Mucoepidermoid carcinoma

  Mucoepidermoid carcinoma 

  Definition
  
  The mucoepidermoid carcinoma is one of  the most common salivary gland malignancies.  

  Histogenesis 
  
  It origenates  from  excretory duct epithelium. 

  Clinical features 

  Occurs most commonly in the parotid gland. 
  The palate is the most common intraoral site. 
  Low grade neoplasms appear as benign tumors. 
  High grade neoplasms appears as:  
-     Painful, rapidly growing mass. 
-    The tumor  is fixed  to underlying tissues (when tumor cells infiltrate the surrounding structures). 
- Facial nerve paralysis (if the neoplasm affects the parotid). 
- Ulceration. 
  Neoplasms of minor salivary glands appears as:  
-  Swelling or ulcerated mass. 
-  Swelling may be fluctuant and have a blue color (resemble mucocele). 
-  It is painless in early stages. 
-  May affects the palate, buccal mucosa, tongue or lip. 

  Histopathologic features 

  Mucoepidermoid carcinoma is composed of a mixture of : 
-  Mucous – producing cells. 
-  Squamous ( epidermoid ) cells.  
-  Intermediate cell , which is believed to be a progenitor of both the mucous and the epidermoid cells. 
  The mucous – secreting cells are , 
-  cubical or  columnar with foamy cytoplasm. 
-  They tend to line the cystic spaces , or  arranged in solid  sheets .  
  The epidermoid cells  , 
-  Form solid sheets or line the cystic spaces.  
-  These cells are of squamous epithelial type having a polygonal shape . 
  Intermediate cells are smaller than either mucous or epidermoid cells . They appear as small basaloid cells. 

   Low-grade tumors show: 

-  High proportion of mucous cells, prominent cyst formation, minimal cellular atypia. 

  High-grade tumors show:  

-  High proportion of solid sheets of squamous and intermediate cells.  
-  cells demonstrate considerable pleomorphism, and mitotic activity. 
-  few cystic spaces. 

  Intermediate-grade tumors show: 
-  Features between those of the low-grade and high-grade neoplasms. 
  
  NB

  Intraosseous mucoepidermoid carcinomas (central mucoepidermoid carcinomas) may develop as a result of: Neoplastic transformation of the lining of a dentigerous cyst (odontogenic 
epithelium).