Unusual Case of a Caruncular Oncocytoma.

Oncocytomas are benign neoplasms that are most often found in the salivary glands and kidneys. Ocular oncocytoma typically present as an asymptomatic dark blue papule on the lacrimal caruncle. Histologically, the tumor is composed of oncocytes, cells notable for eosinophilic cytoplasmic granules representing large quantities of dysfunctional mitochondria. The neoplastic proliferation may be partially or totally encapsulated and may be surrounded by myoepithelial cells. Discussed is the pathophysiology and histopathology of an ocular oncocytoma from the right lacrimal caruncle of a 68-year-old man. The patient complained of a foreign body sensation and tearing associated with a purpuric 1 × 1-mm papule of the right caruncle that had been present for 6 months. An excisional biopsy showed an oxyntic neoplasm with small cystic glandular spaces associated with goblet cells and mucin, confirmed by mucicarmine stain. Given the rarity of ocular oncocytomas and presence of mucin, exclusion of an endocrine mucin-producing sweat gland carcinoma was necessary. Peripheral myoepithelial cells noted on p63 immunostaining are seen in both endocrine mucin-producing sweat gland carcinoma and oncocytomas. However, endocrine mucin-producing sweat gland carcinoma is excluded by the presence of goblet cells, the uniform oxyphilic cytoplasm of the epithelial cells, and the negative immunohistochemical staining for neuron-specific enolase, chromogranin, synaptophysin, estrogen receptor, and progesterone receptor. Complete surgical excision is the treatment of choice for oncocytomas. This case highlights the clinical and histopathological presentation of ocular oncocytomas and raises awareness of this rare entity for both the practicing dermatologist and dermatopathologist.