|Year : 2012 | Volume
| Issue : 2 | Page : 85-88
Low grade mucoepidermoid carcinoma of the tongue: An unusual presentation
Department of Oral Medicine and Radiology, School of Dental Sciences, Krishna Institute of Medical Sciences University, Karad, Maharashtra, India
|Date of Web Publication||1-Oct-2012|
Department of Oral Medicine and Radiology, School of Dental Sciences, Krishna Institute of Medical Sciences University, Karad - 415 110, Maharashtra
Source of Support: None, Conflict of Interest: None
Mucoepidermoid carcinoma is the most common malignant salivary gland tumor of epithelial origin. It is an unusual type of tumor and varies in its aggressiveness from a low grade to a high grade rapidly growing tumor. Low-grade mucoepidermoid carcinoma at times misleads the clinician because of its atypical location and innocent appearance. Immunohistochemical studies prove indispensable in identifying such a tumor as routine histopathology may be inconclusive.
Keywords: Minor salivary gland tumor, mucoepidermoid carcinoma, tongue tumor
|How to cite this article:|
Ambika L. Low grade mucoepidermoid carcinoma of the tongue: An unusual presentation. J Sci Soc 2012;39:85-8
| Introduction|| |
Mucoepidermoid carcinoma (MEC) of the major salivary gland was first described by Stewart et al in 1945.  The tumor was initially titled 'Mixed epidermis and mucous secreting carcinoma', a term later replaced by 'MEC'.  This tumor comprises about 4-9% of all salivary gland tumors, among which 11% are found in the major salivary gland, and 8% in the minor salivary glands. MEC behaves both like a benign and a malignant tumor with variable prognosis. Histologically there are three variants of MEC viz. Low grade, intermediate grade and high grade. The low grade typically shows a locally invasive and relatively non-aggressive course unlike the high-grade tumor. MEC of the minor salivary glands is rare in the pediatric population and occurrence on the tongue is even more unusual.
| Case Report|| |
A 12-year-old male child visited our department with a chief complaint of an asymptomatic swelling on his tongue since two months. He presented with unremarkable medical, dental, surgical, family and drug histories. The swelling had an insidious onset and had gradually increased in size over the past two months. The patient had not noticed any fluctuation in the size of the swelling. Although there was no difficulty in speech, tongue movements or breathing, the patient did complain of difficulty in swallowing. On general physical examination the child was moderately built and nourished with satisfactory vital signs. There were no significant extra oral findings.
Intra oral soft tissue examination revealed a solitary, sessile, well defined, roughly ovoid midline swelling at junction of oral and pharyngeal portion of the tongue, measuring approximately 2x1.5 cm in size [Figure 1]. The mucosa over the swelling appeared smooth with no evidence of ulceration, sinus, scar or discoloration. The swelling was non-tender with distinct borders and was firm in consistency. It was non-fluctuant, non- compressible, non reducible and no discharge was noted on application of digital pressure. The patient was subjected to relevant investigations. Complete hemogram depicted normal values. On ultrasonographic examination both the lobes and isthmus of the thyroid gland were normal in size and echotexture suggesting a normal study. Thyroid function tests using radioimmunoassay revealed that the patient was in euthyroid state.
An excisional biopsy [Figure 2] with wide margins was performed under general anesthesia with the pediatrician's consent. Histopathological sections [Figure 3] revealed intact surface stratified squamous epithelium, minor salivary glands in lamina propria and cystic spaces distended with mucin. There was no evidence of thyroid tissue. Mucous cells, intermediate cells and squamous cells were not seen. The histopathology was inconclusive and did not rule out or confirm any pathology. However, Mucoepidermoid carcinoma was considered a possibility. This prompted immunohistopathological investigations of tissue sections. The S-100 protein marker was positive in myoepithelial cells [Figure 4] and Cytokeratin was positive in both mucous secreting and squamous cells [Figure 5], favoring the diagnosis of low-grade mucoepidermoid carcinoma. A final diagnosis of Low- grade mucoepidermoid carcinoma was arrived at. The patient is being followed up every three months and no recurrence has been noted.
|Figure 3: Histopatholology of the growth showing stratified squamous epithelium, minor salivary gland in lamina propria and cystic spaces distended with mucin (H and E, ×40)|
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|Figure 4: S-100 protein marker showing positivity in myoepithelial cells|
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|Figure 5: Cytokeratin showing positivity in both mucous secreting and squamous cells|
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| Discussion|| |
A study by Li LJ,  3461 cases of salivary gland tumors were retrospectively evaluated. They found that mucoepidermoid carcinoma had the most frequent occurrence. A Clinico pathologic study of 311 intra oral salivary gland tumors in Thais by Dhanuthai K et al,  depicted that mucoepidermoid carcinoma was the most common malignant tumor.
Buchner A  studied relative frequency of individual intra-oral minor salivary gland tumors (IMSGT). IMSGT were identified in 380 (0.4%) cases of 92 860 accessed among which 224 (59%) were benign and 156 (41%) were malignant. Mucoepidermoid carcinoma was the most common (21.8%) malignant tumor encountered.
Malignant neoplasms represents one-third of all pediatric salivary gland tumors. MEC composes 51% of malignant tumors and 16% of all salivary gland neoplasms in pediatrics.  It is most prevalent in the age group of 30 - 39 years.  Occurrence of neoplasm in first 10 years of life is extremely rare (1.1%). 
The palate is the most common location of the tumor.  In a study by Hicks J,  26 pediatric patients with salivary gland MECs were evaluated retrospectively. Only one of them was located on the base of tongue. Median tumor size was 2.5 cms (range 1.5-5 cms). Among them, 9 were low grade (LG), 15 intermediate grade (IG) and two high grade (HG) tumors. A study by Goldblatt LI  55 cases of primary salivary gland tumors of the tongue from the files of the Armed Forces Institute of Pathology were analyzed of which 50 were malignant and over 85% of them involved the base of the tongue. The most common malignant tumor was the low-grade mucoepidermoid carcinoma (38%).
The clinical manifestations of mucoepidermoid carcinoma depends upon its histological grade, the low- grade variety are slow growing painless masses. Large lesions on the base of the tongue can cause dysphagia as in our case. Intraoral lesions can present as bluish or red- purple, fluctuant, and smooth surfaced masses often clinically mistaken for the Mucocele. 
Microscopically, the grading of mucoepidermoid carcinoma is based on three factors, the amount of cystic formation, degree of cytological atypia and relative number of mucous, epidermiod and intermediate cells. Additional criteria often considered are growth pattern and cellular differentiation. Incisional biopsy is essential to establish the histological grade of the tumors and guide to therapy. 
About two third of cases belongs to the low-grade type. Prominent cystic structures are the hallmark of the lesion and this feature is accompanied by the presence of numerous mature cellular elements, including mucous cells and often abundant extracellular mucin. Several large cysts may occasionally form a large portion of the tumors. The cysts may infiltrate adjacent salivary gland parenchyma and connective tissue. 
It was found that both high-grade and low-grade tumors retained the ability to synthesize a heterogeneous variety of mucins and therefore discrimination between grades was not possible with histopathology. The unique cellular antigens have been defined in any salivary gland malignancy, panels of multiple and less specific immunomarkers may be of use in pathology. Antigenic profiles, as determined through immunohistochemical studies, may provide enough chance to select and to serve as an adjuncts to diagnosis and classification. 
MEC are thought to arise from undifferentiated cells associated with salivary gland excretory ducts. Because putative myoepithelial cells have been reported recently in the base of these ducts, and because some myoepithelial cell associated antigens (vimetin, glial fibrillary acidic protein, and actin) have been found in some MECs, it has been suggested that the myoepithelial cell may have a significant role in the development of MECs. The five antigenically distinct intermediate filaments (keratins, vimetin, desmin, glial fibrillary acidic protein, neurofilaments) that are limited individually to normal cells, also generally characterize their neoplastic counterparts. S-100 positive tumor cells have also been reported.  In our case immunohistochemistry was indispensable in identifying the tumor and arriving at a diagnosis.
MEC's of the minor salivary glands generally have a good prognosis because of their low grade. However, tumors of the tongue and floor of mouth are less predictable and may exhibit an aggressive behavior. 
| Conclusion|| |
Mucoepidermoid carcinoma is the commonest among the salivary gland tumors, which can occur at any site in the oral cavity. At times, atypical locations and innocent appearance of the tumor such as the one reported can mislead the clinician and can lead to an erroneous diagnosis. Routine investigations may at times be inconclusive, pressing the need for more specific and advanced laboratory procedures.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]