USP6 gene rearrangement differentiates primary paranasal sinus solid aneurysmal bone cyst from other giant cell-rich lesions: report of a rare case.

Aneurysmal bone cysts (ABCs) mostly occur in the metaphysis of long bones. Primary paranasal ABCs are extremely rare, and most reported cases reveal typical histopathological features including cystic space with fibrous septa and hemorrhage. Solid-variant ABCs or solid ABCs lacking cyst formation may be histologically indistinguishable from giant cell reparative granulomas, giant cell tumor of bone, and brown tumor. Here we report the case of a 24-year-old woman with a paranasal mass diagnosed as USP6-rearranged solid ABC, mimicking giant cell reparative granuloma, giant cell tumor of bone, and brown tumor. For paranasal sinus bone or soft tissue tumors containing numerous giant cells, molecular analysis including the USP6 gene may serve as a useful diagnostic tool to distinguish solid ABCs from other giant cell-rich lesions.