Peritoneal strumosis and the role of imaging in the diagnostic workup: A case report.

Peritoneal strumosis, also termed highly differentiated follicular carcinoma of ovarian origin (HDFCO), is a rare entity arising from struma ovarii, with extra-ovarian dissemination of thyroid tissue. Radiologic descriptions remain limited. We report a case of a 38-year-old woman with a known diagnosis of struma ovarii, a monodermal teratoma mainly of benign thyroid tissue, who presented with multiple peritoneal lesions detected on imaging. Magnetic resonance imaging (MRI) revealed diffusion-restricting enhancing soft tissue implants throughout the abdomen and pelvis, while nuclear medicine imaging demonstrated no I-123 radiotracer uptake. Biopsy confirmed well-differentiated thyroid tissue. This case highlights the role of MRI and nuclear medicine in identifying peritoneal strumosis and emphasizes the need to include this rare entity in the differential when radiologists encounter unexplained peritoneal nodules. Radiologists should consider HDFCO in the differential when encountering peritoneal nodules in patients with prior struma ovarii.