Differentiating parotid tumors by quantitative signal intensity evaluation on MR imaging

There have been no reports about quantitative evaluations of enhancing components of parotid tumors on conventional MR imaging.

To evaluate the signal intensity of the enhancing components of tumors, including pleomorphic adenomas (PAs), Warthin tumors (WTs) and malignant tumors (MTs), on various MR sequences and to assess the usefulness of quantitative evaluations for differentiation among the three groups of tumors.

A total of 39 histologically proven tumors, including 15 PAs, 17 WTs and 7 MTs, were enrolled in this study. The tumor-to-spinal cord contrast ratio (TSc-CR) was calculated by dividing the signal intensity of the lesion by that of the spinal cord on MR sequences, including T1-weighted imaging (T1WI), T2-weighted imaging (T2WI) and postcontrast gadolinium-enhanced T1WI (CE-T1WI). The mean apparent diffusion coefficient (ADC) value was selected in each tumor. Furthermore, the differences in the TSc-CRs and the ADC values among the three groups of tumors were statistically evaluated. Cutoff values were determined for the prediction of tumor histology.

The TSc-CRs of PAs were significantly higher than those of WTs and MTs on T2WI and CE-T1WI. The sensitivities and specificities were 100% and 87.5%, respectively, at a cutoff value of 1.31 for the TSc-CR of T2WI; and 83.3% and 100%, respectively, at a cutoff value of 2.00 for the TSc-CR of CE-T1WI. For the ADC values, sensitivity and specificity for discriminating PAs from WTs or MTs were both 100% when the cutoff value of the ADC was set at 1.40×10^-3mm²/s.

ADC maps and the quantitative evaluations using the TSc-CRs on T2WI and CE-T1WI were useful for discriminating WTs or MTs from PAs. However, discrimination between WTs and MTs was difficult using any MR sequence.