An appendiceal mucocele associated with inverted epithelium and submucosal hyperplasia at the appendiceal root: a rare case report.

A 54-year-old woman was referred to our hospital because of abnormal colonoscopic findings, including a submucosal protuberance at the appendiceal root. A biopsy showed no malignant findings. Computed tomography revealed a 20-mm cystic lesion with thick walls at the appendiceal root, suggestive of an appendiceal mucocele. Laparoscopic ileocecal resection was performed based on the preoperative diagnosis of a suspected mucinous appendiceal neoplasm. The resected specimen showed a closed appendiceal orifice surrounded by a mucus-containing submucosal tumor. Histopathologically, the appendiceal epithelium was circumferentially inverted in the appendiceal root, with hyperplasia of the submucosal connective tissue. No atypical epithelium was observed. We hypothesized that repeated partial invagination of the appendiceal root caused submucosal hyperplasia and drainage disturbance of the appendiceal content, leading to the development of a mucocele.