Lipoma arborescens of the knee - A case report

Lipoma arborescens is a very uncommon benign intra-articular tumour of unknown etiology that is characterized by diffuse villous proliferation of the synovium and replacement of the sub-synovial tissue by mature adipocytes. Patients with lipoma arborescens often have a gradually worsening swelling of the affected joint, which may also be accompanied by effusion, a restricted range of motion, and pain. MR imaging narrow downs the possible diagnosis. We report an unusual case of knee swelling in a patient with HIV infection. The patient underwent an open total synovectomy. Histopathological specimen revealed hyperplastic synovial tissue with synovial lining, with sub-synovial tissue showing lobules of mature adipocytes with dense chronic inflammatory infiltrates containing lymphocytes, eosinophils, and plasma cells suggestive of lipoma arborescens. The patient was completely asymptomatic with near total range of knee movements at the two-year follow-up and there were no signs of recurrence. Lipoma arborescens is indeed a rare condition and necessitates a high index of suspicion for such a precise diagnosis. HIV infection can be one of the associations with lipoma arborescens. Early treatment is necessary to stop the condition's progression toward joint degeneration, and open synovectomy with a very low recurrence rate provides excellent functional outcomes.