Role of mri in rectal carcinoma

Role of MRI in Rectal Carcinoma
Mohammed Fathy Bayomy, MSc, MD
Lecturer
Clinical Oncology & Nuclear Medicine
Faculty of Medicine
Zagazig University

Extension of Rectum
Rectosigmoid junction
(Variable location from sacral
promontory to S3 level )

Extension of Rectum
Anal verge

Extension of Rectum
Anal verge
Intra-gluteal
cleft

Extension of Rectum
The rectum extends from the anorectal junction to the
sigmoid.

Extension of Rectum
The rectum extends from the anorectal junction to the
sigmoid.
Anal verge
Anorectal
ring
Rectosigmoid
junction
Rectum
Apex of
prostate

Length of Rectum
Approximately 15 cm
long

Parts of Rectum
Rectum can be divided*
into 3 parts:
 Lower 1/3:
0- 6 cm from the anal
verge.
 Mid 1/3:
6-10 cm from the anal
verge.
 Upper 1/3:
verge.
* This division implies that low rectum
comprises the anal canal as well as the
lowermost part of the rectum just above
the anorectal junction.

Parts of Rectum
Rectum can be divided*
into 3 parts:
 Lower 1/3:
0- 6 cm from the anal
verge.
 Mid 1/3:
verge.
 Upper 1/3:
verge.
* This division implies that low rectum
comprises the anal canal as well as the
lowermost part of the rectum just above
the anorectal junction.
5cm
4cm
6cm

Parts of Rectum
Rectum can be divided
into 3 parts:
 Lower 1/3:
0-4 (0-5) cm from the
anorectal ring.
 Mid 1/3:
anorectal ring.
 Upper 1/3:
8-12 (10-15) cm from
the anorectal ring.

Parts of Rectum
Rectum can be divided
into 3 parts:
 Lower 1/3:
anorectal ring.
 Mid 1/3:
anorectal ring.
 Upper 1/3:
8-12 (10-15) cm from
the anorectal ring.
4cm
4cm
4cm

Layers of Rectum
On T2 weighted images, the layers
of the rectal wall can be identified
 The mucosal layer is the fine
innermost low signal intensity
layer (not always seen
separately).
 The submucosal layer is just
deep to the mucosa, is thicker,
and higher signal intensity.
 The muscularis propria (MP) is
the outer, darkest layer.

• Submucosa
(asterisk).
• Muscularis propria:
hypointense band
(white arrowheads)
• Mesorectal fat
(daggers).
• Mesorectal fascia:
thin hypointense line
(black arrowheads)
• Peritoneal attachment
to anterior aspect of
rectum (arrow).
Layers of Rectum

Layers of Rectum
 Mucosa (white arrow).
 Sub-mucosal layer (green
arrow).
 Internal muscular layer
(yellow arrow).
 External muscular layer (red
arrow).

Normal rectum with hyperintense
submucosa (*) and darkly hypointense
muscularis propria (arrow)
Layers of Rectum
• Mucosa: thin hypointense line
• Submucosa: thicker band of high
signal
• Muscularis propria: outer low signal
intensity line

Layers of the bowel wall. Transaxial view demonstrating the layers of
the bowel wall. This image was acquired following radiotherapy, so the
layers of the bowel wall are exaggerated due to tissue oedema
Layers of Rectum

Anal Sphincter Complex
(A) Levator–sphincter complex. (B) Coronal T2W MRI. Levator
ani (dashed arrow) inserting into puborectalis (arrowhead);
anorectal junction (horizontal line); anal canal (vertical
line); internal sphincter (*), intersphincteric space (curved
arrow). Block arrows show the thickest part of external
sphincter (continuous with puborectalis above).

RI showing anatomy of the sphincter complex. Coronal image and
accompanying diagram demonstrating the anatomy of the sphincter
complex as seen on MRI. Note that the rectum goes out of plane and
therefore is not seen in the middle portion of the image (grey box)

Normal appearances of internal anal sphincter (white arrow),
intersphincteric plane (yellow arrow) and external anal
sphincter (black arrow)

Peritoneal cover (Reflection)
 The rectum is partially covered anteriorly and posteriorly by a
peritoneal lining.
 The transition points between peritonealized and
non‐peritonealized aspects of the rectum are called “peritoneal
reflections”.

 The locations of the peritoneal attachments/reflection are
variable between genders and individual patients.
 Anteriorly: peritoneal reflection is typically located deeper in the
pelvis (caudal) than it is posteriorly.
• In women: anterior peritoneal reflection (Douglas pouch) is
often found along posterior aspect of lower uterine segment.
• In men: it is typically found at level of prostate base/seminal
vesicles (recto-vescical pouch).
 Posteriorly: peritoneal reflection is located more superiorly than
it is anteriorly.
 The peritoneum typically attaches along the posterior rectal wall
in a V‐shaped configuration (seagull sign).

(A) Sagittal T2W MRI and (B) axial T2W MRI show the anterior
peritoneal reflection (arrows) at the level of urinary bladder
dome. Both sagittal and axial images have to be viewed.

Sagittal T2-weighted image in 52-
year-old man shows peritoneal
attachment (arrow) above tip of
seminal vesicles (arrowhead).
Sagittal T1-weighted image in
male shows peritoneal
attachment (arrows) above tip of
seminal vesicles.

Mesorectal fascia (MRF)
(A) Sagittal and (B) coronal diagrams show rectum (R),
mesorectal fat (yellow), mesorectal fascia (MRF) in blue,
anterior peritoneal reflection (red), bladder (B), prostate (P). (b)
Cross section at upper, mid, and low rectum shows peritoneal
reflection (red) and MRF (blue)

Mesorectal fascia (MRF)
(A) Axial T2W MRI and (B) coronal T2W MRI. White arrows show
mesorectal fascia (MRF). Black arrow in (A) shows obturator vessels.
Vertical arrows in (B) show the levator ani, forming the roof of ischiorectal
fossa (IRF). MRF thins out as it reaches the levator ani

Major problem of Rectal Cancer
Local
Recurrence
Incomplete
Removal
Adverse
prognostic
factors
Inadequate
treatment
Select
patient to
optimal
treatment

Major problem of Rectal Cancer
CRM: Circumferential resection margin; DRM: Distal resection margin. DMM: Distal
mesorectal margin; LNs: Lymph nodes; MMF: Mesorectal microfoci.

Different Risk groups
Low-risk
group
High-risk
group
Intermediate-risk
group

Two Advancements in Rectal cancer ttt
Neoadjuvant
Chemotherapy

Shortage of other evaluation method
Digital rectal
examination
(DRE)
Endorectal
Ultrasound
(ERUS)
Computed
Tomography
(CT)
N staging
CRM
T staging
N staging
CRM
T staging
CRM
Operator
dependent
Stenosing
lesion
Sphincter
status
T4a

MRI is required to
Select patients
for upfront
surgery or for
NACT-RT
Plan RT
Plan surgery
after NACT-RT

Technical Points
High resolution MRI
Showing Early T2 tumour
Non-High resolution
Same patient – T stage?
High Resolution MRI is needed

Technical Points
 Phased array Coil positioning
critical.
 High Resolution Axial
perpendicular to rectal wall.
 Coronal imaging parallel to
anal canal.
 Don’t forget nodes.
Ensure planes are correct

Technical Points
 Scans should be obtained
perpendicular to the rectal wall, the
sagittal MRI scans are used to plan
the oblique axial images.
 Coronal images should be
undertaken parallel to the anal
canal to visualize the distal
anorectum and distal mesorectal
plane.
Ensure planes are correct
 High resolution coverage should include at least 5cm above the top of the
tumour and to the L5/S1 level for all tumours to ensure that discontinuous
tumour deposits are visualized.

I- Local Tumor Staging
1- Primary Tumor
A) Distance from the Anal Verge
 Tumor location is assessed using
the anal verge as a landmark.
 The anal verge is the distal most
portion of the anal canal, and serves
as the transition point between the
anal mucosa and perianal skin.
 It can be most easily identified on
sagittal T2 weighted images, as
the lowest portion of the anal
sphincter complex at the level of
the inter-gluteal cleft.
 Distance from the verge to the
lowest rolled edge of the tumor is
measured.
Pitfall in this interpretation may arise due
to difficulty in precise identification of the
position of the AV

1- Primary Tumor
 Tumor location is assessed using
the anal verge as a landmark.
 The anal verge is the distal most
portion of the anal canal, and serves
as the transition point between the
anal mucosa and perianal skin.
 It can be most easily identified on
sagittal T2 weighted images, as
the lowest portion of the anal
sphincter complex at the level of
the inter-gluteal cleft.
 Distance from the verge to the
lowest rolled edge of the tumor is
measured.
Anal
sphincter
(lower
portion)
Pitfall in this interpretation may arise due
to difficulty in precise identification of the
position of the AV

1- Primary Tumor

1- Primary Tumor
Low rectal tumor Mid rectal tumor Upper rectal tumor

1- Primary Tumor
B) Craniocaudal length
 This measurement is best
obtained by examining
sagittal T2 weighted
images, obtained parallel
to the long axis.

1- Primary Tumor
B) Craniocaudal length
Upper border
Lower border
 This measurement is best
obtained by examining
sagittal T2 weighted
images, obtained parallel
to the long axis.

1- Primary Tumor
 The puborectalis muscles
converge inferiorly to become
the external sphincter muscles.
C) Distance to the anorectal junction
 The top of the sphincter
complex is identified at the
apex of this curvature, when
the puborectalis curves
inferiorly and vertically,
paralleling the anal canal

1- Primary Tumor
C) Distance to the anorectal junction
Rectal cancer can be divided into:
 Low rectal cancer:
Distal border is 0- 5 cm from the anorectal angle
 Mid rectal cancer:
Distal border is 5-10 cm from the anorectal angle
 High rectal cancer:
Distal border is 10-15 cm from the anorectal angle

1- Primary Tumor
The o’clock position of
tumor on axial view
D) Circumferential location
Tumor extend from 12 o’clock to 8
o’clock

1- Primary Tumor
Angulation
Proper angulation is of vital importance in correctly identifying
tumor borders.
E) Tumor borders

1- Primary Tumor
In this example the axial images were originally not properly angulated (red lines not
perpendicular to the tumor). This resulted in the false impression that the MRF was
involved on the anterior side (red circle). After proper angulation it was clear that the
MRF was not involved (yellow circle).
E) Tumor borders

1- Primary Tumor
Routine axial plane
(dotted lines) planned
on sagittal T2-weighted
image. Arrow shows
tumor axis.
E) Tumor borders
40-year-old woman with upper rectal cancer. This case shows impact of high-resolution
oblique T2-weighted imaging on T staging.
On axial T2-weighted
image, rectal tumor
seems to invade
posterior surface of
uterus (arrowheads).
Thinner slices with
plane (dotted lines)
perpendicular to axis of
rectum and tumor
(arrow)
On HR oblique T2-WI,
there is no invasion of
uterus with visible fat
plane (arrows).

1- Primary Tumor
F) Relationship to the Anterior Peritoneal Reflection
 Based on this assessment, the radiologist determines whether the
tumor is “above”, “below”, or “straddles” (extends both above and
below) the anterior peritoneal reflection.
 The anterior peritoneal reflection can be identified in most cases on
sagittal T2 weighted images, appearing as a thin, low signal line
extending approximately from the posterior aspect of the dome of the
bladder to the ventral aspect of the rectum.
 Interpretation of the anterior peritoneal reflection can be
challenging.
 Proper evaluation requires careful review of T2 weighted axial and
sagittal images.

1- Primary Tumor

1- Primary Tumor
On axial imaging, the apex of the
peritoneum attaches to the anterior rectal
wall in a V‐shaped configuration.

1- Primary Tumor
 The point at which the peritoneal
reflection commences can also be
recognized on axial MRI images
through the mesorectum.
 Serial axial images show the
anterior mesorectal fat becoming
progressively thinner.
 The point where no anterior
mesorectal fat is seen is generally
where the peritoneal reflection
begins.

1- Primary Tumor
G) Tumor Morphology
Solid mass Annular Polypoid with stalk
Polypoid
Semiannular

1- Primary Tumor
G) Tumor Morphology
Semiannular
Rectal doughnut

1- Primary Tumor
G) Tumor Morphology
Transaxial view demonstrating a
polypoidal tumour entirely filling
the rectal lumen. There is
invasion through the base of the
stalk (white arrow). The surface
of the tumour has clefts
containing mucin secretion (black
arrow)
Polypoid with stalk

1- Primary Tumor
H) Signal Intensity
 Rectal adenocarcinoma is
commonly intermediate
signal on T2 weighted
images (slightly higher than
skeletal muscle; moderately
higher signal compared to
the muscularis propria)

1- Primary Tumor
H) Signal Intensity
 Mucinous rectal adenocarcinoma can be recognized by markedly
hyperintense T2 signal (like fluid).
 The degree of mucin is variable; some lesions are almost entirely
mucinous, while others may contain small pockets of mucin.

1- Primary Tumor
H) Signal Intensity
Mucinous tumour.
Sagittal view showing a
mucinous tumour (white
arrow). The invasive border
(posteriorly) is diffusely
infiltrating

2- MR T Category
 T category is based on depth of tumor invasion (extent of the
tumor within the rectal wall and extramural spread into the
perirectal tissues and organs).
 Rectal cancer begins as a mucosal process and as it
advances can invade into deeper layers of the bowel wall and
beyond the wall into the mesorectal fat.
 T staging is decided by examining the T2W signal intensity.

 Tx: primary tumor cannot be assessed
 T0: no evidence of primary tumor
 T1: tumor invades submucosa
 T2: tumor invades muscularis propria
 T3: tumor invades through the MP into the perirectal tissues
 T4a: tumor invades through the visceral peritoneum
 T4b: tumor directly invades or is adherent to other organs or
structures.
2- MR T Category
According to the 7th edition of TNM system
The current method for describing the depth of tumor invasion
on MRI is based on the AJCC T staging system.

2- MR T Category
Tumors extend upto the submucosaT1

2- MR T Category
T1
No invasion of the
muscularis propria
layer

2- MR T Category
Tumors extending into the muscularis propria.T2

2- MR T Category
Semicircular T2 tumor in the
distal rectum, with sharply
demarcation of the external
muscular layer.
T2

2- MR T Category
T2
Partial interruption of
the hypointense
muscular ring

2- MR T Category
Spread beyond the muscularis propria into the perirectal fat. This is well seen on
HR-MRI as loss of continuity of the muscularis propria with extension of the
tumor signal intensity into the perirectal fat or as perirectal fat stranding.
T3

2- MR T Category
T3

2- MR T Category
MRI Category T3 – Coronal and axial oblique high resolution T2W images
demonstrate T3 rectal tumor penetrating through the rectal wall into the mesorectal
fat in two different patients (white arrow).
T3

2- MR T Category
T3 MRF- rectal cancer. Semicircular mid rectum tumor with tumor
invasion into the mesorectum, extending from app. 1-4 o’clock of the
circumference.
T3

2- MR T Category
T3
Interruption of the
hypointense
muscular ring with
invasion of the
surrounding fat tissue

2- MR T Category
T4
a

2- MR T Category
MRI Category T4a – Sagittal T2W image
demonstrates a T4a rectal tumor
penetrating through the rectal wall and
involving the peritoneal reflection (white
arrow).
T4a

2- MR T Category
T4a

2- MR T Category
Axial T2W MRI. (a and b) The anterior peritoneal reflection (arrows) is invaded by a
rectosigmoid tumor (*) –stage T4a; needs preoperative radiation to minimize local
recurrence.
Rectosigmoid tumors without peritoneal invasion are offered upfront surgery
T4a

2- MR T Category
Peritoneal metastases
T4a

2- MR T Category
MRI Category T4b – Sagittal and axial T2W images demonstrating T4b disease.
In the image on the left, a high T2 signal mucinous tumor is invading the prostate gland
(white arrow).
In the image on the right, tumor is invading vagina and at least abutting puborectalis
(white arrow points to vaginal wall, vagina contains high signal intensity gel).
T4b

2- MR T Category
T4b

2- MR T Category
Rectal cancer with invasion of seminal vesicle
T4b

2- MR T Category
MRI category T4b – Axial T2W
image demonstrates T4b disease
with bulky tumor invading the
sacrum (white arrows)
T4b

2- MR T Category
40-year-old man with rectal tumor
invading right seminal vesicle
(arrow) and levator ani
(arrowheads).
T4b

2- MR T Category
53-year-old woman with rectal
tumor (asterisk) invading left
posterior vaginal wall (arrow).
T4b

2- MR T Category
T1/T2
Differentiation between T1 and T2 tumors confined to the rectal
wall can be difficult by MRI and may be supported by EUS, this
is typically only required when considering local resection.
Assigning MRI T‐Categories by MRI has several
challenges:

2- MR T Category
MRI Category T1/T2 – High resolution oblique axial and sagittal T2W images through
the rectal cancer demonstrate T1/T2 tumors confined to the rectal wall in two
different patients (arrows). The low signal intensity outer muscularis propria is
preserved in both cases.

2- MR T Category
T2/T3
Spiculation of the perirectal fat
 Nodular or broad based tumor extensions into the
mesorectal fat should be reported as T3 tumor
 Very fine, low signal intensity spicules should be considered
fibrosis, not tumor.
 Intermediate signal intensity thicker spicules may be
considered suspicious for tumor extension.

2- MR T Category
Low rectal tumor in 58-year-old man with
tumoral spiculations (intermediate signal
intensity) of mesorectal fat (arrowheads).
Non-tumoral spiculation (low signal intensity) of
mesorectal fat without nodular extension to
tumor (arrowheads) beyond muscularis propria
in 67-year-old woman; pathology revealed T2
tumor.

2- MR T Category
Low rectal tumor in 63-year-old man with
nodular extension to mesorectal fat. Double-
headed arrow shows shortest distance from
most penetrating part of tumor and mesorectal
fascia.
Midrectal tumor in 80-year-old man with
massive extension to mesorectal fat and
mesorectal fascia infiltration (arrowheads).
Double-headed arrow shows extramural depth
of invasion.

2- MR T Category
(A) there was perirectal tumor invasion.
(B) the tumor was limited to the bowel wall, i.e. a T2-tumor.
The perirectal stranding in the latter case was the result of a
desmoplastic reaction.

2- MR T Category
Thin arrows show darkly hypointense spicules (T2 tumor with
desmoplastic reaction).

2- MR T Category
T3
 The most common appearance of rectal
cancer on MRI is an annular or
semiannular tumor of intermediate
signal intensity projecting into the bowel
lumen. As tumor advances and
increases in size, the tumor frequently
begins to ulcerate centrally.
 The area of deepest invasion of a tumor often overlies a central
area of ulceration and is rarely at the margin or raised, rolled edges
of the tumor.

2- MR T Category
Diffusion weighted imaging (DWI) can
be useful for tumor and lymph node
detection in primary staging.
The figure shows a semicircular T3
tumor with perirectal invasion
extending from 3-9 o'clock of the
circumference.
Corresponding diffusion restriction on
the ADC map and calculated DWI (b =
1000 s/mm2)

2- MR T Category
T4b
 Definite invasion: loss of
intervening fat plane and
corresponding T2 signal
abnormality within the adjacent
structure.
 Possible invasion: loss of
intervening fat plane but no
corresponding T2 signal
abnormality within the organ.

2- MR T Category
 No invasion: preservation of the
intervening fat plane.
It is not possible on imaging to
determine whether the tumor abuts or
is adherent to adjacent structures if
there is loss of fat plane but no
abnormal T2 signal within the structure
to indicate definite invasion. It is best
to describe abutment with possible
invasion in this instance.

2- MR T Category
Axial T2W MRI.
(A) No invasion: Solid arrow shows clear plane with prostate that shows normal
signal intensity (dashed arrow).
(B) Definite invasion: Tumor (*) invades prostate showing altered signal (arrow).
(C) Possible invasion of prostate in midline (arrow) by tumor (*)

2- MR T Category
On the sagittal T2W-image there is loss of fat plane between the rectum and
the posterior wall of the vagina.
On axial images the relatively low signal intensity of the tumor is seen to
extend into the posterior wall of the vagina (arrow).

2- MR T Category

2- MR T Category
These images demonstrate a tumor extending into the posterior wall of the
uterus.

2- MR T Category
T4 tumour. Transaxial view
showing a T4 tumour with
invasion into the prostate
anteriorly (white arrows)

3- Extramural Depth of Invasion (EMD)
 Defined as the extension
of tumor into the
perirectal fat beyond the
muscularis propria
 EMD should be reported
for all T3 tumors
 For T1 and T2 tumors,
EMD should be
recorded as “0 mm”.

 Measuring EMD from outer
edge of muscularis propria to
outer edge of leading tumor

 Measuring EMD
from outer edge of
muscularis propria
to outer edge of
leading tumor.

 EMD is measured for the
definitive tumor border only and
does not include spiculations
into the perirectal fat.
 Invasive border may be from
broad based bulging or nodular
tumor mass or from EMVI if in
continuity with the primary tumor
mass.

EMD = 5 mm EMD = 21 mm

Although not considered in the AJCC staging system (7th edition)
T3 subcategories are incorporated into various MR reporting
templates based on EMD:
 T3a: < 1mm
 T3b: 1 ‐ <5 mm
 T3c: 5‐15 mm
 T3d: > 15 mm
Measuring EMD of < 1mm can be challenging because of surrounding
desmoplastic reaction, fibrosis, or inflammation and can be sources of
measurement error.

T3a (EMD <1 mm) T3b (EMD =1-5 mm)

T3c (EMD =5-15 mm) T3d (EMD >15 mm)

T3d (EMD > 15 mm)

4- Low Rectal Tumor
 Low rectal cancers are defined as tumors that arise
within 5 cm of the anal verge and account for 1/3rd of
all rectal cancers.
 Tumors in this region warrant special mention due to
challenges these tumors pose from treatment
perspective.
 Surgical treatment of low rectal tumors is technically
more difficult as the mesorectal fascia tapers
downwards in this region.

4- Low Rectal Tumor
 Given this anatomy, there is a higher incidence of
threatened CRM and local recurrence in low rectal
cancers.
 Further low rectal cancers may involve the anal
sphincter complex, pre‐operative knowledge of which
is vital as that determines surgical approach.
 If the anal sphincter is not involved by the tumor,
patients are treated with sphincter preserving, low
anterior resection

4- Low Rectal Tumor
 If the anal sphincter is involved by the tumor, surgical
approach depends upon the radial extent of the
tumor.
 If the intersphincteric plane and mesorectal fascia are
not involved by the tumor, it may still be feasible to
consider intersphincteric resection with ultra‐low
coloanal anastomosis.

4- Low Rectal Tumor
 However, if the tumor breaches the intersphincteric
plane, anal sphincter preservation may no longer be
possible as these would require radical extra‐ levator
abdominoperineal resection with permanent
colostomy.
 When reporting MRI of low rectal cancers, it is
important to first identify the relationship of the inferior
margin of the rectal tumor to the top border of
puborectalis

4- Low Rectal Tumor

4- Low Rectal Tumor
 Based on this relationship, low rectal tumors may be
broadly classified as:
(i) tumors in which the lower extent of the tumor is
clearly above the top border of puborectalis and
(ii) tumors in which the lower extent of the tumor is at or
below the top border of puborectalis.

4- Low Rectal Tumor
 Low rectal tumors in which the lower margin of the
tumor is above the top border of puborectalis may be
amenable to sphincter sparing low anterior resection
and should be reported similarly to upper and mid
rectal tumors.

4- Low Rectal Tumor
 For low rectal cancers in which the lower extent of the
tumor is at or below the top border of puborectalis, it
is important to specify the degree of radial extent of
the tumor as follows:
• Invades internal sphincter only
• Invades internal sphincter and extends into
intersphincteric plane
• Invades into or through external sphincter

4- Low Rectal Tumor
Coronal T2W MRI
showing sphincter status.
(A) Arrow
shows intersphincteric
space (ISS) spared by
tumor (*). (B) Arrow
shows ISS invasion. (C)
Mucinous tumor (*)
invades ISS and external
sphincter (arrow). (D)
Tumor (*) invades levator
ani (arrow). Dashed
lines show incision for
extra-levator abdomino-
perineal resection

4- Low Rectal Tumor
Low rectal tumor with involvement of the internal sphincter but intersphincteric
plane is not involved. This would be amenable for intersphincteric dissection.

4- Low Rectal Tumor
Low rectal cancer with extension of the tumor in the internal sphincter and
intersphincteric space. The longitudinal muscle layer within the right
intersphincteris space, can still be depicted (arrow)

4- Low Rectal Tumor
Low rectal tumor invading the internal sphincter, intersphincteric plane and
extending to external sphincter. This tumor is not amenable for sphincter
sparing surgery.

4- Low Rectal Tumor
Low rectal tumor invading the external anal sphincter

4- Low Rectal Tumor
Low rectal tumor invading the internal sphincter, intersphincteric plane
and external anal sphincter.

4- Low Rectal Tumor
Low rectal tumor extending beyond the intersphincteric plane and invading
levator ani in another patient. This would require extra levator
abdominoperineal resection with colostomy.

4- Low Rectal Tumor
Axial T2-weighted Contrast-enhanced T1-weighted
Large locally advanced low rectal cancer invading sphincter complex, extending laterally to right
ischiorectal fossa and right obturator externus muscle, and invading anterior vagina. In this
patient, conventional abdominoperineal resection (dotted line) would result in positive margin.
Wide abdominoperineal excision and pelvic exenteration (solid line) were performed on basis of
MRI findings.

Involves removal of the rectum and anal canal, requiring a permanent
colostomy. It is performed in tumors reaching AV or less than 1 cm from AV,
but sparing the intersphincteric space, levator, and adjacent pelvic organs.
Performed in upper rectal and mid-rectal cancers with anastomosis at 5 cm
and 2 cm distal to tumor margin, respectively. Anal canal is intact.
4- Low Rectal Tumor
Anterior resection (AR)
Offered in low rectal cancers above the anorectal ring with anastomosis at 1
cm distal to the tumor margin. Sphincter is preserved.
Low Anterior resection (LAR)
Abdomino-perineal resection (APR)

Offered in rectal cancer invading adjacent organs, but not reaching lateral
pelvic wall. It involves removal of the rectum with pelvic organs such as
prostate, seminal vesicles, bladder, or vagina and/or uterus.
Performed in tumors that invade intersphincteric space, external sphincter/
levators, but spare adjacent pelvic organs. Entire levator ani is removed along
with APR.
4- Low Rectal Tumor
Intersphincteric resection
Performed in select tumors close to anorectal ring, which involve the internal
sphincter but spare the intersphincteric space as well as adjacent pelvic
organs. The external sphincter is preserved averting the need for permanent
colostomy.
Extra-levator APR
Exenteration

4- Low Rectal Tumor
Thetumoris5cm
ormoreabovethe
AV(freesphincter)
Thetumoris0-5cm
fromtheAV
Invade internal sphincter (T2) &
>1cm from AV
<1cm from AV
*Invade inter-sphincteric space (T2)
*Invade External sphincter (T3)
*Invade Levator Ani
AR or LAR
Inter-sphincteric
APE
APR
ELAPE

4- Low Rectal Tumor
Coronal schematic diagram of lower rectum (left) and MR image of lower rectum (right) in 58-year-
old woman depict anal sphincter complex and surgical dissection planes. Standard low anterior
resection (LAR) is reserved for mid- and high-rectal tumors without invasion to pelvic flor muscles.
Intersphincteric resection (ISR) dissects internal anal sphincter at about level of dentate line.
Abdominoperineal resection (APR) involves removal of rectum along with sphincter complex. AV =
anal verge, EAS = external sphincter complex, IAS = internal anal sphincter, ISP = intersphincteric
plane, PR = puborectalis, LA = levator ani.

4- Low Rectal Tumor
Incision lines for surgical procedures: Anterior resection (green);
intersphincteric resection (red), APR (dotted), extra-levator APR (orange).
Sphincter is removed in the latter two surgeries.
ES: External sphincter, IS: Internal sphincter

5- Extramural vascular invasion (EMVI)
 Refers to the extension of rectal tumor beyond the muscularis
propria into the adjacent vessels in mesorectum
EMVI
Negative
 Pattern of tumor extension
through muscularis propria is
not nodular or no tumor
extension in the vicinity of
any vascular structure.
 If stranding is demonstrated
near extramural vessels,
these vessels are of normal
caliber with no definite tumor
signal within.

EMVI Positive
 Intermediate signal intensity within vessels in the vicinity of the
tumor or obvious irregular vessel contour.

Axial and coronal T2 weighted images show locally advanced rectal cancer extending beyond
muscularis propria and into the mesorectal vessel (white arrow). Note the tumor signal intensity
replacing the normal flow void within the mesorectal vein.

EMVI is suspected if a vascular structure in close proximity to the tumor is expanded, irregular or
infiltrated by tumor signal intensity

The image shows a circular T3 tumor with extramural vascular invasion (EMVI), bridging to the
right extra-mesorectal space (yellow arrow).

Coronal T2-weighted image of right-side lesion shows irregularly expanded vessel with
heterogeneous tumor signal intensity (arrowheads) in vicinity of rectal tumor (asterisk) indicative
of EMVI.

(A) Axial T2W MRI and (B) coronal T2W MRI show rectal tumor (*) from
12o’clock to 7o’clock position with finger-like extramural venous invasion
(EMV) into left perirectal veins (white arrows). Black arrow in (B) shows a
metastatic left perirectal node

6- Circumferential Radial Margin (CRM)
 CRM is a pathologic term that is specific to the surgically
dissected surface of the specimen.
 It does not refer to the imaging boundaries visible on MRI.
 The CRM is marginated by the anterior peritoneal reflection,
and it refers specifically to the non‐peritonealized, or caudal
aspect of the rectum.

 The configuration of the CRM depends on the location of the
rectal tumor:
• Low rectal tumors have a circumferential CRM (completely
caudal to peritoneal reflection)
• Mid rectal tumors have a CRM that is present posteriorly
and laterally, but absent anteriorly (as the anterior surface is
peritonealized).
• High rectal tumors have a small, focal CRM.

 The CRM is determined pathologically by the extent of the
surgical resection, and therefore cannot be predicted on MRI.
 The term “mesorectal fascia” (MRF) is considered the imaging
equivalent of the CRM, and by convention, is used for MR
based staging and synoptic reporting
 Based on the above, the CRM is not applicable to tumors
located above the anterior peritoneal reflection, where the
rectum is peritonealized.

 Similar to the pathological CRM, the MRF is only
circumferential for rectal tumors below the anterior peritoneal
reflection. The term does not apply to upper, anterior, and
anterolateral tumors above the peritoneal reflection where the
rectum is peritonealized.
 The minimum distance to the MRF refers to the shortest
distance of the most penetrating margin of primary tumor to the
MRF.

 A positive CRM is defined as the nodular or pushing border of
the tumor, within 1 mm of the MRF. (This does not include
spiculations or haziness in the perirectal fat.)
 Potentially suspicious lymph nodes, tumor deposits, and EMVI
are not used as criteria for a positive CRM, but may be
described for purposes of surgical planning.
 The minimum distance to the MRF should be reported only for
≥T3 stage tumors, where the MRF can be adequately seen or
reasonably estimated (i.e. at the level of the prostate and
seminal vesicles).

T3 MRF+ tumor within 1mm of MRF
MRF- no tumor within 1 mm of MRF

CT and MRI showing tumour distance to mesorectal fascia. Transaxial views
through a tumour at the same level on MRI (left) and CT (right). The anterior
margin (white arrows) appears involved on CT, but a clear margin can be seen
on MRI

Low rectal tumor with involved mesorectal fascia

 In addition to the distance to the MRF, the location, image and
series number of the penetrating component of disease should
be reported. Location may be provided by laterality (left or right
perirectal space), clockface convention, and location relative to
the tumor (e.g. above/below primary lesion).
 The distance to the MRF should be reported as “not applicable”
for any tumor above the peritoneal reflection that involves the
peritonealized portion of the rectum (i.e., upper, anterior and
anterolateral tumors).

 T4 tumors involving the peritonealized portion of the rectum
(i.e., T4a tumors), the distance to the MRF should be reported
as “not applicable”
 For T4 tumor involving adjacent structures (i.e., T4b), the
distance to the MRF should be reported as “0”.

 A tumor – MRF distance > 2 mm is CRM negative status.
 A distance of <1 mm between the advancing tumor edge and
MRF is indicative of a CRM-positive status. Also, CRM positivity
could be due to tumor/perirectal nodes/deposits/tumor
stranding reaching <1 mm of the MRF.
 When the tumor/node/deposit–MRF distance is between 1 and
2 mm, the CRM is regarded as “threatened”.

 A potential positive margin is
defined as tumor lying within 1mm
if the mesorectal fascia.
 This applies to
A- Suspicious lymph node.
B- The main tumor.
C- Extramural vascular invasion.
D- Tumor deposit (a tumor deposit
< 3mm is classfied as a nodule
and >3mm is classified as
node)

Axial T2W MRI. (A) Black arrow shows the mesorectal fascia (MRF).
Distance between tumor and MRF is wide as shown by double-ended
arrow (CRM -ve).
(B) Perirectal tumoral stranding from 9 o’clock to 2o’clock position
(arrows) reaching the MRF at 12o’clock position (CRM +ve).

Axial T2W MRI.
(a) Tumor deposit in the right mesorectal fat (arrow) located <1mm
from the MRF (CRM +ve).
(b) Left mesorectal node (arrow), 1-2 mm from the MRF indicating a
threatened CRM. Node has heterogeneity and irregular margins

The mesorectal fascia is
threatened
posterolaterally on the
left side (white arrows)

Dashed line outlines the mesorectal
fascia, which is the CRM in a T3a
tumor with predicted clear CRM.

T3a tumor far away from the
mesorectal fascia (black arrow).
However, suspicious lymph node on
the mesorectal fascia (white arrow)
raises the possibility of potential
CRM involvement (CRM = 0 mm).

T3d tumor confined within muscularis
propria where the tumor is abutting the
mesorectal fascia (arrows; at this level
the tumor is T2). Invasive border
appears to be posterolaterally on left
(white arrowhead). The CRM
regarding the tumor is evaluated at 5
mm. However, there are two mixed
signal intensity lymph nodes (black
arrowhead) abutting the mesorectal
which leads to a CRM of 0 mm.

T3c tumor with EMVI bordering the
peritoneum (white arrow) and irregular,
heterogeneous signal intensity lymph
nodes–there is tumor extension
through the lymph node capsule,
which is abutting the mesorectal fascia
(black arrow) (predicted CRM = 0
mm).

II- Lymph Nodes
In the TNM system, disease involving only the
regional lymph nodes, including the mesorectal and
obturator/internal iliac lymph nodes, accounts for N
stage; involvement of other nodes is regarded as
metastatic disease (M1)

II- Lymph Nodes
Any mesorectal lymph node or tumor deposit with
an irregular border, mixed signal intensity and/or
size > 9 mm in the short axis should be reported as
“suspicious”
1- Mesorectal Lymph Nodes and Tumor Deposits

II- Lymph Nodes
Malignant
Characteristics
Indistinct Heterogenous Round
Size
(Short axis)
< 5 mm 5-9 mm > 9 mm
+ 3
malignant
characteristics
+ 2
malignant
characteristics
Always
suspicious

II- Lymph Nodes
 Metastatic LNs distribute across wide range of nodal sizes so
small met LNs are under staged while large sized reactive LNs
are over staged.
 A size criterion of equal to or greater than 9 mm in the short
axis has been selected.
 All of the mesorectal lymph nodes will be resected during a
standard TME surgery. Diffusion weighted and post contrast
imaging can be helpful in detecting lymph nodes but are not
suitable for characterization.
A) Lymph Node Size

II- Lymph Nodes
A) Lymph Node Size

II- Lymph Nodes
 Lymph node border and signal properties appear to be more
specific predictors of lymph node metastasis than size criteria.
 Notably, irregular borders and mixed signal intensity on T2-
weighted imaging are individually highly specific and, in
combination, are sensitive and specific to predict lymph node
metastasis
B) Lymph node border and signal characteristics

II- Lymph Nodes
Heterogeneous and irregular perirectal lymph nodes, likely metastatic.

Oblique axial T2W image through
a mucinous tumor demonstrates
high signal intensity within a
metastatic mesorectal lymph node
(white arrow), similar in intensity to
the primary tumor. Sometimes
because of the relative iso-
intensity with the mesorectal fat,
these can be overlooked.
II- Lymph Nodes

Axial T2-weighted image shows three
heterogeneous enlarged lymph nodes in upper
mesorectum and right obturator region
(arrowheads).
II- Lymph Nodes
Involved nodes shows heterogeneous
enhancement (arrows) on contrast-enhanced
T1-weighted image.

II- Lymph Nodes
On this sagittal T2W-image a low rectal cancer with multiple nodes in the
mesorectal fat on the posterior side. Some of the nodes on this image are
heterogenous and have irregular borders.

II- Lymph Nodes
Inverted Diffusion weighted images can be helpful in detecting lymph nodes

II- Lymph Nodes
Axial T2W MRI shows a hyperintense mucin containing node in the left
peri-prostatic region (arrow), which could be overlooked due to inadequate
contrast.

II- Lymph Nodes
Axial T1W MRI shows the node (arrow) which is hypointense against the
bright fat

II- Lymph Nodes
Arrows at 1-2 o’clock show perirectal spread (T3 tumor). Left mesorectal
node (white arrow).

II- Lymph Nodes
Axial T2 W MRI shows a 5-mm-sized right mesorectal node (long arrow)
and a left mesorectal deposit <3mm (short arrow).

II- Lymph Nodes
On axial T2-weighted image, two oval nodules
suggestive of mesorectal nodes are evident on
right (arrowhead) at 9-o’clock position and left
(arrow) at 3-o’clock position of rectum.
Coronal T2-weighted image of left-side lesion
(arrow) shows that lesion remains oval in shape,
which suggests that lesion is metastatic
mesorectal lymph node.

II- Lymph Nodes
C) Distribution
 Most involved mesorectal lymph nodes are found at or
proximal to the level of the tumor. Although mesorectal lymph
nodes below the level of the tumor are uncommon, they may
affect the extent of both the radiation field and surgery.

(A) Axial T2W MRI shows rectal tumor (*) from 7o’clock to 1o’clock
position; T2 tumor (no spread into mesorectal fat).
(B) Coronal T2W MRI. White arrows in (a and b)show mesorectal
fascia; black arrow in (B) shows perirectal deposits (<3 mm).
II- Lymph Nodes
C) Distribution

II- Lymph Nodes
D) Other
 The primary role of staging MRI is to differentiate between
node negative (N0) and node positive (N+) disease.
 Total number of lymph nodes and of suspicious lymph nodes
can be detected by MRI.
 The IMA nodes are important for treatment planning
(especially in higher risk patients with positive mesorectal
nodes or positive EMVI).

II- Lymph Nodes
2- Extra‐mesorectal lymph nodes
 For locoregional extra-mesorectal non-TME lymph nodes (i.e.,
internal iliac or obturator) we recommend using the same
criteria as for mesorectal lymph nodes.
 Non total mesorectal excision (TME) extra-mesorectal lymph
nodes (including external and common iliac and inguinal
lymph nodes) are considered metastatic (M1) disease.
 For M1 lymph nodes, we recommend using a 1 cm short axis
cut off (as commonly used in the rest of the body), or smaller if
lymph nodes have obvious signal heterogeneity and/or
irregular borders.

II- Lymph Nodes

T2W coronal (left) and axial (right) images demonstrate metastatic internal
iliac lymph nodes (white arrows).
II- Lymph Nodes

Circular T3 tumor with extramural vascular invasion (EMVI), bridging to the right
extra-mesorectal space (yellow arrow). there is a suspicious extra-mesorectal
lymph node (green circle).
II- Lymph Nodes

Left iliac node (thick arrow).
II- Lymph Nodes

T2 rectal tumor (*) with a left extra-mesorectal node (arrow)
II- Lymph Nodes

Synoptic MRI report (checklist) for primary staging

MRI findings that justify preoperative chemo-radiation
CRM +ve or threatened
T3b tumors with >5 mm spread into perirectal fat
Sphincter complex involved
Extra-mesorectal nodes (MRI used to re-plan RT field)
T2 and T3 disease with bulky mesorectal nodes
Adjacent organ invasion (for pelvic exenteration)
Invasion of the anterior peritoneal reflection

Post-treatment Changes
Include the following:
 Edematous submucosa that appears uniformly T2 hyperintense
masking the residual tumor. Precise DRE notes are invaluable
in assessing the MR images
 Intense perirectal stranding may be difficult to evaluate. Dark
hypointensity in the stranding could represent fibrosis,
particularly if the previous stranding showed intermediate
signal intensity
 Thickening of the MRF circumferentially could be due to post
RT fibrosis.

 Thickening of the MRF circumferentially could be due to post
RT fibrosis.
 Darkly hypointense tissue extending into the mesorectal fat
may represent fibrosis, but could harbor small residual tumor.
Intermediate signal intensity usually represents residual tumor,
but cannot rule out fibro-inflammatory response. Only complete
disappearance of the tumor with a normal two-layered rectal
wall is a sign of yT0 , i.e. complete pathologic response.

A: Tumor remain with mainly gross nodular
pattern.
B: Scarring contiguous to mesorectal
fascia. A thick scar cannot exclude
residual tumor, careful evaluation of
signal intensity can be helpful.
C: Thin, linear scar extending to
mesorectal fascia can be interpreted as
fibrotic reaction.
D: Multiple linear thin scars in the
mesorectum can be interpreted as
fibrosis, if they demonstrate very low
signal intensity.

(A) Coronal T2W MRI shows thickened hyperintense submucosa
due to edema (long arrow) with the intact muscularis (short
arrow).
(B) Axial T2W MRI with diffusely thickened mesorectal fascia
(arrows)

Tumor response
 Currently, MRI is the technique of choice for local restaging
following NACT-RT and addition of a DWI sequence is useful.
 The use of routine contrast-enhanced T1W images is currently
not recommended even in the post treatment assessment
protocol.
 DWI-MRI added to T2W sequences helps evaluate the
response of the primary lesion, but was less useful in predicting
response in the nodes

Tumor response
 There is also research in progress evaluating the accuracy of
dynamic contrast-enhanced MRI (DCE-MRI) in detecting
response in rectal cancer. It is a useful tool for nodal staging,
but not for tumor stage or CRM involvement or detecting
complete response.
 Lymph node specific MRI contrast agent (gadofosveset) has
also been evaluated for nodal restaging in rectal cancer with
reported high performance.

Tumor response
 Ideally, response is evaluated by comparing with pre NACT-RT
MRI. However, if the pretherapy MRI is not available, the
disease stage and information for surgical planning could be
described in the post-treatment MRI (that is ordered 6-8 weeks
after completion of NACT-RT).
 Tumor response (yT stage and CRM) and nodal response (yN
stage) are assessed by studying the T2 signal intensity.

Response is assessed by the following:
Tumor response
 Studying tumor signal intensity in the submucosa, muscularis
propria, and extramural component.
 If the outer surface of the muscularis is intact with a complete
dark hypointense ring with no mesorectal extension, the tumor
is yT2 stage
 Persistent mesorectal extension represents a tumor of yT3
stage.

Tumor response
 Non-mucinous tumors may show response in the form of
mucinous degeneration. This is seen as pools of mucin that are
homogeneously brightly hyperintense areas on T2W-MRI
 Mucinous tumors may respond by disappearance of the
previous intermediate signal intensity areas (persistence of
which signifies non-response).

Tumor response
Nonmucinous tumor
(arrow)
Mucinous degeneration
‘’hyperintense focus) (arrow)
Before CRT After CRT

Tumor response
 Regression in tumor size: (a) by measuring the craniocaudal
extent in cm; (b) there is no consensus on using tumor
volumetry measured with dedicated software.
 Regression in CRM status: if a well-defined fat plane (that was
previously absent) appears between the MRF and the
stranding, it represents response.
 Regression in nodal size with homogeneity replacing previous
heterogeneity is an indicator of sterilized node. Increase in size
and number of nodes indicates progression.

Tumor response
Tumor (solid arrows)
and node (dashed
arrows) with
intermediate signal
Tumor (solid arrows) and node
(dashed arrows) with
hypointense signal and both
regress in size
Before CRT After CRT

Tumor response
Before
CRT
After
CRT
Large with intermediate
signal intensity
Restricted diffusion Large tumor enhancement
Marked fibrosis Non-Restricted diffusion Marked interval decrease in
tumor size and enhancement.

Histopathologic grading of tumor regression in
colorectal carcinomas:
Tumor response

MRI Grading for Rectal Tumor Regression:
Tumor response

Tumor response
MRI Tumor regression grade (mrTRG)
mrTRG 1: Complete radiologic response; no evidence of any abnormality.
mrTRG 2: Good response: dense fibrosis (>75%); no obvious residual tumor or minimal
residual tumor.
mrTRG 3: Moderate response > 50% fibrosis or mucin, and visible tumor).
mrTRG 4: Slight response: small areas of fibrosis or mucin, but mostly tumor.
mrTRG 5: No response, same appearance as original tumor.

Synoptic MR report (checklist) for restaging after
preoperative chemo-radiation

This axial T2W-image is of a patient with extramesorectal nodal recurrence
after TME (arrow).
II- Lymph Node Recurrence

Role of mri in rectal carcinoma

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Role of mri in rectal carcinoma

Similar to Role of mri in rectal carcinoma (20)

More from Mohammed Fathy

More from Mohammed Fathy (20)

Recently uploaded

Recently uploaded (20)

Role of mri in rectal carcinoma