Morphologic Clues Identify Muscularis Propria at Colonic Biopsy and Warn of Potential Perforation

Abstract

Abstract Objectives Perforation is currently believed to be a rare but potentially serious complication of colonic biopsies performed with cold forceps. Most reported cases have occurred in the setting of colitis. The presence of muscularis propria in specimens from colonic biopsies might portend increased risk of perforation. However, identifying muscularis propria at time of biopsy is difficult for many reasons, including histologic overlap with muscularis mucosa. Incidental muscularis propria obtained in this manner has yet to be studied. We hypothesized that differences in nuclear density could distinguish muscularis propria from muscularis mucosa. Methods We retrospectively reviewed 3 specimens from colonic biopsies performed with cold forceps for which muscularis propria was presumed to be visualized based on the presence of smooth muscle with lower nuclear density compared to areas known to be muscularis mucosa. All patients were adults clinically suspected to have colitis. These specimens were then compared to a full-thickness section from normal colonic tissue obtained via colectomy that served as control to confirm whether nuclear density or other features could distinguish muscularis propria from muscularis mucosa. Results Muscularis propria in the control tissue had lower nuclear density, more cytoplasmic pallor, greater maximal thickness, and smoother texture than the corresponding muscularis mucosa in the control tissue. The constellation of these features was consistently seen in all three specimens obtained via biopsy and therefore confirmed the presence of muscularis propria in all three specimens, although all patients lacked perforation clinically. Surprisingly, all three specimens had histologically normal mucosa. Conclusion We showed that several morphologic features, including low nuclear density, identify muscularis propria at time of colonic biopsy and alert endoscopists to the possibility of perforation, and we showed that muscularis propria can accompany normal mucosa obtained via biopsy with cold forceps. Additional studies are necessary to further validate these findings.