Physiologic Menstrual 18F-FDG Uptake in Uterine Didelphys Mimicking Metastasis in a Patient With Ovarian Immature Teratoma

A 27-year-old woman with ovarian immature teratoma underwent 18F-FDG PET/CT for preoperative staging, which revealed intense FDG uptake in 2 distinct pelvic structures, mimicking primary endometrial cancer or metastasis. Although MRI showed no anatomic lesions in either uterus, it confirmed uterine didelphys-a rare Müllerian duct anomaly. This case illustrates that physiological menstrual uptake within a duplicated uterus can simulate malignancy. Clinicians must recognize such anatomic variants to avoid diagnostic pitfalls and accurately stage pelvic malignancies on PET/CT.