Intraoperative recognition of low-grade appendiceal mucinous neoplasm masquerading as a right ovarian tumor: a case report

Abstract Background Low-grade appendiceal mucinous neoplasm (LAMN) is a mucin-producing epithelial tumor arising from the appendix. When the appendix is displaced into the pelvis and becomes cystically enlarged, LAMN may mimic a right ovarian mucinous tumor. Because rupture of LAMN may cause mucin spillage and pseudomyxoma peritonei, accurate intraoperative recognition and careful surgical handling are important. Case presentation A 75-year-old Japanese woman was referred to our department with a right adnexal mass suspected to be an ovarian tumor. Pelvic magnetic resonance imaging revealed an approximately 7-cm cystic mass in the right adnexal region, and a right ovarian mucinous tumor was suspected preoperatively. Serum carcinoembryonic antigen was mildly elevated, whereas carbohydrate antigen 19-9 and cancer antigen 125 were not markedly elevated. Laparoscopic surgery was performed under the preoperative diagnosis of a right ovarian tumor. Intraoperatively, the uterus and bilateral adnexa were grossly normal. Instead, a cystic mass was identified near the right adnexal region and was continuous with the appendix and ileocecal region. The lesion was carefully resected without intraoperative rupture or mucin spillage. Intraoperative frozen section analysis showed no evidence of malignancy, and ascites cytology was negative. Histopathological examination revealed LAMN with a negative surgical margin. Immunohistochemical findings were consistent with an appendiceal origin and supported the diagnosis of LAMN. Postoperative computed tomography showed no evidence of residual disease or pseudomyxoma peritonei. Conclusion LAMN can mimic a right ovarian tumor. In right-sided mucinous adnexal masses, appendiceal origin should be considered, and rupture-free complete resection is essential to prevent pseudomyxoma peritonei.