What is an oncocytoma of the caruncle?

Oncocytoma
Definition: Oncocytomas are benign tumors that arise most commonly in the caruncle or canthal conjunctiva but may also occur in the lacrimal glands (including accessory glands) and lacrimal sac.
Incidence/Prevalence: Oncocytomas are considered rare tumors.
Etiology: Oncocytoma are believed to arise from oncocytic metaplasia of ductal and acinar cells of lacrimal epithelium or perhaps conjunctival epithelium.
Clinical Findings: Oncocytomas most commonly present in women of middle age or older (>50 years) as a red-yellow mass (arrow 1 in the clinical photograph). In this case the mass is red to pink in color, located in the caruncle and has a cystic appearance. Note the yellow lesion, a pingueculum near the limbus (arrow 2).

Histopathology: Oncocytomas are characterized by large eosinophilic cells that form glandular or ductular spaces (number 1 in the low mag photomicrograph). Between the ducts there are solid trabeculae of cells. The abundant eosinophilic cytoplasm and the relatively small round to oval nuclei that are located in the middle of the epithelial cell (arrow 2) are key features. The cells may contain small nucleolar organizer regions (nucleoli) and their may be clearing of the nuclear material in some cells. Electron microscopy shows numerous mitochondria.
Treatment: Excision is usually curative.
Prognosis: It is believed by some that malignant transformation may occur to produce oncocytic adenocarcinoma, although this mode of transition has not been proven.