Intraosseous gout mimicking giant cell tumor of the patella.

Intraosseous gout involving the patella is an unusual presentation of the common inflammatory crystal deposition disease. In most reported cases of gout in the patella, there is prominent involvement of the adjacent patellar or quadriceps tendons of the extensor mechanism. A report from Japan describes another pattern of deposition, with a lesion arising in the synchondrosis of a bipartite patella. We present a case of a patient with no known history of gout experiencing vague anterior knee pain and subtle but rapidly progressive findings of a patellar lucent lesion on radiographs. No other cause for the patient's pain was identified on imaging. No prominent involvement of surrounding tendinous structures on MRI, unipartite patellar morphology, normal serum uric acid levels, rapid growth, and nonspecific appearance of the lesion led to a working diagnosis of patellar giant cell tumor. Biopsy of the lesion was performed to guide further management, which yielded the unexpected result of crystalline deposits consistent with gout.