A Rare Case Report of Plasmacytoid Myoepithelioma of Hard Palate

On extra-oral examination, no abnormality detected except palpable, firm and non-tender right and left solitary submandibular lymph nodes, whereas intraoral examination (Figure 1) revealed a welldefined 3×4 cm sized ovoid solitary swelling in the palate extending anteroposteriorly mesial of 23 to distal of 28 and mediolaterally from palatal gingival margin of 23-28 to 2 cm away from the palatal gingival margin of contralateral side, with red color change indicating engorged vessels and without any change on the surface of swelling. To palpate, swelling was firm and non-tender. The adjacent teeth 27, 28 were mobile and were assigned grade II to grade III mobility respectively.


Introduction
Salivarygland neoplasms with exclusively of myoepithelial cells are unusual and intriguing [1,2]. Myoepitheliomas are rare tumor of salivary gland constituting less than 1% of all salivary gland tumors [3]. Sheldon, first used the term "Myoepithelioma" in 1943 and was included in the 1991 revised WHO classification of salivary gland tumors [3,4].
The growth patterns may be solid, myxoid or reticular and the component cells may be spindle shaped, plasmacytoid, hyaline, clear or epitheloid [5]. The plasmacytoid myoepithelioma from palatal salivary glands is considered as a very rare entity [6]. Palatal masses often lead to a diagnostic dilemma because of their similar presentations.
Here, we report a case of Plasmacytoid Myoepithelioma of palate which resembles pleomorphic adenoma of palate.

Case Report
A 51 year old lady reported to our department with the slowly growing painless palatal mass of 2 years duration which was insidious in onset. Patient gave a history of discomfort while chewing and swallowing since 6 months and negative history of fever, trauma and any other swelling in the body.
Medical records suggested patient was known hypertensive since 2 years, but she was not on medication. During examination, patient was found to be in good general and physical health.
On extra-oral examination, no abnormality detected except palpable, firm and non-tender right and left solitary submandibular lymph nodes, whereas intraoral examination ( Figure 1) revealed a welldefined 3×4 cm sized ovoid solitary swelling in the palate extending anteroposteriorly mesial of 23 to distal of 28 and mediolaterally from palatal gingival margin of 23-28 to 2 cm away from the palatal gingival margin of contralateral side, with red color change indicating engorged vessels and without any change on the surface of swelling. To palpate, swelling was firm and non-tender. The adjacent teeth 27, 28 were mobile and were assigned grade II to grade III mobility respectively.
Considering history and clinical examination, case was provisionally diagnosed as "Pleomorphic Adenoma of hard palate".
Occlusal and Para nasal radiographs (Figures 2 and 3) revealed no abnormality. FNAC was done as a part of investigation and cytological features were suggestive of Myoepithelioma. Results of hematologic, biochemical investigations were within normal limits and HbsAg, HIV-1 & 2 tests were also negative ( Table 1).
The patient underwent wide surgical excision along with a rim of surrounding normal tissue under general anesthesia in a private clinic. Patient was followed up after 3 weeks, wherein inflammation and persistence of oronasal communication was seen ( Figure 4). Histopathological examination, revealed predominantly proliferation of plasmacytoid cells arranged in discrete & clusters with eccentrically situated nuclei having abundant cytoplasm. Few clusters consist of round to polygonal cells & few were spindle to epitheloid type with elongated nuclei & eosinophilic cytoplasm ( Figure 5). Features were suggestive of Plasmacytoid Myoepithelioma of minor salivary gland in the hard palate.
After a month patient was followed up wherein oronasal communication was existing, subsequently patient was provided with the maxillary obturator ( Figure 6).
Myoepitheliomas are rare tumor of salivary gland constituting less than 1% of all salivary gland tumors [3]. Myoepithelial cells are thin      and spindle shaped and situated between the basement membrane and epithelial cells and these are the normal constituents of major and minor salivary glands, having the contractile properties, assisting in the secretion of saliva [3].
Myoepitheliomas appear to be rare and this contrast with the active role of myoepithelial cells in the histogenesis of several types of salivary gland tumors [2].
The most common location for myoepithelioma of the head and neck region are the parotid gland (40%) and the palate (21%) [2]. This neoplasm seems to result from a monoclonal proliferation of myoepithelial cells, which may partially differentiate into spindleshaped or plasmacytoid cells. Their histogenesis from myoepithelial cells is reflected in their most frequent location that is the parotid gland, wherein myoepithelial cells are more common [7].
The mean age at presentation of benign Myoepithelioma is about 50 years and the sex incidence is roughly equal. Most patients complain of a well-circumscribed mass, usually 10-50 mm in diameter in either major or minor salivary glands [4].
Myoepithelioma generally shows several cellular patterns namely spindle, plasmacytoid, epitheloid, clear cell. Growth patterns namely solid, myxoid, reticular may be seen. Myoepitheliomas of the minor salivary glands tend to be composed of plasmacytoid cells and those of the parotid; it may be epitheloid or spindle cells. The clear cell variant can occur in both major and minor salivary glands, but is relatively rare [4].
The rarity of Myoepithelioma makes it a surprise diagnosis; identifiable only histopathologically. Its clinical differential diagnosis usually consists of the more common salivary gland tumors. In the parotid region, Pleomorphic Adenoma, Warthin tumor, Basal cell adenoma, Adenoid cystic carcinoma or Mucoepidermoid carcinoma would be appropriate. In oral sites, the same differential would generally prevail except Warthin tumor and the canalicular adenoma which would be substituted for the basal cell adenoma [7].
Myoepitheliomas frequently mistaken for cellular Pleomorphic Adenoma, because both the tumors consist of abundant myoepithelial cells [8]. It has been proposed that if the neoplasm contains <5% ductal and acinar components, it must be named myoepithelioma and if there is ductal predominance, pleomorphic adenoma diagnosis should be established [3].
Immunohistochemically, a large number of markers have been used for establishing the diagnosis of myoepitheliomas, which includes Muscle Specific Actin (MSA), a marker of myogenous differentiation and epithelial filaments of cytokeratin [3].
With Immunohistochemical techniques, myoepithelial cells stain positive for cytokeratin, MSA, occasionally express S-100 protein and Glial Fibrillary Acidic Protein (GFAP). The neoplastic myoepithelial cells consistently demonstrate cytokeratin S-100 and MSA immunoreactivity whereas reactivity for vimentin and GFAP is more variable [2].
Biologically, in most cases myoepitheliomas are benign, but occasionally infiltrate locally and metastasize. The prognosis of myoepithelioma would appear to be good, provided surgical excision is complete [5].
In conclusion, Myoepithelioma of salivary glands are unusual tumors with plasmacytoid variants still sporadic. Because of their infrequence variable growth patterns and often because of increased cellularity they can be misdiagnosed. However, ultra structural study of myoepithelial cells establishes fine structural criteria on which positive identification could be made. Therapy should be directed towards complete surgical extirpation and close follow up is mandatory for all cases.