Massive aneurysmal bone cyst of the skull base treated with denosumab

Background: Aneurysmal bone cysts are rare, benign expansile tumors most commonly involving long bones and vertebrae in patients younger than age 20. Skull base involvement is rare. Aneurysmal bone cysts shares radiological and histological features with other bone tumors, posing a diagnostic challenge. Methods/Results: We report the case of a 32-year-old man who presented with facial pain, epistaxis, and cranial neuropathies secondary to a massive tumor of the maxillary sinus and anterior skull base. The tumor was originally misdiagnosed as osteosarcoma. However, genomic analysis revealed a rearrangement in the USP6 gene, elucidating a diagnosis of primary aneurysmal bone cysts. The patient was treated with denosumab. Within 5 months, the patient was asymptomatic with CT showing ossification of the tumor. Conclusions: This case highlights (1) the utility of genomic analysis in aggressive bone tumors when the diagnosis is unclear and (2) the effectiveness of denosumab as a treatment for aneurysmal bone cysts when surgical resection is unfavorable.