Usefulness of diffusion-weighted MR imaging for differentiating between Warthin's tumor and oncocytoma of the parotid gland.

PURPOSE: To assess the efficacy of diffusion-weighted (DW) MR imaging for differentiating between Warthin's tumor and oncocytoma of the parotid gland. METHODS: Forty-five histopathologically confirmed parotid gland tumors (41 Warthin's tumors and 4 oncocytomas) were examined by MR imaging including DW imaging. (18)F-fluorodeoxyglucose PET/CT was also performed in 9 Warthin's tumors and 3 oncocytomas. We retrospectively reviewed the images and compared the MR signal intensities, apparent diffusion coefficients (ADCs), and maximum standardized uptake values (SUVmax) of the solid components between the two pathologies. RESULTS: The signal intensity ratios (SIRs) on both T2-weighted images (0.92 +/- 0.18 vs 0.65 +/- 0.13, p < 0.01) and DW images (1.24 +/- 0.42 vs 0.43 +/- 0.16, p < 0.001) were higher in Warthin's tumors than in oncocytomas. ADCs (0.79 +/- 0.11 vs 1.06 +/- 0.06 x 10(-3) mm(2)/s, p < 0.001) were lower in Warthin's tumors than in oncocytomas. No significant differences in the SIRs on T1-weighted images (1.09 +/- 0.12 vs. 0.99 +/- 0.07, p = 0.051) and SUVmax (8.22 +/- 3.86 vs. 8.11 +/- 1.33, p = 0.864) were found between Warthin's tumor and oncocytoma. CONCLUSION: DW imaging with ADC measurements is useful for the differentiation of Warthin's tumor from oncocytoma of the parotid gland.