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EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2018
a)
c)
100 µm 50 µm b) d)
100 µm
20 µm
20 µm
Fig 2: a) Haematoxylin and Eosin [H&E] photomicrograph of mucosal layer showing intense hyperaemia and mixed cellular infiltrate (few eosinophils), with extensive loss of mucosal epithelial cells and sloughing into the intestinal lumen. b) H&E photomicrograph of submucosal layer with eosinophil dominated diffuse cellular infiltrate (arrows). c) H&E photomicrograph of muscularis layer with multifocal infiltrate with a focal central accumulation of eosinophilic debris, surrounded by macrophages, and lymphocytes. d) H&E photomicrograph of serosal layer with hyperaemia and diffuse eosinophilic infiltrate.
The lesions in the current series were evident as visibly
striking, focal, hyperaemic lesions with serosal petechiation, oedema and marked thickening of the intestinal wall, characterised histologically as a focal and severe eosinophilic and granulomatous colitis. Eosinophilic colitis lesions identified in the large colon have been reported to have marked thickening and oedema of the colon wall, with variable serosal changes from petechiation, or erythema to discrete, well defined areas of serosal necrosis and with histopathological abnormalities of varying severity (Edwards et al. 2000). Idiopathic focal eosinophilic enteritis lesions are characterised as single or multiple, palpably thickened and hyperaemic focal serosal plaques or circumferential bands with histological evidence of submucosal oedema, haemorrhage and mucosal swelling (Archer et al. 2006). In contrast to colitis lesions, serosal necrosis has not been described as a characteristic of IFEE lesions. A clear demarcation between affected and normal bowel at the edge of the segmental lesion has been reported in the large colon (Edwards et al. 2000), which is similar to the lesions
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identified in the small colon and those affecting the small intestine (Archer et al. 2006). The lesions described in the current study had several
similarities to those occurring in the large (ascending) colon. In a series of horses with eosinophilic colitis lesions of the large colon, partial colon resection was performed in 16/22 (72%) cases, where the external appearance of the serosa and transmural necrosis indicated lack of tissue viability (Edwards et al. 2000). Large colon resection was considered unnecessary in five cases where the appearance of the intestine was relatively normal and luminal occlusion was minimal, but the authors considered that there was a risk of progressive intestinal necrosis post-operatively in cases that did not undergo intestinal resection (Edwards et al. 2000). Short-term survival (defined as discharge from the hospital) for horses with eosinophilic colitis of the left dorsal colon was 82% (18/22), with 73% (16/22) alive at 3 months to 7 years post- operatively (Edwards et al. 2000). Resection of IFEE lesions was previously considered necessary and undertaken in 10/12 cases in one series, with
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