A Mature Cyst Teratoma with Malignant Transformation in Squamous Cell Carcinoma Presenting Like a Sigmoid Fistula: A Case Report of a Rare Differential Diagnosis of a Giant Colonic Diverticulum

Mature cystic teratoma is the most common form of ovarian germ cell tumor. Mature cystic teratoma is a benign tumor, mainly diagnosed in young women, with non-specific symptoms. However, the risk of malignant transformation exists (1-2%). Squamous cell carcinoma is the most frequently encountered histological form. Giant colonic diverticulum is a rare complication of diverticular disease, characterized by a diverticulum larger than 4 cm which can sometimes be confused with other digestive pathologies (appendicitis, small bowel perforation ...). We report a case of an ovarian squamous cell carcinoma arising from a mature cystic teratoma, presenting like a sigmoid fistula, with an initial doubt with the diagnosis of a giant colonic diverticulum. A 68-year-old woman was admitted for chronic hypogastric abdominal pain with a doubt concerning the diagnosis between a mature cystic teratoma and a giant colonic diverticulum. A computed tomography scan was performed revealing a perisigmoid cyst with hydro-aeric level in favor of a giant colonic diverticulum. The pelvic MRI rather suggested a left ovarian cyst, fistulated in the sigmoid colon. Finally, the colonoscopy confirmed this hypothesis with the visualization of a sigmoid fistula located 15cm from the anal margin in connection with a cavity containing hairs. Biopsies revealed a squamous cell carcinoma. After a negative extension assessment, a posterior pelvectomy was performed with pelvic and lumbo-aortic lymph node dissection. The pathological diagnosis was an ovarian pT4N1R0 squamous cell carcinoma. An adjuvant chemotherapy is still in progress.