Pseudodiverticula of the Small Intestine Associated With Idiopathic Smooth Muscle Hypertrophy in Domestic Rabbits (Oryctolagus cuniculus)

Abstract

Acquired outpouches of the intestinal tract are referred to as pseudodiverticula or false pulsion diverticula. In contrast to true diverticula, in which the wall contains all layers of the intestinal tract, the wall of pseudodiverticula lacks the tunica muscularis. Smooth muscle hypertrophy of the small intestine is commonly considered a cause of pseudodiverticulosis in animals due to increased intraluminal pressure. This study reports pseudodiverticula associated with idiopathic smooth muscle hypertrophy of the small intestine in lagomorphs. Four domestic rabbits had single or multiple (up to 200) pseudodiverticula of various size in the small intestine. In all cases the tunica muscularis was diffusely thickened, significantly exceeding reference thickness of 14 rabbits (mean, 112.3 µm; range, 26.3-389.0 µm). Clinical signs were considered to be caused by severe necrosis and inflammation of the wall of large pseudodiverticula, leading to perforation with subsequent peritonitis and mesenteric and omental abscess formation in 2 cases.

Small intestinal pseudodiverticulosis in a pony mare

“…8,10 In contrast, pseudodiverticula lack the tunica muscularis, and the walls of these dilations are composed of the mucosa, submucosa, and serosa. 1,2,10 As seen in our case, pseudodiverticula are frequently seen concurrently with hypertrophy and hyperplasia of the tunica muscularis of the adjacent intestinal wall. Hypertrophy and hyperplasia of the smooth muscle can be idiopathic (primary) or secondary (compensatory) to increased contraction force as a result of partial aboral stenosis or obstruction.…”

“…3,11 Hence, pseudodiverticula may occur because of a weakened tunica muscularis and/or increased intraluminal pressure, resulting in expulsion of the mucosal and submucosal layers through a defect in the tunica muscularis. 2,8 Pseudodiverticulosis, the disease associated with the formation of pseudodiverticula as in our case, has been described in the small intestine of horses, pigs, sheep, cats, elk, a wallaby, and most recently, rabbits. 1,5,[7][8][9]12 Small intestinal pseudodiverticula are uncommon in horses, with only a handful of cases reported.…”

“…[3][4][5][6][7][8][9]12 These abnormalities have been classified as either true diverticula or acquired diverticula, which are also known as pseudodiverticula or false pulsion diverticula. 2 True diverticula consist histologically of all layers of the intestinal wall. In humans, true diverticula occur as a result of improper embryologic development, and clinical signs most frequently occur at a young age 1 ; likewise, in animal species, true diverticula often appear congenitally.…”

“…3,11 Hence, pseudodiverticula may occur because of a weakened tunica muscularis and/or increased intraluminal pressure, resulting in expulsion of the mucosal and submucosal layers through a defect in the tunica muscularis. 2,8…”

Duodenoduodenal intussusception in a 16‐year‐old German Warmblood mare

“…Muscular hypertrophy of the tunica muscularis of small intestines in combination with a pseudodiverticulum has been described in several species including horses, cats, pigs, rabbits and sheep. Muscular hypertrophy can be idiopathic (if no predisposing cause can be identified) or secondary to chronic partial obstruction in an aboral intestinal segment that increases the workload on the smooth muscle (Bertram et al, 2019; Bettini et al, 2003; Chaffin et al, 1992; Cordes & Dewes, 1971).…”