Mucoepidermoid carcinoma of salivary glands

Last revised by Frank Gaillard on 22 Jun 2023

Mucoepidermoid carcinoma is a tumor that usually occurs in the salivary glands. It can mimic most other tumors of the glands, and therefore is often considered in the differential. 

Mucoepidermoid carcinomas are seen throughout all adult age groups but are most common in middle age (35-65 years of age) 5. However, it is the most common malignant salivary gland tumor of childhood 4,5. Overall, mucoepidermoid carcinomas account for 1,5:

They are the most common malignant primary parotid gland tumor. A slight female predilection has been described, and radiation has been implicated as a risk factor 5.

Mucoepidermoid carcinomas most frequently arise in the parotid gland followed by the hard palate 7, and present as a painless swelling, with or without facial nerve involvement. These tumors can however be found anywhere there are salivary glands. Overall distribution across various glands is as follows 5:

  • major salivary glands: ~50%

    • parotid gland: ~40%

    • submandibular gland: ~7%

    • sublingual gland: ~3%

  • minor salivary glands: ~50%

As such, the presentation will depend on the anatomic location.

The tumors are composed of a mixture of:

  1. mucus-secreting cells (muco-)

  2. squamous cells (-epidermoid)

  3. lymphoid infiltrate often also present 3

Histology will often show clear mucin-containing cells, which stain reddish pink with the mucicarmine stain. Mucoepidermoid tumors are graded histologically into:

  • low grade (the most frequent) 7:

    • well-differentiated cells with little cellular atypia

    • high proportion of mucous cells

    • prominent cyst formation

  • intermediate grade: intermediate features

  • high grade

    • poorly differentiated with cellular pleomorphism

    • high proportion of squamous cells

    • solid with few if any cysts

Radiographic appearances largely depend on grade, making preoperative imaging important in planning and counseling. 

Typically a well-circumscribed hypoechoic lesion, with a partial or completely cystic appearance. The lesion stands out against the relatively hyperechoic normal parotid gland.

Low-grade tumors appear as well-circumscribed masses, usually with cystic components. The solid components enhance, and calcification is sometimes seen. They have appearances similar to pleomorphic adenomas

High-grade tumors, on the other hand, have poorly defined margins, infiltrate locally and appear solid.

Again, imaging is dependent on grade. 

Low-grade tumors have similar appearances to pleomorphic adenomas:

  • T1: low to intermediate signal; low signal cystic spaces

  • T2: intermediate to high signal; cystic areas will be high signal

  • T1 C+ (Gd): heterogeneous enhancement of solid components

High-grade tumors, on the other hand, have lower signal on T2 and poorly defined margins, and infrequent cystic areas:

  • T1: low to an intermediate signal

  • T2: intermediate to low signal

It is essential to image the cranial nerves with fat-saturated post-contrast T1 sequences to assess for perineural spread, and as such the base of the skull should be imaged up to and including the cavernous sinus and inner ear. 

Treatment is dependent on grade and location:

  • low grade (well-circumscribed) can usually be treated with wide local excision and preservation of the facial nerve, without the need for neck dissection or adjuvant radiotherapy

  • high grade (poorly-circumscribed) usually requires complete parotidectomy, often with the sacrifice of the facial nerve, neck dissection (as nodal metastases are common), and adjuvant radiotherapy

Prognosis is also very dependent on grade, with low-grade tumors having a 90-98% survival and a low local recurrence rate, compared to a 30-54% survival and a very high local recurrence rate for high-grade tumors 1,5.

Additionally, this tumor has a predilection for perineural spread, and careful and long-term follow-up is therefore required.

The differential is therefore different according to appearance.

For well-circumscribed lesions consider:

For infiltrative lesions consider:

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