Dx: Ischemic colitis (with acute mucosal necrosis pattern)

The colonic mucosa shows features of acute mucosal necrosis:

• necrosis of epithelium
• eosinophilic appearance of lamina propria
• loss of normal plasma cell population in the lamina propria
• diffuse erythrocyte extravasation in the lamina propria
• regenerating microcrypts
• little neutrophilic infiltrate

The two most important differential diagnoses of this pattern include ischaemic colitis and verotoxin-producing E coli. Correlation with the clinical scenario is important. Ischaemia tends to affect older patients. E coli O157-colitis tends to affect younger patients and produces a haemorrhagic segment, especially in the proximal colon. Clostridium difficile rarely can give rise to acute mucosal necrosis without pseudomembrane. In such cases, the history and correlation with the stool toxin test is important. NSAID is also alledged to be a rare cause for acute mucosal necrosis in big-time NSAID users but this is not well documented. Irradiation is a valid differential diagnosis because it can affect vessels and cause ischaemia. We have seen cases that looked like healing acute mucosal necrosis. However, irradiation colitis usually presents with features resembling the late changes of ischaemia, such as atrophy, glandular distortion and fibrosis. The right clinical setting obviously help arriving at the correct diagnosis and irradiation almost always affect the rectum.

Marks were deducted from participants (369, 515, 448) who had not put ischaemic colitis on top of the differential list. Marks were also deducted from a participant (515) who just mentioned the broad category of infection without specifying the right organism, E coli O157. 10 marks were deducted from participants (663, 448) who mentioned "chronic" because acute mucosal necrosis represents the early changes of ischaemia. The chronic ones are less diagnostic and include atrophy, glandular distortion, fibrosis and stricture. (Drs YF Lo/MS Tsui)

1. Norris HT. Re-examination of the spectrum of ischemic bowel disease. In: Norris HT (ed), Pathology of the Small Intestine, Colon and Anus. 2nd ed, New York, Churchill Livingstone, 199, pp 414-425.
2. Kelly J, Oryshak A, Wenetsek M, et al. The colonic pathology of Escherichia coli O157:H7 infection. Am J Surg Pathol 14:87-92.
3. Bjarnason I, Hayllar J, Macpherson AJ, Russell AS. Side effects of nonsteroidal anti-inflammatory drugs on the small and large intestines in humans. Gastroenterology 104:1832-1847, 1993.

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