Interest of diffusion-weighted and gadolinium-enhanced dynamic MR sequences for the diagnosis of parotid gland tumors

Abstract

Purpose: This study aimed to evaluate the value of diffusion-weighted imaging (DWI) and gadolinium-enhanced dynamic magnetic resonance imaging (MRI) for differentiating benign and malignant parotid gland tumors, and for characterizing the various histological types (pleomorphic adenoma, and Warthin's and malignant tumors).

Patients and methods: This retrospective study involved 60 patients with suspected parotid gland tumors (mean age: 59.4 years), and was carried out from April 2005 to February 2008. All had undergone pathological examination. All MRI examinations were performed using the Siemens Magnetom Avanto 1.5T MRI system. Non-enhanced T1-weighted (T1W), gadolinium-enhanced fat-suppressed T1W and T2-weighted (T2W) images were obtained for all 60 patients, with diffusion-weighted echoplanar imaging (DW-EPI) and apparent diffusion coefficient (ADC) evaluation in 59 patients, and gadolinium-enhanced dynamic MRI sequences in 51 patients. Interpretation was carried out by two experienced radiologists (the first evaluation used T1W, gadolinium-enhanced fat-suppressed T1W and T2W images; the second evaluation used T1W, T2W, DWI and dynamic MRI) and, for each case, the benign/malignant nature of the tumor and its histological type were determined.

Results: After the second reading, increases were noted in sensitivity, specificity, malignant positive predictive value (PPV) and negative predictive value (NPV), as well as in accuracy (90-100% for the first observer, and 90-97% for the second observer). Interobserver reliability also showed a significant increase from the first to the second reading (kappa=0.63 to 0.87, respectively).

Conclusion: Gadolinium-enhanced dynamic MRI and DW-EPI with ADC evaluation improved the performance of MRI in distinguishing between benign and malignant parotid gland tumors, and characterizing the different histological types of benign tumors (pleomorphic adenoma and Warthin's), thus leading to greater consensus in interpretation of the images.

Keywords: Apparent diffusion coefficient; Benign and malignant tumors; Gadolinium-enhanced dynamic MRI; MRI; Parotid gland; Time–signal intensity curves.