Appendiceal intussusception induced by tubulovillous adenoma with carcinoma in situ: report of a case.

Appendiceal intussusception is an uncommon pathologic condition; however, villous adenoma of the appendix is a distinctly rare entity. We report herein a case of appendiceal intussusception induced by tubulovillous adenoma with carcinoma in situ. A 67-year-old man was admitted to our hospital with a 1-year history of lower abdominal pain for investigation. Barium enema showed a filling defect with an irregular surface in the cecum, and colonoscopy revealed a cecal tumor with a granular surface. Pathological examination of biopsy samples revealed tubulovillous adenoma with well-differentiated adenocarcinoma, and a diagnosis of cecal cancer in tubulovillous adenoma was made. Surgery was performed and the resected specimen was found to contain a tumor arising from the appendix. The tumor was 5.5 x 4.5 cm in size in the cecal cavity, and the appendix had invaginated into the cecum at its base. The cut surface of the appendix showed the villous tumor filling the appendiceal lumen and projecting into the cecal cavity. Microscopic examination revealed well-differentiated adenocarcinoma in tubulovillous adenoma. To the best of our knowledge, this is the first report of appendiceal intussusception caused by tubulovillous adenoma with carcinoma of the appendix.