Visualization of orbital involvement of Erdheim-Chester disease on PET/CT.

: We report a 58-year-old man who presented with swelling and redness in his left eye, headache, and blurred vision. A contrast-enhanced CT of the orbits revealed bilateral orbital masses. Whole-body PET/CT showed bilateral retrobulbar hypermetabolic soft tissue lesions, multiple areas of soft tissue involvement, and osseous lesions in bilateral lower extremities. An open surgical biopsy of the left orbital mass revealed xanthomatous non-Langerhans histiocytic infiltrate with Touton giant cells, positive for CD68 but negative for CD1a, establishing a diagnosis of Erdheim-Chester disease.