Colitis, ulcerative

There is a possible genetic aetiology but autoimmune mechanisms and "psychological" factors also play an aetiological role. This hypothesis is supported by the fact that extraintestinal manifestations such as arthritis and cholangitis are frequently associated with ulcerative colitis (UC).

Grossly UC is characterized by a uniform and continuous inflammatory process, with haemorrhages and ulcerations of the colonic mucosa. The rectum is involved in the large majority of patients. The term "backwash ileitis" designates involvement of a 5 - 25 cm segment of the terminal ileum that may occur in patients with involvement of the entire colon. Fistulae and pericolic abscesses are rarely seen in patients with UC. During the chronic phase fibrosis with retraction and shortening of the colon causes haustral loss and development of inflammatory pseudopolyps without malignant potential (Fig.1). However, the risk of associated carcinoma of the colon is markedly elevated for patients with long standing UC.

The clinical symptomatology of UC includes bloody diarrhoea with pus, low grade fever and weight loss. Extracolonic manifestations of UC include arthritis, skin changes and hepatobiliary disturbances. The clinical course of UC is characterized by periods of remissions and exacerbations. UC affecting the rectum has a different clinical presentation than classical UC. The disease is usually limited to the rectum without extension to the other colon segments, it may follow a hyperacute clinical course and the extracolonic manifestations are usually not prominent or may even be absent.

The most important complications of UC are colon perforation and toxic megacolon.

Radiological diagnosis

The role of radiological study in patients with UC is mainly to confirm the endoscopic findings, to evaluate the extent and the severity of the mucosal lesions and to demonstrate complications such as strictures, pseudopolyposis, toxic megacolon, perforation and malignancy.

On plain radiography of the abdomen the diagnosis of UC is suggested by the striking absence of residue in the colon. Abnormally located free air collections may indicate free perforation in the peritoneal cavity. Air may also be detected within the wall of the colon indicating severe tissue necrosis.

Barium examination is the most appropriate technique to reveal the typical mucosal changes observed in UC. In patients with active disease the usual procedure for colon preparation cannot be applied because laxatives may cause an exacerbation of the inflammation and the examination itself should be conducted with great care in order to reduce the discomfort for the patient. During the early stage of the disease hyperaemia and oedema leads to a fine granular mucosal pattern composed of small dots of barium or to a more coarse granular pattern composed of reticular or ring-like structures. During the ulcerative phase of the disease superficial and linear ulcerations become apparent, commonly located at the site of the attachment of the teniae. The ulcerations may also become deeper and extend over a short or longer distance in the submucosa (Fig.2). Polypoid lesions may first occur during the acute phase of the disease and are then composed of the remaining areas of normal mucosa or of islands of regenerative mucosa, which are dispersed among the numerous ulcerations. During the chronic phase of the disease or in patients with quiescent disease, another type of pseudopolypoid structure caused by chronic inflammation of the mucosa leading to marked tissue proliferation is commonly obser On intravenous contrast medium enhanced scans and using water as endoluminal contrast medium three different layers may be visible within the thickened colonic wall: the thickened muscularis mucosae and lamina propria have a high attenuation, a middle ring with low attenuation corresponds to the submucosal fat and the outer layer again has a higher attenuation due to the thickened muscularis propria. Although the CT features visible in UC are quite striking they are not considered to be specific. Thus CT should not be recommended for the routine management of patients with UC as its findings do not contribute to the diagnosis nor to the differential diagnosis of Crohns disease of the large bowel.

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