PET/CT of Salivary Gland Tumors

Abstract

Salivary glands are exocrine glands that produce and secrete saliva. They include three paired major glands (parotid gland, submandibular gland, and sublingual gland) and minor salivary glands that widely exist in the entire respiratory and digestive tract. Many minor salivary gland tumors are located on the hard palate. The global annual incidence of salivary gland tumors is 0.4/100,000–13.5/100,000, and that of malignant tumors is 0.4/100,000–2.6/100,000, accounting for 0.7%–1.6% of all malignant tumors and 2.3%–10.4% of head and neck malignant tumors. Most of the salivary gland tumors are benign, but about 20% of parotid gland tumors are malignant; the incidence of submandibular gland and minor salivary gland malignant tumors is about 50% and 80%, respectively. Nearly 80% of salivary gland tumors occur in the parotid gland, most commonly in the superficial lobe, less than 1% in the sublingual gland, and 9%–23% in the minor salivary glands. The proportion of malignant tumors is different in different parts: 20%–30%, 45%–60%, and 70%–85% in the parotid gland, submandibular gland, and sublingual gland, respectively; 80%–90% of salivary gland tumors in the tongue, floor of the mouth, and retromolar area are malignant. Salivary gland tumors are slightly more common in women, with the peak age of onset ranging from 50 to 70 years, but the peak age of pleomorphic adenoma, mucoepidermoid carcinoma, and acinus cell carcinoma is 20–40 years. Among all salivary gland tumors, pleomorphic adenoma is the most common, accounting for about 50%, usually occurring in young adults aged 30–50 years without significant gender difference. The second most common is Warthin tumor (adenolymphoma), which is common in men over 50 years old; it is usually multiplex or bilateral, mostly located in the inferior superficial lobe of the parotid gland; almost all of Warthin tumors come from the parotid gland or peripheral lymph nodes. Others such as hemangioma, lymphangioma, and lipoma are rare. The most common malignant tumor is mucoepidermoid carcinoma.