{'fraction_non_alphanumeric': 0.017530864197530863, 'fraction_numerical': 0.0044444444444444444, 'mean_word_length': 5.24191063174114, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Ischaemia: another possible cause of yet another entity

Ischaemia of the colon is known to be precipitated by a wide variety of aetiological factors ranging from major vascular occlusion to small vessel disease, from therapeutic medication to shock and from haematological disorders to long distance running! Gandhi et al. in 1996 [1] proposed an excellent classification of such a vast array of conditions affecting the colon creating an interesting long list of differential diagnoses. Robert et al. in 1993 [2] suggested that the rectum is seldom involved by ischaemia. There are however other less known entities associated with ischaemia which may be confused clinically or pathologically with inflammatory bowel disease (IBD) including fulminant and obstructive colitides [3– 5]. Toner and colleagues were the first to describe the entity of obstructive colitis and have shown that in areas proximal to an obstruction, which is usually due to diverticular disease or carcinoma, there are variable segments of dilated colon that show separate or confluent ulceration with intervening surviving islands of normal mucosa. These are always separated from the obstructed areas by relatively normal segments of colon. To the unwary pathologist they may give the impression of IBD [6]. Although Toner et al. [5] were advancing the thesis that the cause of this reaction is a primary ischaemia, Levine & Price suggested that the condition may be due to hypoperfusion secondary to increase in intra luminal pressure. Acute dilatation of the colon can also be seen in ischaemia. At least two reports have described fulminant colitis due to ischaemia [3,4]. This condition too can be confused with IBD. In this issue Villanacci and colleagues have expanded the list of diseases that could lead to or be caused by ischaemia to include diversion colitis. Diverting faecal material for whatever reason has been reported first by Goltzer et al. to be associated with well-described clinical and anatomical changes [7]. Subsequently, large numbers of publications have confirmed their finding. Histologically the condition is characterized by a variable degree of inflammation particularly a chronic lymphocytic infiltrate frequently with lymphoid follicle formation. The latter leads in some cases to the typical ‘bumps’, or nodularity seen endoscopically. Histologically this is sometimes difficult to differentiate from inflammatory bowel disease although crypt distortion is unusual unless the diversion is carried out on the background of IBD. This is thus another clinicopathological entity in which the close collaboration of clinician and pathologist taking the history into account is of paramount importance in achieving a diagnosis. There are many hypotheses as to the cause of diversion colitis and the mucosal deprivation of short chain fatty acids is the most popular. Other aetiologies have also been suggested including ischaemia which has been mentioned as a possible cause by Warren & Shepherd without detailed microscopical validation [8]. In the series of Villanacci et al., the histological evidence of ischaemia was suggested by the presence of collagen and, in some cases, of iron deposition in the lamina propria. Although collagen deposition is a feature of chronic ischaemia, it can also be seen in a variety of other conditions such as collagenous colitis. In both diversion colitis and the spectrum of collagenous colitis, which includes lymphocytic colitis, there is increase in collagen deposition and lymphocytic infiltration. One then must ask the question whether ischaemia is another cause of collagneous colitis or whether it is a secondary phenomenon, as is possibly the case in diversion colitis. Villanacci’s paper directly and indirectly emphasizes the point that clinicopathological correlation is very important in reaching a final diagnosis as many conditions can mimic IBD. It also begs the question whether ischaemia may be a causative factor or simply one of a long list of seemingly unrelated clinical conditions.