Objective This study aimed to determine the frequency of malignant pathology in a macroscopically normal appendix during surgery for a borderline or malignant mucinous ovarian tumor (MOT).

Methods Women with borderline and malignant MOT were identified from the pathology database from 2000 to 2014. Women who had a benign MOT and had an appendicectomy were excluded from the study. Data were collected from the electronic patient record and case notes.

Results Of 310 women identified with MOT, 203 patients with benign MOT were excluded. Of the remaining 107 patients, 15 patients with previous appendicectomy were also excluded. The study population consisted of 92 patients. There were 57 (62%) patients with borderline MOT and 35 (38%) patients with malignant MOT. In the borderline subgroup, 40/57 (70%) patients had appendicectomy of whom 8 (20%) had macroscopically abnormal appendices. One patient had pseudomyxoma peritonei secondarily involving the appendix and 7 patients had a histologically normal appendix. Normal histology was found in all macroscopically normal appendices. In the malignant subgroup, 29/35 (83%) patients had an appendicectomy. There were 8 (27.5%) macroscopically abnormal appendices with a malignant pathology in 7 (87.5%) patients and 1 patient had a resolving appendicitis. There were 21 macroscopically normal appendices of which, serrated adenoma was found in 1 (4.8%) patient, whereas the remaining 20 (95.2%) patients had normal histology.

Conclusions In MOT, an abnormal appearing appendix should be excised. If the appendix is grossly normal, our data do not support performing an appendicectomy as part of a surgical staging procedure.