Mucoepidermoid carcinoma of the palate: A rare case report.

Mucoepidermoid carcinomas (MECs) of minor salivary gland origin are rare in children and adolescents and have been reported rarely. Literature regarding their clinical features and biologic behavior is scanty. The purpose of this case report is to discuss the clinical manifestation, diagnosis, and treatment plan of MEC of the palate. A 16-year-old male subject visited the Department of Periodontics, The Oxford Dental College and Hospital, Bangalore, India complaining of a painless swelling in the left posterior area of the hard palate since 6 months. Several clinical, radiographic, and histopathological investigations were carried out to rule out the lesion. Incisional biopsy of the lesion confirmed the diagnosis of lesion as MEC of the palate following which a wide surgical excision with adjacent free margins was carried out. This case report highlights the need for proper diagnosis and treatment plan in the cases of malignant tumors as it can lead to morbidity and mortality.

INTRODUCTION

Mucoepidermoid carcinoma (MEC) is the epithelial salivary gland neoplasm of the oral cavity. It accounts for <3% of all head and neck tumors. About 5% of these tumors occur in patients younger than 18-year-old with women mostly affected.[12] As its name implies, it is composed of mucus-producing, squamous, and intermediate type cells.[3] About two-third arise within the parotid gland, and one-third arise within the minor salivary glands. When MEC arises in minor salivary glands, it can be located on the palate, retromolar area, floor of the mouth, buccal mucosa, lips, and tongue. Rarely, it can arise as primary jaw tumor or as laryngeal, lacrimal, nasal, paranasal, tracheal, or pulmonary tumor. It occurs most frequently in adults during the fifth and sixth decades of life. Although uncommon, it is the main malignant salivary gland tumor in children, particularly adolescents and affects women more often than men (3:2).[4]

MEC was first reported by Massao and Berger in 1942 and by Stewart et al. in 1945 as a distinct pathologic entity.[5] All mucoepidermoid tumors are malignant, albeit in degree.[6] Histologically, MECs are classified into low-, intermediate-, and high grade.[7] Low grade tumors commonly develop a nesting pattern with multiple well-circumscribed squamous nests containing numerous clear cells. Intermediate-grade tumors are less cystic and show a greater tendency to form large sheets of squamous cells and often have a more prominent intermediate cell population. High-grade tumors are predominantly solid, with greater degrees of atypia.

CASE REPORT

A 16-year-old male subject visited the Department of Periodontics, The Oxford Dental College and Hospital, Bangalore complaining of bleeding gums following brushing and painless swelling in the left posterior area of the hard palate since 6 months. His medical and family history was noncontributory and was in good physical condition. The extraoral examination was unremarkable. No other abnormality was found.

Oral hygiene status of the subject was satisfactory. Intraoral examination showed the presence of swelling in the left posterior area of the hard palate of approximately 2 cm × 1 cm in size and color similar to that of palatal mucosa with slight bluish hue in the center of the lesion with a presence of sinus opening [Figure 1]. On palpation, the lesion was nontender and firm in consistency around the borders and soft at the center of the lesion. There was purulent discharge through the sinus tract.

Figure 1

Swelling in the left posterior area of the hard palate

Electrical pulp vitality test results were positive. To track the sinus tract, intraoral periapical radiograph was taken with gutta-percha point placed through the sinus opening. The gutta-percha point extended till the apex of mesial root of a maxillary first molar. There were no signs of alveolar bone resorption in the panoramic, periapical, and occlusal radiographs. The floor of the maxillary sinus appeared intact. Complete hemogram showed all the parameters within the normal range. Computed tomography peripheral nerve sheath reported soft tissue density on the left side of palate causing smooth bony indentation [Figure 2].

Figure 2

Computed tomography peripheral nerve sheath

Initially, the differential diagnosis of the swelling was made as periodontal abscess, palatal region vascular malformations such as hemangioma, mucocele, sialometaplasia, pleomorphic adenoma, adenoid cystic carcinoma, MEC, and adenosquamous carcinoma.

Incisional biopsy was done to establish a definitive diagnosis, to assign a histological grade and prescribe adequate therapy. On histopathological examination, H and E staining showed three groups of cells, namely large mucous cells with an empty cytoplasm and peripherally placed nucleus, intermediate cells with basaloid nucleus, and epidermoid cells with eosinophilic cytoplasm suggestive of intermediate-grade MEC [Figure 3]. Mucicarmine stain, a specific stain for the diagnosis of MEC, highlights cytoplasmic mucin in the tumor cells. This staining showed large mucous cells with magenta pink colored cytoplasm indicating the presence of mucous, intermediate cells with basaloid nucleus, and lastly epidermoid cells with abundant cytoplasm. In areas, cystic areas filled with magenta pink colored material could be appreciated indicative of mucous, suggestive of intermediate-grade MEC [Figure 4]. The treatment consisted of wide surgical excision of the lesion with free surgical margins which was carried out under local anesthesia with an electrocautery. Boundaries of excision extended anteriorly until canine, medially up to midline, posteriorly until junction between hard and soft palate, and laterally until marginal gingiva. The Greater palatine vessel was ligated [Figure 5]. The excisional biopsy report confirmed the diagnosis of intermediate-grade MEC. Postoperative healing was uneventful.

Figure 3

H and E staining: Magnification at 400×

Figure 4

Mucicarmine staining: Magnification at 100×

Figure 5

One-day postoperative view

The patient was recalled at 1, 3, 6 months and 1-year postoperatively to check for any recurrence. At 1-year healing was uneventful [Figure 6].

Figure 6

One-year postoperative view

DISCUSSION

It has been estimated that about 1–5% of all salivary gland tumors develops in children and adolescents.[89]

The percentage of benign tumors occurring in the palate is higher than that of malignant tumors.[10] Most of the malignant neoplasms of the salivary gland in children and adolescents are in the parotid gland. Only a few have been well-documented in minor salivary glands.[2] Epithelial neoplasms originating in the minor salivary glands account for approximately 15% of all salivary gland neoplasm.[1112]

MEC is believed to arise from pluripotent reserve cells of excretory ducts that are capable of differentiating into squamous, columnar, and mucous cells.[13] It occurs commonly in parotid glands with minor glands being the second most common site. It accounts for <3% of all head to neck tumors with a female predilection.[14] MECs are generally found between the ages of 10 and 16 years.

Clinically, the majority of palatal MEC appears as firm, painless swellings, and may mimic mucoceles or vascular lesions. Clinical findings and investigations in the present case indicated a surface lesion. Blue to red color of the lesion may suggest it to be either of vascular or of salivary gland origin. As in this case, mucus was discharged from the tumor through a small sinus tract.

When a compressible palatal mass is observed in adolescent, reactive and neoplastic lesions should be included in the differential diagnosis. The other minor salivary gland neoplasms, mainly pleomorphic adenoma, as well as benign and malignant mesenchymal tumor, should also be considered. A fluctuant light blue mass in an intraoral salivary gland bearing area, MEC and mucocele should be at the top of the list.[15]

Although MECs are considered rare in the children adolescent age group, they must be considered when a lesion appears to be similar to a mucocele but mucocele is frequently seen fluctuant reactive lesion of salivary glands most common in the lower lip and rarely in the palate. The present case was not similar to a mucocele because of the mucous discharge from a sinus opening. Since the MEC tends to have a blue or red surface hue, this salivary gland tumor may resemble a hemangioma which can be differentiated by clinical examination and imaging. The other most common entity is the palatal space abscess, which is characterized by a tender, diffuse, and erythematous swelling of sudden onset. Typically, pulpal necrosis of a permanent molar is the etiology. Nontender lesion with no clinical and radiographic evidence of inflammatory pulpal disease excludes the palatal space abscess from consideration. Adenoid cystic carcinoma and adenosquamous carcinoma can be differentiated by histological examination.

Histologically, MECs are divided into low-, intermediate-, and high grade types, which correlate with clinical behavior. In the present case, a histopathological diagnosis confirmed the lesion to be intermediate-grade MEC. Low-grade MEC macroscopically is small and partially encapsulated and microscopically characterized by the presence of more mucous-producing cells.[1617] The intermediate-grade MEC comprises solid rather than cystic architecture with more intermediate cells. All of these features were found in the present case. The high-grade tumor demonstrates solid islands of squamous and intermediate cells which demonstrate considerable pleomorphism and mitotic activity. Mucous cells are infrequent. The histologic grade of the MEC often reflects the clinical manifestations of the tumor. Intraorally, MEC's tend to be asymptomatic enlargements of prolonged duration.[18]

Moraes et al. suggested that low to intermediate-grade MECs originating from intraoral minor salivary glands in children and adolescents can be effectively managed by wide local surgical excision that ensures tumor-free surgical margins.[19] In this case, wide surgical excision of the lesion with free surgical margins was done. If there is no evidence of bony involvement, as in the present case, the tumor is dissected down to the periosteum. However, if there is any evidence of gross periosteal involvement or bone erosion, removal of a portion of the involving bone is necessary. High-grade tumors require more aggressive surgical approach with or without postoperative radiotherapy and chemotherapy. Furthermore, it should be considered that micro-marsupialization, cryosurgery, and laser therapy are contraindicated in the management of an intraoral submucosal mass/nodules in children particularly if the palate is involved. These kinds of treatments may result in local spread of the tumor, and more aggressive surgery may be needed. Healing was uneventful.

Low- to intermediate-grade MECs originating from intraoral minor salivary glands has a very low recurrence rate (<10%) and a high survival rate (95–100%).[13] This is keeping with the general consensus that low and intermediate grade MECs have an indolent clinical course and a minimal chance for metastasis. Nevertheless, close clinical follow-up should be for lifetime because low and intermediate-grade MEC in this age group can recur many years after initial removal and also at risk of developing a secondary malignancy following the treatment.[820]

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