Parotid Gland Lesions: Multiparametric Ultrasound and MRI Features

High-resolution ultrasound (US), as a readily available, cost-effective and harmless imaging technique, is appropriately the initial imaging modality for salivary gland lesions. Benign tumors are reported to present with regular and well-defined margins, a homogeneous hypoechoic structure and demarcated vessel distribution, whereas malignant lesions are irregular, heterogeneous and diffusely perfused. Ultrasound and color Doppler features of benign and malignant salivary gland lesions overlap, and many benign tumors, particularly pleomorphic adenomas, may appear irregularly shaped, with a heterogeneous echo-structure indistinguishable from a malignant lesion. Often skilled US operators are not always able to differentiate benign from malignant lesions. The introduction of US contrast agents has allowed further perspectives in the possible improvement of lesion characterization, and the emergence of US elastography, an innovative tool for assessing lesion stiffness/elasticity characteristics, has been advocated for differentiating salivary gland lesions. When lesions are atypical on US, contrast-enhanced magnetic resonance (MR) imaging is usually the definitive imaging modality. We present a current review of benign and malignant parotid gland tumors with emphasis on the role of multiparametric US and MR imaging.