oncocytes are defined as modified epithelial cells with characteristic finely granular eosinophilic cytoplasm , which are abundant in mitochondria [ 1 , 2 , 3 , 4 ] .
tumors composed of oncocytes have been described in the major and minor salivary glands , the thyroid , parathyroid , pituitary , and adrenal glands as well as in the kidneys , testes , pharynx , larynx , trachea , pancreas , respiratory tract , skin , and other organs [ 1 , 5 ] . in the vast majority of cases , oncocytic lesions of the ocular adnexa
occur in the caruncle ; other locations rarely include the conjunctiva , plica semilunaris , lacrimal sac , eyelid , and lacrimal gland [ 1 , 4 , 6 ] .
oncocytic lesions occur more commonly in elderly patients , usually in their seventh decade of life , with a 2:1 female : male ratio , especially for those occurring in the caruncle [ 1 , 5 , 6 ] .
the most common presenting symptom is a mass or lump , although patients are usually asymptomatic [ 4 , 5 ] .
oncocytic lesions of the eye are generally benign , and complete surgical excision is the preferred treatment since it has often proved to be curative .
a 69-year - old woman was referred to the ocular oncology service for the evaluation of a pigmented mass in the caruncular region of the right eye .
the patient was regularly followed for chronic blepharoconjunctivitis in both eyes and dry eye syndrome , treated with lubricant eye drops .
the patient took daily medications for hypertension and was suspected to have rosacea . aside from this , her personal medical history and family history were unremarkable .
the patient complained of a tan - colored lesion on her right caruncle , but denied symptoms of bleeding , discharge , an increase in size , or a color change of the lesion .
on ocular examination , visual acuity was 20/20 and intraocular pressure was 16 mm hg in both eyes .
slit lamp biomicroscopy revealed a well - circumscribed , partially pigmented lesion in the caruncle of the right eye .
no involvement of the lacrimal system was noted , and the dilated fundus examination of both eyes was unremarkable .
the patient was diagnosed with conjunctival nevus of the right caruncle . due to the lesion 's unfavorable location ,
histopathological examination disclosed a benign , cystic , tubular , well - circumscribed lesion composed of tall , columnar , granular eosinophilic cells ( fig .
1b ) . a thin fibrous tissue capsule penetrating the tumor from the periphery was also present . the pigmented macroscopic appearance of the lesion was thought to be due to concretions within the tumor ( fig . 1b ) . a diagnosis of oncocytoma of the caruncle was made
an oncocytoma is a rare benign tumor that usually arises in the glandular epithelia of tissues throughout the body . among cutaneous sites ,
oncocytomas have also been known as oxyphil adenomas , papillary cystadenomas , adenolymphoma - like tumors , and warthin 's tumor .
the lesion is usually composed of large oval cells with eosinophilic granular cytoplasm filled with malformed mitochondria , most likely representing an age - associated metaplastic and neoplastic transformation of the glandular epithelium . clinically , caruncular oncocyto - mas occur more frequently in female elderly patients [ 1 , 4 , 6 ] and usually present as a mass or lump that rarely shows a tendency to grow .
they are commonly red - blue or orange  tan in color , sometimes with a lobulated , fleshy , or cystic appearance .
histopathologically , oncocytomas have been attributed with four main architectural patterns : cystic - micropapillary , confluent - glandular , solid - organized , and solid - disorganized .
benign lesions are commonly described as having a cystic - micropapillary pattern , while potentially aggressive growth is associated with solid patterns .
reported atypical features of oncocytomas include the presence of pigmentation , feeder vessels , keratinization , a pedunculated growth pattern , and superficial lobulations .
furthermore , it has been reported that oncocytomas that are not dark blue in color are more likely to be misdiagnosed preoperatively .
surgical treatment outcomes are excellent for benign oncocytic neoplasms , with no recurrence found after surgical excision [ 1 , 4 ] .
several entities must be taken into consideration in the differential diagnosis of carun - cular lesions .
nevi ( 40.7% ) , squamous papillomas ( 8.5% ) , and oncocytomas ( 5.1% ) are the most common lesions at this body site .
more specifically , oncocytomas are clinically often mistaken for hemangiomas , nevi , and cysts .
the case we reported showed several atypical characteristics : the lesion was partially pigmented and lobulated and its macroscopic appearance resembled that of a conjunctival nevus .
conjunctival nevi tend to remain stationary throughout life , with less than 1% risk for transformation into malignant melanoma . nevertheless , malignant melanoma of the conjunctiva is a potentially life - threatening tumor .
tumors found in unfavorable locations such as the palpebral conjunctiva , fornices , plica , caruncle , and lid margins have been associated with a higher rate of metastatic death . given this knowledge ,
nevertheless , complete surgical excision had already been performed , and no further treatment was required . at follow - up after 12 months ,
the patient remained asymptomatic , with no signs of recurrence of the oncocytoma . in conclusion , although nevi are the most common lesions present in the caruncle , onco - cytoma should be considered in the differential diagnosis of a pigmented caruncular mass , especially in elderly female patients .
 we report an unusual case of a pigmented oncocytoma of the caruncle . the lesion presented the following atypical features : a well - circumscribed , partially pigmented , and lobulated mass that macroscopically resembled a caruncular nevus . 
 however , an excision biopsy revealed an oncocytoma instead . 
 thus , although nevi are the most common lesions found in the caruncle , oncocytoma should also be considered in the differential diagnosis of a pigmented caruncular mass , especially in elderly female patients . 