Malignant lymphoma involving the patella.

The majority of skeletal lesions affecting the patella are benign and include entities such as chondroblastoma, giant cell tumor, osteomyelitis, and gout. Malignant processes involving the patella are distinctly unusual. Isolated occurrences of plasmacytoma, osteosarcoma, hemangiosarcoma, and metastatic disease have been reported. Malignant lymphoma involving the patella is extremely uncommon, although lymphomatous infiltration of the skeletal system is not a rare event, especially with the histiocytic lymphoma. The most frequent radiologic manifestations of skeletal lymphoma include osteolytic lesions with ill-defined margins involving the metaphysis of the long bones of the lower extremities. Involvement of the short tubular and flat bones, as well as the axial skeleton, occurs less commonly. The prognosis for lymphoma involving the skeleton is poor.