Abstract

Solitary circumscribed neuroma (SCN), known as palisaded encapsulated neuroma is a benign neural neoplasm, commonly presenting as a painless solitary firm skin-colored papule on the head and neck of elderly patients. Histologically, it is characterized by well-defined superficial dermal nodule composed of intersecting fascicles of spindled cells with elongated fusiform nuclei, frequently separated by clefts. Common histologic variants include plexiform, multinodular and fungating; however, the epithelioid variant is extremely rare and only one case has been reported so far in English literature. Here, we present two such cases: (1) a 49-year-old woman with prior history of rectosigmoid adenocarcinoma presented with a tender 2 mm sclerotic papule of ~12-month duration on the left medial lower leg; (2) a 52-year-old man with history of mantle cell lymphoma, presented with a tender pearly pink papule of few-months duration on the right dorsal forearm. Punch biopsies revealed well-defined superficial to mid-dermal proliferation of small monomorphous epithelioid cells with abundant amphophilic, somewhat fibrillary and syncytial cytoplasm, small round nuclei, lacking mitotic activity or perifascicular clefts. The leg lesion had an ovoid contour, while the forearm lesion showed plexiform architecture. Immunohistochemical studies revealed the lesional cells were diffusely positive for S100 and NF1 (highlights axons) and peripherally ensheathed by CD34/EMA-positive perineurial cells. The histopathological features and immunophenotype supported a diagnosis of SCN with epithelioid features. Epithelioid variant of SCN may histomorphologically overlap with hybrid nerve sheath tumors or epithelioid schwannoma and should be considered in the histologic differential diagnoses of dermal tumors with epithelioid morphology.