Solitary Conjunctival Reticulohistiocytoma

A 31-year-old healthy man presented with a circumscribed “salmon-colored” forniceal conjunctival nodule (Fig A). Pathology revealed a subepithelial circumscribed infiltrate (Fig B, hematoxylin-eosin, 100×) comprising mononuclear and multinucleated histiocytes with large ovoid eccentric nuclei, prominent nucleoli, and abundant finely granular, “ground glass-like” eosinophilic cytoplasm in a background of lymphocytes (Fig C, hematoxylin-eosin, 400×). The histiocytes were CD163-positive and S100-negative. Strong diffuse nuclear cyclin D1 expression (Fig D, 400×) was consistent with the extracellular signal-regulated kinase pathway activation. The findings were compatible with solitary reticulohistiocytoma, a non-Langerhans cell histiocytosis, which rarely presents as an isolated conjunctival lesion in a young adult (Magnified version of Fig A-C is available online at www.aaojournal.org).