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A swelling in the middle of the hard palate should bring to mind torus palatinus, but not in this case. There are many reasons for this, the most important being that the consistency of this swelling is firm but not as hard as bone. Tori and exostoses would have a bony hard consistency that this swelling lacked. So torus palatinus is off the list of the differential diagnosis. The differential diagnosis for a firm soft tissue swelling would include a salivary gland neoplasm. The location is good for that diagnosis and the color is more in favor of a mucoepidermoid carcinoma. The histology, however, is not supportive of this diagnosis.
Mucoepidermoid carcinoma is a malignant neoplasm of salivary gland origin that can present as a smooth-surfaced swelling or a non-healing ulcer on the palate, usually the posterior lateral palate. It occurs in a wide age range and has three histologic types: low, intermediate and high; the low-grade type is more common in the oral cavity. Mucoepidermoid carcinoma accounts for 10% of all salivary gland neoplasms. While the majority of MECs occur in the parotid gland, some also occur in minor salivary glands, especially the palate, tongue, buccal mucosa, lips, and retromolar pad areas. It can occur at any age with a predilection for occurrence in young people. Studies by the Armed Forces Institute of Pathology (AFIP) find 44% of cases occurring in patients under 20 years of age, most commonly on the palate. Their youngest patient was nine months old. The low-grade lesions are slow-growing and painless, and not encapsulated; they sometimes resemble a mucocele, especially those at the retromolar pad area. Mucoceles of the retromolar pad area are rare, and for that reason it is best to biopsy them early to exclude the possibility of a mucoepidermoid carcinoma masquerading as a mucocele. High-grade lesions tend to be more common in the parotid gland; they present as rapidly growing, painful lesions with facial nerve paralysis and sometimes with regional lymph node metastasis. Histologically, mucoepidermoid carcinomas consist of a variety of cell types and architectural patterns which constitute the three histologic gradings. Although low-grade mucoepidermoid carcinoma is characterized by an abundance of mucous-producing cells and duct-like structures with cystic dilation, the mere presence of certain types of cells and architecture should not be used to determine the histologic grade. Complete surgical removal with clean margins is the preferred treatment for the low-grade type. Radiation therapy has also been successfully used, especially when the tumor involves the surgical margins.