Solid aneurysmal bone cyst of the humerus mimics metastasis or brown tumor

Solid aneurysmal bone cyst (ABC) is a rare subtype of ABC that most commonly involves the small bones of the hands or feet. We present a case of a solid ABC of the distal humerus in a 52-year-old man with a history of chronic kidney disease and renal cell carcinoma. On imaging with plain radiographs, CT, and MRI, this expansile lucent lesion with solid internal enhancement had an appearance that overlapped with metastasis or brown tumor of hyperparathyroidism. On 18F-FDG PET-CT, this lesion was hypermetabolic with an SUVmax of 9.9. Only 37 cases of solid ABC have previously been reported to involve the long bones in the literature, and only 4 in the humerus. We review the clinical, imaging, and histopathological findings and differential diagnosis of solid ABC, and highlight the usefulness of identifying the USP6 gene rearrangement on FISH to distinguish this lesion from other lesions with secondary ABC formation.