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Figure 2: (a) Lateral and (b) sky line view radiographs of the patella demonstrate a well-defined slightly expansile lytic lesion with sclerotic margin in the mid lateral aspect of the patella (arrowheads) and knee joint effusion (star). On the skyline view, there is also evidence of a bipartite patella (black arrows). Sagittal (c) T1-WSE and (d) T2-WGE and (e) coronal T2-WSE MR images demonstrate a well-defined mass in the patella (black arrows) that displays intermediate SI on T1-W and moderately increased SI on T2-W MR images. Note the prepatellar bursitis (chevrons) and reactive joint effusion (white arrow). Axial T1-WSE fat saturated (f) before and (g) after gadolinium MRI images, show avid enhancement of the patellar lesion (black arrows), involvement of the adjacent lateral parapatellar soft tissues and lateral retinaculum (arrowhead), and enhancing reactive synovitis (chevrons). (h) Core biopsy at low power, (i) core biopsy at medium power, and (j) core biopsy at high power stained with H&E. There are aggregates of amorphous eosinophilic material with a surrounding foreign body giant cell and histiocyte reaction consistent with gout.