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

Abstract

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 (> or =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 (SIRmin) 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 x 10(-3)mm2/s) was significantly lower (P < .01) than that of malignant tumors (1.19 +/- 0.19 x 10(-3)mm2/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.

Fig 1.

Images of a Warthin tumor in the left parotid gland of a 70-year-old man. A, STIR image (4000/30), obtained in the axial plane, shows the tumor with moderate-to-high signal intensity. The high-signal-intensity area is a cystic lesion (*); the area showed no enhancement on contrast-enhanced images (see panel C, region of interest 2). B, T1-weighted image (400/9), obtained in the axial plane, shows a hypointense tumor. C, Fat suppression contrast-enhanced T1-weighted image (300/20), obtained in the coronal plane, shows solid (region of interest 1) and cystic (region of interest 2) tumor in the inferior pole of the parotid gland. D, Signal intensity graph shows that the washout ratio of the solid component was 41%. The cystic region shows no enhancement (type E). The ADC values of the solid and cystic components were 0.96 × 10⁻³ mm²/s and 2.74 × 10⁻³ mm²/s, respectively. The ADC value of the spinal cord was 1.02 × 10⁻³ mm²/s. E, Axial section of the specimen shows solid and large cystic components (*). The large cyst lost its contents. F, Solid component has slitlike or dendriform spaces (*) lined with papillary proliferation of bilayered oncocytic epithelia, with supporting stroma composed largely of lymphoid tissue (**). The small slitlike cysts are filled with proteinous secretion.

Fig 2.

Images of a Warthin tumor in the left parotid gland of a 61-year-old man. A, STIR image (4000/30), obtained in the axial plane, shows the tumor to be iso- to hypointense to the parotid gland. Characteristically small low-signal-intensity foci (arrows) can be detected. The margin of the tumor also has hypointense foci. B, T1-weighted image (400/9), obtained in the axial plane, shows the tumor to have the isointensity of muscle and relatively high-signal-intensity areas, whereas the STIR image shows low-signal-intensity areas (arrows). The margin of the tumor also is hypointense on T1-weighted images. C, Axial dynamic contrast-enhanced image shows all areas of this tumor to have type B perfusion curves. D, Signal intensity graph shows that foci that showed hypointensity on the STIR image and relatively high signal intensity on the T1-weighted image (region of interest 1) had a low washout ratio (3%) and the other region (region of interest 2) had a high washout ratio (54%). E, Axial section of the specimen shows cysts containing proteinous fluid with inflammatory cells (*).