Ulcerative colitis
Ulcerative colitis (UC) is an inflammatory bowel disease which predominantly affects the colon, but also has extraintestinal manifestations.
Epidemiology
Typically ulcerative colitis manifests in young adults (15 - 40 years of age) and is more prevalent in males 1,3. A combination of environmental and genetic factors are thought to play a role in the pathogenesis, although the condition remains idiopathic.
Clinical presentation
Clinically patients have chronic diarrhoea associated with tenesmus, pain and fever 1.
Pathology
Unlike Crohn's disease which is characteristically a transmural disease, ulcerative colitis is usually limited to the mucosa 1. Chronic disease is associated with a significantly elevated malignancy risk, of up to 0.5-1.0% per year after 10 years of disease.
The diagnosis is often made with endoscopy, which also allows biopsy of any suspicious areas.
Associations
Radiographic features
Involvement of the rectum is almost always present (95%) 1, with the disease involving variable amounts of the more proximal colon, in continuity. The entire colon may be involved, in which case oedema of the terminal ileum may also be present (so-called back-wash ileitis).
In very severe cases, the colon becomes atonic, with marked dilatation, worsened by bacterial overgrowth. This leads to toxic megacolon which although uncommon has a poor prognosis.
Plain film
Mural thickening is common, with thumbprinting also seen in more severe cases.
Barium enema
Double contrast barium enema allows for exquisite detail of the colonic mucosa, and also allows bowel proximal to strictures to be assessed. It is however contraindicated if acute severe colitis is present due to the risk of perforation.
Mucosal inflammation lends a granular appearance to the surface of the bowel. As inflammation increases, the bowel wall and haustra thicken.
Mucosal ulcers are undermined (button-shaped ulcers). When most of the mucosa has been lost, islands of mucosa remain giving it a pseudo-polyp appearance.
In chronic cases the bowel becomes featureless with loss of normal haustral markings, luminal narrowing and bowel shortening (lead pipe sign).
Small islands of residual mucosa can grow into thing worm like structures (so-called filiform polyps)
Colorectal carcinoma in the setting of ulcerative colitis is more frequently sessile and may appear to be a simple stricture.
CT
CT will reflect the same changes that are seen with a barium enema, with the additional advantage of being able to directly visualise the colonic wall, the terminal ileum and identify extra-colonic complications, such as perforations or abscess formation. It is important to note however that CT is insensitive to early mucosal disease 2.
Inflammatory pseudopolyps may be seen if large enough, in well distended bowel. In areas of mucosal denudation, abnormal thinning of the bowel may also be evident 2.
A cross section of the inflamed and thickened bowel with have a target appearance, due concentric rings of varying attenuation, also known as mural stratification 1,2.
In chronic cases, submucosal fat deposition is seen particularly in the rectum (fat halo sign). Also in this region, extramural deposition of fat, leads to thickening of the perirectal fat, and widening of the presacral space 1,2.
Strictures are also common, and are not all malignant. These are predominantly due to marked muscularis mucosa hypertrophy, which is also in part responsible for the lead pipe sign.
Colorectal carcinoma is often sessile. Focal loss of mural stratification or excessive mural thickness ( > 1.5 cm ) should prompt endoscopic evaluation 2.
MRI
The current status of MRI in ulcerative colitis is that of a promising, noninvasive technique for imaging extent of more severe disease.
The most striking abnormalities in UC are wall thickening and increased enhancement.
The median wall thickness in UC ranges from 4.7 to 9.8 mm. In general, the more severe the inflammation, the thicker the colonic wall. A colonic wall thickness <3 mm is usually considered as normal, 3 to 4 mm as a "gray zone," and > 4 mm as pathological.
Enhancement of the mucosa with no or less enhancement of the submucosa producing a low SI stripe the so-called submucosal stripe.
Other features are the loss of haustral markings, backwash ileitis shows mild enhancement and no wall thickening and there is increased SI of the pericolonic fat noted .
Complications
Approximately 10 - 15 % of cases initially presenting as ulcerative colitis can later progress to crohn's disease
Treatment and prognosis
Total colectomy is curative of both the intestinal symptoms and of the potential risk of colorectal carcinoma. Medical therapy is able in some cases to control colonic disease but does not remove the need to carefully and regularly screen for malignancy.
Due to close surveillance patients with ulcerative colitis have a normal or even slightly improved survival compared to normal population 3. This is clearly not the case if the disease is not diagnosed or treatment not available.
Differential diagnosis
The most important differential diagnosis is Crohn's disease (see Crohn's disease vs. ulcerative colitis). Otherwise the differential includes other causes of colitis:
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