Femur Mass in a 43-Year-Old Woman

Abstract

A 43-year-old woman was seen in consultation for a lesion in her left distal femur. One year earlier she began experiencing pain in her left knee after a fall. The pain was worse at night and awakened the patient from sleep. The patient had a 26-year smoking history. Her family history was significant for a father who had an unspecified sarcoma of the leg. Physical examination showed full ROM in the extremities, with no lymphadenopathy, palpable masses, or reproducible tenderness. Complete blood count, chemistries, and erythrocyte sedimentation rate were normal whereas her C-reactive protein was slightly elevated at 5.3 mg/L (reference, 0–4.9 mg/L). The patient underwent plain radiography (Fig. 1), CT (Fig. 2), MRI (Fig. 3), and bone scintigraphy (Fig. 4). Based on the history, physical examination, laboratory studies, and imaging studies, what is the differential diagnosis at this point?