Mucoepidermoid Carcinoma

Question 1

Prevelance

Answer 1

-Most common malignant salivary gland tumor
-2nd most common salivary gland tumor
- Most common salivary gland tumor of childhood (11-15 y/o mean is 13)

Question 2

Sites

Answer 2

-Common in the parotid
-2nd most common in the palate usually for patients under 40 y/o

Major: parotid>submandibular>sublingual

Minor: palate>BM>Retromolar region

Question 3

Epidemiology

Answer 3

Wide age range 15-86 years (mean 49)
Slight female predilection

Question 4

Etiology

Answer 4

Ionizing radiation or prior exposure to radiotion in the H&N area is a risk factor

Question 5

Clinical features

Answer 5

Painless swelling with pressure and discomfort.

Presents as a fixed, rubbery/soft mass without facial nerve involvement

In minor glands it typically presents as a bluish flu tint swelling that could be mistaken for a mucocele

Question 6

Pathology

Answer 6

Tumors consist of a mixture of:

1. Mucus secreting cells (muco)
2. Squamous cells (epidermoid)
3. Lymphoid infiltrate

Low-grade tumors present as a slow-growing painless mass. They are well-circumscribed with solid and cystic areas filled with mucin.
The tumors contain four cell types:
1. Mucin-producing
2. Squamous
3. Intermediate
4. Clear
Mucin-producing cells are the predominant cell type in low-grade MEC.

High-grade mucoepidermoid carcinomas present as rapidly growing mass which may be painful. They are solid tumors with no cyst formation. They are mostly solid with an infiltrative growth pattern.
In high-grade lesions: Squamous cells, Intermediate cells and Clear cells are the dominant cell population. Mucinous cells are scanty.

Question 7

Histology

Answer 7

Clear mucin containing cells which stain reddish pink with the mucicarmine stain

Three types of grades

Question 8

Investigations

Answer 8

(i) Radiographs

1. Ultrasound
   Typically a well-circumscribed hypoechoic lesion, with a partial or completely cystic appearance. The lesion stands out against the relatively hyperechoic normal parotid gland.
2. CT
   Low-grade tumours 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 tumours, on the other hand, have poorly defined margins, infiltrate locally and appear solid.

3. MRI
   Imaging is dependent on grade.

Low-grade tumours 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 tumours, 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.

(ii) Biopsy
Fine Needle Aspiration. If two FNA are inconclusive then take an incisional biopsy

Question 9

Treatment and prognosis

Answer 9

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 tumours 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 tumours 1,5.

Favorable prognostic indicators include younger age, female sex, and parotid location. Adverse prognostic indicators include submandibular location, extraglandular extension, necrosis, vascular invasion, and high mitotic rate.

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

Question 10

Differential diagnosis

Answer 10

The differential is therefore different according to appearance.

For well-circumscribed lesions consider:

1. Pleomorphic adenoma: can be indistinguishable
2. Warthin tumour
3. Adenoid cystic carcinoma

For infiltrative lesions consider:

1. Adenoid cystic carcinoma
2. Lymphoma (NHL)

Metastasis (especially squamous cell carcinoma metastases to intraparotid nodes)