A 47-year-old woman who, with no previous digestive symptoms, was found to have carcinoembryonic antigen (CEA) levels of 20.2 ng/ml in a routine follow-up analysis by her gynaecologist. She underwent: a) an abdomino-pelvic ultrasound scan that revealed the presence of a 6.5 x 5.6 cm retrouterine mass that appeared to be dependent on the right adnexa; b) a complete colonoscopy with no findings; and c) a diagnostic laparoscopy that revealed the presence of a mass dependent on the cecum, highly vascularised and with a smooth whitish surface, with both adnexa normal and a hypoplastic uterus. Referred to our department, a computerised axial tomography (CAT) scan of the abdomen and pelvis confirmed the existence of a pelvic mass of cystic appearance measuring 11 x 8 cm, anterosuperior to the bladder and close to the terminal ileum, which was encapsulated and without signs of infiltration of neighbouring organs, ascites or adenomegaly in the vicinity. Elective surgery was performed, describing the presence of an appendicular mucocele of 12 cm in diameter with no free fluid or implants in the peritoneum, and an oncological right ileocolectomy with ileotransverse anastomosis was performed; the postoperative period was uneventful, and the patient was discharged on the 5th postoperative day.

The histopathological study of the specimen showed an ileocaecal appendix measuring 9 x 5.5 cm occupied by mucoid material, being reported as "mucocele secondary to appendiceal mucinous tumour of uncertain malignant potential"; it was not possible to certify the degree of local invasion due to parietal calcification. The eight lymph nodes isolated from the resection specimen were free of neoplasia.

After 3 years of follow-up, the patient is asymptomatic and her most recent tumour markers and CT scans are absolutely normal.