Aneurysmal Bone Cyst of the Patella: Three-Phase Bone Scintigraphic Findings and Differential Diagnoses

The authors report a rare case of aneurysmal bone cyst of the patella in a 16-year-old girl who had swelling of the left knee joint. Radiographs of the left knee joint suggested giant cell tumor or aneurysmal cyst of the patella. A three-phase bone scan revealed increased vascularity in initial blood-flow and blood-pool images and a doughnut-shaped appearance in delayed images, in keeping with the final histopathologic diagnosis of aneurysmal bone cyst of the patella. This case highlights the importance of obtaining lateral views in possible disease of the patella and various differential diagnoses of doughnut-shaped appearance on a patellar bone scintigram.