Subserosal Supernumerary Muscle Layer of the Intestine: A Peculiar Bowel

The presence of a supernumerary subserosal muscle layer of the bowel is an extremely unusual congenital development. The following is a report of diffuse involvement of the intestine with a supernumerary subserosal muscle coat. The current patient, a 29-year-old male, was evaluated in January 2022 for a long-standing history of subacute intestinal obstruction (SAIO). A preoperative CT scan of the abdomen and pelvis suggested mild dilatation and clumping of ileal loops in the right iliac fossa, with a subtle wall thickening of up to 5 mm. Intraoperatively, dense adhesions were noted between clumped bowel loops and the anterior abdominal wall. Following adhesiolysis, ileocecal resection with ileocolic anastomosis was done. The histopathological examination of the resected bowel segment showed irregular hypertrophy of circular and longitudinal muscle layers with the presence of an additional smooth muscle coat outer to the outer longitudinal layer that was seen in the ileum as well as the appendix. No evidence of vacuolar degeneration was noted, and ganglion cells were seen to be adequately present. The presence of additional smooth muscle bundles in the subserosa was confirmed with positive actin immunostaining. Additionally, CD117 staining was done that revealed a normal network of interstitial cells of Cajal. No evidence of active inflammation was noted in the resected bowel segment. Findings from the current case bring to light an extremely rare malformation of the muscularis propria of the intestine, namely a supernumerary subserosal muscle coat.