Hibernomas are benign tumors derived from residual brown adipose tissue, which usually is present in-utero and among infants. Unlike lipomas, they are very rare, with less than 200 reported cases in the literature. Hibernomas most often occur proximally to the axial skeleton, where brown fat existed in the fetus and has persisted into adulthood. Specifically, intrascrotal hibernoma is extremely rare with only two cases reported to date. In comparison, scrotal liposarcomas are a rare cause of scrotal mass, though much more common than hibernomas. About 7% of paratesticular malignancies arise from the spermatic cord and are thought to originate in the mesenchymal tissue. Most malignant paratesticular tumor are sarcomas, and about 5–7% are liposarcomas

A 62-year old male presented at the outpatient clinic with a 10-month history of an enlarging, right inguinoscrotal mass. This was not associated with abdominal or scrotal pain. The patient had an unremarkable past medical history. The patient was a retired soldier. On physical examination, the patient had a soft nontender abdomen, with note of a well circumscribed, movable, firm, nontender mass at the right scrotum extending to the inguinal area measuring approx 13cm x 11cm. The patient had CT scan of the whole abdomen with IV contrast, showed large fat-attenuating non-enhancing mass occupying the right external inguinal canal and scrotal sac measuring 11.5 x 14cm, fairly-defined, and displacing the right testis superiorly. He then underwent inguino-scrotal exploration, and wide excision of right scrotal mass. Intraoperatively, the mass was well delineated from the right testis and spermatic cord. The mass had no intraabdominal component extending deep to the external inguinal canal. The left testis was unremarkable. Specimen was then sent for histopathology.

The final read is a well-differentiated lipomatous tumor cannot totally rule out well-differentiated liposarcoma, additional stain for MDM2 (Murine Double Minute 2) oncoprotein done. MDM2 determination via fluorescence in situ hybridization (FISH), which turned out to be negative, leading to the final diagnosis of intrascrotal hibernoma.

The diagnosis of intrascrotal hibernoma is established through histopathological examination, and confirmed with immunohistochemical testing.