oncocytes are observed in lesions of several organs such as the thyroid , kidney , pancreas , ovary , liver , and salivary gland . in the salivary glands ,
oncocytes are known to arise in warthin tumor , oncocytoma , oncocytic carcinoma , and oncocytosis .
oncocytosis is a rare non - neoplastic lesion that is classified as diffuse oncocytosis and multifocal adenomatous oncocytic hyperplasia ( maoh ) ; it comprises approximately 0.1% of salivary gland lesions [ 3 , 4 ] . the correct cytological diagnosis of oncocytosis can be difficult because oncocytes are seen in a variety of other salivary gland lesions , and it is usually diagnosed by histological examination [ 5 , 6 , 7 , 8 ] . here
she consulted an otolaryngology clinic because of discomfort at the left side of her neck . at the clinic
, a mass was noted in the left side of her neck and she was referred to our hospital .
a 1.5-cm mass with no lymph node swelling was identified using magnetic resonance imaging . from the above clinical findings , warthin tumor or a malignant parotid tumor was suspected .
five slides were prepared for cytological evaluation , including 3 fixed smears for papanicolaou staining , 1 air - dried smear for may - grnwald giemsa ( mgg ) staining , and 1 smear examined by liquid - based cytology ( lbc ) based on the lbc technique .
papanicolaou staining of direct smears revealed a loose sheet - like cluster formed of round to polygonal cells with granular cytoplasm against a hemorrhagic background .
the cells had round to oval , centrally located nuclei with granular chromatin and without distinct nucleoli .
in the lbc preparation , the cytoplasm showed microvacuoles in contrast to the direct smear ( fig .
there were only a few lymphocytes , and basophils were not detected in any of the smears .
the cut surface of the resected lesion revealed a milky - white lobular mass with an unclear border ( fig .
microscopically , the lesion was formed of many variable - sized nodules that comprised oncocyte - like cells with small round nuclei and eosinophilic granular cytoplasm .
a definite capsule was not seen around the nodules and the surrounding adipose tissue and acinus .
the oncocyte - like cells were diffusely positive for cytokeratin antibodies and strongly positive for mitochondrial antibodies ( fig .
basophils were not detected in the lesion , using immunohistological staining based on anti - cd117 ( c - kit ) antibodies .
typical findings for low - grade cancer of the salivary glands were not observed . from the above findings
it has been reported that maoh develops in women in their 60s and is localized unilaterally in the parotid glands .
histologically , maoh is thought to arise from the ductal epithelium and the remnants of the original salivary gland .
the lesion was observed unilaterally in the left parotid gland in a 71-year - old woman .
the remnants of the existing salivary ducts were observed by p63 and ck34e12 staining , and a strong response to mitochondrial antibodies was found in the cytoplasm . from the above findings
described the cytological findings of maoh in a case report : ( 1 ) a low n / c ratio ; ( 2 ) central round nuclei ; ( 3 ) anisonucleosis ; ( 4 ) prominent nucleoli ( in part of the cells ) , and ( 5 ) abundant eosinophilic cytoplasm . in the present case ,
however , we could not make a diagnosis of maoh cytologically because of the high n / c ratio and because the nucleoli were unclear .
cytologically , the major lesions in which oncocytes are observed include warthin tumor , oncocytoma , and oncocytic carcinoma .
typical cytological findings of warthin tumor reveal oncocytes and lymphocytes with an inflammatory or necrotic background .
have reported that mast cells are present with oncocytes in fine - needle aspiration preparations .
kobayashi et al .   have investigated the frequency of mast cells in cytological samples , as compared with immunocytochemical identification using human mast cell tryptase antibodies in warthin tumor , and have indicated that mast cells are frequent in the epithelial cell component .
in contrast , there are no reports to suggest any association with mast cells of other lesions .
we also searched for mast cells by cytological mgg staining and immunohistochemical staining using the cd117 ( c - kit ) antibody .
. the identification of basophils seems to be a diagnostic checkpoint when differentiation from warthin tumor is necessary .
however , the typical cytological findings such as a lymphocyte and/or basophil appearance were not observed in any of the cases , which may thus be mistakenly diagnosed as oncocytoma   or maoh .
cytological features of oncocytoma comprise large , round to polygonal cells with abundant granular cytoplasm , centrally located nuclei , prominent nucleoli , binucleation , sheet - like clustering , and an often necrotic background . in oncocytic carcinoma , although the neoplastic cells are pleomorphic , with nuclear atypia and hyperchromatism , other findings overlap with oncocytoma [ 7 , 8 , 13 ] .
thus , it can be difficult to differentiate between maoh , warthin tumor , and oncocytoma .
in addition , a case of oncocytoma arising from maoh has been reported . however , the distinction between maoh and oncocytoma is possible by capsular interpretation .
therefore , it should be noted that neoplastic identification can not be achieved from partial samples microscopically .
furthermore , oncocytic metaplasia has recently been shown in other salivary gland lesions ( e.g. , pleomorphic adenoma , myoepithelioma , and mucoepithelial carcinoma ) , except for maoh , warthin tumor , and oncocytic tumor .
therefore , it is necessary to carefully carry out the assessment of oncocytes . when oncocytes are observed , it is necessary to perform a surgical resection .
the authors have no potential conflicts of interest with respect to the authorship and/or publication of this article .
 multifocal adenomatous oncocytic hyperplasia ( maoh ) is a non - neoplastic lesion that is classified as oncocytosis . 
 maoh is a rare entity of the parotid gland and accounts for approximately 0.1% of salivary gland lesions . here 
 , we report a case of maoh of the parotid gland . 
 the patient was a 71-year - old woman who presented with discomfort at the left side of her neck . 
 fine - needle aspiration cytology of the parotid gland revealed a loose sheet - like cluster of round to polygonal cells with granular cytoplasm against a hemorrhagic background . 
 the cells had round to oval , centrally located nuclei with granular chromatin and without distinct nucleoli . 
 histologically , the lesion was formed of many variable - sized nodules , comprising oncocyte - like cells with small round nuclei and eosinophilic granular cytoplasm that was positive for mitochondrial antibodies . 
 the diagnosis of maoh is difficult to make by cytology alone , because the findings overlap with those of other oncocytic lesions . in particular , the cytological findings of maoh have not been sufficiently reported to date . a correlation of cytology and histology was expected . 
Introduction
Case Presentation
Cytological Findings
Histological Findings
Discussion
Disclosure Statement