RESUMEN
Abdominal hibernoma is a rare slow-growing tumor originating from brown adipose tissue. Due to its rarity, only a few case reports have been published so far. Pelvic localization is anedoctal and preoperative differential diagnosis with other malignancies may be challenging. We present the case of a woman who, due to a lower abdominal pain, underwent an abdominal ultrasonography with diagnosis of a 15 cm hyperechogenous pelvic mass. A subsequent MRI showed a 16 × 5.8 × 7.8 cm3 lesion anterior to the left iliacus muscle, with an intra- and extrapelvic component longitudinally extending from the left anterior superior iliac spine until the lesser trochanter. Surgical resection was performed and final histopathology was consistent with hibernoma. This report emphasizes the necessity to include hibernoma among differential diagnosis when a retroperitoneal abdominal mass is diagnosed and the difficulty to perform preoperatively this diagnosis due to the extreme rarity of these neoplasms.