Radiology cases, Ulcerative Colitis

To see Case List first.

Ulcerative Colitis

Ulcerative colitis is an inflammatory process in the bowel that can be found at any age, but has its peak incidence in young adults (about 80% between 20 and 40 years in UK.). The bowel is typically involved by a fairly superficial mucosal inflammation in a continuous area of bowel. The presence of a continuous pattern of colitis with rectal bleeding helps to distinguish the condition from Crohn's disease. The distal part of the bowel is involved in Ulcerative Colitis with more extensive cases having greater involvement of the proximal bowel. The mucosa may become oedematous, particularly if there is haemorrhage or secondary infection by opportunist or commensal organisms. The absorption of toxins from the bowel contributes to the clinical picture.

The Radiology contributes to the management, but the management of a toxic colitis will often depend on general clinical assessment, including colonoscopy. The plain film will often give a clue to the degree of involvement. Since normal peristalsis has to affect short segments of bowel, by definition, the presence of visible gas-filled long segments of bowel implies an ileus. The plain film abdomen may demonstrate visible gas-filled anhaustral colon, without its usual faecal contents. The extent of the emptying of the faecal material from the colon can give an indication of the extent of colitis. At barium enema, the view will show superficial ulceration and a shortened bowel, often without the usual haustral pattern. The ulcers are typically shallow and can be wide mouthed with undercutting of the mucosa, sailor hat ulcers. The mucosa may slough off (incompletely) and leave oedematous tags of mucosa, the pseudo-polyps.

Inflammation, by its effect on peristalsis, may give an appearance of proximal bowel dilatation. Given the abundance of intraluminal material (and gas) that goes through the ileo-caecal valve and accumulates from colonic inflammatory exudate, it is worth noting that colonic bacterial fermentation will not be completely suppressed by problems with colonic wall movement. The colon may show atonic gaseous dilatation and this can be a Radiological indication of a Toxic Colitis. The assessment of possible developing colitis must include clinical features. Recognisably dilated colon on the plain film may arrive a little too late to benefit the patient, if surgery proves necessary. The plain film may hint at the degree of wall involvement, but is not accurate at predicting the point of failure.

Bowel dilatation can increase to a point where the tension and stretching of the wall may impair its blood supply. Even if relative pressures inside the bowel and abdomen remain the same, the geometry means that an increase in radius 'r' will mean an increase in the tension 't' in the wall. The point at which normal bowel may perforate is about 10 cm. diameter. The crucial point is that abnormal bowel may perforate earlier. At some stage, surgical intervention may be necessary. This is where co-operative clinical assessment becomes so important. The last thing anyone wants is for the surgeon to have to operate on necrotic bowel. The presence of a severe colitis may be indicated by mucosal thickening, widely dilated bowel, extensive involvement and gas in the bowel wall. If you wait for these without paying attention to the clinical features, then Surgery might be too delayed. A colleague once described the situation "like trying to sew up wet blotting paper" (loose weave soft paper), not to mention the greater risk of faecal soiling of the peritoneum. The text book definition of Toxic Dilatation of the Colon is of systemic toxicity in a patient whose colonic diameter exceeds 6cm, but no author would recommend delaying surgery on a particular measurement.

In addition to the general symptoms of ill-health, there may be an arthropathy, often with a Sacro-iliitis, sometimes with a uveitis as well. Erythema nodosum, pyoderma gangrenosum may also occur in combination with inflammatory bowel disease. Longer term complications of Ulcerative colitis include ascending cholangitis. It's not a bad idea to ask for a history of bowel disorder in unknown chronic liver disease, especially if the bile ducts appear a little irregular on Liver ultrasound. Strictures with fibrosis rarely occur in Ulcerative colitis. If there is a long history you should consider the possibility of Carcinoma being the cause of an smooth stricture of the colon. In a patient with a long history, not only is carcinoma a higher risk, up to 30% in some families, but the presentation may be atypical. Multiple tumours are also commoner than the usual 5%. Each case of Ulcerative Colitis is managed individually and supervised by regular colonoscopy. It is not appropriate to make a general statement about the time to proceed to pre-emptive colectomy, but indications include epithelial dysplasia and polyp formation.