US of the Major Salivary Glands: Anatomy and Spatial Relationships, Pathologic Conditions, and Pitfalls

Ultrasonography (US) is useful for differential diagnosis of diseases of the salivary glands. In acute inflammation, salivary glands are enlarged and hypoechoic with increased blood flow; they may contain multiple small, oval, hypoechoic areas. In chronic inflammation, salivary glands are normal sized or smaller, hypoechoic, and inhomogeneous. Sialolithiasis appears as markedly hyperechoic lines or points with distal acoustic shadowing. Sialosis appears as enlarged hyperechoic glands without focal lesions or increased blood flow. The US features of advanced Sjögren syndrome include inhomogeneous salivary glands with scattered small, oval, hypoechoic or anechoic areas, usually well defined, and increased parenchymal blood flow. Pleomorphic adenomas are usually hypoechoic, well-defined, lobulated lesions with posterior acoustic enhancement that may contain calcifications; Warthin tumors are usually oval, hypoechoic, well-defined lesions that often contain anechoic areas and are often hypervascularized. Malignant neoplasms of the salivary glands may have irregular shapes, irregular borders, blurred margins, and a hypoechoic inhomogeneous structure or may have a benign appearance. Salivary gland cysts have well-defined margins, anechoic contents, posterior acoustic enhancement, and no internal blood flow. However, US appearances of some diseases may overlap, thus producing diagnostic pitfalls.