Primary Bone Lymphoma of the Knee: A Rare Entity

Abstract

Introduction: The World Health Organization (WHO) defined primary bone lymphoma as a single bone lesion with or without regional lymph node involvement or multiple bone lesions without distant visceral or lymph node involvement. It is a rare entity; indeed, primary bone lymphomas represent 1-3% of non-Hodgkin's lymphomas, 5% of extra-nodal non-Hodgkin's lymphomas and 3% of primary bone tumors [2, 3]. Objective: The objective of our work is to clarify the imaging of a rare entity of primary bone lymphoma in a 6-year-old boy, who had been complaining for 1 month of pain in his right lower limb without functional impotence. Case Report: A 6 year old boy, who had been complaining for 1 month of pain in his right lower limb without functional impotence or other associated signs. The clinical examination revealed a child in good general condition, apyretic, with a limp when walking, limitation of all the articular amplitudes of the left he knee, a swelling of the homolateral thigh with discreet quadricipital amyotrophy. Examination of the lymph nodes did not identify any adenopathies. Standard radiographs of the left knee showed multiple lesions involving the lower extremities of the femur and the upper extremities of the tibia, with confluent intraspongiosa and areas of osteocondensation associated with localized cortical fracture without periosteal reaction. The biological workup revealed no abnormalities, including an LDH in the normal range. An MRI of the right thigh was requested for a better characterization of the lesion and to establish a locoregional extension assessment. It showed a large epiphyseal-metaphyseal lesion process of the lower end of the femur and epiphyseal-metaphyseal of the upper end of the left tibia in T1 hyposignal, locally infiltrating T2 heterogeneous hyper signal with vascular enclosure and popliteal ADPs. The CT scan was requested as part of the extension work-up and did not reveal any secondary lesion. The patient underwent a bone ........