Appendiceal Mucocele Caused by Adenocarcinoma in Ulcerative Colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease associated with an increased risk of colorectal cancer. We report a case of adenocarcinoma of the appendix, not detectable although of meticulous colonoscopy performed by an experienced colonoscopist, but diagnosed by the complementary examination of the patient with UC. The case was a 44-year old man with a 21- year history of UC (pancolitis), who was followed in another specialized service, and was introduced to our service because of increased serum carbohydrate antigen 19-9 (CA19-9). The finding of the surveillance colonoscopy was compatible with UC in remission, including the orifice of the appendix. However, the positron emission tomography / computed tomography revealed an appendiceal mucocele of 80 mm diameter and 18-fluorodeoxyglucose uptake in the middle portion of appendix. Based on these findings, malignant tumor of the appendix was suspected, and the laparoscopic appendectomy was indicated as a minimally invasive diagnostic procedure. Histopathological examination revealed adenocarcinoma with mucinous component beyond the serosa in the middle portion of the appendix. This case strongly suggested the need of careful surveillance of patients with UC involving the whole body of appendix to avoid missing malignant tumors, which, although a rare condition, may be of higher risk in patients with pancolitis type of UC.