The Parotid Gland Tumors: Evaluation With Diffusion-weighted MR Imaging

Purpose: The purposes of this study were to determine if there were differentinfluences of solid and cystic constituents within parotid gland tumors on mean apparentdiffusion coefficient (ADC) values，to evaluate the diagnostic value of diffusion-weightedMR imaging (DW-MRI) in differentiating benign tumors from malignant tumors of theparotid gland and then verify the consequences concluded from the previous study.Materials and methods:32subjects who suffered from the solid-cystic parotidgland tumors (22benign tumors and10malignant tumors) and162subjects who sufferedfrom parotid gland tumors (108benign tumors and54malignant tumors) were performedwith conventional MR imaging and diffusion-weighted echo-planar MR imaging prior tosurgery and pathologic verification. Mean ADC value was obtained with both b factors of0,500and0,1000s/mm2, and was separately measured in entirety, solid and cystic ROI（region of interest）samples in each parotid gland tumor from the32subjects. The meanADC values of the parotid gland tumors from the162subjects were obtained from thesolid portion of each parotid gland tumor. Statistical methods were used to determine thedifferences among the mean ADC values from different ROI methods and various kinds ofparotid gland tumors.Then we collected69cases with preoperative parotid gland tumors performed withconventional MR imaging and DW（Ib=0，1000s/mm2）. According to the cut-off obtained from previous retrospective research，the radiological diagnosis was given first，and thencompared the pathological results to evaluate the reliability.Results:①The mean ADC values were significantly different (p<0.01) among theentirety (1.73[b=0,500s/mm2] and1.35[b=0,1000s/mm2]×10-3mm2/s), solid portion(1.35[b=0,500s/mm2] and1.12[b=0,1000s/mm2]×10-3mm2/s), cystic region (2.44[b=0,500s/mm2] and1.94[b=0,1000s/mm2]×10-3mm2/s) of these32parotid tumors. Inaddition, there were statistically different (p<0.01) in the mean ADC values of solidportions among pleomorphic adenoma (10cases), Warthin tumor (6cases)，other benigntumor（6cases），and malignant tumor（10cases）.②In the162lesions，the mean ADC values were significantly different (P<0.01)among parotid pleomorphic tumors (n=47,1.46±0.29×10-3mm2/s), Warthin tumors (n=47,0.86±0.14×10-3mm2/s) and other benign epithelial tumors (n=14,1.15±0.36×10-3mm2/s).Also, the mean ADC values were significantly different (P<0.01) between malignantepithelial tumors (n=37,0.96±0.21×10-3mm2/s) and other malignant tumors (n=17,12lymphomas and5sarcomas,0.71±0.13×10-3mm2/s).There were significant differences ofmean ADC values between parotid benign tumors (1.15±0.36×10-3mm2/s) and malignanttumors (0.88±0.22×10-3mm2/s). A cut-off ADC value at1.125×10-3mm2/s yielded asensitivity of88.9%, specificity of50.0%, accuracy of63.0%, for distinguishing benignand malignant tumors.③In the69tumors，distinguishing the malignant tumors from the benign ones byusing the cut-off ADC value at1.125×10-3mm2/s solely，could obtain a sensitivity of82.6%, specificity of65.2%, accuracy of71%. Combining conventional MR imaging withADC values could obtain a sensitivity of73%, specificity of87%, accuracy of81%, fordistinguishing benign and malignant lesions.Conclusion:①The different ROI samples (entirety, solid, and cystic portions) in the parotid gland tumors can result in different mean ADC values. It is believed that themean ADC values with b value of0,1000s/mm2obtained from the solid portions ofparotid gland tumors may provide more valuable information for diagnosis.②DWI is able to provide valuable information for the differentiation between parotidgland benign and malignant tumors.③Combining conventional MR imaging withADC values could improve theaccuracy for distinguishing benign and malignant lesions.