Histological Evaluation of Resected Tissue as a Predictor of Survival in Horses with Strangulating Small Intestinal Disease

SIMPLE SUMMARY: Equine colic is a serious and potentially life-threatening clinical problem. This is particularly the case when the condition is due to strangulation of the small intestine, which requires part of it to be surgically removed (resected). Failure to re-establish functional motility post-operatively is a common reason for post-operative euthanasia, even if surgery has been successfully accomplished. The margins for a resection are typically determined by gross appearance of the small intestine combined with appropriate preservation of vascular supply to the remaining tissue. We hypothesized that histological evaluation of resected intestine could highlight changes indicative of unhealthy gut tissue left in situ, which could predict the likelihood of continued intestinal dysfunction and therefore survival. We graded the histological appearance of grossly normal and abnormal tissue resected from horses with strangulating small intestinal lesions and control tissue taken from horses euthanised for reasons unrelated to intestinal disease. There was no difference between the histological scores of grossly looking normal regions of the resected tissue and control tissues, nor was this associated with survival post-surgery. Grossly abnormal resected tissue was significantly different to the control tissue, and those horses in which the histological appearance showed greatest tissue disruption proximally (orally) demonstrated longer survival times. ABSTRACT: Strangulating small intestinal disease (SSID) in horses carries a poor prognosis for survival, especially following resection of ischaemic tissue. The margins of a resection are principally based on visual appraisal of the intestine during surgery. We hypothesized that histological evaluation of resected tissue may identify occult changes indicative of prognosis. Small intestinal samples from 18 horses undergoing resection for SSID and 9 horses euthanised for reasons unrelated to gastrointestinal pathology were utilised. Histological appearance was used to generate a ‘total damage score’ (TDS) for the control tissue, grossly normal tissue at oral and aboral extremities (sections OR1 and AB1) of the resected intestine, and oral and aboral extremities of visually abnormal tissue (sections OR2 and AB2) from SSID horses. The relationship between TDS and long-term post-operative survival was investigated. TDS was not different between control tissues and OR1 and AB1 sections. Five surgical cases were alive at follow-up, the longest follow-up time being 2561 days. Based on the median scores for SSID cases versus controls, cut-off values were generated to evaluate post-operative survival versus TDS. Only OR2 TDS was significantly associated with survival, with a higher (worse) score indicating longer survival. More severe tissue insult may expedite rapid progression to surgery, improving post-operative outcomes.