Advanced magnetic resonance imaging findings in salivary gland tumors

Abstract

Salivary gland tumors (SGTs) make up a small portion (approximately 5%) of all head and neck tumors. Most of them are located in the parotid glands, while they are less frequently located in the submandibular glands, minor salivary glands or sublingual gland. The incidence of malignant or benign tumors (BTs) in the salivary glands varies according to the salivary gland from which they originate. While most of those detected in the parotid gland tend to be benign, the incidence of malignancy increases in other glands. The use of magnetic resonance imaging (MRI) in the diagnosis of SGTs is increasing every day. While conventional sequences provide sufficient data on the presence, localization, extent and number of the tumor, they are insufficient for tumor specification. With the widespread use of advanced techniques such as diffusion-weighted imaging, semi-quantitative and quantitative perfusion MRI, studies and data have been published on the differentiation of malignant or BTs and the specificity of their subtypes. With diffusion MRI, differentiation can be made by utilizing the cellularity and microstructural properties of tumors. For example, SGTs such as high cellular Warthin’s tumor (WT) or lymphoma on diffusion MRI have been reported to have significantly lower apparent diffusion values than other tumors. Contrast agent uptake and wash-out levels of tumors can be detected with semi-quantitative perfusion MRI. For example, it is reported that almost all of the pleomorphic adenomas show an increasing enhancement time intensity curve and do not wash-out. On quantitative perfusion MRI studies using perfusion parameters such as Ktrans, Kep, and Ve, it is reported that WTs can show higher Kep and lower Ve values than other tumors. In this study, the contribution of advanced MRI to the diagnosis and differential diagnosis of SGTs will be reviewed.

Keywords: Salivary gland tumors; Magnetic resonance imaging; Diffusion-weighted imaging; Dynamic contrast-enhanced imaging; Perfusion-weighted magnetic resonance imaging

Core Tip: Conventional magnetic resonance imaging (MRI) provides more data than other radiological modalities in determining the extent of tumor extension and evaluating its relationship with vascular and neural structures in salivary gland tumors (SGTs). Advanced MRI techniques, which have been increasingly used in the radiological evaluation of SGTs in recent years, contribute to obtaining more information about the nature of the lesion compared to conventional sequences. Different features such as cellularity, microstructural features and vascularity of tumors can be evaluated by diffusion MRI or perfusion MRI techniques, and they can contribute to the differentiation of benign or malignant tumors.