Structural Features of the Equine Small Intestinal Mesenteric Attachment Predisposing to Rupture.

Overview

• This study investigates why the equine jejunum (a part of the small intestine) tends to rupture at the point where it attaches to the mesentery, a membrane that supports the intestines.
• The research explores the anatomical features that could make this area weaker and more prone to rupture, using experimental testing, imaging, and examination of a real colic case.

Introduction and Background

• Rupture of the small intestine in horses sometimes leads to the formation of a pouch of ingesta (intestinal contents) within the mesentery, causing severe colic.
• Previous studies using jejunal segments reconstructed through anastomosis (surgical connection) have shown ruptures occurring at sites away from the surgical connection, particularly at the mesenteric attachment point.
• This suggests an inherent structural predisposition of the jejunum to rupture at the mesenteric attachment area rather than other sites.

Aims of the Study

• To determine the exact location of jejunal rupture under high internal pressure conditions.
• To identify anatomical features that might weaken the jejunum at the mesenteric attachment, making rupture more likely.
• To correlate experimental findings with an actual colic case in a horse, demonstrating rupture into the mesentery in a natural setting.

Methods

• Jejunal segments were collected from five horse cadavers (total of 22 segments).
• The segments were inflated with water to increase intraluminal pressure until rupture occurred or the system disconnected.
• Tissue samples from ruptured jejunum (RJ) and unruptured controls (UC) were taken for detailed study.
• Histological analysis was done to view microscopic tissue structure.
• High-resolution magnetic resonance imaging (MRI) at 14.1 Tesla was used to visualize anatomical details non-invasively.
• A naturally occurring colic case was also examined, with jejunum resected for gross and histological evaluation.

Key Findings

• Most jejunal ruptures (18 out of 22) happened at the mesenteric attachment rather than other locations.
• Four segments failed by disconnecting from the pressure source rather than rupturing, suggesting that under ideal conditions, rupture sites are consistent.
• MRI and histology of unruptured jejunum showed regular gaps (“fenestrations”) in the muscularis externa layer at the site of mesenteric attachment.
• These fenestrations correspond to areas where blood vessels from the mesentery enter the jejunal wall and reach deep into the submucosal layer.
• The clinical colic case confirmed rupture occurring along these vascular fenestrations at the mesenteric attachment site.

Interpretation and Significance

• The muscularis externa (main smooth muscle layer of the jejunum) has natural anatomical ‘windows’ or fenestrations at the mesenteric attachment to allow blood vessels to pass through.
• These fenestrations create a structural weakness in the intestinal wall because the muscle is thinner or absent where vessels enter.
• Under increased pressure inside the intestine, such as during colic, these weaker areas are predisposed to rupture.
• This explains why ruptures often occur at the mesenteric attachment rather than along the free part of the jejunal wall.
• The findings can help veterinarians better understand the pathology of equine colic and could influence surgical or diagnostic approaches by highlighting vulnerable locations.

Conclusions

• The study elucidates a clear anatomical reason—the presence of periodic fenestrations in the muscularis externa for mesenteric vasculature—that predisposes the equine jejunum to rupture at its mesenteric attachment.
• Recognizing this predisposition may improve clinical management and preventive strategies for horses suffering from intestinal rupture and colic.