Warthin tumor of the parotid gland: Diagnostic value of MR imaging with histopathologic correlation

BACKGROUND AND PURPOSE: The purpose of our study was to describe the MR imaging appearance of Warthin tumors multiple MR imaging techniques and to interpret the difference in appearance from that of malignant parotid tumors. METHODS: T1-weighted, T2-weighted, short inversion time inversion recovery, diffusion-weighted, and contrast-enhanced dynamic MR images of 19 Warthin tumors and 17 malignant parotid tumors were reviewed. MR imaging results were compared with those of pathologic analysis. RESULTS: Epithelial stromata and lymphoid tissue with slitlike small cysts in Warthin tumors showed early enhancement and a high washout rate (≥30%) on dynamic contrast-enhanced images, and accumulations of complicated cysts showed early enhancement and a low washout ratio (<30%). The areas containing complicated cysts showed high signal intensity on T1-weighted images, whereas some foci in those areas showed low signal intensity on short tau inversion recovery images. The mean minimum signal intensity ratios (SIR_min) of Warthin tumor on short tau inversion recovery (0.29 ± 0.22 SD) (P < .01) and T2-weighted images (0.28 ± 0.09) (P < .05) were significantly lower than those of malignant parotid tumors (0.53 ± 0.19, 0.48 ± 0.19). The average washout ratio of Warthin tumors (44.0 ± 20.4%) was higher than that of malignant parotid tumors (11.9 ± 11.6%). The mean apparent diffusion coefficient of Warthin tumors (0.96 ± 0.13 × 10^-3mm²/s) was signficantly lower (P < .01) than that of malignant tumors (1.19 ± 0.19 × 10^-3mm²/s). CONCLUSION: Detecting hypointense areas of short tau inversion recovery and T2-weighted images or low apparent diffusion coefficient values on diffusion-weighted images was useful for predicting whether salivary gland tumors were Warthin tumors. The findings of the dynamic contrast-enhanced study also were useful.