Histopathology

Mucoepidermoid carcinoma is characterized by squamoid (epidermoid), mucus producing and cells of intermediate type. The proportion of different cell types and their architectural configuration (including cyst formation) varies in and between tumours.

Fig. 5.5 Mucoepidermoid carcinoma. A Low-grade. B Intermediate grade.
Pas Stain Mucoepidermoid

Fig. 5.6 Mucoepidermoid carcinoma (MEC). A Parotid gland MEC, intermediate grade, showing epidermoid cell anaplasia and mucous cells. Mucicarmine stain. B High grade parotid gland MEC exhibiting solid growth pattern of predominately epidermoid cells. C High grade. PAS stain showing scattered positive mucous cells. D Clear cell variant.

Fig. 5.6 Mucoepidermoid carcinoma (MEC). A Parotid gland MEC, intermediate grade, showing epidermoid cell anaplasia and mucous cells. Mucicarmine stain. B High grade parotid gland MEC exhibiting solid growth pattern of predominately epidermoid cells. C High grade. PAS stain showing scattered positive mucous cells. D Clear cell variant.

They are usually multicystic with a solid component and sometimes the latter predominates. Some tumours have defined borders but infiltration of gland parenchyma is evident. Cystic spaces are lined by mucous cells with basaloid or cuboidal intermediate cells interspersed, and to a lesser degree, polygonal epidermoid cells, but keratinization is rare. Mucous cells are large, with pale cytoplasm and peripherally displaced nuclei. They typically constitute less than 10% of the tumour. Sialomucin content is demonstrated by mucicarmine or Alcian blue staining. Intermediate cells usually predominate. Clear, columnar and/or oncocytic cell populations may be present and occasionally are prominent {985, 1198,1996}. Clear cells demonstrate minimal sialomucin, but are diastase-sensitive periodic acid-Schiff positive, indicating glycogen content {666}. Focal sclerosis and/or mucus extravasation with inflammation is common. A scleros-ing variant has been described {2657}. Neural invasion, necrosis, increased mitoses or cellular anaplasia are uncommon. At the tumour edge, a lymphocytic infiltrate with possible germinal centre formation can mimic nodal invasion {83}.

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