Primary periosteal lymphoma--rare and unusual.

We describe a primary periosteal lymphoma that involved only the periosteum without affecting the adjacent medulla or the regional lymph nodes. No other lymphomatous foci were found in either the distant lymph nodes or viscera. This unusual presentation simulates the imaging appearance of surface lesions of bone, namely benign and malignant tumors, and departs from the typical appearance of primary lymphoma of bone. Therefore, this rare type of lymphoma should be considered in the differential diagnosis of surface bone lesions.