Chapter 6: The lower gastrointestinal tract

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Chapter 6: The lower
gastrointestinal tract

This chapter covers: also. Supine AXR will give information
Common conditions concerning small and large bowel gas
• Appendicitis pattern, free intraperitoneal air, soft
• Colonic obstruction tissues and bony structures.
• Diverticular disease
• Neoplasia: polyp, carcinoma Once initial clinical assessment has
• Sepsis been made and a working diagnosis
• Colitis formulated, many patients will require
• Volvulus further imaging. Discuss the case with
Common presentations in which the radiologist to identify the best
imaging can help way (including endoscopy) to reach a
• Altered bowel habit: obstruction, diagnosis.
carcinoma, diverticular disease
• Acute abdominal distension: US
obstruction
• Acute abdominal pain: obstruc- US in colorectal disease can be helpful
tion, colitis, diverticulitis for initial assessment of:
• Rectal bleeding: carcinoma, di- • Possible bowel-related mass
verticular disease, colitis • Free fluid or abscess formation
Look for hepatomegaly or an • Solid organs.
abdominal mass on clinical
examination. By their nature, many pathologies of
the colon are associated with significant
Patients should undergo perianal bowel gas and when combined with an
and rectal examination at presenta- elderly, immobile or obese patient the
tion. This task is often delegated to use of US may be limited.
the house officer. If you are unsure,
ask for help from a senior colleague. CT

Imaging strategy CT can provide significant additional
diagnostic information in patients with
Initial imaging in acute presentations bowel-related masses and suspected in-
usually involves a supine AXR and an flammatory disease or malignancy. CT is
erect CXR. CXR may demonstrate increasingly being used as an early inves-
free intraperitoneal air beneath the tigation in the elderly and frail to avoid
diaphragm (see Chapter 5), and many rectal contrast studies.
patients who are acutely ill may have evi-
dence of chest sepsis or cardiac failure Contrast enema

This is an essential tool for evaluation of

81

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82 CHAPTER 6

the rectum and colon (combined with The classic signs of appendicitis are
endoscopy). absent in up to one-third of patients
and there is a significant rate of clinical
Unprepared contrast enema, usually misdiagnosis.
using water-soluble iodinated contrast,
may be used to exclude an obstructing Imaging may be particularly helpful
lesion in patients with large bowel ob- in:
struction. Mucosal detail is poor and, if • The elderly, where symptoms and
the study is negative, follow-up barium signs may be minimal
enema or colonoscopy is often needed. • Children, where history and examina-
tion are often difficult
Contrast enema should not be per- • Young women who may have a gynae-
formed in patients at risk of perforation cological cause for pain.
(e.g. toxic megacolon). Barium causes
peritonitis if it extravasates outside the Accurate and appropriate imaging
bowel and should not be used in patients reduces the number of normal laparo-
who may have perforation or where recent tomies and will help to exclude other
deep biopsies have been performed. causes of appendix-type pain. However,
Water-soluble contrast should be used. imaging is often not needed following
clinical assessment.
Maximum diagnostic information is
obtained using the double-contrast AXR
technique (air and barium) with good
bowel preparation. However, a significant Look for:
number of elderly patients cannot retain • Laminated calcified appendicolith
air and/or barium and may be immobile. (10–15% of patients)
In some of these patients, CT may be • Evidence of ileus, often localized to
used to exclude a gross mass lesion. the right iliac fossa
• Distortion of psoas margin
MR • Bubbles of air in associated appendix
abscess.
MR has a role in staging colorectal car-
cinoma, but its use is currently limited US
otherwise.
This represents a non-invasive modality
NM for assessment of atypical patients. US
is most accurate in children and young
This has a limited role, but it can be used and/or pregnant women, where the
to assess the extent of inflammatory appendix is not obscured by gas. US fea-
colitis. tures of appendicitis include identifica-
tion of the appendix as an abnormal,
Appendicitis thick-walled and non-compressible
structure with a distended lumen (Fig.
This is the most common surgical 6.1). An appendicolith or associated
emergency, with a peak incidence in the abscess formation may also be seen.
second and third decades.

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LOWER GASTROINTESTINAL TRACT 83

Fig. 6.1 Transverse ultrasound section of the appendix in a patient with appendici-
tis. The appendix has a thickened wall (callipers) with a dilated lumen (arrow) and
a target appearance.

CT Colonic obstruction

CT is highly accurate in the evaluation of The major causes of large bowel ob-
appendix inflammation and local extent. struction are carcinoma, diverticular
It is the technique of choice in the disease and volvulus. Carcinoma, most
elderly, obese or very tender patients or commonly within the sigmoid, accounts
where US has been unhelpful and clini- for > 50% of cases. Symptoms are of ab-
cal concern persists. dominal distension and pain with associ-
ated vomiting. A mass may be palpable.
Barium studies
The integrity of the ileocaecal valve is
Barium studies of small or large bowel important. If it is competent, this pre-
may be helpful in some patients where vents passage of air into the small bowel
initial US or CT have indicated bowel if the large bowel is obstructed, leading
pathology not clearly related to the to rapid and pronounced colonic and
appendix. caecal dilatation, with the risk of is-
chaemia and perforation. An incompe-
tent ileocaecal valve allows colonic
decompression, with passage of air into

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84 CHAPTER 6

the small bowel. Onset of symptoms may • Dilated gas-filled colon proximal to
then be more gradual. the site of obstruction (Fig. 6.2)
• Paucity of gas in collapsed colon distal
AXR to the obstruction
On supine AXR, look for: • Haustral pattern to differentiate from
small bowel

Fig. 6.2 Supine AXR in a patient with large bowel obstruction secondary to
sigmoid carcinoma. There is gaseous distension of the large bowel down to the left
pelvis at level of obstruction (arrow).

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LOWER GASTROINTESTINAL TRACT 85

• Small bowel dilatation also if ileocae- exclude a mechanical obstruction in pa-
cal valve incompetent tients who do not settle with conserva-
• Evidence of perforation. tive treatment.

If large bowel obstruction is diag- Diverticular disease of
nosed, rectal and sigmoidoscopic exami- the colon
nation should be performed to exclude a
low obstructing lesion. If negative, the This is the most common colonic disease
patient should be considered for contrast in the West, with diverticula present in
enema examination of the large bowel. up to 50% of people of 50 years of age,
with the sigmoid colon most frequently
CXR involved. Diverticula are out-pouchings
of colonic mucosa and submucosa that
On erect CXR, look for evidence of free penetrate between circular muscle fibres.
intraperitoneal air, lung metastases and Circular muscle hypertrophy and mus-
other pathology. cular spasm are common. Diverticular
disease is generally diagnosed during
Contrast enema barium enema examination, often as an
incidental finding (Fig. 6.4). Complica-
Although barium is the ideal agent, it can tions of diverticular disease include
cause problems. It is contraindicated in diverticulitis, fistula formation and
patients at risk of perforation and can haemorrhage.
cause impaction if no obstruction is
present, as well as interfering with future Diverticulitis
colonoscopy and CT (see Chapter 2). Io-
dinated contrast (water-soluble) is often Diverticulitis is the most common com-
used and will exclude gross obstruction plication of diverticular disease, occur-
(Fig. 6.3). ring in up to 25% of patients. It occurs
secondary to mucosal abrasion by faecal
CT matter within a diverticulum, causing
local perforation, inflammation and
This can be useful in assessing bowel abscess formation. Patients present with
and adjacent structures, particularly if left iliac fossa pain, fever and often an
patients are elderly or frail and cannot inflammatory mass.
tolerate a contrast enema.
AXR
Pseudo-obstruction
AXR may demonstrate air within an
Marked dilatation of the large bowel abscess or secondary ileus. Chronic in-
may occur in elderly, bedridden patients flammation and stricturing with large
or those with neurological or psychiatric bowel obstruction is unusual.
disorders. Gaseous distension often in-
volves the rectum also, and faecal loading
may be present. Sigmoidoscopy and
contrast enema are often needed to

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86 CHAPTER 6

Fig. 6.3 Water-soluble contrast enema film from splenic flexure region shows an
obstructing carcinoma. Note ‘apple core’ appearance of stricture with shouldering.

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LOWER GASTROINTESTINAL TRACT 87

Fig. 6.4 Film from double-contrast barium enema series showing florid sigmoid di-
verticular disease. Note diverticula and circular muscle hypertrophy. The sigmoid
colon is tortuous and is an area of weakness for barium enema — mucosal lesions
can easily be overlooked. Another problem here is the presence of significant small
bowel reflux of barium, which partially obscures the sigmoid region.

Barium enema investigation for patients with left iliac
fossa pain and may demonstrate bowel-
This is excellent at demonstrating diver- wall thickening, a mass or fluid collection
ticular colonic muscular hypertrophy in diverticulitis. However, US is often
and spasm, and local contrast extravasa- non-diagnostic.
tion into walled-off pericolic abscess. Pa-
tients often do not tolerate barium enema CT
during an acute episode, and enema does
not delineate pericolic inflammation. Patients often proceed to CT, which accu-
rately delineates diverticula, bowel-wall
US thickening, pericolic inflammatory change
and abscess formation (Fig. 6.5), and will
US is often requested as a first-line guide aspiration or drainage of abscess.

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88 CHAPTER 6

Fig. 6.5 Post-contrast CT demonstrates a sigmoid colon diverticular abscess. There
is an irregular mass containing fluid and air (long arrow). Thick-walled sigmoid
colon abuts the abscess (short arrow).

Note: associated changes in the sigmoid
It is important to remember that colon. Coloenteric (Fig. 6.6), colovaginal
perforated carcinoma can mimic diver- and colocutaneous fistulae may also
ticulitis, and once the acute episode occur.
has settled, patients should undergo
endoscopic examination. Remember that fistula formation also
occurs with malignancy and this should
Fistula formation be excluded.

A fistula is a communication between Haemorrhage
two surfaces lined by epithelium. A
colovesical fistula is the commonest This is not related to diverticulitis.
type of indiverticular disease and is It occurs in 30–50% of patients with
secondary to recurrent inflammation — diverticular disease and may be life-
these patients present with pneuma- threatening. Haemorrhage is usually
turia. Air in the bladder may be apparent self-limiting, but re-bleeding is common.
on AXR. The fistula can be demarcated
during barium enema. CT is very sensi- Barium enema or colonoscopy is indi-
tive at detecting air in the bladder, with cated if bleeding is to be investigated
as an outpatient. Catastrophic haemor-
rhage may require angiography to iden-

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LOWER GASTROINTESTINAL TRACT 89

Fig. 6.6 Film from a single-contrast barium enema in the sigmoid region. There is
irregular narrowing in the mid-sigmoid region (long arrow) with adjacent divertic-
ular disease. Contrast passes via a fistula (short arrow) to communicate with small
bowel. This was secondary to diverticular disease, but exclusion of malignancy is
essential.

tify the site and to allow potential em- (50%). Fifty per cent of carcinomas are
bolization of the bleeding vessel. in the rectum or sigmoid and in range of
the flexible sigmoidoscope.
Colorectal carcinoma
Patients with a colorectal carcinoma
Colorectal carcinoma is the second most are at risk of synchronous (carcinoma
common cause of cancer death. Risk elsewhere in large bowel) and metachro-
factors include family history, adenoma- nous (colonic carcinoma at a later date)
tous polyposis syndromes, chronic ul- lesions and it is important to evaluate the
cerative colitis and Crohn’s disease. The entire colon at the time of diagnosis.
vast majority of colorectal carcinomas
begin as benign adenomas, which grow Polyp detection
over time and undergo malignant trans-
formation. Adenomas of > 1 cm are at Clearly, polyp detection and removal
risk and > 2 cm malignancy is likely prior to malignant change is essential for
prevention of colorectal carcinoma, al-
though large-scale population screening

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90 CHAPTER 6

Fig. 6.7 Decubitus spot film of the hepatic flexure from a double-contrast barium
enema series demonstrates a pedunculated polyp on a stalk (arrows). Note gravi-
tational pooling of barium.

is still under investigation. Several Adenomatous polyps may be:
imaging modalities are available; all have • Pedunculated (on a stalk): where risk of
strengths and weaknesses. Colonoscopy malignancy is low (Fig. 6.7)
is often preferred. • Sessile (flat): villous change and malig-
nancy is more likely (Fig. 6.8).
Barium enema
Colonoscopy
Double-contrast barium enema is highly
accurate and comparable to colonoscopy Endoscopic assessment of the colon
in the identification of polyps > 1 cm. allows identification and also removal of
This accuracy falls off < 1 cm in size. polyps. This modality is theoretically the
Completion rate to the caecum is better ideal, but does have the complications of
with barium enema. Diagnostic accuracy sedation and perforation, and technical
is impaired: failure is common, for similar reasons, to
• With poor bowel preparation barium enema.
• If patients cannot retain air or barium
• With tortuosity of the bowel, espe- CT colonography
cially in the sigmoid
• With extensive associated diverticular This three-dimensional virtual-reality
disease CT technique, following air insufflation
• The lower rectum is often not well of the colon, has shown initial promising
seen, particularly if a balloon catheter is results.
used.

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LOWER GASTROINTESTINAL TRACT 91

Fig. 6.8 Film from double-contrast barium enema demonstrates a large sessile
polyp in the upper rectum (arrow). The surface of the polyp is irregular and, when
combined with the size, malignancy is likely.

Adenocarcinoma CT

This may be diagnosed by the three CT is useful for identifying primary
modalities outlined above — again, colo- tumour and is the most reliable method
noscopy offers the opportunity for for staging:
histological examination. • Luminal mass and bowel wall thicken-
ing (Fig. 6.10)
Barium enema • Stranding and nodularity of adjacent
fat — may indicate local invasion
Look for: • Invasion of local structures
• Fungating, polypoidal lesion • Presence of mesenteric disease, as-
• Annular, ulcerating — ‘apple core’ cites, significant adenopathy
with shouldering (Fig. 6.9) • Liver and lung metastases.
• Scirrhous lesion (uncommon).

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92 CHAPTER 6

Fig. 6.9 Film from double-contrast barium enema in a patient with a large trans-
verse colon carcinoma (large arrow). There is irregular stricturing of the bowel
with shouldering apparent. Note lung metastases at lung bases (small arrows).

US surgery, radiological insertion of an ex-
panding metallic stent over a guidewire
Transabdominal US can identify bowel- can relieve obstruction, giving palliation.
related masses and will assess the liver Surgery can be considered when the
parenchyma for metastases. patient’s condition has improved.
• Fistula formation (see earlier)
Transrectal US and MRI accurately • Perforation: patients may go straight
delineate the layers of the rectal wall and to theatre for surgery.
are useful for local staging of disease.
Bulky and locally invasive rectal car- Follow-up of treated
cinomas will receive local radiotherapy colorectal cancer
prior to surgery.
Residual large bowel post-resection is
Local complications of followed-up regularly, either endoscopi-
colorectal carcinoma cally or by barium enema.

• Obstruction: this is common (see CT is the modality currently of choice
earlier). In patients unfit for immediate for identifying extraluminal local recur-

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LOWER GASTROINTESTINAL TRACT 93

Fig. 6.10 Post-contrast CT in a patient with caecal carcinoma. There is marked
thickening of the caecal wall (arrows).

rence or metastatic disease and is pancreatic and hepatic abscesses are
also used to monitor patients with covered elsewhere.
known metastatic disease undergoing
treatment. Intraperitoneal abscess

Hepatic metastases may be considered Usually results from secondary infection
for ablation or resection (see Chapter 7). of collections of blood, bile or ascites and
may arise in patients who have under-
Abdominal sepsis gone bowel or hepatobiliary surgery. If
patients have pyrexia or a raised white
Sepsis in the abdomen is a very impor- cell count only, with no significant ab-
tant cause of patient mortality, mor- dominal symptoms, make sure there is
bidity and increased length of hospital no evidence of chest, urinary or skin
stay. Cases are often complex and great sepsis (e.g. infected cannula) prior to
benefit may be obtained through direct further investigations.
discussion with a radiologist.
AXR
This section concentrates on in-
traperitoneal, subphrenic, psoas and AXR may show an ileus or mottled
pelvic abscess formation. Diverticular,

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94 CHAPTER 6

gas densities within an intraperitoneal Subphrenic abscess
abscess and is worth arranging if there This usually follows bowel surgery or
are abdominal symptoms. appendicectomy.

US AXR
AXR may show mottled gas densities in
US is the next investigation of choice abscess but air–fluid level and sympa-
for the identification of abdominal and thetic pleural effusion is best appreci-
pelvic fluid collections. Bandaging, ated on erect CXR (Fig. 6.11).
suturing, pain, obesity and gas often
degrade US; CT would then be US and CT
recommended. US or CT will confirm diagnosis if
necessary.
Percutaneous drainage under US or
CT guidance can be performed in post-
operative abscess formation.

Fig. 6.11 Erect CXR demonstrates a large right subphrenic abscess post-
cholecystectomy. Note air–fluid level (arrows) and right basal pleural effusion.

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LOWER GASTROINTESTINAL TRACT 95

Psoas abscess Colitis

Psoas abscess often relates to adjacent The three most common forms of colitis
vertebral, bowel or renal sepsis. Look for are dealt with here: ulcerative, Crohn’s
evidence clinically of psoas irritation and ischaemic.
and painful hip flexion.

AXR Ulcerative colitis

AXR may show psoas enlargement and This is a common inflammatory disease
abnormal gas densities. Look carefully of the colon and rectum of uncertain
for renal tract calcification and vertebral aetiology, which initially involves the
body abnormality (tuberculous or bowel mucosa but extends to involve
metastatic bony involvement). deeper layers. The disease usually
commences in the rectum and extends
US and CT proximally, with the diagnosis made
on sigmoidoscopic biopsy. The terminal
US is often limited in evaluation of the ileum may be involved (‘backwash
retroperitoneum and CT is the ideal ileitis’).
modality for psoas assessment and
abscess drainage (Fig. 6.12). Ulcerative colitis runs a variable
clinical course — usually with periods of

Fig. 6.12 CT of left psoas abscess secondary to renal calculus disease. A large sep-
tated fluid collection involves the left psoas and iliacus muscles (long arrow). Note
normal right psoas muscle (short arrow).

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96 CHAPTER 6

relapse and remission, although an acute Postinflammatory polyps
and fulminant illness may occur. Extra- Terminal ileitis
colonic manifestations are recognised
(e.g. arthritis, iritis, rash) in 10%. Complications of ulcerative colitis

AXR • Toxic megacolon: an acute fulminant
illness with colonic dilatation (> 6 cm)
Look for: and high risk of perforation. It carries a
• Extent of faecal residue — where it high mortality. Toxic megacolon can be
is absent this is suggestive of colitic diagnosed on AXR (Fig. 6.14). Contrast
involvement enema should not be performed because
• Bowel wall thickening of the risk of perforation.
• Colon diameter (> 6 cm in traverse • Colonic adenocarcinoma: annual inci-
colon suspicious of toxic megacolon). dence of 10% after first decade of the
Colon narrows in chronic disease disease. Carcinomas are often multiple
• Loss of haustration or mural and flat, and scirrhous in nature (Fig.
thickening 6.13). Patients with ulcerative colitis
• Evidence of perforation. should undergo regular colonoscopic
screening with random biopsies to detect
Barium enema dysplasia.

This is a useful investigation in ulcera- Crohn’s colitis (see Chapter 5)
tive colitis. It is used to assess dis-
ease extent, to differentiate ulcerative This is a granulomatous colitis particu-
colitis from other forms of colitis and larly involving the right colon, with
to detect disease complications (e.g. sparing of rectum and sigmoid colon.
malignancy). However, perianal disease (abscess,
fistula, ulceration) is strongly suggestive
Barium enema features of ulcerative of Crohn’s.
colitis

Acute changes AXR
Granular mucosa pattern
‘Collar-stud’ ulcers (shallow ulcera- Look for:
• Extent of faecal residue, bowel-wall
tion underlying mucosa) thickening, haustral loss or thickening
Haustral thickening (‘thumb-printing’) (Fig. 6.15)
Inflammatory polyps • Also look for gallstones, sacroiliitis
and avascular necrosis (femoral heads),
Chronic changes (Fig. 6.13) which are associated with Crohn’s (and
Haustral loss ulcerative colitis).
Colon shortening
Luminal narrowing (‘lead-pipe’ colon)

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LOWER GASTROINTESTINAL TRACT 97

Fig. 6.13 Films from double-contrast barium enema in a patient with long-
standing ulcerative colitis involving the colon around to the hepatic flexure. Note
granular mucosa with colon lumen narrowed and haustral pattern absent.
A complicating carcinoma is seen at the splenic flexure (arrow). Note normal
haustral pattern in the right colon.

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98 CHAPTER 6

Fig. 6.14 AXR in a patient with ulcerative pancolitis and toxic dilatation of the
transverse colon. Note absence of faecal residue and thickening of haustra
(arrows). There is a pelvic intrauterine contraceptive device (IUCD).

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LOWER GASTROINTESTINAL TRACT 99

Fig. 6.15 AXR in a patient with Crohn’s colitis. The transverse colon is narrowed
and thumb-printing (mucosal oedema) is present (arrows).

Barium enema features of Crohn’s colitis Complications of Crohn’s colitis

Early • Fistula: enterocolic, enterocutaneous,
Nodular lymphoid hyperplasia perianal
Aphthous ulcers • Toxic megacolon: less common than
‘Cobblestoning’ resulting from longi- ulcerative colitis
• Adenocarcinoma: ileum and colon
tudinal and transverse ulcers sepa- • Abscess formation.
rated by oedema — ulcers are deep
Thickened haustra Ischaemic colitis
Inflammatory pseudopolyps
Discontinuous involvement (‘skip Patients present with acute abdominal
lesions’) pain and rectal bleeding, and ischaemic
colitis tends to involve the splenic flexure
Late and descending colon at the ‘watershed’
Loss of haustration area of blood supply between superior
Strictures (‘string’ sign) and inferior mesenteric arteries. It is
Fistulae more common in the elderly with a
Pseudodiverticula history of cardiovascular disease.

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100 CHAPTER 6

Fig. 6.16 Post-contrast CT in a severely ill patient with ischaemic colitis. Air is iden-
tified peripherally distributed within portal veins in the liver (small arrows). Ascites
is present (large arrows).

AXR long mesentery allowing the caecum to
AXR may show segmental muco- rotate so it lies in the mid-abdomen or,
sal oedema with thumb-printing. Diag- more commonly, the left upper quadrant.
nosis can be confirmed with barium
enema. AXR

CT AXR reveals a dilated gas-filled caecum
CT demonstrates segmental mural in the left upper quadrant (Fig. 6.17).
thickening, and also intramural and The medially placed ileocaecal valve may
portal venous gas in severely ill patients cause an indentation, giving a kidney or
(Fig. 6.16). ‘coffee-bean’ appearance.

Caecal volvulus If the ileocaecal valve is incompetent,
there will be coexisting small bowel di-
Caecal volvulus accounts for 3% of latation. The normal caecal gas pattern
colonic obstructions and is associated is absent in the right iliac fossa.
with malrotation of the right colon and a
A contrast enema is helpful if AXR is
atypical, with the tapered end of the
obstructed contrast column pointing
toward the torsion.

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LOWER GASTROINTESTINAL TRACT 101

Fig. 6.17 Supine AXR in a patient with caecal volvulus and an incompetent ileo-
caecal valve. Note distended air-filled caecum in left upper quadrant (large arrow)
and dilated small bowel loops (small arrows).

Sigmoid volvulus colon extending into the upper abdo-
men, converging to the left iliac fossa
This accounts for 1–2% of colonic ob- (Fig. 6.18)
structions and tends to occur in elderly • Often dilated large bowel proximally
or psychiatric patients with large redun- • Absence of gas in the rectum.
dant sigmoid colons.
A contrast enema may be required in
Patients present with abdominal pain some patients where radiographical
and distension. findings are equivocal. This demon-
strates a tapered narrowing of the con-
AXR trast column at level of volvulus.

On supine AXR, look for: Once the diagnosis has been made, a
• Markedly dilated loop of sigmoid flatus tube can be passed to decompress
the sigmoid colon to allow patient stabi-
lization prior to sigmoid colectomy.

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102 CHAPTER 6

Fig. 6.18 Supine AXR in a patient with sigmoid volvulus. Note markedly dilated
sigmoid colon (arrows) with ‘inverted-U’ configuration, converging to the left iliac
fossa. Calcified gallstones are seen in the right upper quadrant.

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LOWER GASTROINTESTINAL TRACT 103

Further reading Double Contrast Gastrointestinal
Radiology, 3rd edn. Philadelphia:
Gore RM, Levine MS, eds. Textbook of Saunders, 2000.
Gastrointestinal Radiology, 2nd edn. Miller FH, ed. The Radiological Clinics of
Philadelphia: Saunders, 2000. North America: Radiology of the Pan-
creas, Gall bladder and Biliary Tract,
Levine MS, Rubesin SE, Laufer I, eds. Vol. 40. 2002.