Brown tumor of the knee as the first presentation of primary hyperparathyroidism caused by parathyroid adenoma: A case report.

Brown tumor of the knee is a focal benign cystic lesion of bone. The etiopathogenesis of brown tumor is believed to be abnormal bone metabolism in patients with hyperparathyroidism. We present a case of a 32-year-old male with recurrent knee pain, weakness of the lower limb and a nodular mass on left inferior lobe of thyroid. Timely identification of the underlying cause and localization of lesion(s) is important because the management and prognosis vary based on the etiology. The diagnosis of a brown tumor is the result of the sum of the medical history of patients with clinical, radiographic imaging, histopathological, hematological, and biochemical laboratory investigations.