Ovarian epithelial tumors are common in adults, and the median patient age at presentation is 55 years. In children, epithelial tumors are rare and mostly benign. Mucinous cystadenocarcinoma is reported in only 11 cases less than 15 years old.

This report describes the case of a 15-year-old postmenarchal Omani girl with ovarian mucinous carcinoma. She was admitted with severe epigastric pain and abdomen distension. CT scan showed a huge cystic lesion arising from the left adnexa filling the entire abdominal and pelvic cavity. The patient underwent laparotomy with left ovarian cystectomy and omental biopsy which revealed a 35 x 30 cm left ovarian cyst filled with turbid straw color fluid. Histopathology was reported as mucinous carcinoma. The patient later underwent cytoreductive surgery with left salpingo-oophorectomy, omentectomy, appendicectomy, and lymph node dissection that were negative for malignancy or metastatic disease. During follow-up, she developed a lymphocele in the pelvic cavity that was drained. There were no other significant issues during follow-up, as well as no evidence of recurrence or metastasis.

Epithelial tumors of the ovary are rare in young girls, with malignant tumors being exceedingly rare. Fertility-sparing surgery is adopted over radical surgery in these patients, even though the recurrence rates with this treatment protocol are high. All cases should be under follow-up to look for recurrence and timely management.