Mucoepidermoid Carcinoma of the Hard Palate in a Middle-Aged Man

Significance

Mucoepidermoid carcinoma can mimic other tumors of the salivary gland and should be considered in the differential diagnosis, given that it is the most common malignant tumor of the salivary gland. Imaging appearance on computed tomography (CT) and magnetic resonance imaging (MRI) modalities guides preoperative planning and treatment options.

Case Description

We present a case of a 37-year-old man presenting for evaluation of a hard palate lesion. He noted that the mass had been persistent and unchanged. He reported a remote smoking history but denied any history of chewing tobacco use.

Physical examination revealed a well-circumscribed, non-tender submucosal soft mass to the right of midline in the hard palate, with a 1-millimeter (mm) black nodule on the mass that was firm on palpation. Diagnosis of mucoepidermoid carcinoma in this patient was established by CT of the head and neck and subsequent excisional biopsy.

CT of the head and neck with contrast demonstrated a 17 x 17 x 15 mm circumscribed, heterogenous mass within the mucosa overlying the inferior surface of the maxilla, with chronic-appearing bone remodeling of the inner table of the maxillary bone with questionable subtle erosion (Figure 1). Excisional biopsy was performed without any complications. Pathology demonstrated admixed epidermoid cells, well-differentiated mucous cells, intermediate and clear cells with infiltrative growth, and perineural invasion consistent with a low-grade mucoepidermoid carcinoma. Re-excision was performed 2 months later due to positive margins without any complications. CT of the head and neck was conducted 6 months after the repeat excision and demonstrated no evidence of residual disease within the hard palate.

Figure 1.

CT of the head and neck with contrast demonstrates a 17 x 17 x 15 mm enhancing lesion (red arrow) within the mucosa overlying the inferior surface of the maxilla on axial (A), sagittal (B), and coronal (C) reformats. Note that the parotid and submandibular glands are normal and symmetric.

Discussion

Composed of three types of cells in various amounts—mucus secreting, squamous, and poorly differentiated intermediate cells, mucoepidermoid carcinoma most often presents within the parotid gland, followed by the palate.^1,2 Mucoepidermoid carcinoma typically presents as an indolent, painless hard mass and is present across all age groups, most commonly within the middle-aged population. ³ Risk factors include female sex, history of radiation exposure, and a t(11;19)(q21;p13) translocation that results in an MECT-MAML2 fusion gene.^3,4 Appearance on imaging depends strongly on tumor grade and guides preoperative planning. Treatment of low-grade tumors is conservative, usually necessitating solely wide local excision; treatment of high-grade tumors often requires complete parotidectomy with involvement of the facial nerve, neck dissection, and adjuvant radiotherapy. Low-grade tumors have a better prognosis when compared to high-grade tumors and have higher survival and lower recurrence rates. ⁵

Across most modalities, low-grade tumors appear similar to benign mixed tumors while high-grade tumors demonstrate poorly defined margins. On ultrasound, low-grade tumors are well-circumscribed hypoechoic lesions that contrast the hyperechoic gland. On CT, low-grade tumors appear as well-circumscribed masses with a mixed appearance, including hyperattenuating solid components, cystic components, and occasional calcification. In contrast, high-grade tumors are solid with poorly defined margins and local infiltration. Low-grade mucoepidermoid carcinoma demonstrates low to intermediate signal intensity on T1 weighted images with low T1 signal intensity within cystic spaces. On T2 weighted images, low-grade mucoepidermoid carcinoma demonstrates intermediate to high signal intensity with high T2 signal intensity within cystic spaces. Fat-saturated post-contrast T1 weighted images of the cranial nerves and skull base are important in assessing for perineural spread, especially involving high-grade lesions. High-grade tumors are more solid with infrequent cystic areas and poor margins, with low signal intensity on T2 weighted images.

Though mucoepidermoid carcinoma may resemble other salivary gland tumors, it is the most common malignancy of the salivary glands. Benign mixed tumor, Warthin tumor, and adenoid cystic carcinoma are other possible diagnoses for well-circumscribed lesions. Adenoid cystic carcinoma, Non-Hodgkin’s Lymphoma, or metastases should be considered for poorly circumscribed lesions. Treatment is guided by familiarity with the patient’s clinical history, along with the distinguishing imaging features on CT and MRI.