Erdheim-Chester disease: an unusual aetiology of bilateral lipomatous perinephric masses.

A 53-year-old man presented with a history of progressive abdominal distention for 1 year. Physical examination revealed large palpable masses in the bilateral flank regions. Contrast-enhanced CT of the abdomen showed bilateral, symmetrical large perinephric masses with fat attenuating areas, which was further confirmed on MRI. CT of the paranasal sinuses revealed circumscribed extraconal soft tissue mass in the left orbit, causing scalloping and erosion of the left orbital roof. Fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography/CT showed FDG uptake in the bilateral perinephric masses. Based on imaging appearance, a diagnosis of Erdheim-Chester disease (ECD) was suggested. Ultrasound-guided biopsy from perinephric masses revealed a sheet of histiocytes with sprinkled lymphocytes and plasma cells in the background. The histiocytes were immunopositive for CD68, S100 and immunonegative for CD1a, which confirmed the diagnosis of ECD. The patient was started on interferon-α-2a and showed symptomatic improvement.