Value of Apparent Diffusion Coefficient Calculation in the Differential Diagnosis of Parotid Gland Tumors

Background: The differential diagnosis of parotid gland tumors is often difficult with conventional magnetic resonance imaging. Purpose: To determine whether the calculation of the apparent diffusion coefficient (ADC) is valuable for making the differential diagnosis of parotid tumors. Material and Methods: Thirty parotid masses in 28 patients and 24 healthy parotid glands in 12 controls were examined in this prospective study. Diffusion-weighted magnetic resonance imaging with echo-planar spin-echo sequences was used to evaluate each subject. The ADC of each tumor and each healthy parotid gland was calculated. Tumor diagnoses were confirmed by the results of histopathologic analysis. Results: The following types of masses were identified: 11 Warthin tumors, nine pleomorphic adenomas, seven malignant tumors, one basal cell adenoma, and two benign cysts. The mean ADC value for the Warthin tumors was 0.97±0.16×10−3 mm2 s, for the pleomorphic adenomas was 1.74±0.37×10−3 mm2 s, for the malignant tumors was 1.04±0.35×10−3 mm2 s, and for the normal parotid glands was 0.34±0.20×10−3 mm2 s. The respective ADC value for the single basal cell adenoma was 1.40×10−3 mm2 s. Statistically significant differences were identified between the subjects with pleomorphic adenoma and those with another type of parotid tumor, and between subjects with healthy parotid glands and those with a tumor. Conclusion: Calculating the ADC appears to be useful in differentiating pleomorphic adenomas from other types of parotid gland tumors.