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Mucoepidermoid carcinoma (MEC) is a malignant epithelial tumor of the salivary glands composed of mucous, epidermoid (squamous), and intermediate cells, often forming cystic and solid areas. It displays a wide histological and clinical spectrum, ranging from low-grade indolent tumors to high-grade aggressive malignancies.

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Epidemiology

Most common malignant salivary gland tumor (~30–35% of all salivary gland malignancies)
Most frequently involves the parotid gland
Also occurs in:
- Minor salivary glands (e.g., palate)
- Submandibular glands
All age groups affected, including children (most common salivary malignancy in pediatrics)

Etiopathogenesis

Arises from ductal epithelial cells
Genetic association: t(11;19)(q21;p13) translocation → CRTC1-MAML2 fusion (seen in low/intermediate-grade tumors)
Graded into:
- Low-grade: well-circumscribed, cystic, mucinous
- Intermediate-grade
- High-grade: solid, infiltrative, cellular atypia, necrosis

Clinical Features

Low-grade MEC	High-grade MEC
Painless, slow-growing mass	Rapidly enlarging, painful mass
Often well-circumscribed	Poorly defined, invasive
Rare facial nerve involvement	Facial nerve palsy common
Often asymptomatic	Skin fixation, ulceration possible

Radiology

Modality	Imaging features
US	• Solid or cystic-solid mass
• Ill-defined or lobulated margins in high-grade
• Internal vascularity on Doppler
CT	• Variable appearance based on tumor grade:

◦ **Low-grade**: well-defined, cystic or mixed
◦ **High-grade**: solid, ill-defined, invasive

• Contrast-enhancing solid components • May show: Calcifications, necrosis and bony invasion in advanced cases | | MR | Low-grade: • T1: Hypo- to isointense • T2: Hyperintense cystic areas • Post-contrast: Mild to moderate enhancement High-grade: • T1: Iso- to hypointense • T2: Low to intermediate signal (due to cellularity) • Heterogeneous enhancement, necrotic areas • Perineural spread: Nerve thickening, enhancement, foraminal widening |

![A 47-year-old woman with low-grade mucoepidermoid carcinoma of the left parotid gland. (a) T2-weighted image shows an ill-defined, heterogeneously hyper- to isointense lesion (arrow). (b) T1-weighted image shows an ill-defined, hypointense lesion (arrow)

Kato, H. (2020). Diagnostic Imaging of Salivary Gland Tumors. In: Ojiri, H. (eds) Diagnostic Imaging in Head and Neck Cancer. Springer, Singapore. https://doi.org/10.1007/978-981-15-3188-0_8](attachment:d5929780-1288-4f98-875f-56f4c7636955:f85f98da-4b16-4e40-b330-043aea55b8e1.png)

A 47-year-old woman with low-grade mucoepidermoid carcinoma of the left parotid gland. (a) T2-weighted image shows an ill-defined, heterogeneously hyper- to isointense lesion (arrow). (b) T1-weighted image shows an ill-defined, hypointense lesion (arrow)

Kato, H. (2020). Diagnostic Imaging of Salivary Gland Tumors. In: Ojiri, H. (eds) Diagnostic Imaging in Head and Neck Cancer. Springer, Singapore. https://doi.org/10.1007/978-981-15-3188-0_8

![A 79-year-old man with high-grade mucoepidermoid carcinoma of the right parotid gland. (a) T2-weighted image shows an illdefined, heterogeneously hypo- to isointense lesion (arrow) with invasion of the masseter muscle (arrow head). (b) Fat-suppressed gadolinium-enhanced T1-weighted image shows an infiltrative lesion (arrow) with extensive invasion of surrounding tissues

A 79-year-old man with high-grade mucoepidermoid carcinoma of the right parotid gland. (a) T2-weighted image shows an illdefined, heterogeneously hypo- to isointense lesion (arrow) with invasion of the masseter muscle (arrow head). (b) Fat-suppressed gadolinium-enhanced T1-weighted image shows an infiltrative lesion (arrow) with extensive invasion of surrounding tissues

Kato, H. (2020). Diagnostic Imaging of Salivary Gland Tumors. In: Ojiri, H. (eds) Diagnostic Imaging in Head and Neck Cancer. Springer, Singapore. https://doi.org/10.1007/978-981-15-3188-0_8