. a myoepithelioma classically presents as an asymptomatic mass that slowly enlarges over a long period of time . however , recurrent and malignant ones have also been described .
they are more likely to occur in the parotid gland , but rare cases arising from minor salivary glands are also on record.[35 ] the authors present an exceptionally rare case of sinonasal myoepithelioma with recurrent and resistant to treat clinical course . to our knowledge and regarding the medline database ,
the patient was a 57-year - old iranian male living in dargaz , a small district in north east of iran .
he was admitted to the e.n.t ward , ghaem hospital , mashhad university of medical sciences in june 2010 .
first , at 1993 , he accidentally discovered a small painless mass of the palate , which was excised in an outpatient care facility .
thereafter , the patient had five more debulking surgeries . at the time of admission ,
the patient was complaining of nasal fullness , hyponasal speech , snoring , oral breathing , and loss of hearing on left side . on oral examination , the hard palate in the right side had been removed and a nasal mass was obvious through it .
both computed tomography scan and magnetic resonance imaging demonstrated a huge bilateral lobulated sinonasal mass with extension to cribriform plate and near the dura , medial walls of both orbits , and upper gingival area [ figure 1 ] .
t1-weighted transverse ( left ) and sagittal ( right ) planes show a huge bilateral sinonasal mass the patient underwent a functional endoscopic sinus surgery to debulk the tumor .
the removed specimen was stored in 10% buffer formalin and sent to the pathology department .
the specimen was made by multifragmented irregular - shaped brownish soft tissue with the dimensions of 3.5  3  2 cm .
the whole tissue was processed , cut , and stained with h and e. microscopically , the specimen showed a hypercellular tumoral tissue composed of plasmacytoid cells with eccentrally located round - ovoid nuclei and acidophilic cytoplasms .
the neoplastic cells were arranged in nests , cords , and sheaths intermixed with partially mucoid and hyalinized collagenous stroma . scattered gland - like structures bordered by neoplastic cells were seen constituting less than 5% of the tissue .
dispersed foci of spindle cells were also present surrounded by plasmacytoid cells [ figure 2 ] .
( b ) plasmacytoid cells in the background of mucoid material on immunohistochemistry staining , the specimen showed strong and diffuse reactivity for vimentin , cytokeratin , smooth muscle actin and s-100 confirming the myoepithelial nature of the tumoral cells [ figure 3 ] .
( a ) the specimen strongly expresses vimentin , ( b ) cytokeratin , ( c ) smooth muscle actin , and s-100 ( d ) confirming its myoepithelial nature the patient refused to undertake any more treatments . after 15 months of follow - up
myoepithelioma is a generally benign neoplasm that constitutes approximately 11.5% of all salivary gland neoplasms .
they are more likely to occur in the parotid gland , but rare cases arising from minor salivary glands such as in palate , gingiva , lips , nasopharyngeal space , orbit , and middle ear are also on record.[35 ] exceptionally , they can occur in the sinonasal cavity , with only seven reports , including our case , present in the literature.[611 ] histologically , myoepitheliomas are classified as spindle , plasmacytoid , reticular , epitheliod , and clear cell types . the most common is the spindle type , whereas the others are very rare .
all the previously reported sinonasal myoepitheliomas were composed mostly of spindle cells and to a lesser extent of plasmacytoid/ epithelioid cells.[611 ] however , the present case was almost entirely composed of plasmacytoid cells , with dispersed foci of spindle cells . the most important differential diagnosis of myoepitheilomas includes pleomorphic adenoma .
there is a general tendency to put myoepitheliomas at one end of the histologic spectrum that includes pleomorhic adenomas at the other end .
this claim is supported by the fact that these two entities are very similar in biologic course , distribution , morphology , and even immunohistochemical aspects .
world health organization proposes that if the neoplasm contains less than 5% of ductal components they must be named myoepithelioma .
furthermore , several mesenchymal neoplasms such as fibrosarcoma , leiomyoma , schwannoma , and myxoma are in the differential diagnoses of the spindle cell myoepitheliomas , but they all lack the immunoreactivity for cytokeratin .
however , in the presented case , the non- spindle ( plasmacytoid ) appearance of the neoplastic cells can easily rule out these entities .
myoepitheliomas are characteristically immunoreactive for cytokeratins , s-100 , calponin , smooth muscle actin , myosin , vimentin , glial fibrillary acidic protein , and carcinoembryonic antigen . in the presented case ,
conventional myoepitheliomas are not more aggressive than pleomorphic adenomas , but invasive myoepitheliomas that infiltrate the adjacent tissues have been described .
the malignancy is assisted by the infiltrative margins , necrosis , marked pleomorphism , and prominent mitotic activity , which were all absent in the presented case . moreover ,
recurrence is associated with involved surgical margins at the first excision . in the present case ,
the tumor had a benign morphology with a progressive , invasive , and recurrent clinical course , as the tumor has been recurred six times within 17 years .
therefore , the surgical excision must be done with wide healthy margins and an appropriate follow - up is also recommended .
myoepitheliomas are generally well - circumscribed solid masses that measure less than 3 cm in diameter . however , in our case , the tumor was a huge bilateral sinonasal mass , which showed prominent extension to cribriform plate , dura , both orbits , and upper gingiva , so that complete surgical removal was practically impossible . to our knowledge , this is the most extensive myoepithelioma of its kind . some of the malignant myoepitheliomas have been arisen from pleomorphic adenomas . regarding our case , the primary lesion had been diagnosed as a myoepithelioma ; thus , the further transform of a pleomorphic adenoma seems improbable .
we reported the seventh case of myoepitheliom of the sinonasal cavity ever diagnosed regarding the medline database until 2012 .
immunohistochemical investigation may be a useful tool in order to reach to the appropriate diagnosis while a myoepithelioma is in the differential diagnosis of a tumor of the oral / sinonasal cavity .
 myoepithelioma is an uncommon benign neoplasm that most likely occurs in the parotid gland . 
 extra - salivary myoepitheliomas are rare , with less than 10 cases reported in the sinonasal cavity . 
 we present a rare case of benign myoepithelioma with recurrent behavior , abundant extensions to adjacent structures , and resistant to treat clinical course , which influenced the patient s quality of life for more than 18 years . 
 histologic , immunohistochemical , and the potential differential diagnoses are discussed . 
 the patient refused to undertake any more treatments , but after 15 months of follow - up , the lesion did not progress further . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONCLUSION