True brachial artery aneurysm secondary to arterial wall infiltration by Langerhans cell histiocytosis.

Langerhans cell histiocytosis is a rare histologic disorder that can affect and damage any tissues and organ in the body. A 40-year-old man with multisystem Langerhans cell histiocytosis presented with a painful distal arm mass. Imaging demonstrated a 3.6-cm true distal brachial artery aneurysm and progressive hypermetabolic activity of the affected artery on the retrospective review of serial positron emission tomography/computed tomography scans. The patient underwent aneurysm resection and arterial reconstruction using a reversed great saphenous vein bypass. Histopathology confirmed infiltration of the intima and media by Langerhans cells with destruction of the elastic lamina. Subsequent disease-specific therapy achieved a complete metabolic response, and vascular reconstruction remains patent.