This chapter covers:Common conditions Appendicitis Colonic obstruction Diverticular disease Neoplasia: polyp, carcinoma Sepsis Colitis VolvulusCommon presentations in whichimaging can help Altered bowel habit: obstruction,carcinoma, diverticular disease Acute abdominal distension: obstruction Acute abdominal pain: obstruc-tion, colitis, diverticulitis Rectal bleeding: carcinoma, di-verticular disease, colitisLook for hepatomegaly or an abdominal mass on clinical examination.

Patients should undergo perianaland rectal examination at presenta-tion. This task is often delegated tothe house officer. If you are unsure,ask for help from a senior colleague.

Imaging strategy

Initial imaging in acute presentationsusually involves a supine AXR and anerect CXR. CXR may demonstrate free intraperitoneal air beneath the diaphragm (see Chapter 5), and manypatients who are acutely ill may have evi-dence of chest sepsis or cardiac failure

also. Supine AXR will give informationconcerning small and large bowel gaspattern, free intraperitoneal air, softtissues and bony structures.

Once initial clinical assessment hasbeen made and a working diagnosis formulated, many patients will requirefurther imaging. Discuss the case withthe radiologist to identify the best way (including endoscopy) to reach a diagnosis.

US

US in colorectal disease can be helpfulfor initial assessment of: Possible bowel-related mass Free fluid or abscess formation Solid organs.

By their nature, many pathologies ofthe colon are associated with significantbowel gas and when combined with anelderly, immobile or obese patient theuse of US may be limited.

CT

CT can provide significant additional diagnostic information in patients withbowel-related masses and suspected in-flammatory disease or malignancy. CT isincreasingly being used as an early inves-tigation in the elderly and frail to avoidrectal contrast studies.

Contrast enema

This is an essential tool for evaluation of

Chapter 6: The lower gastrointestinal tract

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the rectum and colon (combined withendoscopy).

Unprepared contrast enema, usuallyusing water-soluble iodinated contrast,may be used to exclude an obstructinglesion in patients with large bowel ob-struction. Mucosal detail is poor and, ifthe study is negative, follow-up bariumenema or colonoscopy is often needed.

Contrast enema should not be per-formed in patients at risk of perforation(e.g. toxic megacolon). Barium causesperitonitis if it extravasates outside thebowel and should not be used in patientswho may have perforation or where recentdeep biopsies have been performed.Water-soluble contrast should be used.

Maximum diagnostic information isobtained using the double-contrast technique (air and barium) with goodbowel preparation. However, a significantnumber of elderly patients cannot retainair and/or barium and may be immobile.In some of these patients, CT may beused to exclude a gross mass lesion.

MR

MR has a role in staging colorectal car-cinoma, but its use is currently limitedotherwise.

NM

This has a limited role, but it can be usedto assess the extent of inflammatorycolitis.

Appendicitis

This is the most common surgical emergency, with a peak incidence in thesecond and third decades.

The classic signs of appendicitis areabsent in up to one-third of patients and there is a significant rate of clinicalmisdiagnosis.

Imaging may be particularly helpfulin: The elderly, where symptoms andsigns may be minimal Children, where history and examina-tion are often difficult Young women who may have a gynae-cological cause for pain.

Accurate and appropriate imagingreduces the number of normal laparo-tomies and will help to exclude othercauses of appendix-type pain. However,imaging is often not needed followingclinical assessment.

AXR

Look for: Laminated calcified appendicolith(1015% of patients) Evidence of ileus, often localized tothe right iliac fossa Distortion of psoas margin Bubbles of air in associated appendixabscess.

US

This represents a non-invasive modalityfor assessment of atypical patients. US is most accurate in children and youngand/or pregnant women, where the appendix is not obscured by gas. US fea-tures of appendicitis include identifica-tion of the appendix as an abnormal,thick-walled and non-compressiblestructure with a distended lumen (Fig.6.1). An appendicolith or associatedabscess formation may also be seen.

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CT

CT is highly accurate in the evaluation ofappendix inflammation and local extent.It is the technique of choice in theelderly, obese or very tender patients orwhere US has been unhelpful and clini-cal concern persists.

Barium studies

Barium studies of small or large bowelmay be helpful in some patients whereinitial US or CT have indicated bowelpathology not clearly related to the appendix.

Colonic obstruction

The major causes of large bowel ob-struction are carcinoma, diverticulardisease and volvulus. Carcinoma, mostcommonly within the sigmoid, accountsfor > 50% of cases. Symptoms are of ab-dominal distension and pain with associ-ated vomiting. A mass may be palpable.

The integrity of the ileocaecal valve isimportant. If it is competent, this pre-vents passage of air into the small bowelif the large bowel is obstructed, leadingto rapid and pronounced colonic andcaecal dilatation, with the risk of is-chaemia and perforation. An incompe-tent ileocaecal valve allows colonicdecompression, with passage of air into

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) anda target appearance.

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the small bowel. Onset of symptoms maythen be more gradual.

AXR

On supine AXR, look for:

Dilated gas-filled colon proximal tothe site of obstruction (Fig. 6.2) Paucity of gas in collapsed colon distalto the obstruction Haustral pattern to differentiate fromsmall bowel

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

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Small bowel dilatation also if ileocae-cal valve incompetent Evidence of perforation.

If large bowel obstruction is diag-nosed, rectal and sigmoidoscopic exami-nation should be performed to exclude alow obstructing lesion. If negative, thepatient should be considered for contrastenema examination of the large bowel.

CXR

On erect CXR, look for evidence of freeintraperitoneal air, lung metastases andother pathology.

Contrast enema

Although barium is the ideal agent, it cancause problems. It is contraindicated inpatients at risk of perforation and cancause impaction if no obstruction ispresent, as well as interfering with futurecolonoscopy and CT (see Chapter 2). Io-dinated contrast (water-soluble) is oftenused and will exclude gross obstruction(Fig. 6.3).

CT

This can be useful in assessing bowel and adjacent structures, particularly ifpatients are elderly or frail and cannot tolerate a contrast enema.

Pseudo-obstruction

Marked dilatation of the large bowelmay occur in elderly, bedridden patientsor those with neurological or psychiatricdisorders. Gaseous distension often in-volves the rectum also, and faecal loadingmay be present. Sigmoidoscopy andcontrast enema are often needed to

exclude a mechanical obstruction in pa-tients who do not settle with conserva-tive treatment.

Diverticular disease of the colon

This is the most common colonic diseasein the West, with diverticula present inup to 50% of people of 50 years of age,with the sigmoid colon most frequentlyinvolved. Diverticula are out-pouchingsof colonic mucosa and submucosa thatpenetrate between circular muscle fibres.Circular muscle hypertrophy and mus-cular spasm are common. Diverticulardisease is generally diagnosed duringbarium enema examination, often as anincidental finding (Fig. 6.4). Complica-tions of diverticular disease include diverticulitis, fistula formation andhaemorrhage.

Diverticulitis

Diverticulitis is the most common com-plication of diverticular disease, occur-ring in up to 25% of patients. It occurssecondary to mucosal abrasion by faecalmatter within a diverticulum, causinglocal perforation, inflammation andabscess formation. Patients present withleft iliac fossa pain, fever and often an inflammatory mass.

AXR

AXR may demonstrate air within anabscess or secondary ileus. Chronic in-flammation and stricturing with largebowel obstruction is unusual.

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

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Barium enema

This is excellent at demonstrating diver-ticular colonic muscular hypertrophyand spasm, and local contrast extravasa-tion into walled-off pericolic abscess. Pa-tients often do not tolerate barium enemaduring an acute episode, and enema doesnot delineate pericolic inflammation.

US

US is often requested as a first-line

investigation for patients with left iliacfossa pain and may demonstrate bowel-wall thickening, a mass or fluid collectionin diverticulitis. However, US is oftennon-diagnostic.

CT

Patients often proceed to CT, which accu-r