Three adult horses (3, 3, and 9 y) were referred to the Veterinary Teaching Hospital, Western College of Veterinary Medicine with a history of acute abdominal pain that was unresponsive to medication. All horses were clinically dehydrated and had increased heart rate, packed cell volume, and total serum protein. Two had nasogastric reflux and distended loops of small intestine on transrectal examination. Transrectal examination of the 3rd horse revealed a gas distended large colon. Venous blood gas analysis revealed metabolic acidosis in 2 horses. A complete blood cell (CBC) count was available for 1 horse and revealed a mild neutrophilia with a left shift and toxic changes. Cytological examination of peritoneal fluid was available for 2 horses and showed an elevated nucleated cell count and total protein. One horse had intracytoplasmic and free bacteria (long rods) in the peritoneal fluid; it was euthanized because of the poor prognosis.
On necropsy, 60 cm of the distal jejunum and proximal ileum was strangulated by a fibrous band that originated from the right side of the mesentery, dorsal to the proximal ileum, and attached to the antimesenteric side of the ileum. The strangulated bowel was entrapped in the triangular space formed by the fibrous band, the mesentery of the proximal ileum, and the ileum itself. A clear demarcation between grossly normal jejunum/ileum and the strangulated intestine was present, with the diseased bowel appearing severely congested and edematous. On histopathologic examination, fibrous strands of mature collagen scattered with fibroblasts was consistent with a persistent vitelline artery.
The other 2 horses were unresponsive to analgesics, so exploratory laparotomy was recommended. One horse received xylazine (Rompun; Bayer, Toronto, Ontario), 0.25 mg/kg bodyweight (BW), IV; the other received xylazine, 150 mg, and butorphanol tartrate (Torbugesic; Ayerst Canada, Guelph, Ontario) 10 mg, IV.
On abdominal exploration, multiple loops of small intestine were incarcerated between a band extending from the intestinal mesentery to the antimesenteric border of either the proximal ileum (horse 1) or the distal jejunum (horse 2). In horse 1, the strangulated bowel was deemed nonviable and a hand sewn side-to-side jejunocecostomy was completed; in horse 2, transection of the band released the entrapped intestines. Histopathologic examination of the resected band from horse 1 revealed a membranous structure consisting of loose fine connective and adipose tissue, covered on its exposed surfaces by a mesothelial lining. The etiology of the band was reported as an anomalous developmental remnant of the vitelline artery, which was consistent with the band being a mesodiverticular band. Both horses recovered from surgery and were discharged a few days later from the hospital.
During early embryonic development, the connection between the midgut and the yolk sac is reduced to a narrow duct (vitelline) (2). Associated with this duct, there are 2 vitelline arteries that reach the yolk sac (3). This connection is ultimately lost and the site is occasionally seen as a small diverticulum (Meckel's) of the adult jejunum (2). Sometimes, the vitelline or omphalomesenteric duct persists and forms a fibrous ligament or vitelloumbilical band between the intestine, or Meckel's diverticulum, and the umbilicus (4). The remnant can be attached to the mesentery or to a loop of intestine, or it can be partial and not reach the umbilicus (4). Either form of band may become involved in strangulation, obstruction, or herniation of the intestines (4). The mesodiverticular band, which is the result of a persistent vitelline artery and is occasionally patent, extends from the cranial mesenteric artery, or from a spot partway along the mesenteric vein, to the antimesenteric side of the intestine, or the site of Meckel's diverticulum (4). The band is usually located in the distal jejunum, about 1.5 m from the ileocecal junction (5). The triangle formed by the band may lead to strangulation of the small intestine and, sometimes, secondary volvulus may result (5). Shortening of the mesentery by the mesodiverticular band at the point of attachment may lead to small intestinal volvulus (5). The mesodiverticular band can be found as an incidental finding; although it is a congenital anomaly, it can cause an intestinal obstruction in mature horses (1,5). In the present cases, the mesodiverticular band was significant and accounted for the clinical signs.
To the authors' knowledge, in the equine literature, only one case series describes the history, clinical presentation, and findings of a mesodiverticular band in adult horses (6); 3 of 4 cases had a single vessel with an associated mesentery where the mesentery of the jejunum had ruptured and the entrapped intestine became strangulated (6). In the present cases, the mesodiverticular remnant was a single band of tissue without an associated mesentery.
While mesodiverticular band causing small intestinal strangulation is a rare finding, it should be considered as a possible differential diagnosis in cases with clinical findings suggestive of small intestine strangulation.
Footnotes
Address all correspondence to Dr. Sameeh M. Abutarbush; e-mail: sameeh75@hotmail.com
Reprints will not be available from the authors.
References
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