Original ArticlesCrohn Disease Infrequently Affects the Appendix and Rarely Causes Granulomatous AppendicitisMostyka, Maria DO*; Fulmer, Clifton G. MD, PhD†; Hissong, Erika M. MD‡; Yantiss, Rhonda K. MD*Author Information *Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY †Robert J. Tomsich Pathology and Laboratory Medicine Institute, The Cleveland Clinic, Cleveland, OH ‡Department of Pathology, Michigan Medicine, Ann Arbor, MI Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: Maria Mostyka, DO, Department of Pathology and Laboratory Medicine, New York Presbyterian Hospital, 525 East 68th Street, New York, NY 10065 (e-mail: [email protected]). The American Journal of Surgical Pathology: December 2021 - Volume 45 - Issue 12 - p 1703-1706 doi: 10.1097/PAS.0000000000001734 Buy Metrics Abstract Data from previous studies suggest Crohn disease of the appendix accounts for ∼25% of granulomatous appendicitis cases. However, we have found that granulomatous inflammation in appendectomy specimens rarely heralds Crohn disease. We suspect that appendiceal involvement by Crohn disease is uncommon, even when patients have severe ileocolonic inflammation. We performed this study to determine the prevalence and nature of appendiceal inflammation among patients with Crohn disease. We reviewed 100 ileocolic specimens with strictures and fistulizing Crohn disease for the nature and distribution of inflammatory changes in the appendix and compared them with 100 appendices on colectomy specimens from age-matched and sex-matched patients with ulcerative colitis. We also evaluated 27 additional cases of granulomatous appendicitis in appendectomy specimens to determine the frequency with which this finding represented Crohn disease. The appendix was usually normal (26%) or showed fibrous obliteration (50%) in ileocolic resection specimens from patients with Crohn disease. Mucosal inflammation was much less common in appendices from patients with Crohn disease than ulcerative colitis (6% vs. 28%, P<0.0001); only 4 cases contained epithelioid granulomata, 3 showed mural fibrosis and lymphoid aggregates, and 10 displayed only periappendiceal inflammation. None of the patients with granulomatous appendicitis in appendectomy specimens had, or developed, evidence of Crohn disease. We conclude that Crohn disease infrequently affects the appendix. Interval appendectomy and infection are more important considerations when appendectomy specimens feature granulomatous inflammation and/or mural lymphoid aggregates, especially if there is no history of idiopathic inflammatory bowel disease. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.