Highly differentiated follicular carcinoma of the ovary with omental and peritoneal spread in a 22-year-old girl; A diagnostic and counseling challenge.

Introduction And Importance: Highly differentiated follicular carcinoma of the ovary (HDFCO) is a rare type of thyroid carcinoma originating from struma ovarii, consisting of benign-appearing thyroid follicles spread outside the ovarian tissue.

Case Presentation: We present a 22-year-old girl who underwent left salpingo-oophorectomy, omental, and peritoneal biopsies for a complex left ovarian mass. Microscopic examination and Immunohistochemical staining led to the diagnosis of HDFCO with tumor deposits affecting the omental and peritoneal biopsies.