Tumors: Most tumors of the salivary glands are benign. Skin cancers may metastasize to the salivary glands.
Most parotid gland tumors are benign while roughly half of minor salivary gland tumors are malignant. Following are the common benign tumors of the salivary glands:
i) Pleomorphic adenoma: It arises from intercalated stem cells of the parotid gland. Pleomorphic adenoma is the commonest parotid gland tumor and is seen more often in middle-aged women. Prior radiation exposure is a risk factor. It manifests as a slow growing, painless mass. On gross examination, it is pseudo-encapsulated, smooth, lobulated and greyish-blue, semi translucent on a cut surface. Microscopically, it shows a “pleomorphic” mixture of epithelial or ductal cells, myoepithelial cells and chondromyxoid stroma. Treatment is with local surgical resection. Local recurrence is common even after surgical resection.
ii) Warthin’s tumor: It is a benign tumor seen most commonly in the parotid gland in middle-aged to older men. It often presents as bilateral parotid tumors. It arises from lymphoid tissue and is often associated with TB and brucellosis. On gross examination the tumor is encapsulated, with cystic spaces filled with milky fluid and hemorrhagic areas . Microscopically it shows a characteristic double layer of epithelial cells resting on dense lymphoid stroma with germinal centers, cystic spaces, polypoid projections, rarely signet or goblet cells and areas of squamous metaplasia. No myoepithelial elements are seen.
Following primary malignant tumors are seen in the salivary glands:
i) Mucoepidermoid carcinoma: It is the most common malignant tumor of the salivary glands and mainly affects the parotid gland. Exposure to radiation carries high risk of developing mucoepidermoid tumors. The tumor arises from excretory stem cells. It is associated with t(11;19) resulting in the formation of the MECT1 gene that causes unregulated growth and inhibition of apoptosis. Microscopically, it shows a mixture of mucinous, squamous, intermediate and clear cells with local infiltration. Metastases to regional lymph nodes are seen.
ii) Adenoid cystic carcinoma or cylindroma: It is associated with NOTCH1 and 2 mutations. It arises from intercalated stem cells of the minor salivary glands. It characteristically infiltrates along nerve sheaths. Pulmonary metastases are seen. Microscopically tubular or cribriform patterns are seen with myoepithelial elements.
iii) Acinic cell carcinoma: It arises from intercalated stem cells of the parotid gland. Cells are arranged in acini or sheets and filled with basophilic cytoplasm.
iv) Polymorphous adenocarcinoma: It arises from intercalated ductal cells of the minor salivary glands. Microscopy is typical of any other adenocarcinoma with glandular structures.
v) Squamous cell or epidermoid carcinoma: It arises from excretory stem cells in the parotid and submandibular glands. Skin infiltration and keratin formation is seen. Metastases to regional lymph nodes in the neck area are seen.
vi) Non-Hodgkin lymphoma: Locally infiltrating lymphocytes can progress to NHL. Some cases of Sjogren’s syndrome may develop NHL.
Infections of the salivary glands: Mumps virus causes epidemic parotitis of parotid glands. Other viruses like HIV, Hep C and Coxsackie viruses also cause parotitis. Bacterial parotitis with S.aureus or Streptococci is seen in DM, immunodeficiencies, post-surgery etc. It presents with local swelling, pain and fever.
Acute sialadenitis or inflammation of the salivary glandular ducts is precipitated commonly by stones or sialolithiasis. Imaging can be done in recurrent cases or if an abscess develops, by sialography, ultrasound, CT, MRI or PET scan.
Chronic inflammation in the salivary glands is seen in chronic sialolithiasis, strictures, autoimmune disorders, TB or fungal infections, sarcoidosis and syphilis and can be visualized by contrast-enhanced CT or MRI.
