The rectum has three lateral curves: the upper and lower are convex to the right
and the middle is convex to the left. These curves correspond intraluminally to the
folds or valves of Houston. The two left-sided folds are usually noted at 7-8 cm
and at 12-13 cm, respectively, and the one on the right is generally at 9-11 cm.
The middle valve is the most consistent in presence and location and corresponds
to the level of the anterior peritoneal reflection, they can vary in number or even be
absent.Alvin C. S.et al. (2006), Beck D.E. and Roberts P. L. (2009).
The rectum is characterized by its wide, easily distensible lumen, and the absence
of taeniae, epiploic appendices, haustra, or a well-defined
mesentery.Beck D.E. and Roberts P. L. (2009).
Mesorectum & mesorectal fascia
The mesorectal fascia (fascia propria of the rectum) is a connective tissue sheath
that encloses the rectum and the perirectal tissue (mesorectum), including lymph
nodes and lymphatic vessels down to the pelvic floor and acts as a natural barrier
for tumor spread.Klessen C.et al. (2007).
4

Peritoneal coverings
The upper third of the rectum is anteriorly and laterally invested by peritoneum,
the middle third is covered by peritoneum on its anterior aspect only, while the
lower third of the rectum is entirely extraperitoneal.Beck D.E. and Roberts P. L.
(2009).
Anal canal
The anatomical anal canal extends from the perineal skin to the linea dentata.
Surgically, the anal canal extends from the perineal skin to the anorectal ring; this
is the circular upper border of the puborectal muscle and lies approximately 1-1.5
cm above the linea dentata.Tonino S. and Smithuis R. (2009).
Prediction of sphincter involvement is important in choosing the appropriate
treatment. The anal sphincter is comprised of three layers
1. Internal sphincter: continuance of the circular smooth muscle of the rectum. At
the level of the top of the anal sphincter, fibers from the puborectalis sling join
those of the outer muscle coat and together these form the conjoint longitudinal
coat, which forms a thin muscular layer between the internal anal sphincter and the
external anal sphincter.
2. Intersphincteric space.
3. External sphincter: voluntary striated muscle, divided in three layers that
function as one unit. These three layers are continuous cranially with the
puborectal muscle and levator ani.Tonino S. and Smithuis R. (2009),Salerno G.et
al. (2006).
5

Blood supply of the rectum
• The superior rectal artery: Terminal branch from the inferior mesenteric artery.
Contributing more than 80% to the rectal blood supply.HeroldA .et al. (2008).
• The middle rectal arteries: Arises from the internal iliac arteries. They are
inconstant and bilaterally present in only 10 %.
• The inferior rectal artery: Arises from the internal pudendal arteries Herold A.et
al. (2008). Skandalakis L.J.et al. (2009).
Fig (2) Coronal illustration of arterial supply, venous & lymphatic drainage of the rectum and
anal canal McGraw-Hill.(1983)
Venous Drainage of the Rectum
• The superior rectal veins; which enter the inferior mesenteric veins (IMV) and
drain into the portal system.
6

• The middle rectal veins,
• Inferior rectal veins; both enter the internal iliac vein and thus drain into the
systemic circulationSkandalakis L.J.et al. (2009).
This helps explain the two distinct hematogenous metastatic patterns of rectal
cancer. In the absence of liver metastases, rectal cancer can manifest with lung
metastases when a distal tumor is drained by the systemic venous system and the
inferior vena cava to the pulmonary capillary bed. However, liver metastases are
more commonly formed by way of the IMV and portal venous system or by means
of endolymphatic spread along the course of the IMV, which is the usual pathway
for the rest of the gastrointestinal tract.Alvin C. S.et al. (2006).
Lymphatic Drainage of the Rectum
Similar to the blood supply the main lymphatic drainage of the rectum is achieved
by intramural lymphatic vessels passing initially to mesorectallymph nodes, which
shows:
Upward spread along the ascending branch of the inferior mesenteric vein to
inferior mesenteric lymph nodes.
Lateral lymphatic drainage along the middle rectal artery into the internal
iliac lymph nodes.
Low rectum and anal canal shows downward spread to the perineum and
inguinal lymph nodes.Herold A.et al. (2008).
Pelvic tumors usually metastasize first to regional lymph nodes, which are specific
groups of nodes for each tumor, and are classified as N-stage disease. If tumor
spreads to a lymph node outside the defined regional nodes, this is considered M-
7

stage disease. Para-aortic nodes and Inguinal nodes are non-regional, and spread to
these nodes constitutes M1 (stage IV) disease.McMahon J.C.et al. (2010).
Nerve Supply of the Rectum
The rectum and upper anal canal are supplied by autonomic nerves, theautonomic
nerves are at risk during rectal resection, and the lower anal canaland the anus
receive a somatic input via the pudendal nerves.HeroldA.etal.(2008
8

MRI ANATOMY
MRI anatomy
Therectal wall consists of three different layers thatcan be recognized at MR
imaging. T2-weighted MR imaging sequences are the mostsuitable for depicting
the rectal wall anatomy.
MR imaging can help distinguish an inner hyperintenselayer, which represents the
mucosa andsubmucosa(no differentiation is possible betweenthese two
components); an intermediate hypointense layer, which represents the muscularis
propria;and an outer hyperintense layer, which representsthe perirectal fat tissue.
Fig (3)Axial T2-weighted sequence shows normal rectal wall anatomy. Innermost
hypointense layer: mucosa(arrow). Middle, hyperintense layer: submucosa(small
arrow). Outer hypointense layer: circular and longitudinal muscle (arrowhead). Winter
L.et al. (2007)
10

MRI ANATOMY
The mesorectal fascia can also be identified as a thin, low-signal intensitystructure
that envelops the mesorectumand the surrounding perirectal fat. The
mesorectalfascia is clearly visible on the posterolateralview, although it is difficult
to differentiate thisentity from the Denonvillier fascia in the anterior wall.
Fig (4)Axial T2 weighted image shows: Rectum is surrounded by mesorectal fat within
the mesorectal fascia (red arrows). P: prostate and V: seminal vesicles. On MRI the
mesorectal fat has high signal intensity on T1- and T2-weighted images. The mesorectal
fat is bounded by the mesorectal fascia, which is seen as a fine line of low signal intensity
(red arrows).Max Lahaye.et al. (2010).
The anal canal is also visualized during MRimaging of the lower rectum. Even if
the spatialresolution is low compared with endoanal coil imaging all of the major
anatomic structures(Levator ani muscle, puborectal muscle, internaland external
11

MRI ANATOMY
anal sphincters, anal canal) can easilybe evaluated with a phased-array surface
coil.FrancoIafrate. et al. (2006)
Fig (5)Coronal turbo spin-echo T2-weighted MR image shows the normal anatomy of the
rectum. The white line indicates the lower limit of the rectum at the insertion of the levator ani
muscle (arrows) on the rectal wall. The levator ani muscle forms the ceiling of the ischiorectal
fossa. Franco Iafrate. et al. (2006)
Indeed, phased-array surface coil MR imaging allows optimal visualization of the
analsphincter complex. The anal canal is seen as a cylindric structure that extends
from the insertion of the levator ani muscle onto the rectum to theexternal anal
margin. The most important componentof the anal sphincter complex is the
puborectalmuscle. This muscle inserts into the funnel shapedlevator ani muscle,
which in turn anchors the sphincter complex to the internal portion of the
pelvis.Franco Iafrate. et al. (2006).
12

MRI ANATOMY
Fig (6)Normal anatomy of the mesorectum (A) Axial turbo spin-echo T2- weighted MR image
shows the mesorectal fascia as a thin, hypointense layer(white arrowheads) surrounding
hyperintense mesorectal fat. On the anterior aspect, the mesorectal fascia appears more thickened
and is difficult to differentiate from the Denonvillier fascia (black arrowheads).
(B) Photograph of a section of the explanted rectum shows perirectal fat surrounded by the
mesorectal fascia.
(C) Coronal turbo spin-echo T2-weighted MR image obtained with a phased-array surface coil
shows a normal anal sphincter complex. The levator ani muscle (straight arrows) appears as a
funnel-shaped muscular layer that extends from the obturator ani muscle to the anal canal. The
puborectalis muscle (arrowheads) is depicted at the insertion of the levator ani muscle onto the
anal canal. The external (curved arrows) and internal (*) sphincter muscles are also seen .Franco
Iafrate. et al. (2006).
13

Pathology
Macroscopic picture
Non-exophytic (ulcerated) tumors tend to be more locally advanced. Exophytic
(polypoidal) tumors: have a pronounced protuberant appearance with the tumor mass
projecting into the lumen. A number of studies have observed that such polypoidal
lesions are often of a relativelylow-grade malignancy.
Morphology was not shown to be an independent predictor of outcome aftertumor
excision.McCourt M. et al. (2009), Martling A.et al. (2003).
Microscopic picture
(A)Epithelial tumors:
1- Adenocarcinoma
2-Other types:
Mucinous adenocarcinoma, signet ring adenocarcinoma, squamous cell carcinoma,
adenosquamous carcinoma, undifferentiated carcinoma, unclassified carcinoma,
Carcinoid tumors
(B)Nonepithelial tumors:
Leiomyosarcomas, hematopoietic and lymphoid neoplasms
Adenocarcinomas account for the vast majority (98%) of rectal cancer.
Other rectal tumors are relatively rare and include carcinoid tumors
(0.1%)lymphoma (1.3%), and gastrointestinal stromal tumors (1%).Iafrate F.et al.
(2006).
14

Pathology
Colloid or mucinous adenocarcinomas are defined by the large amountsof
extracellular mucin retained within the tumor (The amount of mucinrequired to
warrant a diagnosis of mucinous carcinoma, as set by the World
Health Organization, is at least ≥ 50% of the mucin pool occupying thetumor
mass).They have been associated with a higher incidence of lymph node metastases
and poorer prognosis and that they are also poor candidatesfor local excision even if
confined to the muscularis propria. The productionof mucus under pressure allows
the cancers to separate tissue planes in thebowelwall and thus to more frequently
gain access to the peritoneal cavity. In addition, the fluid produced by these tumors
is taken up by lymphaticswhich helps propel the tumor into the regional lymph
nodes.McCourt M. et al. (2009),Kim M-J.et al. (2003).
Staging
Staging is the method of summarizing the anatomical extent of a malignant tumor,
thereby communicating information regarding prognosis.Smith N. and Brown G.
(2008).
Stage classifications
I. Dukes Classification
This system divided tumor classification into 3 stages, as follows
Table
(1)illustration of modified duke's staging. Aspinall and Taylor-Robinson,(2001)
15

Pathology
฀ Dukes A: Tumor limited to the rectal wall
฀ Dukes B: Tumor extended through the rectal wall into extra-rectal tissues
฀ Dukes C: Metastases to regional lymph nodes.Hassan I. (2009).
This system was modified by others to include subdivisions of stages B and C, as
follows
฀ Stage B was divided into
B1; tumor penetration into muscularis propria
B2; tumor penetration through muscularis propria
฀ Stage C was divided into
C1; tumor limited to the rectal wall with nodal involvement
C2; tumor penetrating through the rectal wall with nodal involvement
฀ Stage D was added to indicate distant metastases.Hassan I. (2009).
Fig (7) Diagrammatic illustration of T stage.Cancer Research UK (2003)
16

Pathology
II. TNM classification:
Primary tumor (T)
TX: Primary tumor cannot be assessed
T0: No evidence of primary tumor
Tis: Carcinoma in situ: intraepithelial or invasion of the lamina propria.
T1: Tumor invades submucosa.
T2: Tumor invades muscularis propria.
T3: Tumor invades through the muscularis propria into the subserosa, or into the
nonperitonealized perirectal tissues
T4: Tumor directly invades other organs, structures or the visceral Peritoneum.
Table (2) illustration of TNM staging.Alamo City Cancer Council (2001).
17

Pathology
Regional lymph nodes (N)
NX: Regional nodes cannot be assessed
N0: No regional lymph node metastasis
N1: Metastasis in 1-3 regional lymph nodes
N2: Metastasis in 4 or more regional lymph nodes
Distant metastasis (M)
MX: Presence of distant metastasis cannot be assessed
M0: No distant metastasis
M1: Distant metastasis
Table (3) Comparison between TNM & Dukes staging systems.Zampino M.et al. (2009)

CLINICAL REVIEW
Incidence:
Colorectal cancer (CRC) is the third most common cancer in both sexes
combined worldwide, after prostate and breast cancer. Around 30% of all
CRCs are diagnosed in the rectal anatomic site (accounting for 5% of
malignant tumors, and ranks as the fifth most common cancer in
adults).Valentini V. et al. (2008).
Rectal cancer is more prevalent in the elderly population with a greater than
10-fold increase in the incidence beyond 65 years old. A decreasing trend in
the age incidence has been observed in the last decade, with a higher
incidence among males. Valentini V.,et al. (2008).Kirke R.,et al. (2007).Koo
B.C.,et al. (2006).
Risk factors:
The key risk factors identified for rectal cancer are:
1. Dietary components (e.g. meat, fat, and selenium), obesity, alcohol, some
medical therapies like Non-Steroidal Anti-inflammatory drugs(NSAIDs),
Hormone Replacement Therapy(HRT), statins and oralcontraceptives,
medical conditions (inflammatory bowel diseases, diabetes).Valentini V. et
al. (2008).Herold A.et al. (2008).
2. Genetic factors: Individuals with a first degree relative with colorectal
cancer have approximately a twofold risk of developing colorectal cancer.
Familial adenomatous polyposis, hereditary non-polyposisare at increased
risk of developing rectal cancer.Valentini V. et al. (2008).Herold A.et al.
(2008).
19

CLINICAL REVIEW
3. Synchronous lesions: Approximately 5% of colorectal cancers demonstrate
multiple lesions at diagnosis. In 35% of patients diagnosed with a primary
colorectal carcinoma, an adenomatous polyp is present elsewhere in the
colon or rectum. Second tumors are likely to be overlooked.Valentini V. et
al. (2008), HassanI. (2009).
4. Irradiation: Patients with Previous irradiation to the pelvis is known to
increase the incidence of rectal cancer.Valentini V. et al. (2008).Herold A.et
al. (2008).
5. Precancerous lesions:
Most rectal cancers are thought to primarily develop from
adenomatous polyps over a period of 10-15 years, known as the
adenoma-carcinoma sequence. The incidence of polyps increases with
age and the risk of malignant transformation of a polyp markedly
increases with its diameter.
The rate of malignant transformation is about 1% for polyps less than
1 cm in diameter, but 10% for larger ones.Klessen C.et al(2007).
Prognosis:
•Despite advances in the diagnosis and treatment of rectal cancer, five-year
survival rates continue to hover around the 50% mark. For cancers limited to the
bowel wall, the survival rate climbs to 83%-90%, and drops to less than 10% if
there are distant metastases, highlighting the importance of early detection and
treatment.Jemal A. et al. (2005),Alvin C. S.et al. (2006).
•The prognosis of rectal cancer is directly related to a number of factors:
1. Depth of tumor invasion (local tumor extent) (T stage).Wieder H.A.et al. (2007).
2. Tumor involvement in the circumferential resection margin (CRM).
20

CLINICAL REVIEW
The presence of a positive CRM has been shown to correlate with an increasing
incidence of local recurrence, systemic failure and poor survival.Burton S. et al
(2006).
3. Extramural venous invasion. It has been shown to be an independent poor
prognostic factor in colorectal cancer.Burton S. et al (2006).
4. The number of metastatic lymph nodes (N stage).Wieder H.A.et al. (2007).
5. Distant metastases (M stage).Kim C.K., et al. (2007).
6. Higher grade and mucinous adenocarcinomas show worse prognosis,
specifically with signet ring histology.Lahaye M.J.et al. (2005).
Clinical picture:
• The most common presenting symptoms in rectal cancer are altered bowel habit,
tenesmus (a feeling of incomplete evacuation) together with mucus discharge and
fresh rectal bleeding.
Rarely complete rectal cancer may present with large bowel obstruction or profuse
rectal bleeding.Herold A. et al. (2008).
• The differential diagnosis of rectal cancer includes almost all common
proctological conditions, particularly haemorrhoids, anal fissure, solitary rectal
ulcer, benign polyps, rectal prolapse and inflammatory bowel disease. In addition it
is important to distinguish carcinoma of the anal canal. Herold A. et al. (2008).
Treatment:
Traditionally rectal cancer surgery consisted of excision of the tumor
with amargin of surrounding perirectal fat
21

CLINICAL REVIEW
This however resulted in high local recurrence rates up to 40%.
In 1982 the surgeon Richard John Heald introduced the total mesorectal excision.
After many years TME was widely accepted, which caused a drop in local
recurrence rates from 40% to 11%.Max Lahaye.et al. 2010.
Total mesorectal excision
Total mesorectal excision (TME) is the best surgical treatment for rectal cancer
provided that the resection margin is free of tumor. In TME the entire mesorectal
compartment including the rectum, surrounding mesorectal fat, perirectal lymph
nodes and its envelope, i.e. the mesorectal fascia is completely removed. This
minimizesthe chance of tumor remnants in the surgical bed.
Fig (8) Coronal illustration of the rectum with a tumor extending through the rectal wall into the
mesorectal fat and with some lymph nodes, mesorectal fascia is not involved TME can be
performed Notice the anal verge (blue arrow).Max Lahaye.et al. (2010
22

IMAGING MODALITIES
Endorectal ultrasound
Fig (9) Transverse plane of endorectal US exam of rectal carcinoma showing a mass lesion
(measured) and LN deposit (labeled). Kasr el-ainy hospital- general surgery department (2013).
• Endorectal or transrectal ultrasonography (TRUS) has a major role in rectal
cancer with up to 95% accuracy for determining trans-mural penetration and up to
74% accuracy for determining perirectal node status. TRUS is very accurate for
staging of superficial rectal tumors but is not useful for staging advanced rectal
cancer.Zampino M.et al. (2009), Beets-Tan R.G.H. and Beets G.L. (2004).
• In the imaging work up of patients with rectal metastases, abdominalUS is highly
efficient in helping to distinguish between two groups of patients with liver
metastases: the group of patients with diffuse metastases who are no longer eligible
for curative treatment and the group with no metastases or a very limited number
of them. The patientsin the latter group require CT, MR imaging, or FDG PET for
the selectionof appropriate therapeutic approaches.Bipat S. et al. (2005).
23

IMAGING MODALITIES
Computed tomography (CT)
• The advances in CT technology such as multiplanar reformatting have raised
interest for the potential role of CT for the detection and staging of rectal cancer.
However, MRI is the most reliable technique to determine the local staging of
rectal cancer because of inherently high soft tissue contrast resolution in MRI.
While CT is still primarily used for detection of metastatic disease.Kim C.K. et al.
(2007).
Fig (10) Oblique coronal CT reformatted image perpendicular to the tumor axis shows
mesorectal fascia (Arrow-heads( speculations extending into the peri-rectal fat (arrows) indicates
stage T3 disease. Sinha R.et al.(2006).
Perfusion CT can have a role in staging and restaging of patients after
chemoradiotherapy. CT colonography is a potential alternative to conventional
colonoscopy for colorectal cancer screening and can be performed after incomplete
colonoscopy to assess for synchronous lesions and metastases.Zampino M.et al
(2009).
24

IMAGING MODALITIES
Positron emission tomography (PET) and PET/CT
Fig (11) axial and sagittal fused PET/CT images of the pelvis showed increased FDG uptake of
recurrent rectal carcinoma after resection & chemoradiotherapy. M.Fouad Alpha scan radiology
center (2013).
• FDG-PET (18F-fluorodeoxyglucose positron emission tomography) and
FDG-PET/CT has mainly been used for M-staging of rectal cancer to assess
hepatic metastatic disease. Bipat S.et al. (2005).
Current Uses:
Detection of residual/recurrent disease.
Staging of rectal cancer using PET/CT colonoscopy.
Radiotherapy planning; by the detection of occult nodal or distantmetastases,
change in radiation dose or intention of treatment, anda change in tumor target
volume delineation.
Predicting response to neoadjuvant chemoradiation
25

IMAGING MODALITIES
Future uses:
Markers for response assessment to targeted therapies.Valentini V. et al.
(2008).
Magnetic resonance (MR) imaging
MR imaging of the rectum may be performed with either an endorectal coil
or a phased-array surface coil. In terms of patient preparation, pulse sequences, and
plane acquisition, the imaging protocols are identical (Iafrate et al., 2006).
Patient preparation
No special patient preparation is required.
Few papers report rectal cleansing 2 hours before the MRI examination with
rectal suppositories.( Chun et al.,2006).
A full bladder is unnecessary and is uncomfortable with the compression from
the body coil.( Klessen et al.,2007).
Premedication
A spasmolytic agent (e.g.butylscopolamine at a dose of 20-40 mg) to
prevent artifacts caused by peristalsis of the small intestine and to distend the
sigmoid and rectum. The agent has a short half-life and is therefore injected
intramuscularly immediately before MRI(Brown et al.,2005).
Another opinion is that small bowel movement is not a problem and
therefore antiperistaltic agents are not indicated(Klessen et al.,2007).
26

IMAGING MODALITIES
Contrast medium
IV contrast medium: Current data in the literature suggests that IV contrast
medium administration does not improve staging of rectal tumors by MRI.
Overstaging as a result of desmoplastic tumor reaction still occurs, and
identification of the individual rectal wall layers, particularly the submucosal layer,
can still be difficult after contrast enhancement. The gadolinium-enhanced MR
sequences can therefore be omitted, thus saving acquisition time and examination
costs and avoiding potential allergic reactions(Vliegen et al.,2005).
Enteral contrast medium: Some authors recommended administration of a
positive or negative (e.g. warm water administered with a balloon-tipped rectal
tube about 150-400 ml) enteral contrast medium, to aid visualization of the primary
tumor, with the intention of improving local T staging(Klessen et al.,2007).
However, this seems not to be necessary as suggested by current data in the
literature; it is increasingly recognized that local T stage may be less informative in
terms of preoperative management than the distance between the tumor and the
mesorectal fascia. In particular, T3 tumors, although penetrating through the rectal
wall by definition, may variously be several millimeters away from the mesorectal
fascia or involve it directly, with the result that preoperative treatment is variable
despite identical T staging. Also, T2 tumors located at the anorectal junction come
very close to the resection margin despite not penetrating the bowel wall (Slater et
al.,2006).
In this point of view any procedure that impairs accurate measurement of the
distance between the tumor and the mesorectal fascia should be avoided as rectal
overdistension significantly reduces the distance between the rectal wall and the
mesorectal fascia (fig.32), this effect would be more pronounced to anterior rectal
27

IMAGING MODALITIES
cancer, presumably because there is a greater depth of tissue anterior to the
presacral fascia(Kim et al.,2004).
Figure (12):(a,b) Axial T1-weighted image of pelvis at level of sacro-coccygeal junction in patients with
(a) and without (b) administered rectal gas. Measurements from rectal wall to mesorectal fascia are
demonstrated(Slater et al.,2006).
Patient position
The patient is positioned comfortably on the back.
Phased-array surface coil is placed on the pelvis in such a way that the lower
edge of the coil comes to lie well below the pubic bone(Klessen et al.,).
Hardware
Magnet
A 1.0 T/1.5 T system can be used. The main consequence of using a 1.0
T/1.5 T magnet is the longer image acquisition times. Using 1.5 T magnet, the total
examination time required for good image resolution is about 45-65 minutes, this
problem can be overcome with a 3 T MRI system because the increase in signal-to-
noise ratio (SNR) at 3 T can decrease the number of signals averaged, so the
examination time is quite a bit shorter ranging from 19 to 22 minutes. In addition,
28

IMAGING MODALITIES
the higher SNR can improve spatial resolution and allow acquisition of thinner
sections. However, SNR is not solely determined by magnetic field strength, thus
optimization of the imaging parameters and improvement of phased-array
radiofrequency coils are important for maximal SNR in body imaging(Chun et
al.,2006). (Brown et al.,2005).
Coil choice :
Conventional external body coils are unable to provide adequate bowel wall
assessment, having similar overall accuracies to CT (Brown et al.,2005).
Phased array coils :
Rectal MR imaging with a phased-array surface coil yields high-spatial-
resolutionimages, thereby providing a full evaluation of the rectal wall layers, and
has the additional advantage of a large field of view. Moreover, the use of a
phased-array surface coil improves patient comfort compared with the use of an
endorectal coil.Finally, stenosing lesions and tumors at the rectosigmoid junction
can be evaluated in all cases, and the mesorectal fat and mesorectal fascia can be
visualized (Figure 33) (Laghi et al., 2002).
29

IMAGING MODALITIES
Figure (13): Rectal adenocarcinoma. Sagittal turbo spin-echo T2-weighted MR image obtained with a high-
resolution phased-array surface coil shows a stenosing lesion (arrow) of the rectal lumen (*). This lesion is
outside the potential field of view of endorectal US and endorectal coil MR imaging (Laghi et al., 2002).
Endorectal coils:
Surface coils, such as the endorectal coil (fig.34), are designed to maximize
signal return from the small area being imaged. These coils comprise an oval
receive only loop coil mounted on the inner surface of an inflatable balloon and
have the advantage of placement against the surface of the tissue being imaged
such as the rectal wall. A gap of several millimeters is present between the surface
of the coil and the surface of the lesion and the balloon needs to be distended in
order to maintain the position of the loop coil close to the primary tumor(Brown et
al.,2005).
The coil design permits improved SNR, allowing image acquisition using a
smaller field of view and thinner slices. Thus endorectal MRI provides high-
resolution images that depict bowel wall layers fully, however, clear differentiation
between mucosa and submucosa is still difficult. Studies comparing endorectal
MRI and transrectal ultrasound for staging superficial tumors have shown the two
techniques to have comparable accuracy(Brown et al.,2005).
30

IMAGING MODALITIES
Limitations:
There are limitations related to the use of any endoluminal technique in
which stenosis, stricturing, pain and discomfort, bowel wall motion, difficulty
placing the probe in the upper rectum and coil migration all hamper image
acquisition.
Small volume of sensitivity; The area that can be imaged using such coils
amounts to a total distance of one coil diameter away from the coil with a very
rapid drop in signal intensity beyond the immediate vicinity of the coil. Reports
have showed poor resolution of pelvic structures surrounding the rectum, such as
mesorectal fat, mesorectal fascia, and lymph nodes outside the field-of-view.
These are significant limitations of using an endoluminal technique and
therefore such devices are not recommended in the routine staging of rectal
cancer(Brown et al.,2005)
31

IMAGING MODALITIES
Figure(14): (a,b) (a) Endorectal coil. (b) T2 weighted image using the endorectal coil. The bowel wall
layers are shown but there is insufficient detail from the surrounding mesorectum to adequately stage
rectal tumors(Brown et al.,2005).
Pulse sequences
The initial sagittal T2 scans are used to plan the thin section weighted
oblique axials (Figure 35) (Brown, 2005).
Figure (15): The sagittal T2 weighted scans are used to plan thin-section axial oblique scans. It is important to
ensure the scans are obtained in a plane orthogonal to the tumour to prevent over-estimation of tumour spread
(Brown, 2005).
For tumours arising below the level of the levator origins (<6 cmfrom the
anal verge), it is essential to undertake high resolutioncoronal or paracoronal
imaging (Figure 36) and to evaluatethe sagittal images carefully, as well as the
standard obliqueaxial sections, in order to avoid the common pitfall of
overestimating betumour spread in
taken to plan scans orthogonal to the rectal wall in orderto avoid problems with
partial voluming(Brown, 2005)
32

IMAGING MODALITIES
Figure (16): For tumours arising below the origin of the levator muscle, scans are obtained in a coronal or
paracoronal plane as shown (Brown, 2005)
To adequately assess the nodal status, scans must include themesorectum
above the tumour, as nodal spread will be in a cranialdirection within the
mesorectum. Inadequate coverage will leadto understaging. For the lower third
rectal tumours, the restof the mesorectum can be staged for nodes by planning a
block (Brown,of paracoronal slice
2005)
33

IMAGING MODALITIES
Figure (17): Scan planes used for assessing mesorectal lymph nodes. The mesorectum can be assessed for
lymph nodes by planning a block of coronal slices that run parallel to the sacrum (Brown, 2005).
High-resolution T2-weighted TSE sequence with a small FOV and a slice
thickness of 3 mm. It is mandatory to place the slices perpendicular to the
longitudinal axis of the tumor or the intestinal lumen in the vicinity of the tumor.
With this sequence, it is possible to precisely evaluate the tumor, mesorectal fascia
and mesorectal lymph nodes(Klessen et al.,2007).
For visualization of more distant lymph nodes a T1 to proton-density-weighted
two-dimensional (2D) TSE sequence in axial orientation with a slice thickness
5 mm which covers the entire area up to the aortic bifurcation can be used.
Alternatively, a T1-weighted 3D gradient-echo sequence can be used for this
purpose, allowing for the reconstruction of thinner slices(Klessen et al.,2007).
Since differentiation with the T2-weighted sequences is based on the contrast
between the high-signal-intensity mesorectal fatty tissue and the rather low signal
intensity of the tumor, spectral fat suppression techniques are not needed. The
duration of the MRI protocol as just outlined is about 25-30 min, including
planning (Brown et al.,2005).
3D MR imaging cannot replace 2D MR imaging for local staging of rectal
cancer. High-resolution 2D T2-weighted MR images yielded superior results with
regard to rectal wall layer visibility and prediction of muscularis propria invasion
compared to 3D T2-weighted MR imaging, (3D)-data sets are time consuming, and
sensitive for motion and susceptibility artifacts. Perirectal tissue invasion was
adequately visualized with both 2D and 3D techniques with almost similar results.
3D MR imaging can be used for visualization of the complex pelvic anatomy for
treatment planning purposes(Futterer et al.,2008).
34

IMAGING MODALITIES
Whole-body MRI: The recent introduction of powerful whole-body MRI systems
enables imaging of the whole body in a single session through repeated table movement.
Several studies have already demonstrated the benefit of this approach for a variety of
diagnostic queries in oncologic patients. This technique may be used for rectal cancer
staging in the future allowing for local staging and whole-body staging in a single
session(Schmidt et al.,2005).
Major disadvantages of whole-body MR coverage in the past have been long
examination times caused by time-consuming patient repositioning processes and
changing of the array configuration. In addition, it was difficult to integrate the
different anatomic regions to be examined into a single comprehensive scan.
Recent improvements in hard- and software, had substantially reduced the
individual scan times, resulting in shorter overall examination times without
compromising spatial or temporal resolution. Now, dedicated assessment of
individual organs by sequences with various soft tissue contrast, image orientation,
spatial resolution, and contrast media dynamics can be combined with whole-body
anatomic coverage(Schmidt et al.,2005).
35

IMAGING MODALITIES
Figure.(18): Overview of the applied sequences on a whole-body magnetic resonance protocol for a 32-
receiver channel scanner (Magnetom Avanto; Siemens Medical Solutions, Erlangen, Germany). Total
scan time is 55minutes (Schmidt et al., 2005).
Potential factors that may impair the quality of images
Coil positioning
In order to prevent poor signal to noise ratio from the anorectal junction, it is
important that the phased array coil is centered optimally from the level of the
sacral promontory to below the symphysis pubis
(Brown et al., 2005).
36

IMAGING MODALITIES
Figure(19):Poor coil positioning. The images shown (top left and right) have been obtained with the
lower edge of the pelvic coil placed at the level of the symphysis pubis. Consequently there is poor signal
to noise ratio from the lower rectum and anal sphincter region. Repositioning the coil restores adequate
signal to noise ratio (Brown et al.,2005
Figure (20): It is important to centre the coil correctly to the whole rectum. Thus the
37

IMAGING MODALITIES
lower edge of the coil needs to be placed so that it lies at least 10cm below the symphysis pubis in order
to ensure adequate signal is obtained from the lower rectum and anorectal junction. The uppermost limit
for coil placement is the sacral promontory (Brown et al., 2005).
Choice of sequences
T1 weighted imaging:
Although the availability of short repetition time/echo time (TR/TE) volume
imaging can provide images of high spatial resolution, images obtained fail to
depict either tumor or the layers of the bowel wall due to similar relaxation rates of
tumor and bowel wall.(Brown et al.,2005)
Figure (21): A T1 weighted image has been obtained with a high spatial resolution but the bowel wall
layers cannot be distinguished (Brown et al., 2005).
Fat saturation and contrast enhancement:
A contrast enhanced technique requires the high signal from surrounding perirectal
fat on T1 weighted images to be suppressed to permit visualization of high signal
enhancement of tumor. This results in a further reduction in signal to noise ratio and
potential overstaging of tumors due to enhancement of adjacent non-tumor tissue
namely vessels, desmoplastic reaction and normal nodes (Brown et al., 2005).
38

IMAGING MODALITIES
Figure(22):T1 fat saturated image with contrast enhancement. The bright fat signal intensity from
perirectal fat (asterisk) has been suppressed and is of low signal intensity, there is florid enhancement of
the entire bowel wall (arrow) and perirectal vessels (arrowheads) which would not be readily
distinguishable from tumor if it were present(Brown et al.,2005).
Tumor not seen on initial sagittal sequences:
On occasion, lack of clinical detail or the presence of a small tumor prevents
the tumor being seen on the sagittal images. In these instances, tumor may only be
visible on the high resolution images. In order to ensure that the tumor has not
been missed it will be necessary to perform high resolution scans along the entire
length of the rectum(Brown et al.,2005).
Patient unable to tolerate long scan:
Some patients (5%), either due to co-existing medical conditions or
claustrophobia, find the scan impossible to tolerate; a combination of
patient discomfort, excessive motion of the anterior abdominal wall may
result in motion artifact. This is seen as horizontal bands across the image. Of all of
39

IMAGING MODALITIES
the sequences the oblique high resolution scans are the most important. The sagittal
views can be shortened by altering the parameters; the large field of view axials are
performed last and may even be omitted if the patient is inconsiderably
discomfort(Brown et al.,2005).
Figure(23):(a,b) Motion artifact. (a) This characteristically produces a series of bands that degrade the
image. (b)This can often be overcome by ensuring the patient is not in discomfort, by repositioning the
patient and ensuring adequate abdominal compression and repeating the sequence again after swapping
phase and frequency directions(Brown et al.,2005).
Magnetic resonance imaging has inherent limitations with foreign bodies that are
MRI incompatible. Foreign bodies that are compatible, such as surgical clips, may
also obscure images (Skandadajah et al., 2006)
Has been shown to be mandatory in preoperative local staging.
40

IMAGING MODALITIES
Fig (24) Sagittal turbo spin-echo T2-weighted MR image obtained with a high-resolution
phased-array surface coil shows a stenosing lesion (arrow) of the rectal lumen (*).Franco
Iafrate.et al. (2006).
41

Imaging Manifestations
MR Imaging Manifestations of Rectal
Cancer
The identification and staging of rectal cancers at MR imagingis largely based
on differences in T2 signal intensity betweenthe tumor, the mucosa and submucosal
layers, the muscular layer,the perirectal fat, and the mesorectal fascia. The perirectal
fat has high signal intensity on turbo spin-echo T2-weighted images and surrounds the
low-signal-intensity muscularis propria.The tumor itself has an intermediate signal
intensity betweenthe high signal intensity of the fat tissue and the low signal
intensity of the muscular layer. Furthermore, its signal intensity is higher than that of
the mucosal and submucosal layers (Figure 25) (Iafrate et al., 2006).
Figure (25): Rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image shows a stage T1 tumor (*)
of the rectum. The tumor has an intermediate signal intensity between the high signal intensity of the fat
tissue (jagged line) and the low signal intensity of the muscular layer (black arrow). The inner layer of the
rectal wall (white arrow) consists of mucosal and submucosal layers and has high signal intensity (Iafrate et
al., 2006)
42

The mesorectal fascia appears as a thin, hypointense line surroundingthe
hyperintense perirectal fat. However, the spatial resolutionof phased-array surface
coil MR imaging is not adequate to allowdifferentiation between the mucosal
and submucosal layers ofthe inner layer (Iafrate et al., 2006).
MR tumor radiological appearance
Exophytic or polypoidal tumors are shown as intermediate signal intensity,
rounded, protuberant mass lesions that project into the lumen. The surface of these
polypoidal tumor mass lesions often shows high signal intensity clefts
corresponding to mucinous fluid on the tumor surface(Martling et al.,2003).
Figure(26): High-resolution T2-weighted image demonstrating a T1 polypoid carcinoma (arrow). There
is partial preservation of the submucosal layer (short arrow) seen as a thin rim of high signal intensity
deep into the tumor. The tumor does not extend into the muscularis propria layer(Martling et
al.,2003).
43

Rectal tumors are most commonly demonstrated as an elevated plaque of
intermediate signal that projects into the lumen forming a U-shaped thickened disc
corresponding to an annular or semiannular plaque of tumor on histologic
sections(Martling et al.,2003).
Figure(27):Axial T2-weighted FSE MR image demonstrating a semiannular plaque of tumor with central
ulceration (arrowhead) and raised rolled edges (arrows) (Martling et al.,2003).
T staging criteria on MR imaging:
T0:Normal rectal wall layers, no visible tumor.
T1:Mucosa and submucosa affected, no extension beyond the
hypointense layer of muscularis propria.
T2:Hypointense layer of muscularis propria invaded, no extension to serosal and
perirectal fat.
T3:Invaded perirectal fat.
T4:Tumor signal intensity extends into an adjacent structure or viscus(Donmez et
al.,2008).
44

In T1, the tumor signal intensity is confined to the submucosal layer and has
relatively low signal intensity compared with the high signal intensity of the
surrounding submucosa(Klessen et al.,2007
Figure (28): Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image shows a huge
pedunculated tumor (T) on the left lateral rectal wall. The integrity of the muscular layer (arrow) appears
not to be disrupted. The mesorectal fat (*) has a homogeneous appearance without tumoral
involvement.The mesorectal fascia (arrowheads) is also well depicted (Iafrate et al., 2006)
Table (4) illustration of T-stage of rectal cancer.Max Lahaye. et al. (2010).
45

Figure (29): Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image shows the tumor
(T) invading the rectal wall without infiltrating the perirectal fat (arrow). In this imaging plane, the
distance of the tumor from the plane of the levator ani muscle (L) and from the anal sphincter complex (A)
can easily be evaluated (Iafrate et al., 2006)
Figure (30): Stage T1 rectal carcinoma.Axial turbo spin-echo T2-weighted MR image shows a polypoid
tumor (T) on the right lateral aspect of the rectal wall protruding into the rectal lumen. It is difficult to
determine whether the muscular layer (arrow), which appears thinned, is infiltrated or spared (Iafrate et al.,
2006).
46

In T2, the tumor signal intensity extends to the muscle layer, leading to
irregularity or thickening of the muscle layer, but without perirectal tissue
invasion, the outermost margin of the muscularis propria will remain intact with
stage T2 tumors or less (Klessen et al.,2007).
Figure (31):Stage T2 rectal carcinoma. Coronal T2-weighted MR image shows a stenosing neoplastic
lesion (*) of the rectal lumen involving the mucosal, submucosal, and muscular layers. The muscular
layer is visible as a continuous hypointense line, and no neoplastic spread into the mesorectal fat (arrow)
is seen. The major criterion for differentiating between stage T2 and stage T3 tumors is the presence of
neoplastic tissue within the mesorectal fat(Iafrate et al 2006).
Figure (32): Stage T2 rectal carcinoma. Unenhanced T2-weighted fast spin-echo image Shows
mesorectal fascia (arrowheads) as fine linear hypointense structure enveloping mesorectum. Tumor
(T) is revealed as being confined in muscularis propria(mp) Akasu et al., 2005).
47

The major criterion for differentiating between stage T2 and stage T3
tumors is the presence of neoplastic tissue within the mesorectal fat. In
differentiating isbetween stage T2 an
involvement of the perirectal fat, which is characterizedby the in ability to
visualize the interface between the muscularlayer and the perirectal fat, with a
rounded or nodular advancing margin (Iafrate et al., 2006).
In stage T3 tumors, the muscularis propria is totallydisrupted and cannot be
clearly distinguished from the perirectal 2fat (Figure 33 ) (Iafrat
Figure (33): Stage T3 rectal cancer .Transverse contrast material-enhanced T1-weighted turbo spin-echo
MR image shows rectal tumor (black arrow) with transmural stranding (arrowheads) in mesorectal fat.
Mesorectal fascia (white arrows) is clearly depicted (Beets et al.,2001).
In T3, the tumor signal intensity extends through the muscular layer into the
perirectal tissue, or angiolymphatic tumor invasion (irregularly thickened strands)
present in the mesorectum. The appearances of nodules (figure(34), an interruption
of the outer wall of the rectum or an irregularly thickened spiculations(Klessen et
al .,2007).
48

(b)
(a)
Figure(34)(a,b) (a) Axial high-resolution T2-w image showing a tumor with a pushing edge. The
advancing edge of the tumor has a well-circumscribed margin with a sharp border between the advancing
edge of the tumor and the perirectal fat. This is the most common pattern of tumor spread. (b) Axial T2-w
FSE image showing nodular extension with ill-defined margins. The tumor is spreading into the perirectal
fat at its leading edge(Martling et al.,2003).
fine spiculations which cannot be considered as a reliable sign for the
presence of extramural invasion as it can be caused by fibrosis, are considered to
be indicators of the T3 stage on MRI. A further feature that may lead to incorrect
diagnosis is that of small interruptions of the outer contour of the muscle coat,
which may incorrectly stage the tumour as T3 (Chun et al.,2006).
Any isolated tumor deposit in the immediate perirectal space, measured to
be within 3mm of the bowel wall and with the same MRI signal as the primary
tumor, can be interpreted as extramural spread.
49

Tumor deposits further than 3mm from the bowel wall can be assumed to
represent metastatic spread. Tumor deposits of more than 3mm in size are
considered as involved lymph nodes even if no lymphoid tissue was present.
For T3 tumors with disease-free circumferential margins, it was shown that
> 5 mm spread of tumor beyond the bowel wall predicts a significantly poorer
survival than < 5 mm spread (54% compared to 85% respectively)
(Matthhew,2008)
Circumferential resection margin (CRM):
The most important predictor of local recurrence is CRM infiltration and
tumor mesorectal fascia distance. The actual T staging system does not
differentiate between tumors with a wide CRM and those with a narrow
CRM(Iafrate et al.,2006).
Figure(35). Drawing illustrates the relationship between the CRM and rectal tumors of various stages.
The actual T staging system does not differentiate between tumors with a wide CRM (T3⌂) and those
with a narrow CRM (T3*). Of these stage T3 tumors, the latter poses a higher risk for recurrence. At MR
imaging, it is important to be able to identify patients with infiltrating tumors that have a narrow CRM
50

or that infiltrate the mesorectal fascia who might benefit from neoadjuvant treatment. T1 = stage T1
tumor, T2 = stage T2 tumor, T4 =stage T4 tumor, Ves = vesicle(Iafrate et al.,2006).
The expected CRM can be described as involved if tumor invasion of the
mesorectal fascia is visible or the tumor has a proximity of 1 mm or less to the
mesorectal fascia. Actually there has been a debate whether the distance of CRM
‘≤ 1mm’ or ‘≤ 2mm’ should be regarded as the involved CRM. In recent years, ≤
2mm definition of CRM became widely accepted. A tumor-free CRM can be
assumed with a high degree of accuracy if the shortest distance from the maximum
tumor extension, a mesorectal tumor deposit or a suspect lymph node in the
mesorectum is more than 6 mm(Klessen et al 2007).
Figure(36):CRM is safe if distance of tumor to mesorectal fascia is >6mm(Smith and Brown
2008)
51

Histological analysis demonstrated that a tumor-free resection margin of
2 mm was predicted if the distance between tumor and mesorectal fascia measured
by MRI was at least 6 mm. Tumors that extend towards the mesorectal fascia to a
distance of less than 5 mm on MR images remains controversial(Kim et al.,2008).
Figure(37):Transverse T2-weighted MR image of the middle of the pelvis. The tumor (double-headed
arrow) in the right lateral anterior aspect of the rectum shows extramural extension, with a minimum
distance to the mesorectal fascia (white arrows) of 5mm(Beets-Tan and Beets 2003).,
MR imaging is a highly accurate and reliable techniquefor the prediction of
CRM infiltration and thus represents anoninvasive tool for identifying those patients
who may benefit whofrom preopera
should undergo TME (Iafrate et al., 2006)
CRM is closely related to a high recurrence rate aftersurgery (Figure 38)
(Brown, 2004).
52

Figure (38): Stage T3 tumor with involvement of the mesorectal fascia. Coronal turbo spin-echo T2-weighted
MR image shows a neoplastic rectal lesion infiltrating the mesorectal fat and involving the mesorectal
fascia(arrowheads), which appears thickened. The mesorectal fascia represents the surgical resection
margin. Patients with this kind of tumor benefit from preoperative neoadjuvant therapy to reduce the
postoperative local recurrence rate (Brown , 2004).
Vascular invasion of a rectal carcinoma is associated with an increased rate
of local recurrence and is considered as an important independent prognostic
factor. The typical appearance on MRI, which is the only imaging modality that
has been shown to demonstrate extramural vascular invasion (EMVI) in rectal
cancer is that of discrete serpiginous or tubular projections of intermediate signal
intensity into perirectal fat, following the course of a visible perirectal vessel
(usually a vein). The sensitivity and specificity of MRI for detecting EMVI was
62% and 88% respectively. Some patients with microscopic vascular invasion
could not be resolved on MRI, while others with very obvious EMVI on the pre-
operative images had false-negative histo-pathology due to obliteration of normal
53

venous architecture which makes it difficult for the pathologist to recognize that a
tumor deposit lies within the course of a vessel, something which may be more
readily appreciated on serial MR images((Smith and Brown 2008).,
Figure(39):Extramural vein invasion(Jemal et al.,2007).
Figure(40): rectal carcinoma with EMVI.AxialT2 weighted image showing tumor extending into an
extramural vein. There is serpiginous extension of the tumor into the perirectal fat (arrow) following a
presumed vessel that was shown histologically to be thick-walled extramural venous invasion(Burton
et al 2006).
54

In stage T4 tumors, the signal intensity of the tumor is seeninfiltrating
surrounding structures (ie, other organs and muscularstructures of the pelvic wall
(Figure 60) (Iafrate et al., 2006)
Figure (41): Stage T4 tumor. Axial turbo spin-echoT2-weighted MR image shows a neoplastic rectal
lesion (arrow) disrupting the mesorectal fascia. Tumoral infiltration of the seminal vesicles (*) is also
evident Iafrate et al., 2006).
Figure(42):(a,b) (a) Paraxial T2-weighted FSE sequence and (b) sagittal T2-weighted FSE sequence of
a T4 cancer located in the upper third of the rectum invading the uterus (arrows) (Klessen et
al.,2007).
55

Figure(43):Sagittal T2-w turbo spin-echo MR image in same patient clearly shows that tumor originates
from the rectum (black arrows). Although tumor extends on the dorsal wall to the presacral fascia (arrow
heads), on the ventral wall it is limited to the rectal wall. Hypointense line (white arrows) between tumor
and uterus is a composition of uterine wall, peritoneum, mesorectal fascia, and rectal wall and indicates
that tumor has not yet invaded the uterine body( Beets et al., 2004).
Pitfalls :
Poor differentiation between T1 and T2 tumors, however, in most cases
these tumors are both treated with TME-surgery, so it is not necessary to make the
difference. In a minority of cases a T1 tumor is treated with local excision, in these
cases endorectal US is accurate for staging these superficial tumors(Lahaye et al.,
2010).
Differentiation between T2 and T3 tumors may be difficult with MRI and
over-staging is often caused by perirectal desmoplastic reactions which do not
contain tumor cells(Lahaye et al., 2010).)
To be on the safe side and to avoid understaging, it is advised to stage
tumors with perirectal stranding as T3 tumors. For therapeutic purposes it does not
have any consequences to differentiate accurately between a T2 CRM- and a T3
CRM- tumor, both tumors will be treated with a preoperative low dose
56

radiotherapy followed by TME. Understaging can also occur due to microscopic
invasion of perirectal fat(Chun et al .,2006).
Figure(44)(a,b,c) Difficulty in interpretation of tumor penetration of rectal wall. (a) On this transverse
Gd-enhanced T1-w image, enhancing spiculations (arrows) are seen in mesorectal fat, suggesting tumor
penetration of rectal wall (stageT3). However, histologic examination showed that these spiculations
consisted of fibrosis without tumor cells (stageT2). (b) On this transverse gadolinium-enhanced T1-w
image in a different patient, enhancing spiculations (arrows), indistinguishable from those in a, are seen in
mesorectal fat. In this case, spiculations consisted of fibrosis and tumor cells (stageT3). Spiculations
consisting of fibrosis either with or without tumor cells cannot be discriminated on non enhanced or
gadolinium-enhanced MR images. (c) Clear invasion of mesorectal fat. Coronal T2-w TSE MR of tumor
with pattern of nodular infiltration (arrows) of mesorectal fat in a different patient. Nodular advancing
tumor margin is highly predictive for tumor penetration of rectal wall, as opposed to margin consisting of
spiculations (a, b)(vliegen et al.,2005).
in low bulky tumors, the fat plane between the tumor and the adjacent
structures can be obliterated because of the mass effect of the tumor. In these
57

circumstances, it can be difficult to distinguish compression of adjacent organs
(posterior vaginal wall (fig64), seminal vesicles, prostate, bladder from tumor
invasion into these organs Vliegen et al.,2005).
Fig.(45).Transverse T2-weighted TSE MR image of bulky (voluminous) low anteriorly located tumor.
This tumor (T) causes a mass effect on surrounding pelvic structures (arrow heads indicate vagina) and
stretches fat plane in-between these structures. When surrounding pelvic organs have normal signal
intensity, it can be difficult to differentiate compression from tumor invasion. In this case, histologic
Vliegen et al.,2005). )examination showed invasion of vagina. B=bladder
Assessment of sphincter involvement :
MRI showed 98% specificity and 100% sensitivity for the assessment of
sphincteral involvement. The prediction of a tumor free anal sphincter allowed to
successfully planning a sphincter saving surgery in most patients. The sphincter ani
cannot be saved with less than 1cm minimal distance between the tumor and
dentate line(Winter et al.,2007).
Conversely, the knowledge of the depth of sphincteral involvement did not
influence treatment because there is a policy is to resect all tumors with sphincteral
infiltration by means of abdomino-perineal resection, irrespective of the extent of
infiltration. However, in such a case others proposed an intersphincteric resection
with colo-anal anastomosis provided that the striated sphincters are not
infiltrated(Ferri et al.,2005).
58

Figure(46).Rectal adenocarcinoma with involvement of the sphincter. Coronal FSE T2-w MR image
shows a tumor (T) of the rectal ampulla causing stenosis of the rectal lumen and infiltrating the
sphincteral plane, which is composed of the internal muscular sphincter (*) and the external sphincter
(ES). The levator ani muscle (L) is also evident and appears to be uninvolved(Iafrate et al.,2006).
mucinous carcinoma
On T2-w images, rectal carcinomas appear as wall lesions exhibiting signal
intensity slightly higher than the muscularis propria but lower than the submucosa.
High signal intensity of the tumor on T2-w images higher than that of the
submucosa suggests the presence of mucinous carcinoma (parts of the mucous
lakes) that is isointense to fluid within the layers of the rectal wall, and the layers
can typically show high signal intensity expansion (fig.66) (Klessen et al.,2007).
59

Figure (47): Staget3 rectal mucinous adenocarcinoma. Transverse T2-weighted turbo spin-echo MR
images show hyperintense rectal tumor (arrowheads) extending to mesorectal excision plane on anterior
and left lateral sides (arrows). The hyperintense nature of the lesion on T2-weighted images is
characteristic of mucinous tumor ( Beets et al.,2004).
Figure(48):Axial T2-w FSE MR image demonstrating a mucinous tumor characterized by very high
signal intensity (high water content). The tumor (asterisk) infiltrates the bowel wall without destroying
the boundaries between the individual layers, resulting in accentuation (thickening) of the bowel
wall(Klessen et al.,2007).
60

It is suggested that MRI can help distinguish between mucinous and non mucinous
carcinomas (fig.49).
In some cases where the tumor extended outside the rectal wall, its
extrarectal components were composed largely of mucin pools. Moreover, this
perirectally extended mucin-containing tumor would be difficult to observe during
surgery if it had not been noticed preoperatively, which may contribute to the
relatively high rates of local failure compared with nonucinous tumors. (Kim et al.,
2003)
Figure(49).(a,b,c) 57-year-old woman with a mucinous carcinoma. (a)The axial FSE T2-w image depicts
a large area of hyperintensity extending to the perirectal space, ssuggestive of a mucin pool (arrow).
(b)On the axial T1-weighted image, the tumor shows signal intensity similar to the normal rectum or
muscles. (c)CoronalT2weighted image show the tumor extending into the perirectal fat plane(Kim et
al.,2003).
61

Possible causes of false diagnosis can result from the false positive
interpretation of areas of high signal intensities mimicking mucin pools
innonumcinous carcinomas, such as intratumoral congestion, abscess, necrosis, and
mural edema (fig.69) in the adjacent rectal wall or entrapped fluid between the
tumor and the adjacent rectal wall. These areas are relatively small and scarce
within the tumor or located mainly outside of the tumor, or can result from false
negative diagnosis due to ignoring small mucin pools that were deemed to be
insignificant. The portion of the mucin pools that was missed at MRI or the high
signal intensity that was falsely interpreted as a mucin pool usually comprised only
a small portion of the tumors (Kim et al, 2003)
Additional use of gadolinium enhanced sequences may improve radiologists
ability to different between a mucin pool and edema, necrosis, or abscess because
the tumor mucin pool may be enhanced, whereas the others do not enhance.
However, studies show that unenhanced images alone showed high accuracy for
the differentiation of mucinous and nonmucinous tumors (Kim et al., 2003)
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Figure(50).(a,b) 70-year old woman with a nonmucinous carcinoma. Sagittal (a) and coronal (b) FSE
T2-w images. The areas of the high signal intensity of submucosal edema in the adjacent rectal wall can
be misinterpreted as a mucin pool (arrow heads) and render a false-positive diagnosis of mucinous
carcinoma. Correct identification of a nonmucinous tumor narrowing a segment of the rectum (arrows)
can be made if the extratumoral location of the high signal intensity was correctly identified(Kim et
al.,2003).
N staging :
The majority of involved lymph nodes in patients with primary rectal cancer, as
depicted on preoperative MRI are located at tumor height or above, in the
dorsolateral compartment of the mesorectum (fig.70). Involved nodes distal to the
tumor are not common. Involved extramesorectal nodes are also not common
(fig.71) and occur mainly in patients with distal rectal cancer with nodal metastases
in the mesorectum (Engelen et al.,2008).
63

Figure(51):.Axial T2-weighted fast spin-echo MR image. There is a large lymph node located outside
the mesorectal compartment (white arrow), in the region of the middle rectal artery. The node is located
at same height as the tumor(R). There are also nodes located in the mesorectum (black arrows).U=
uterus(Engelen et al.,2008).
Figure.(52)Axial T2-weighted FSE sequence. Inguinal lymph node metastases (arrows) in a patient with
low rectal cancer(Klessen et al.,2007).
64

N staging criteria on MR imaging:
N0: <5mm, of any number.
N1: >5mm, less than 4 in number, in perirectal area.
N2: >5mm, more than 4 in number, in perirectal area.
N3: metastases in any node along the course of a vascular trunk or in apical
node(Donmez et al.,2008).
Table (5) Illustration of N-stage of rectal cancer.Max Lahaye. et al. (2010).
Diagnostic criteria on MR imaging
1- SIZE :
Lymph node size is not a reliable criterion for metastatic involvement
(fig.72). There is no consensus as to the exact cut-off size, some authors regard any
visible node in the perirectal fat as positive, while others employ size criteria with
cutoff values for nodal positivity that range from 3 to 10 mm(Brown et al.,2003).
65

Figure (53): Rectal adenocarcinoma with metastatic lymphadenopathy. Coronal turbo spin-echo T2-
weighted MR image demonstrates a rectal tumor (*) and two enlarged lymph nodes within the
mesorectal fat (arrowhead) (Kim et al., 2004).
Figure(54):.False-negative diagnosis was made in a 57-year-old man with microscopic tumor cells in a
regional LN. A T2-W axial image shows a shallow ulcero-infiltrative lesion (black arrow) in the
posterior rectal wall. The depth of invasion is confined to the muscular layer. A 3-mm peritumoral LN
(white arrow) is seen in the 5-o’clock direction(Koh et al.,2004).
2- Border :
nodal involvementdetermined on the basis of irregular borders and signal
intensity or charac
66

indistinct node borders and a mottled heterogeneous signalintensity pattern
might help predict nodal involvement (Figure 74) (Kim et al., 2004)
It is well recognized that partial or complete nodal replacement with
a tumor results in gross distortion, and extranodal extension in incompletely
involved nodes leads to irregularity of the surrounding capsule. The high spatial
resolution of the MR imaging technique in assessing this feature, combined with
the heterogeneity of the intranodal signal intensity, produces a powerful predictor
of lymph node status that shows good reproducibility between observers and is
independent of, and greatly superior to lymph node size(Brown et al.,2003).
a
Figure(55):.(a,b) (a) T2-w FSE transverse MR image through the upper portion of the rectum. A node
with an irregular border (arrow) located close to the right lateral mesorectal margin contains mixed signal
intensity.
(b)T2-w FSE transverse MR image through the middle portion of the rectum. A high-signal-intensity
node with smooth borders (arrow) of homogeneous signal intensity is demonstrated close to the right
posterolateral border of the mesorectum. Corresponding histologic examination revealed benign
node(Brown et al.,2003).
67

3- Signal Intensity :
Internal morphology of normal nodes is best demonstrated on T2-weighted
images. It is a common misconception that all lymph nodes of high signal intensity
contain fat. While fat replacement of nodes is well recognized in the axilla and
inguinal nodes, the presence of intranodal fat is not a feature of perirectal lymph
nodes. The high signal intensity is presumed to represent fluid within lymphoid
follicles, and are surrounded by a low-signal-intensity capsule(Brown et al.,2003).
The demonstration of intranodal heterogeneity of signal intensity (ie mixed
signal intensity) is shown to be a highly specific discriminant. However, if used
alone as a marker for nodal involvement it results in a low sensitivity(Brown et
al.,2003).
Evaluation of intranodal signal intensity homogeneity requires high-quality images
that are free of movement artifacts, also and because these qualities are difficult to
obtain in small nodes, we do not feel able to make this assessment in nodes less
than 3 mm(Brown et al.,2003)
Figure(56):.Identification of lymph nodes at transverse T2-weighted MR imaging. Axial image shows
two intermediate-signal-intensity lymph nodes (arrows) in right mesorectum. Vessels are readily
distinguished from nodes as low-signal-intensity tubular structures (arrow heads) (Koh et al.,2004).
68

Figure (57): Rectal cancer with involved lateral node outside mesorectum. Transverse T2-weighted turbo
spin-echo MR image shows enlarged, round, hyperintense lymph node (arrowheads) in left hypogastric
region in, suggestive of a metastatic node. This node is located outside the mesorectum, and with standard
TME it would be left behind. Such nodal involvement can be a risk for local recurrence ( Beets et al.,
2004).
Figure(58)T2-w FSE transverse MR image shows a node of mixed signal intensity with a low-signal
intensity rim (arrow head). A focus of low signal intensity (arrow) is demonstrated within the
predominantly intermediate-signal intensity node. Histologic slice shows low-signal-intensity rim to
correspond to the normal lymph node capsule (arrow head).Within the node, there is tumor with wide
spread necrosis in the area corresponding to the low-signal-intensity area seen on the MR
image(Brown et al.,2003).
69

Real improvement in lymph node characterization willcome with the use of ultra-
small iron-based particles. Theseparticles are selectively taken up by the reticulo-
endothelialcells in normal lymph nodes, which thus have low signal intensityon
proton-density-weighted and T2-weighted MR images.Pathologic lymph nodes, with
reticuloendothelial cells replacedby neoplastic cells, will not take up the contrast
agent andthus will have a relatively bright signal intensity. (Bellin et al., 2000).
Uspio- enhanced MRI
A new promising approach to detect metastatic lymph nodes using
ultrasmall superparamagnetic iron oxide particles (USPIO) as a contrast medium
for systemic MR lymphography(Lahaye et al.,2008).
Dose: The USPIO MR Contrast agent consists of low-molecular-weight iron oxide
coated with dextran, supplied as a powder in a glass vial containing 210 mg, and
must be reconstituted by using 10 mL of normal saline. A dose of 0.13 mL/kg of
body weight (2.6 mg of iron per kilogram) of the reconstituted solution is to be
diluted in 100 mL of normal saline. The contrast agent is given intravenously
within a period of approximately 45 minutes by means of a slow-drip infusion with
a microfilter. Administration is closely monitored for any adverse effects and is
completed 24-36 hours before contrast material-enhanced MR imaging is carried
out(Lahaye et al.,2008).
The nanoparticles cause a decrease in signal intensity (SI) within the node
Variation of SI within a node can be explained on the basis of the concentration of
macrophages (nanoparticles) in a particular region in the node. A region with a
normal concentration of macrophages (nanoparticles) will produce an area with SI
decrease on T2- and T2*-weighted images The involved part of the lymph node
70

will show no SI decrease caused by the replacement of macrophages by tumor
cells, creating a region of increased SI within the node (white region)( Lahaye et
al.,2008).
The percentage of white region within the node on USPIO-enhanced T2*-
weighted MR images either by visual assessment or through quantitative
measurement by dividing the surface area of the white region by the surface area of
the total node determined on a transverse image where the node was the largest by
measurement tools of the workstation(Lahaye et al.,2008).
Estimated area of white region within the node that is larger than 30% is
highly predictive for an involved node, with a sensitivity of 93% and a specificity
of 96%.The larger the area of the white region, the more likely the node is
malignant. Both the estimated and the measured ratio of the white region within
the node are the most accurate predictors for malignant nodes in rectal cancer. The
estimated percentage can serve as a reliable and practical criterion for the
prediction of malignant nodes on USPIO-enhanced MR images(Lahaye et
al.,2008).
The border and SI characteristics of lymph nodes on T2-weighted MR
images can be used for identification of malignant nodes in rectal cancer, however,
they are generally easier to evaluate in larger nodes (>5 mm in diameter). USPIO-
enhanced MR imaging and its characteristics are especially of additional benefit in
the evaluation of these small nodes (<5 mm in diameter) (Lahaye et al.,2008).
Benign conditions such as focal nodal fibrosis, granulomatous disease, or a
fatty hilum also can be depicted as a white region because of the lack of
macrophages, thus mimicking malignant nodes. These white regions, however, are
usually 30% or less of the total node area. Another way to differentiate between a
71

white fatty hilum and a white tumoral region is to compare the T2*-weighted
images with the T1-weighted images: A fatty hilum is depicted as a white region
within the lymph node, whereas a tumor is not. In the same manner, the dark
region can hide small micrometastases. The clinical implication of
micrometastases,
however, is debatable. Although there is a small overlap in MR features of benign
and malignant nodes, a general rule of thumb is that, when the white region is less
than 30% of the total node area, the nodes are most often benign (Lahaye et
al.,2008).
M staging
Hepatic metastases :
Colorectal hepatic metastases most commonly appear as lesions that are
moderately hyperintense on T2-w images and hypointense on T1-w images
(fig.78). ill-defined margin with slightly heterogeneous signal, or, occasionally, a
ring of surrounding high signal, or halo due to central necrosis or biliary or
vascular obstruction. In addition, they may also appear as target lesions with
central high signal and adjacent low signal corresponding to compressed hepatic
parenchyma(Saunders et al.,2002).
72

Figure(59):(a,b,c) (a)Coronal T1 image of the liver in a patient under consideration for metastectomy
showing typical hypointense hepatic metastasis (arrow). (b)Axial T1-w image. (c)Axial T2-w image, the
metastasis has a high signal centre (arrow) with an ill-defined margin (thin arrow) which is unusual in a
benign lesion(Saunders et al.,2002)
Gadolinium-enhanced imaging :
Gadolinium-based intravenous contrast agents can improve the sensitivity of
MRI in detecting metastases. Most metastases are hypovascular and receive their
blood supply from the hepatic artery in contrast to normal liver parenchyma which
receives 60-70% of its blood supply from the portal vein. During dynamically
enhanced scanning, metastases may be of increased signal during the arterial phase
and decreased signal in the portal phase. There may also be peripheral washout,
whereby the periphery of the metastasis is of lower signal than the centre and
adjacent liver. On delayed scanning, metastases may have increased
signal(Saunders et al.,2002).
73

Figure(60)(a,b,c) (a)T1-w transverse scan with fat suppression. The hepatic metastasis at segment V is
hypointense (arrow).
(b)Post-contrast transverse scan at arterial phase shows a hyperintense ring-like enhancement of the lesion
(arrow), which is centrally hypovascular.
(c)Post-contrast transverse scan at portal venous phase illustrates washout of the peripheral enhancement
of the metastasis (arrow), which remains hypovascular compared to the rest of the normally enhanced
liver parenchyma(Karantanas et al.,2007).
74

Advanced MR imaging techniques
Tumor imaging using diffusion-weighted imaging
On DW images, rectal cancer is depicted as hyperintense focal lesion (high
cellularity) with markedly enhanced contrast compared with T2-w image
(fig.80),few normal structures such as lymph nodes, small intestine, prostate,
seminal vesicles, testes and endometrium remain as hyperintense regions. Lower-
signal-intensity regions are seen in most organized normal tissues, cystic spaces,
and vessels(Figueiras et al.,2010).
Figure(61):(a,b) Rectal cancer in a 51-year old female patient. (a) Axial T2WI showed slight focal
thickening of rectal wall (arrow), which were misinterpreted as no cancer present by the two readers.
(b)Axial DWI of the same plane demonstrated focal hyperintense area (arrow), which was found by the
two readers. And endometrium remained as hyperintense regions (arrow head)( Rao et al.,2008).
High signal intensities on DW images are not always reliable indicators of
increased cellularity on their own. Occasionally, fluid, edema, or mucinous
materials remain of high signal intensity because of high proton density. This
observation is called T2-shine through, but this effect can be detected easily by
noting corresponding high signal on ADC maps(Figueiras et al.,2010
75

Figure(62):(a,b,c) T3 rectal carcinoma in 64-year-old patient. (a) Sagittal fast spin-echo T2-weighted
image. (b) Sagittal diffusion-weighted image with high b value (b = 800 s/mm2) show rectal tumor as a
hyperintense lesion. (c) Fusedsuperimposing sagittal T2-w MR image and color-coded map derived
from high-b-value diffusion-weighted image clearly delineates rectal carcinoma (arrows) (Figueiras
et al.,2010).
76

Recent studies have already shown the potential value of DWI :
Detection of colorectal cancer, particularly when lesions are small and when
there is concurrent inflammatory disease with a high sensitivity (91%) and
specificity (100%)(Hoeffe et al.,2009).
Early prediction of treatment response because cell death and vascular
alterations typically occur before size changes. Increases in ADC values with
treatment reflect decreases in cellularity and thus provide indirect assessment of
chemotherapy induced cell death(Figueiras et al.,2010).
Assessing nodal metastases, however, this technique has not yet been shown
to be of value in characterizing lymph nodes in CRC patients. High-b-value DWI
is sensitive for detecting the location of lymph nodes, but its characterization value
is unproven in CRC with necrotic neoplastic nodes yielding false-negative results
and reactive hyperplastic nodes yielding false-positive results(Figueiras et
al.,2010).
Patient selection; Responders to chemoradiation had a lower ADC at
presentation than nonresponders. Higher pretreatment ADC values in
nonresponders may reflect necrotic tumors that are more resistant to therapy
because of concomitant hypoxia which is the same for liver metastases(Figueiras
et al.,2010).
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I. Tumor imaging using dynamic contrast-enhanced MRI (DCE-MRI)
(Perfusion MRI):
To date, there have been few data on the comparative performance of
perfusion CT and DCE-MRI. A study that compared the effectiveness of perfusion
CT with that of DCE-MRI for the assessment of solitary pulmonary nodules
concluded that there was no significant difference between the two techniques.
There are no data for colorectal cancer. In reality, the imaging technique chosen to
assess colorectal cancer vascularity is decided by local expertise, local availability,
perceived radiation burden, need for quantification, and site of disease(Goh et
al.,2007).
II.Tumor imaging using MR colonography
MR colonography for polyp detection has seen relatively little progress and
only limited interest in recent years, there are a several MRI-related factors that
have contributed to its stunted growth. This includes the limited availability and
increased complexity of MRI, the continued use of a hydrocolon (water enema)
over gaseous distension of the colon due to technical issues related to the air-soft-
tissue interface. The hassle of performing an enema in the MRI suite is a major
impediment to wider dissemination(Pickhardt,2010).
Current protocols result in a relatively large number of series that must be
viewed, which can exacerbate reader fatigue. Although the sensitivity for detection
of large polyps and masses has approached that of CT colonography, gadolinium
78

i.v. contrast is needed, which adds cost, time, complexity, and invasiveness over
CT colonography (Pickhardt,2010).
Another one of the major drawbacks of MR colonography is its inability to
detect accurately colorectal lesions smaller than 5 mm. The sensitivity for
detection of large polyps is about 75% with a high specificity(Hoeffel et al.,2009).
Re-staging of patients after chemoradiotherapy
The main purpose of MRI after chemoradiotherapy for locally advanced
rectal cancer is to evaluate treatment response and to determine the new tumor
extent(Torkzad et al.,2008).
Postchemoradiation MRI performed poorly on the prediction of T stage
(overall accuracy 54%). This was largely due to overstaging and the inability of
MRI to reliably distinguish between treatment fibrosis and viable tumor. However,
when considering results for the subgroup of ypT0-2tumors (confined to the rectal
wall)(ypT category:T category at posttreatment histopathologic evaluation), high
accuracy rates were found. . Downstaging of tumors to lesions confined to the
rectal wall with no longer involved lymph nodes can be followed with local
excision of the tumor(Low et al.,2008).
Postchemoradiation MRI has a moderate accuracy (sensitivity 100%,
specificity 32%-59%) for the prediction of tumor invasion of the mesorectal fascia
(MF) because of its limitations for differentiating diffuse “fibrotic” tissue with or
without small residual tumor foci. Specific morphologic tissue patterns identified
at MR imaging highly correspond with a tumor-free or
tumor-invaded MF(Vliegen et al.,2008).
79

MR imaging of nodal involvement is more difficult. The accuracy of MR
imaging for lymph node staging may improve with the recently introduced lymph
node-specific contrast agents(Dresen et al.,2009).
The use of DCE-MRI sequences remains questionable whether these
techniques would offer any help for the detection of small areas of tumor within
poorly vascularized fibrotic tissue(Vliegen et al.,2008).
T staging
The combination of morphologic and volumetric criteria can provide high
positive predictive value (83% to 92%) for the prediction of tumors confined to the
rectal wall (ypT0-2 Tumors) (Dresen et al.,2009).
Prediction of ypT0-2 tumors on basis of volume response to neoadjuvant
chemoradiotherapy:
The maximum diameter is measured on one axial section in two directions
perpendicular to each other (length and width). The maximum height is measured
on one sagittal section. Tumor volume is obtained by multiplying tumor length,
width, and height. Volume reduction rates (as percentages) were defined as 100.
[(Vpre -V post) / Vpre ], where V pre is volume before and Vpostis volu
chemoradiotherapy(Dresen et al.,2009).
Before chemoradiotherapy, if the initial tumor volume was ≤ 50cm3 and the
volume reduction rate after neoadjuvant chemoradiotherapy was ≥75%, then this
combination is predictive of a ypT0-2 tumor(Dresen et al.,2009).
80

All tumors with a volume reduction after chemoradiotherapy of less than
one-third of their original volume were ypT3-4 tumors(Dresen et al.,2009).
Figure(63):(a,b) Sagittal T2-w FSE MR images obtained after administration of chemoradiotherapy to
3
tumor with small volume (3.3x2.6x3.6cm=31cm ) show complete response at histopathologic
examination.
(a) Before chemoradiotherapy, tumor (T) is seen in rectum. (b) After chemoradiotherapy, tumor
completely disappeared and normal rectal wall configuration was seen with dark outer layer (arrow) and
hyperintense inner layer (arrowhead). At histopathologic evaluation, no residual tumor was found.
C=cervix,Co=coccygeal bone(Dresen et al.,2009).
Prediction of ypT0-2 tumors on basis of morphologic criteria:
Returning of the rectal wall to its normal configuration of a two layered
pattern on MR images is always associated with a complete histopathologic
disappearance of the tumor (ypT0 lesion) (Dresen et al.,2009).
Tumor surrounded by an intact hypointense bowel wall is highly predictive
of a tumor limited to the bowel wall. In many ypT0-2tumors, a normal
hypointense bowel wall is indeed visualized. However, when this bowel wall
appearance cannot be delineated, as for example when it has thickened owing to
radiation therapy, fibrosis is suggested. And these lesions are staged as ymrT3-4
tumors to prevent understaging as the interpretation of fibrosis with or without
residual tumor on MR images are difficult(Dresen et al.,2009)
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Mesorectal fascia invasion
Presence of a fat pad larger than 2mm between a residual (tumor) mass and
the MF is a definitive sign of absence of tumor invasion at postchemoradiation MR
imaging(Vliegen et al.,2008).
Presence of diffuse hypointense “fibrotic” infiltration of the MF at MR
imaging (seen in more than 50% of patients). In one of three quadrants, this
fibrotic tissue at MR imaging showed tumor infiltration at histologic examination.
Residual tumor within these fibrotic areas is often confined to small tumor nests. It
is therefore virtually impossible to differentiate these from completely sterilized
areas of fibrosis. “Fibrotic” areas should therefore be considered as potentially
invaded(Vliegen et al.,2008).
of diffuse iso-or hyperintense “tumor” infiltration of the MF at MR imaging
was associated with tumor invasion at histologic examination in 90%(Vliegen et
al.,2008)
Figure(64): (a,b) Diffuse hypointense tissue infiltration at postchemoradiation MR imaging suggestive
of fibrosis can be associated with MF tumor invasion caused by residual tumor nests within fibrosis. V=
seminal vesicle, B=bladder, T=tumor.
82

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