This document provides an overview of imaging techniques used to evaluate the large bowel and various pathologies that can affect it. It discusses anatomy, investigations like barium enema and CT colonography. Conditions covered include large bowel obstruction, colorectal tumors like polyps and adenomas, and polyposis syndromes. Imaging findings for various lesions are presented along with descriptions of features seen on barium enema, CT, and colonoscopy.

1. IMAGING OF THE
LARGE BOWEL
Dr.Archana Koshy
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2. OVERVIEW
1. Anatomy
2. Investigations
3. Large bowel obstruction .
4. Colorectal tumours
5. Diverticular disease
6. Colitis
7. Miscellaneous conditions
8. Rectum and presacral space
9. Anus
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6. • The colon is necessary for optimal absorption of nutrients,
water and electrolytes and transit and storage of residue .
• Colonic innervation is extremely complex .
• Input from the Autonomic nervous system , extra intestinal
autonomic ganglia and the enteric nervous system
• Certain sites are prone to physiological narrowing – Ileocaecal
valve .
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7. RADIOLOGICAL INVESTIGATIONS
• PLAIN FILMS : (ERECT/SUPINE)
1. Intraluminal Colonic gas is normal
2. Close temporal proximity to either sigmoidoscopy or
colonoscopy may cause excessive colonic gas – should not be
mistaken for a pathology .
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8. • BARIUM ENEMA
1. Gold standard technique for imaging fine
mucosal detail .
2. Scrupulous colon cleansing is mandatory for
high quality studies .
3. Barium suspensions are contra indicated if
there is a risk of colonic perforation .
4. A series of films are taken to image the entire
colon in double contrast .
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9. • EVACUATION PROCTOGRAPHY (DEFECOGRAPHY)
1. Images rectal configuration during evacuation of a barium
paste
2. The subject is seated upright on a specifically designed radio
opaque commode.
3. Used to investigate difficult rectal evacuation .
4. May be modified by the addition of bladder , vaginal and
small bowel contrast – the entire pelvic floor .
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10. • COLONIC TRANSIT STUDIES
1. Used to investigate severely constipated patients
2. Measurement of whole gut transit time using radio opaque
markers ,
3. Ingested and followed by an abdominal film after an appropriate
interval .
• RECTAL ULTRASOUND
1. Uses a 360⁰ rotating endoprobe
2. Obtains high resolution axial images of the rectal wall
3. Primarily used to stage tumours .
• ANAL ENDOSONOGRAPHY
1. Modified rectal endoprobe to image the anal sphincters in
patients who are anally incontinent .
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11. LARGE BOWEL OBSTRUCTION
• Acute abdominal emergency with high morbidity and
mortality rates if left untreated.
• Abdominal radiography is usually the initial imaging
study performed .
• Computed tomography is the imaging method of
choice as it can establish the diagnosis and cause of
large-bowel obstruction.
• A contrast agent enema may be used to confirm or
exclude large-bowel obstruction.
• The marked distension of colon proximal to the level of
obstruction leads to
1. Mucosal edema
2. Bowel ischemia
3. If not treated, bowel infarction and perforation.
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12. • Patients with LBO are usually elderly .
• signs and symptoms are often insidious in
contrast to the abrupt onset of symptoms
seen in most SBOs
• Abdominal pain, constipation or obstipation
and abdominal distension .
• The major sites of obstruction include the
cecum, hepatic and splenic flexures and
recto-sigmoid colon.
• Occurs more frequently within the left colon
.
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X-ray abdomen, supine view shows a
HUGELY DILATED LOOP arising from the
pelvis with the “COFFEE-BEAN” SIGN in
a case of SIGMOID VOLVULUS

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64-YEAR-OLD MAN WITH LBO CAUSED BY A COLOCOLONIC INTUSSUSCEPTION.
a) CT scout image shows air-filled dilated colon terminating abruptly in the
left upper quadrant .
(b) Coronal reformatted CT image of the abdomen and pelvis shows a
transverse colonic intussusception.

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Transverse CT image of the pelvis in an 85-year-old woman with
LBO caused by distal fecal impaction. I
CT CONTRAST displayed using Lung window shows a dilated colon
and large mass of impacted stool in the rectum (arrow)..

17. COLORECTAL TUMOURS
• POLYPS
1. Macroscopic circumscribed tumour or mucosal elevation that
projects above a surrounding flat epithelial surface.
2. Polyps smaller than 5 mm diameter are most often inflammatory or
metaplastic lesions that have no malignant potential.
3. Medium (6–9 mm) and large (10 mm and more) polypoid lesions are
frequently neoplastic polyps, most often adenomas.
4. Other non-neoplastic polyps that occur in the colon are
hamartomatous polyps- found in the Peutz–Jeghers syndrome
5. Juvenile polyps may be single or multiple, and may be found in
children and adults.
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18. • Adenomatous polyps are common with the prevalence of 5–
10% in asymptomatic individuals older than 40 years of age.
• A term “ADVANCED ADENOMA” has been introduced to
emphasise the significance of polyps >10 mm diameter,
whereas small polyps (<10 mm) are frequently considered
inconsequential.
• Adenomatous polyps are SHARPLY CIRCUMSCRIBED, SESSILE
OR PEDUNCULATED LESIONS that tend to arise more
frequently in the rectosigmoid region, with a similar
distribution of carcinomas
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19. Radiologicalsignsofa polypondoublecontrastenema
(1) MENISCUS SIGN- A meniscus of barium forms around the base of
the polyp. When viewed en face, there is a ring shadow with a
sharp inner ring due to the soft tissue-barium interface and a
fuzzy outer ring due to fading of the barium peripherally.
(2) When it lies within a pool of barium, it appears as a negative filling
defect.
(3) When viewed obliquely, there is a thin meniscus of barium over its
surface creating “the bowler hat sign".
(4) If the polyp is pedunculated, a stalk is visible with a parallel tram
track of barium.
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Small polyp where the meniscal rim of barium between the
polyp base and adjacent mucosa causes the 'bowler-hat' sign.

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WHEN SEEN EN FACE, STALKED POLYPS PRODUCE A 'TARGET'
SIGN.

22. • CT COLONOGRAPHY
1. Facilitates a rapid complete interrogation of the colon and
rectum.
2. The attenuation characteristics of any suspicious lesion
helps differentiate faecal residue from polyp, as variable
attenuation due to some gas content is a distinguishing
feature of residue, but a polyp has uniform attenuation
similar to the bowel wall
3. Faecal residue tends to fall onto the dependent colon
surface, whereas polyps maintain their position despite
patient movement.
4. A definitive diagnosis of a lipoma is based on its fat density
.
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CT COLONOGRAPHY OF A LARGE SIGMOID POLYP WITH
HOMOGENEOUS ATTENUATION

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1. 2D CT colonography of a polypoid lesion in the caecum .
2. On standard abdominal windowing the attenuation of this polyp is the
same as for fat, confirming a lipoma

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Magnified view of the sigmoid colon demonstrates THE MID-
SIGMOID SESSILE POLYP EN FACE .

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SESSILE PEDUNCULATED

27. ADENOMAS :
1. Benign neoplasms of colorectal epithelium .
2. Dysplastic and potentially pre malignant with increased incidence
with age .
3. Villosity and dysplasia –Most important predictors of malignancy.
4. May be (a) Tubular
(b) Tubulovillous
(c) Villous
4. Villous adenomas have characteristic morphology , being broad
and relatively large ,with a frond like surface .
5. Most adenomas are asymptomatic but large polyps may bleed or
causes electrolyte disturbance secondary to mucus secretion .
6. Malignancy is defined by Invasive adenocarcinoma – Cells penetrate
the muscularis mucosa to reach the submucosa .
7. MALIGNANT POLYP – When a focus of invasive carcinoma is found
within an excised adenoma .
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30. POLYPOSIS SYNDROMES
• Seemingly innocuous polyps that carry no risk of malignancy when
single can convey increased risk when multiple.
PEUTZ JEGHERS SYNDROME :
1. Autosomal dominant condition characterised by
mucocutaneous pigmentation and intenstinal
hamartomatous polyps .
2. Patients may suffer from repeated episodes of
intussusception .
3. The hamartomas have no intrinsic malignant potential, but
the overlying mucosa may become dysplastic- increased risk
of upper GI cancer.
4. Increased risk of extra-intestinal cancers, particularly of the
ovary, thyroid, testis, pancreas and breast.
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PEUTZ JEGHERS SYNDROME - A LARGE PEDUNCULATED POLYP AND
A SMALLER SESSILE POLYP PROXIMALLY .

32. • JUVENILE POLYPOSIS
1. Very rare and presents in infancy.
2. The polyps are hamartomatous with cystic epithelial tubules in an
excess of lamina propria – the ‘Swiss cheese’ effect.
3. Typically smooth and pedunculated.
4. 50–200 polyps in the colon, with further lesions in the small bowel
and stomach.
5. Epithelial dysplasia is common in young adults, either in the
juvenile polyps or in coexisting adenomas.
6. Significant risk of colorectal cancer in this condition.
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33. • HEREDITARY NON-POLYPOSIS COLORECTAL CANCER
1. caused by a fault in the DNA mismatch repair gene and probably
accounts for 5 per cent of all colorectal cancer.
2. The criteria for this condition include
(A) three or more relatives with CRC
(B) one of these is a first-degree relative
(C) cases over two or more generations
(D) CRC diagnosed before the age of 50 years.
3. Cancers occur at an earlier age in HNPCC.
4. 70 per cent are in the proximal colon and multiple tumours are
common.
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SMALL RING SIGN EN FACE DUE TO A 3 MM POLYP IN THE DESCENDING COLON OF A
32-YEAR-OLD WOMAN WITH HNPCC

35. • FAMILIAL ADENOMATOUS POLYPOSIS
1. Mutation of the APC tumour suppression gene on chromosome
5q21 and accounts for about 1 per cent of CRC.
2. Classically micro-adenomas develop in the early teens, becoming
macro-adenomas in the late teens.
3. More than 100 adenomas have to be present for the diagnosis, and
typically several hundred polyps are present throughout the large
bowel.
4. Rectal bleeding, diarrhoea and mucus discharge.
5. Two-thirds of symptomatic patients already have an overt cancer .
6. All affected patients eventually develop large-bowel carcinoma, so
that restorative proctocolectomy is now recommended once the
condition has been diagnosed.
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1. Double Contrast Barium
enema view of the
descending colon
2. Multiple small polyps
about 5 mm in size
creating ring shadow
menisci around their
bases, or as a filling
defect in the barium pool

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• Innumerable colonic adenomas.

38. COLORECTAL CANCER
1. Believed to arise from pre existing adenomatous polyps
2. Colorectal cancer incidence increases with age but mortality
rates have fallen over the years, probably due to poylpectomy
3. Risk of developing colorectal cancer is closely related to family
history .
4. Change in bowel habit , rectal bleeding and abdominal pain .
5. The majority of colorectal cancers are believed to arise from
sporadic adenomas ( adenoma-carcinoma sequence )
6. Adenomas are defined by dysplasia and cancer occurs when
the invasive adenocarcinoma crosses the muscularis mucosa to
reach the submucosa .
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39. 1. Surgical excision is relatively straightforward in the
colon unless the tumour is infiltrating locally.
2. The Dukes' and TNM systems both describe the
extent of tumour growth and nodal involvement.
3. Involvement of the mesorectal fascia is particularly
important when planning total mesorectal excision,
as fascial compromise necessitates pre-operative
radiotherapy to prevent local recurrence.
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A POLYPOID CARCINOMA WITH AN IRREGULAR INDRAWN BASE

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A plaque-like carcinoma at the hepatic flexure that has a smooth surface and is
recognized in this view only by its raised edge creating a defect in the barium pool

44. •CT COLONOGRAPHY
1. Shows the extent of wall thickening (normal
distended colonic wall <4 mm) and extramural
infiltration.
2. With standard abdominal CT, the enhancement
within a tumour is usually homogeneous, but
may be heterogeneous with large
adenocarcinomas or mucinous tumours.
3. Extramural spread is suggested by the presence
of irregular projections from the serosal surface
into the surrounding fat, with clouding of the
pericolic fat and thickening of contiguous fascial
reflections.
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45. 1. Loss of normal fat planes is suggestive of local invasion.
2. Enhancement differentiates nodes from vessels. Nodal
enlargement may be due to reactive hyperplasia or
metastatic involvement.
3. The presence of retroperitoneal nodes or pelvic nodes
>1.0 cm in diameter, or clusters of more than three intra-
abdominal nodes, suggests metastatic involvement.
4. Ascites, peritoneal deposits and omental caking indicate
diffuse intra-peritoneal spread.
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46. • Frank carcinomaappearsas anannular , irregular ,ulceratedlesion–APPLE
COREAPPEARANCE
Abrupt , shoulderedmargins
Normalmucosalfolds cannotbetracedthroughthestrictureindicating
mucosaldestruction
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Annular carcinoma revealing the irregular lumen and thickened bowel wall

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64-year-old woman with locally advanced colon cancer presenting as palpable mass
in right upper quadrant.
A- Transverse ultrasound image shows colonic wall thickening .
B- Contrast-enhanced CT image confirms transverse colon mass with greater
nodularity along anterior mural surface and abdominal wall invasion.

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51. SECONDARY CANCER
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1. Dissemination -direct invasion, along mesenteric planes, lymphatic
permeation, intraperitoneal seeding or by haematogenous spread.
2. Gastric cancer may invade the colon via the gastrocolic ligament, and
pancreatic cancer via the transverse mesocolon.
3. Ascitic flow causes tumour implantation mainly in the pelvis, loops of
small bowel in the right iliac fossa, superior border of the colon and
right paracolic gutter.
4. Peritoneal spread also involves the omentum, and omental cakes of
tumour typically involve the root of the omentum at its attachment to
the transverse colon. This is another cause of extrinsic masses
involving the transverse colon.
5. The metastases may be multiple, polypoid with a smooth surface due
to their submucosal location, and are often umbilicated as a result of
differential growth between the centre and the periphery.

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MULTIPLE BIZARRE STRICTURES AND MUCOSAL PLEATING IN A WOMAN
WITH EXTENSIVE PERITONEAL CARCINOMATOSIS FROM AN OVARIAN PRIMARY

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53ENLARGED LYMPH NODES IN A 43-YEAR-OLD MAN WITH METASTATIC COLON
CANCER.
MULTIPLE HEPATIC METASTASES AS WELL AS ENLARGED PORTACAVAL AND
AORTOCAVAL NODES .

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54PULMONARY METASTASES IN A 47-YEAR-OLD MAN WITH COLON
CANCER.
SPIRAL CT SCAN SHOWS NUMEROUS METASTASES IN THE LUNGS.

55. DIVERTICULITIS
• Diverticulosis – acquired pulsion
diverticula due to the increased
colonic segmental pressure .
-Mucosal herniations through
vasular entry sites into pericolic fat
.
• Diverticulitis – Super imposed
inflammation
• Diverticular disease –
Encompasses both concepts .
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56. 1. The sigmoid colon is typically affected .
2. Muscular thickening due to elastosis ---Luminal narrowing
3. Causes progressive elastosis ----Longitudinal foreshortening
and accentuation of sigmoid corrugations .
4. Due to micro/macroperforation pericolic fibrosis and
inflammation also contribute .
5. Muscles covering the diverticula tend to atrophy as they
enlarge so that mucous membrane , connective tissue and
peritoneal tissue cover the mature diverticula .
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57. 1. The diverticula appear as flask or rounded like out pouchings
.
2. The produce ring shadows .
3. Projection beyond the bowel wall and the presence of a fluid
level within it- differentiates it from a polyp
4. Muscular change results in a serrated like appearance
5. Pronounced and persistent spasm, which reflects abnormal
motility .
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BARIUM ENEMA- SEVERE SIGMOID DIVERTICULAR DISEASE
WITH A COMPLICATING FISTULA TO THE VAGINA

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FOCAL, MASSLIKE THICKENING OF THE SIGMOID COLON (STRAIGHT ARROWS)
WITH ADJACENT STRANDING OF THE PERICOLIC FAT MINIMAL ADJACENT
MESENTERIC FLUID (CURVED ARROW) FAVORED DIVERTICULITIS.

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WALL THICKENING IN THE SIGMOID COLON (ARROWS) WITH ADJACENT
INFLAMMATORY CHANGES IN THE PERICOLIC FAT.

61. COMPLICATIONS
1. Diverticulitis results in pericolic abcess and localised
peritonitis .
2. Obstruction may complicate an episode of diverticulitis
and spasm may be severe enough to obiliterate the lumen.
3. Extension of the inflammation to a neighbouring viscera
may lead to FISTULATION
4. Symptoms – Pneumaturia and recurrent UTI .
5. Diverticular disease – cause of torrential and life
threatening haemorrhage in the elderly
6. Accounts for majority of Lower GI bleeds in this age group .
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62FOCAL WALL THICKENING IS SEEN IN THE LEFT POSTERIOR PART OF THE
BLADDER ADJACENT TO THE INFLAMED SIGMOID (ARROW). A MODERATE
AMOUNT OF AIR IS ALSO PRESENT IN THE BLADDER, A FINDING
COMPATIBLE WITH A COLOVESICAL FISTULA.

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CT WAS USED TO PLACE A PERCUTANEOUS DRAIN INTO THIS
LARGE PARACOLIC COLLECTION SECONDARY TO DIVERTICULAR
DISEASE.

64. COLITIS
• Describes colonic inflammation broadly divided into :
1. IDIOPATHIC
• ULCERATIVE COLITIS
• CROHN’S DISEASE
2. ISCHEMIC
3. INFECTIOUS
• HALLMARK –Mucosal inflammation and ulceration
• Contrast enemas remain the corner stone for the diagnosis .
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65. ULCERATIVE COLITIS
1. Characterised by relapsing and remitting proctitis
2. Rectum is always affected .
3. Affects young adults (15-25 ) years .
4. Attacks are characterised by bloody diarrhea
5. EXTRA INTESTINAL MANIFESTATIONS –
-Arthralgia
-Erythema Nodosum
-Pyoderma Gangrenosum
-Sclerosing Cholangitis
6. Proctoscopy and sigmoidoscopy with biopsy are essential .
7 . The changes progress through mucosal granularity and spontaneous
haemorrhage to frank, continuous ulceration .
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66. PLAIN FILMS
• In total colitis , the reliable features on air enema-
1. -Irregularity of the mucosal edge
2. -Increased thickness of the colon wall .
• In the absence of enough spontaneous intraluminal air to assess the
colonic wall, AIR ENEMA may be done .
• Plain films are used to detect ACUTE TOXIC
MEGACOLON/DILATATION ( when transverse colonic diameter >5.5
cm )
• The transverse colon is the most dilated on plain films , due to the
patients supine position .
• The mucosal line is irregular producing MUCOSAL ISLANDS.
• The colon has a consistency akin to blotting paper, so patients are at
risk of perforation and untimely death .
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TOXIC MEGACOLON – LUMINAL DILATATION , ABNORMAL
HAUSTRATION WITH MURAL THICKENING .

68. • Proctosigmoidoscopy is 10-15% more sensitive
overall for primary diagnosis of early , distal
ulcerative colitis .
• Contrast enema – Can accurately demonstrate
colonic morphology
-Exact location and extent of any stricture can be
identified .
• Any Barium examination is acutely contraindicated
If there is evidence of toxic dilatation .
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69. RADIOLOGICAL FEATURES
1. Earliest change
- Blurring of the mucosal line and a fine granularity when mucosa is
seen en face
- Abnormal barium adherence to altered colonic mucous
- Flecks of barium adhering to superficial erosion .
2. As the disease progresses, the granularity becomes coarser and
eventually frank ulceration develops – Projections of barium
outside the mucosal line .
3. Ulceration is continuous and tends to be superficial
4. Mucosal changes are accompanied by haustral blunting , luminal
narrowing and colonic shortening .
5. A tubular , short , featureless colon is typical of long standing colitis
.
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. CT scan of a patient with long-standing ulcerative colitis
- A SUBMUCOSAL HALO OF FAT WITHIN THE RECTUM
(ARROW)
- PERIRECTAL FIBROFATTY PROLIFERATION (*).

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Transverse CT image in a 32-yearold woman with ulcerative colitis and bloody
diarrhea demonstrates the double halo, or target, sign with inner (mucosa,
arrow) and outer (muscularis propria, arrowhead) rings of high attenuation
separated by a ring of low attenuation, which represents submucosa with
edema.

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72TRANSVERSE CT IMAGE IN A 35-YEAROLD PATIENT WITH ULCERATIVE COLITIS
AND TOXIC MEGACOLON SHOWS MARKEDLY DISTENDED TRANSVERSE COLON
WITH SHAGGY MUCOSA (ARROWS).

73. CROHN’S DISEASE
• Chronic relapsing immune mediated inflammatory
disease, with transmural and segmental involvement of
the small bowel.
• Mouth to anus often with multiple skip discontinuous
areas.
• The most common site is the small bowel (80%), the
terminal ileum being most commonly affected site in
the small bowel.
• Approximately ¼ th will have disease limited to the
large bowel and DD from U. Colitis becomes relevant .
• Abdominal pain, diarrhoea, weight loss- frequent
• Anemia, acute obstruction,

74. First radiological changes are
granularity and aphthous
ulceration .
APHTHOUS ULCERS – Small
and discrete , surrounded by
slightly elevated edematous
mucosa .
-Barium collects in the central
depression with the surrounding
elevation appearing as a
radiolucent halo
-occur on a background of
normal mucosa .
-NEVER SEEN IN ULCERATIVE
COLITIS .
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75. • As the disease
progresses,ulcers
become longitudinal
and deeper –
TRANSMURAL
ulceration .
• Deep longitudinal ulcers
combined with mucosal
edema – COBBLESTONE
APPEARANCE .
• Discontinuous , both
longitudinally and
circumferentially
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CONTRACTION AT THE SITE OF ULCER FORMATION –
PSEUDODIVERTICULA

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US IMAGE OF THE TERMINAL ILEUM-THICKENED (ARROW) WITH THICK,
ECHOGENIC SUBMUCOSA RELATED TO LYMPHEDEMA

78. ISCHEMIC COLITIS
1. The colon is particularly
vulnerable to mesenteric
ischemia .
2. Oedema , haemorrhage and
ulceration .
3. Spontaneous healing followed
by fibrosis – results in
subsequent colonic stricturing ,
4. Plain films – Splenic flexure
irregularity with mural
thickening ,
5. Characteristic edematous
THUMB PRINTING .
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SPLENIC FLEXURE “THUMB
PRINTING “

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DIFFUSE ISCHEMIC COLITIS.
• Diffuse, low-attenuation thickening of the colonic wall (arrows).
• This is an example of the halo sign.
SEGMENTAL ISCHEMIC COLITIS .
Focal thickening of two colonic loops in the left abdomen (arrows).

80. INFECTIOUS COLITIS
1. Bacterial colitis is common and imaging usually reveals non
specific pancolitis .
2. Eg’s : Campylobacter , Salmonella , Shigella , Yersinia
3. TUBERCULOSIS – morphology is similar to crohn’s disease.
-A conical , contracted caecum is characteristic ; Longitudinal and
aphthoid ulcers may occur .
4. NEUTROPENIC COLITIS (TYPHILITIS)- Occurs in
immunocompromised patients , secondary to chemotherapy and
presents with right sided inflammation .
5 . GRAFT VERSUS HOST DISEASE – Non specific colitis
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MODERATE THICKENING OF THE COLON (ARROWS) AND INFLAMMATORY CHANGES
IN THE MESENTERIC FAT. E COLI WAS CULTURED FROM STOOL

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52-year-old woman with infectious colitis.
• Gray-scale ultrasound image shows concentric wall thickening and blurring of
normal mural stratification in colon.
• Power Doppler image reveals marked hyperemia in affected segment.

83. PSEUDOMEMBRANOUS
COLITIS
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Marked colonic wall thickening and mucosal
plaques
• Presents with
diffuse watery diarrhea and
abdominal
cramps.
• The rectosigmoid colon is
almost invariably involved,
with 3–8-mm in diameter,
creamy, white, elevated
plaques or nodules.
• The disease can progress to
toxic megacolon with transmural
injury..

84. • Severe cases show a markedly thickened colonic
wall with a “thumbprinting,” low attenuation from
mucosal and submucosal edema,irregular mucosal
contour with polypoid protrusions, pericolonic
stranding, and ascites
• The colonic diameter is often enlarged.
• After administration of intravenous contrast
material, the target sign may be seen with
enhanced mucosa and serosa.
• The average wall thickness is 14.7 mm.
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85. Marked wall thickening throughout the colon (thickness, 15 mm)
and pericolic inflammation.
• The thickening in the transverse colon is asymmetric
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. IN THE SIGMOID COLON, A SHAGGY THICKENED BOWEL WALL WITH
ALTERNATING AREAS OF NECROSIS AND PLAQUES.

87. THE RECTUM
• The rectum is the last segment of the
gastrointestinal tract and is bounded by the
sigmoid colon the anus.
• The proximal portion located within the
peritoneal cavity and the distal portion being
extraperitoneal.
• The inferior aspect of the rectum, or the
anorectal junction, is defined anatomically by
the dentate line, which spans 5–10 mm of the
anal canal and marks the transitional zone.
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90. RECTAL CANCER
1. 40 % of colorectal cancers occur in the rectum
2. Immobility permits accurate radiotherapy and
accessibility allows transanal local excision.
3. Rectal staging is particularly useful .
4. MRI and TRUS remain a higher modality for
investigation in comparison to CT- Able to
visualise the muscularis propria .
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• An irregular mass in the rectum with an associated enlarged perirectal lymph
node .
• Axial 2D image obtained at the level of the mid abdomen reveals
lymphadenopathy (arrows) along the course of the IMV (arrowhead).

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