Giant mucocele of the colon at the distal stump due to low-grade mucinous neoplasia.

We present the first ever report on a colonic mucocele observed at the distal stump of a transverse loop colostomy caused by neoplasia. A 37-year-old female consulted us because of abdominal pain and vomiting caused by cystic lesions in the upper left abdominal quadrant. A preoperative checkup revealed no sign of neoplastic lesions; however, tumor resection was performed because of the symptoms. The tumor was a mucocele of the distal stump of the transverse colon with obstruction interposed between the mucocele and stoma. Pathological diagnosis was low-grade adenoma; however, it appeared like low-grade mucinous neoplasia of the appendix rather than a normal colonic adenoma. The neoplasia existed in the transitional segment between obstruction and dilatation. As this is the first case of colonic mucocele caused by mucinous neoplasia, no definite consensus for diagnosis and treatment exists. With reference to low-grade mucinous neoplasia, we propose that complete surgical resection be performed for diagnosis and a favorable outcome.