salivary gland tumors are known for their varied histomorphological appearance , which sometimes poses a diagnostic challenge for pathologists .
one of such appearances is the oncocytic change in tumor cells of benign and malignant salivary gland tumors .
morphologically , oncocytes are characterized by abundant eosinophilic granular cytoplasm with pyknotic nuclei , which is usually centrally placed or shifted towards one side .
oncocytic nature of tumor has been associated with warthin s tumor , oncocytoma , and oncocytic carcinoma .
pleomorphic adenoma ( pa ) is the most common salivary gland tumor and accounts for 70% of all the tumors of major salivary glands .
as the name suggests , pa is characterized by plethora of morphological appearances including myxoid , hyalinized , chondroid , osseous , squamous etc . however , predominantly oncocytic cells in pa are extremely rare to occur .
literature search indicates only 18 cases reported till date with largest case series ( 9 cases ) reported by skalova et al . in 1999 ( table 1 ) . in the present paper ,
we report a case of pa showing predominantly oncocytic cells with cholesterol clefts and macrophages .
a 45-year - old male patient reported with a slow growing asymptomatic swelling on the hard palate region since 5 months .
physical examination revealed 4 cm  4.5 cm , diffuse , non - tender , smooth - surfaced , and soft to firm non - fluctuant swelling involving the posterior region of the palate ( figure 1 ) .
based on the clinical and radiographic findings , a presumptive diagnosis of pa of palatal salivary glands was made .
microscopic examination showed homogenous eosinophilic cellular mass composed of epithelial components in the form of tubular and solid pattern .
the abluminal polygonal and oval cells showed abundant dark eosinophilic granular cytoplasm ( figure 2 ) .
cholesterol crystals were evident at few places associated with large oval macrophages showing faint granular eosinophilic cytoplasm along with giant cells ( figure 4 ) .
the tumor was very cellular and devoid of chondromyxoid stroma . based on these findings ,
in 1931 , hamperl coined the term oncocyte ( onkocyten ) to describe a cell having abundant eosinophilic granular cytoplasm and a centrally located hyperchromatic nucleus .
oncocytic metaplasia of ductal and acinar cells is commonly encountered in normal salivary glands in persons over 50 years of age , but primary oncocytic neoplasms and tumour - like lesions are comparatively rare , accounting for less than 1% of salivary tumours .
histomorphological appearance of oncocytes is attributed to abundant mitochondria present in the cytoplasm of cell .
presence of oncocytes in salivary gland tumors is not a rare phenomenon as they are considered as a prominent feature of warthin s tumor , oncocytoma , and oncocytic carcinoma .
even some non - oncocytic tumors like myoepithelioma , acinic cell carcinoma , mucoepidermoid carcinoma , basal cell adenoma , polymorphous low - grade adenocarcinoma , and sebaceous adenoma can show predominantly oncocytic histomorphologic feature
. however , their presence in pa is regarded as an extremely rare phenomenon and can cause diagnostic pitfall in the differential diagnosis . to our knowledge
, only 18 cases of oncocytic pa were reported till date including present case ( table 1 ) .
most common site was parotid gland ( 14 cases ) followed by submandibular ( 2 cases ) , para - pharyngeal area and palate .
recurrence and metastasis has not yet been reported in the literature . in the present case , we have reported cholesterol cleft formation at few places associated with prominent macrophages and giant cells ( figure 4 ) .
macrophages were large oval cells showing faint granular eosinophilic cytoplasm with centrally or peripherally placed pyknotic nuclei .
since cholesterol clefts act as foreign material , they are usually surrounded by macrophages and giant cells .
only one case of pa ( non - oncocytic ) associated with cholesterol crystals and macrophages have been reported in the literature till date . in the present case , we observed clear change in the cytoplasm of oncocytic cells , which again can be regared as a rare phenomenon in oncocytic pa .
oncocytic metaplasia has long been regarded as affecting both secretory and ductal epithelial cells in salivary glands , although askew et al .
provided ultrastructural and light microscopic evidence of both epithelial and myoepithelial oncocytes . in agreement with this , feiner described a case of an oncocytic adenoma of the parotid gland revealing immunohistochemical co - expression of s-100 protein and cytokeratins ( cks ) , which was interpreted as an indication of myoepithelial differentiation of oncocytes .
oncocytic pa showed positivity for ck5/6 , ck8/18 , ck14 , vimentin , alpha - smooth muscle actin , s100 protein , p63 , epidermal growth factor receptor and b - catenin .
however , oncocytic cells in pa usually show a luminal phenotype , expression of anti - mitochondria antibody and reduced b - catenin staining . in normal age related oncocytic metaplasia ,
both luminal and abluminal cells show similar oncocytic morphology indicating similarity with the molecular pathogenesis of oncocyte formation in pa . in oncocytic pa ,
mariano et al . reported positivity for high molecular weight ck in luminal cells and myoepithelial cells .
this suggests that mitochondrial phenotype is present in both the luminal and myoepithelial cells and mutation occurs in more differentiated cells during tumor formation .
the prognosis is good and no recurrent cases have been reported till date . in conclusion , we have reported a rare case of oncocytic pa with histopathological evidence of cholesterol crystals , macrophages and giant cells .
presence of clear cell change in oncocytic cells can also be regarded as a rare event in oncocytic pa as it has not yet been reported in the literature .
 pleomorphic adenoma ( pa ) is the most common salivary gland tumor characterized by histo - morphological diversity in the form of myxoid , hyalinized , chondroid , osseous , and squamous areas . in this paper 
 , we report a rare case of predominantly oncocytic variant of pa in a 45-year - old male patient on the posterior palatal region . 
 microscopic examination showed homogenous eosinophilic cellular mass composed of epithelial components arranged in the form of tubular and solid patterns . 
 the polygonal and oval cells showed abundant dark eosinophilic granular cytoplasm . 
 the cell borders were distinct with a central nucleus showing prominent nucleoli . 
 interestingly at few places , cholesterol clefts were seen surrounded by macrophages and giant cells . 
 the tumor was surgically excised with no evidence of recurrence after 2 years . 
Introduction
Case Report
Discussion