ABSTRACT
Reticulohistiocytoma, a rare form of non-Langerhans cell histiocytoses, usually presents it-self as a single cutaneous nodule mainly on the head and neck of young men without associated arthritis. We describe an 18-year-old male patient with a red dome-shaped nodule of 2 months' duration on the scalp. Histologic examination of the excised mass revealed numerous large, mononucleated or multinucleated histiocytes with abundant eosinophilic, finely granular cytoplasm having a ground-glass appearance. Immunohistochemical staining was positive for vimentin, lysozyme, and factor XIIIa, supporting a dermal dendrocyte lineage. Ultrastructurally, large mononuclear or multinucleated cells exhibiting numerous peripheral villi contained pleomorphic cytoplasmic inclusions, fatty droplets and dense bodies. Our clinicopathologic findings support the concept that reticulohistiocytoma is a variant of adult xanthogranuloma.