Salivary Gland Tumors

Different types of tumor may occur in the salivary gland and may be benign or malignant. A brief discription of the common tumors occuring in the salivary gland is given here:

1. Pleomorphic Adenoma
The pleomorphic adenoma- mixed salivary gland tumor- is a benign tumor, and the commonest salivary gland tumor. It is most commonly seen in the parotid gland and typically forms a mass in the lateral lobe, which slowly enlarges over many years, women in their forties are most often being affected.

Clinical Features
On palpation the tumor is firm, non tender and smooth or lobulated in texture. initially spherical and encapsulated, it may eventually spread more deeply, with the result that recurrence after resection is common. On oral examination the deep part of the gland may have pushed the tonsil and pillar of the fauces towards the midline.

Histology:

Histologically, it is highly variable in appearance, even within individual tumors. Classically it is biphasic and is characterized by an admixture of polygonal epithelial and spindle-shaped myoepithelial elements in a variable background stroma that may be mucoid, myxoid, cartilaginous or hyaline. Epithelial elements may be arranged in duct-like structures, sheets, clumps and/or interlacing strands and consist of polygonal, spindle or stellate-shaped cells (hence pleiomorphism). Areas of squamous metaplasia and epithelial pearls may be present. The tumor is not enveloped, but it is surrounded by a fibrous pseudocapsule of varying thickness. The tumor extends through normal glandular parenchyma in the form of finger-like pseudopodia, but this is not a sign of malignant transformation.

Pleomorphic adenoma consists of mixed epithelial (left) and mesenchymal cell components (right). The latter often exhibits myxofibrous appearance and in some instances shows chondromatous differentiation.
2. Adenolymphoma (Warthin’s Tumor)
It is a bening tumor and the second most common salivary tumor and is found exclusively in the parotid gland. It usually affects males in their fifties, forming a slow growing, painless swelling over the angle of the jaw, there is a high incidence of bilateral disease.

Clinical features
The tumor is smooth, soft and often fluctuant, its superficial nature and slight mobility sometimes giving the appearance that it is separate from the gland.

Histology: 

The appearance of this tumor under the microscope is unique. There are cystic spaces surrounded by two uniform rows of epithelial cells with centrally placed pyknotic nuclei. The cystic spaces have epithelium referred to as papillary infoldings that protrude into them. Additionally, the epithelium has lymphoid stroma with germinal center formation.

3. Less Common Benign Tumors
The other less common benign tumors occurring in the salivary glands include

• Monomorphic Adenoma and
• Oncocytoma.

4. Malignant Tumors
Adenocystic Carcinoma is the commonest malignant salivary tumor and occurs in the sub mandibular, sub lingual and minor glands. In contrast Mucoepidermoid carcinoma predominantlyoccurs in the parotid. other malignant tumor types are adenocarcinoma, squamous carcinoma and malignant mixed tumors.

Clinical Features
Typically malignant tumors produce indistinct, rapidly growing masses and malignant cervical lymphadenopathy. For the sub mandibular gland, numbness of the anterior two-thirds of the tongue from lingual nerve infiltration is diagnostic, whereas sublingual tumors may cause deviation of the tongue from invasion and fixation.

Malignant parotid tumors tend to occur in older age groups and most take the form of solitary hard nodules with deep fixation. there may be local pain exacerbated by opening the mouth.

Squamous cell carcinoma should be considered metastatic, until proven otherwisw, and a primary tumor sought.