Structural features of the equine small intestinal mesenteric attachment predisposing to rupture.

Rupture of equine small intestine with formation of a pouch of ingesta within the mesentery has been reported in clinical colic cases. Multiple ex-vivo studies using anastomosed jejunum observed rupture into the mesentery, distant to the anastomosis. Both scenarios suggest the jejunum is predisposed to rupture at the mesenteric attachment. The aim of the study is to 1) document the location at which equine jejunal segments rupture when subjected to high intraluminal pressures, 2) identify predisposing anatomical features that may confer weakness at the point of rupture and 3) demonstrate jejunal rupture into the mesentery in a naturally occurring colic case. Twenty-two fresh jejunal segments collected from five equine cadavers were subjected to intraluminal infusion of water until rupture occurred. Sections of the ruptured jejunum (RJ) and unruptured controls (UC) were evaluated histologically and imaged using 14.1 T magnetic resonance imaging (MRI) scanner. Eighteen jejunal segments ruptured at the mesenteric attachment, four jejunal segments disconnected from irrigation pump construct instead of rupturing. In addition, resected jejunum from an equine colic case was examined grossly and histologically. MRI and histological analysis of UC sections revealed periodic fenestrations in the muscularis externa at the site of mesenteric attachment, associated with mesenteric-jejunal vasculature. Histological evaluation of the clinical colic case revealed rupture associated with the mesenteric-jejunal vasculature. The mesenteric attachment is the point where mesenteric vasculature enters the jejunal wall, reaching the jejunal submucosa through periodic fenestrations in the muscularis externa. This manifests as a structural weakness, with rupture more likely to occur at this site.