Diseases of the Colon, Rectum and Anus

inflammatory diseases of the colon, colonic diverticular disease, other lesions of the colon



Ischemic Colitis

Ischemic colitis is characterized by the abrupt onset of lower abdominal pain and rectal bleeding. Diarrhea is common, as is abdominal tenderness on physical examination. Most patients are over the age of 50 years, and many have a history of prior cardipyascular disease.

The radiographic appearance of ischemic colitis depends on the phase of the process during which the patient is examined. Because the mucosa is the layer most dependent on intact vascularity, fine superficial ulceration associated with inflammatory edema is the earliest radiographic sign of ischemic colitis. This causes the outer margin of the barium-filled colon to appear serrated, simulating ulcerative colitis. Unlike ulcerative colitis, however, ischemic colitis usually spares the rectum. As the disease progresses, deep penetrating ulcers, pseudopolyposis, and “thumbprinting” can be demonstrated. Thumbprinting refers to sharply defined, fingerlike marginal indentations along the contours of the colon wall. Although these well-circumscribed filling defects seen on plain abdominal radiographs or barium studies are generally considered to be manifestations of colon ischemia or hemorrhage, thumbprinting can occur in any inflammatory or neoplastic disease that produces polypoid masses or substantial enlargement of mucosal folds.

In most cases, the radiographic appearance.of the colon returns to normal within 1 month if good collateral circulation is established. Extensive fibrosis during the healing phase can cause tubular narrowing and a smooth stricture. If blood flow is insufficient, acute bowel necrosis and perforation may result.

The differentiation of ischemic colitis from ulcerative colitis and Crohn’s disease of the colon can be extremely difficult on radiographic or pathologic examination alone. In such cases, the characteristic acute episode of abdominal pain and bleeding, the rapid progression of radiographic findings, and the low rate of recurrence usually permit ischemic colitis to be readily distinguished from ulcerative colitis and Crohn’s disease of the colon, which are typically more indolent, chronic, and recurring.

Although chronic infarction may be caused by embolization or thrombosis of a mesenteric artery, the majority of qases do not have a demonstrable arterial occlusion.

ischemic colitis ulceration · radiographic apperances of colon cancer · what are broad-based ulcerations in colon? ·

Crohn’s Colitis

Crohn’s disease of the colon is identical to the same pathologic process involving the small bowel and must be distinguished from ulcerative colitis, the other main cause of “nonspecific” inflammatory disease of the colon. The proximal portion of the colon is most frequently involved in Crohn’s disease; concomitant disease of the terminal ileum is seen in up to 80 percent of patients. Unlike ulcerative colitis, Crohn’s colitis often spares (he rectum, and isolated rectal disease very rarely occurs. Crohn’s disease usually has a patchy distribution, with involvement of multiple, noncontiguous segments of colon (skip lesions), unlike the continuous colonic involvement in ulcerative colitis. Crohn’s colitis is a transmural disease, affecting all layers of the colon, unlike ulcerative colitis, which is primarily a mucosal disease. Although granulomas can be demonstrated in only about half the patients with Crohn’s disease of the colon, they are virtually a specific histopathologic feature in that they are not seen in patients with ulcerative colitis.

Perianal or perirectal abnormalities (fissures, abscesses, fistulas) occur at some point during the course of disease in half the patients with Crohn’s colitis, but are rare in ulcerative colitis.

The earliest radiographic findings of Crohn’s disease of the colon are seen on double-contrast examinations. Isolated, tiny, discrete erosions (aphthoid ulcers) appear as punctate collections of barium with a thin halo of edema around them. Aphthoid ulcers in Crohn’s disease have a patchy distribution against a background of normal mucosa, unlike the blanket of abnormal granular mucosa seen in ulcerative colitis. These aphthoid ulcers are not specific for Crohn’s disease; morphologically similar lesions can occur in other inflammatory conditions of the colon, such as amebic colitis, tuberculosis, Yersinia colitis, and Behcet’s syndrome.

As Crohn’s colitis progresses, the ulcers become deeper and more irregular, with great variation in size, shape,

and overall appearance. The distribution of ulcers around, the circumference of the bowel in Crohn’s disease is random and asymmetric, not uniform and monotonous as in ulcerative colitis. Deep, linear transverse and longitudinal ulcers often separate intervening mounds of edematous but nonulcerating mucosa, thereby creating a characteristic cobblestone appearance. If the penetrating ulcers extend beyond the contour of the bowel, they can coalesce to form long tracks running parallel to the longitudinal axis of the colon. Penetration ofulcers into adjacent loops of bowel or into the bladder, vagina, or abdominal wall causes fistulas that can often be demonstrated radiographically.

Thickening of the bowel wall due to transmural inflammation and intramural fibrosis leads to narrowing of the lumen and stricture formation. Occasionally, an eccentric stricture with a suggestion of overhanging edges can be difficult to distinguish from annular carcinoma. In most instances, however, characteristic features of Crohn’s disease elsewhere in the colon (deep ulcerations, pseudopolyposis, skip lesions, sinus tracts, fistulas) clearly indicate the correct diagnosis.

Patients with Crohn’s colitis appear to have a higher chance of developing colon cancer than the general population, although this association is less striking than that between colon cancer and ulcerative colitis. Carcinoma complicating Crohn’s colitis is most common in the proximal portion of the colon. It usually appears radiographicaily as a fungating mass with typical malignantfeatures, unlike the mildly irregular stricture characteristic of colon cancer in patients with ulcerative colitis.

Complications of Ulcerative Colitis

Toxic Megacolon

 

Toxic megacolon is a dramatic and ominous complication of ulcerative colitis. It is characterized by extreme dilatation of a segment of colon, or an entire diseased colon, combined, with systemic toxicity (abdominal pain and tenderness, tachycardia, fever, and leukocytosis).

Pathologically, specimens from patients with toxic megacolon show extensive deep ulcerations and acute inflammation involving the muscular layer of the colon and often extending to the serosa. The wall of the colon is extremely thin and friable, predisposing to perforation.

In most patients with toxic megacolon, a simple plain film of the abdomen demonstrating marked distension of the colon (> 5.5 cm) is diagnostic. With the patient supine, the transverse colon is the portion most promiantly distended (since colonic gas rises to the highest segment). The distal descending colon and sigmoid are less frequently dilated; distension of the rectum is uncommon. Gas within the dilated segment of colon is frequently sufficient to silhouette the mucosa and often reveals multiple broad-based, nodular pseudopolypoid projections extending into the lumen, as well as gas-filled crevices that probably represent deep ulcers between the nodular masses.

The major complication of toxic megacolon is spontaneous perforation, which can be dramatic and sudden and cause irreversible shock. Toxic megacolon is associated with a mortality rate of up to 30 percent, though this has been somewhat reduced by early diagnosis and aggressive surgical therapy. Because there is such a high danger of spontaneous perforation, barium enema examination is absolutely contraindicated during a recognized attack of toxic megacolon.

 

Colonic Strictures

Benign colonic strictures develop in up to 10 percent of patients with chronic ulcerative colitis. The most common site of benign stricture is the rectum, followed next in frequency by the transverse colon. Usually asymptomatic, the strictures tend to be short (2 to 3 cm) but can extend up to 30 cm in length. Although most commonly single, strictures in ulcerative colitis can be multiple, especially in patients with universal colonic disease.

Radiographically, a stricture due to ulcerative colitis has a typically benign appearance with a concentric lumen, smooth contours, and fusiform, pliable tapering margins. The stricture occasionally is somewhat eccentric and has an irregular contour, simulating malignancy. Because carcinoma in patients with ulcerative colitis can have a radiographic appearance indistinguishable from that of a benign stricture, colonoscopy or surgery is frequently required to make this differentiation.

Carcinoma of the Colon

Carcinoma of the colon is about 10 times more frequent in patients with ulcerative colitis than in the general population. The incidence of cancer is related to the duration of colitis, the age of the patient at the time of onset, and the linear extent of disease; it is not related to the severity or activity of the inflammatory process.

who develop ulcerative colitis before the age of 25 years and in those with colitis involving the entire colon. Malignant lesions in ulcerative colitis generally occur at a much younger age than in the general population and tend to be extremely virulent. Because cancer in ulcerative colitis is multicentric in up to 20 percent of cases, atypical in its early appearance, and rapidly metastasizing, the diagnosis is often difficult to make and the prognosis is poor.

Carcinoma of the colon in patients with chronic ulcerative colitis often presents as a filiform stricture rather than having the more characteristic polypoid or apple-core appearance of primary colonic malignancy. The tumor is typically a narrowed segment with an eccentric lumen, irregular contours, and margins that are rigid and tapered. Because it is frequently difficult to distinguish carcinoma from benign stricture in patients with ulcerative colitis, colonoscopy or surgery is often required to make an unequivocal diagnosis.

distensión abdominal · desmoid tumor and ulcerative colitis · toxic megacolon perforation complication ·

Ulcerative Colitis

Ulcerative colitis is primarily a disease of young adults, the peak incidence being in persons between 20 and 40 years of age. Ulcerative colitis is highly variable in severity, clinical course, and ultimate prognosis. The onset of the disease, as well as subsequent exacerbations, can be insidious or abrupt. The major symptoms include bloody diarrhea, abdominal pain, fever, and weight loss. A characteristic feature of ulcerative colitis is alternating periods of remission and exacerbation. Most patients have intermittent episodes of symptoms with complete remission between attacks. In fewer than 15 percent of patients, ulcerative colitis presents as an acute fulminating process. Patients with this form of the disease have severe hemorrhagic diarrhea, fever, systemic toxicity, and electrolyte depletion, as well as a far higher than usual incidence of severe complications such as toxic megacolon and free perforation into the peritoneal cavity.

 

Extracolonic manifestations of ulcerative colitis are relatively common and include spondylitis, peripheral arthritis, iritis, skin disorders (erythema nodosum, pyoderma gangrenosum), and various liver abnormalities (pericholangitis, fatty infiltration, sclerosing cholangitis, cholangiocarcinoma, and chronic active hepatitis).

In the radiographic evaluation of a patient with known or suspected ulcerative colitis, plain abdominal radiographs are essential. Large nodular protrusions of hyperplastic mucosa, deep ulcers outlined by intraluminal gas, or polypoid changes with a loss of haustral markings suggest the diagnosis. Plain abdominal radiographs can also demonstrate evidence of toxic megacolon or free intraperitoneal gas, contraindications to barium enema examinations in patients with acute colitis.

Ulcerative colitis has a strong tendency to begin in the rectosigmoid. Although by radiographic criteria alone the rectum appears normal in about 20 percent of patients with ulcerative colitis, true rectal sparing is infrequent, and there is usually evidence of disease on sigmoidoscopy or rectal biopsy. Although ulcerative colitis not infrequently spreads to involve the entire colon (pancolitis), isolated right colon disease with a normal left colon does not occur. The disease is almost always con

tinuous without evidence of the skip areas seen in Crohn’s disease. Except for “backwash ileitis” (minimal inflammatory changes involving a short segment of terminal ileum), ulcerative colitis does not involve the small bowel, a feature distinguishing it from Crohn’s disease, which may involve both the large and small intestine.

Because of reports of complications after the use of routine purgatives and cleansing enemas, the patient with suspected or known ulcerative colitis should receive minimal preparation of the colon prior to a barium enema examination. If time permits, the safest preparation is several days of a clear liquid diet with gentle, small-volume enemas the night before and the morning of the examination. Strong laxatives such as castor oil are con-traindicated. In patients with acute disease, it may be wisest to postpone the barium enema because the increased intraluminal pressure during the examination may precipitate the development of toxic megacolon.

On double-contrast studies, the earliest detectable radiographic abnormality in ulcerative colitis is fine granularity of the mucosa corresponding to the hyperemia and edema seen endoscopically. Once superficial ulcers develop, small flecks of adherent barium produce a stippled mucosal pattern. On full-column examination, an early finding in ulcerative colitis is a hazy or fuzzy quality of the bowel contour with serrated margins that is related to edema, excessive mucus, and tiny ulcerations. It is essential that these ha^y, asymmetric, nonuniform ulcerations be distinguished from innominate lines, tiny spicules that mimic ulcerations but are symmetric and

sharplv defined and represent barium penetration into normal grooves that are present on the surface of the colonic mucosa.

The postevacuation film is frequently of great value in the detection of early changes of ulcerative colitis. Unlike the normal fine crinkled pattern of criss-crossing thin colonic mucosal folds, the folds in ulcerative colitis become thickened, indistinct, and coarsely nodular and tend to course in a longitudinal direction. The thin coating of barium on the surface appears finely stippled because ot countless tiny ulcers that cause numerous spikelike projections when seen in profile.

As the disease progresses, the ulcerations become deeper. Extension into the submucosa may produce broad-based ulcers with a collar-button appearance, a nonspecific pattern that can be seen in numerous forms of ulcerating colitis. Perirectal inflammation can cause widening of the soft tissue space between the anterior sacrum and posterior rectum (retrorectal space).

With chronic disease, fibrosis and muscular spasm cause progressive shortening and rigidity of the colon. The haustral pattern is absent and the bowel contour is relatively smooth because of healing of ulcerations and re-epithelialization. Eventually, the colon may appear as a symmetric, rigid tubular structure (lead-pipe colon).1

barium enemas in ulcerative colitis show haustral patterns · empty abdominal cavity · fluid and electrolyte anagement in ulcerative colitis ·

Inflammatory Diseases of the Colon

Ulcerative inflammation of the colon or rectum is a nonspecific response to a host of harmful agents and processes. In many cases, an ulcerating colitis can be attributed to a specific infectious disease, systemic disorder, or toxic agent. However, in a large group of patients, a precise cause cannot be determined. Most of these “nonspecific” inflammatory diseases ot the colon are generally placed into one of two categories: ulcerative colitis or Crohn’s disease. Although radiographic and pathologic criteria have been established tor distinguishing between these two processes, there Is a substantial overlap in practice. In at least 10 percent of colectomy spec imens for ulcerating colitis, it is impossible to distinguish between ulcerative colitis and Crohn’s disease even with careful gross inspection and multiple microscopic sections. Features of ulcerative colitis and Crohn’s disease often coexist, making a precise histologic diagnosis difficult.