A 56-year-old man presented with a painless prepatellar mass of the left knee. MR images demonstrated a large, well-defined mass with heterogeneous intermediate signal intensity on T1- and proton density-weighted images. Mild, heterogeneous enhancement was noted after the intravenous administration of gadolinium. Diagnostic imaging included atypical soft-tissue infection, fibrogranulomatous reaction, gouty tophus, rheumatoid nodule and xanthoma or possibly malignancy. The histopathological examination revealed sarcoidosis involving the prepatellar bursa.
Keywords: Knee; Prepatellar bursitis; Sarcoidosis.