Role of electron microscopy in diagnosis of parotid tumours Il ruolo della microscopia elettronica nella diagnosi dei tumori parotidei

The classification of salivary gland tumours is extremely complex, due to the morphologic heterogeneity of their anatomic structure and the occurrence of metaplastic changes. The normal parotid gland is composed of several different cell types: acinar cells, myoepithelial cells, intercalated duct cells, striated duct cells. These cells can be distinguished on the basis of their structure and certain cytoplasmic and cell membrane features that can be detected only by electron microscopy (EM). Most of the parotid malignancies originate from, or differentiate toward, these cell lines. Moreover, several histotypes are composed of two or more tumour cell lines showing different features that are present in varying amounts within the same neoplasm. The fact that some of these cells may undergo oncocytic, sebaceous, squamous and chondroid metaplasm results in an even more complex classification and can easily lead to misdiagnosis. The main parotid cell types can be distinguished on the basis of the following ultrastructural features: