Differentiation of various salivary gland tumours using diffusion-weighted MRI and dynamic contrast-enhanced MRI

Purpose
To determine the role of functional magnetic resonance imaging techniques (diffusion-weighted magnetic resonance imaging [DW-MRI] and dynamic contrast-enhanced magnetic resonance imaging [DCE-MRI]) in the differentiation of various salivary gland tumours.

Material and methods
In this prospective study, we evaluated 32 patients with salivary gland tumours using functional MRI. Diffusion parameters (mean apparent diffusion coefficient [ADC], normalized ADC and homogeneity index [HI]), semiquantitative DCE parameters (time signal intensity curves [TICs]) and quantitative DCE parameters (Kep, Ktrans and Ve) were analysed. Diagnostic efficiencies of all these parameters were determined to differentiate benign and malignant tumours as well as to characterize 3 major subgroups of salivary gland tumours, namely pleomorphic adenoma, Warthin tumour, and malignant tumours.

Results
Mean ADC, normalized ADC and HI were insignificant in differentiating benign and malignant tumours but were significant in differentiating pleomorphic adenomas, Warthin tumours, and malignant tumours. Mean ADC was the best parameter in predicting both pleomorphic adenomas and Warthin tumours (AUC: 0.95 and 0.89, respectively). Amongst DCE parameters, only TIC pattern could differentiate between benign and malignant tumours, with an accuracy of 93.75% (AUC: 0.94). The quantitative perfusion parameters aided greatly in characterizing pleomorphic adenomas, Warthin tumours and malignant tumours. For predicting pleomorphic adenomas, the accuracy of Kep and Ktrans was 96.77% (AUC: 0.98) and 93.55% (AUC: 0.95), respectively and for predicting Warthin tumours, the accuracy of both Kep and Ktrans was 96.77% (AUC: 0.97).

Conclusions
DCE parameters (particularly TIC, Kep and Ktrans) had higher accuracy in characterizing various tumour subgroups (pleomorphic adenomas, Warthin tumours, and malignant tumours) than DWI parameters. Hence, dynamic contrast-enhanced imaging adds immense value with only a minimum time penalty to the examination.