Case of the Month
Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO
October 2023
Mucoepidermoid Carcinoma of the Base of the Tongue
- Background:
- Mucoepidermoid carcinoma (MEC) is a relatively common malignant neoplasm originating from the reserve cells of salivary gland ducts and accounts for approximately 35% of all malignancies of the major and minor salivary glands.
- This malignancy has a predominant occurrence in the parotid gland (89.6%), followed by the submandibular gland (8.4%).
- While MEC is commonly found intraorally, it exhibits a strong predilection for the palate. However, the occurrence of MEC at the base of the tongue is rare and has been infrequently reported in the medical literature.
- Given its uncommon location, mucoepidermoid carcinoma of the base of the tongue possesses diagnostic challenges and demands tailored management approaches to optimize patient outcomes.
- MEC of minor salivary glands has 3 histologic cell types: mucous cells, epidermoid squamous cells, and poorly differentiated intermediate cells with dual differentiation ability. Predominant epidermoid cells resemble squamous cell carcinoma, classified as high-grade MEC. Mucin-producing cells in a cystic architecture indicate low-grade MEC. Intermediate-grade tumors are less cystic; form large, irregular nests of squamous cells; and have prominent intermediate cells.
- Clinical Presentation:
- Mucoepidermoid carcinoma of the tongue base gives rise to a rather vague and nonspecific symptomatology.
- Early symptoms include foreign body sensation in the oral cavity, undefined paresthesia, and sialorrhea.
- With the progression of disease, dysphagia, otalgia, and painful swallowing are usually referred.
- Key Diagnostic Features:
- Ultrasonography typically reveals a well-defined hypoechoic lesion with a partially or completely cystic appearance compared with the relatively hyperechoic normal parotid gland.
- On CT, lower-grade tumors appear well circumscribed with a cystic component. Occasionally, enhancing solid components and calcifications may be observed. In contrast, higher-grade tumors present as solid lesions with poorly defined, infiltrative margins.
- MRI characteristics of low-grade tumors resemble those of a pleomorphic adenoma, with low to intermediate signal in T1, intermediate to high signal in T2, and heterogeneous enhancement of solid components. On the other hand, higher-grade tumors exhibit a solid appearance with a lower signal on T2-weighted images and poorly defined margins.
- Differential Diagnoses:
- Lingual thyroid: On CT imaging, a lingual thyroid typically appears as a well-defined, homogeneously enhancing mass in the midline of the base of the tongue. On MRI, it appears as a well-circumscribed mass with intermediate signal intensity on T1-weighted images and intermediate to high signal intensity on T2-weighted images. Post–contrast administration, the lingual thyroid demonstrates homogeneous enhancement, which helps to differentiate it from other lesions in the tongue base.
- Dermoid/epidermoid cyst: On CT imaging, these cysts typically appear as well-defined, round or oval-shaped lesions with low attenuation (hypoattenuating) compared with the surrounding soft tissues. They may contain internal septations or debris, giving them a characteristic "ground-glass" or "soap bubble" appearance. These cysts may also show calcifications, which appear as hyperdense foci within the lesion. On MRI, dermoid and epidermoid cysts display low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. They may show a characteristic "pearl sign," which refers to a hyperintense T2 signal at the periphery of the cyst due to the presence of sebaceous material. The cyst capsule may demonstrate intermediate signal intensity on T1-weighted images and low signal intensity on T2-weighted images. Furthermore, epidermoid cysts have restricted diffusion while dermoid cysts do not.
- Vascular malformations: On CT imaging, they often present as ill-defined soft-tissue masses with heterogeneous attenuation. The density may range from hypoattenuating areas due to slow blood flow to hyperattenuating areas caused by thrombosis or phleboliths within the malformation. They may show enhancement following intravenous contrast administration, which can vary from nonenhancement (lymphatic malformation) to arterial enhancement (arteriovenous malformation) depending on the vascular flow characteristics. On MRI, they appear as heterogeneous lesions with intermediate signal intensity on T1. On T2-weighted images, the lesion shows hyperintense signal due to the slow flow of blood. These lesions can be transspacial.
- Rhabdomyosarcoma: On CT imaging, rhabdomyosarcoma typically appears as a soft-tissue mass with ill-defined margins. They may demonstrate heterogeneous attenuation with areas of necrosis and calcifications, and there can be infiltration into adjacent structures and regional lymph node enlargement. Rhabdomyosarcomas may enhance with contrast administration, but the degree of enhancement can vary depending on their vascularity. On T1-weighted images, the tumor usually appears as a heterogeneous mass with intermediate signal intensity. On T2-weighted images, rhabdomyosarcoma typically demonstrates hyperintense signal, reflecting its high water content and cellular density. The tumor may show enhancement on postcontrast MRI, particularly in the solid portions.
- Squamous cell carcinoma (SCC): On CT scans, SCC typically appears as an irregular, infiltrative soft-tissue mass at the base of the tongue. The tumor may have ill-defined margins and can show invasion into surrounding structures such as the hyoid bone, mandible, or adjacent muscles. CT imaging can also reveal regional lymph node enlargement as a sign of possible metastasis. SCC often enhances with contrast administration. On T1-weighted images, the tumor typically appears as a heterogeneously hypointense mass. On T2-weighted images, SCC generally displays hyperintense signal due to its high water content. The tumor may show irregular or rimlike enhancement on contrast-enhanced MRI.
- Treatment:
- The treatment of choice is surgery, which can be associated with chemotherapy and radiotherapy in cases of high histologic grade.
- The treatment of choice for MECs of minor salivary glands with low to intermediate grade is a radical surgery alone by wide local excision intraorally, if it can be achieved, with adequate tumor-free margins.
- High-grade tumors require more aggressive surgery with or without postoperative radiotherapy and chemotherapy.
- Relapse and distant metastasis are frequent, so strict control must be carried out.
