A Study On The Applicational Value Of Magnetic Resonance Imaging In Parotid Gland Tumor

Objective:To investigate the applicational value of magnetic resonance imaging in the diagnosis and differential diagnosis of parotid gland tumors.Methods:A retrospective analysis of 63 cases of parotid tumor confirmed by surgery and pathology in our hospital from October of 2017 to November of 2018,all cases were performed on routine MRI,DWI,and DCE-MRI.1.General data and conventional MRI signs of benign and malignant parotid tumors were analyzed.2.The ADCmean values,peripheral gland ADC values,ratio of tumor ADC values and peripheral gland ADC values,and ADCmin values of different pathological types of parotid gland tumors were analyzed,and compare each other in pairs,the area under the ROC curve was calculated and the diagnostic efficiency of ADCmean values,peripheral gland ADC values,ratio of tumor ADC values and peripheral gland ADC values,and ADCmin values in the parotid tumor were analyzed.The optimal diagnostic threshold is determined based on Youden’s index,and sensitivity,specificity,positive predictive value,negative predictive value,and accuracy are calculated.3.The time of peak enhancement（Tpeak）and washout ratio（WR）were analyzed to observe the characteristics of the time-intensity curve（TIC）of the parotid tumor.TIC patterns were categorized as follows:type A,was considered to have gradual enhancement;type B,was considered to have early enhancement and high washout;type C,was considered to have early enhancement and low washout;type D,with the TIC flat,was considered to be non-enhanced.Results:1.Among 63 patients with parotid gland tumors,52 were benign tumors and11 were malignant tumors.There was no significant difference in mean age and gender between benign and malignant tumor patients（P>0.05）.Among benign tumors,pleomorphic adenomas are more common in females and adenolymphoma in males,and there is a significant statistical difference between the two（?²=16.097,P<0.001）.Among malignant tumors,the tumors grow across the parotid gland with deep and shallow leaves,irregular morphology,no capsule,and unclear boundaries.There were cystic changes in both benign and malignant tumors of the parotid gland,and there is no significant difference between the two（P=0.248）.Malignant tumors and adenolymphomas can be expressed as equal or low signals on T2WI,and there were no significant difference between the two（P=0.061）.Lobulation can be seen in both pleomorphic adenomas and malignant tumors,and there was no significant difference between them（P=0.690）.2.In general,there was no significant difference in ADCmean values and ADCmin between benign tumors and malignant tumors,but ratio of tumor ADC values and peripheral gland ADC values in benign tumors was higher than that in malignant tumors（P=0.001）,peripheral gland ADC value was lower than malignant tumor,the differences were statistically significant.When take the peripheral gland ADC value of 0.967×10^-33 mm²/s as the diagnostic threshold,the Youden’s index,sensitivity,specificity,positive predictive value,negative predictive value and accuracy were 0.760,81.82%,94.23%,75.00%,96.08%,and 92.06%respectively.3.The ADCmean value,ratio of tumor ADC value and peripheral gland ADC value,and ADCmin value of malignant tumors were lower than that of pleomorphic adenomas,and the difference was statistically significant（P₁=0.005,P₂<0.001,P₃=0.010）,the peripheral gland ADC value was higher than that of pleomorphic adenoma,the difference is statistically significant（P<0.001）.4.The ADCmean value,peripheral gland ADC value and ADCmin value of malignant tumors were higher than those of adenolymphoma,the difference was statistically significant（P₁=0.003,P₂=0.000,P₃=0.007）,there was no statistically significant difference in the ADC values ratio between the two（P=0.117）.5.The ADCmean value,ratio of tumor ADC value and peripheral gland ADC value,and ADCmin value of pleomorphic adenoma were higher than those of adenolymphoma.The difference was statistically significant（P₁<0.001,P₂<0.001,P₃<0.001）,and the difference in ADC values between the two peripheral glands is not statistically significant（P=0.083）.6.The TIC curve of pleomorphic adenoma showed type A in 21 cases and type C in 4cases.The TIC curve of adenolymphoma showed 19 cases of type B and 2 cases of type C;The TIC curve of basal cell adenoma showed type B in 2 cases and type C in4 cases.The TIC curves of malignant tumors were A,B and C in 1,2 and 8 cases,respectively.In contrast to pathology,the A,B,and D curves diagnosing the benign tumors,the C diagnosing the malignant tumors,the diagnostic sensitivity,specificity,positive predictive value,negative predictive value,and accuracy were 72.73%,80.77%,44.44%,93.33%and 79.37%,respectively.7.For the patients with type C TIC curve,combined with the use of peripheral gland ADC values for correction diagnosis,the sensitivity,specificity,positive predictive value,negative predictive value,and accuracy of differential diagnosis of benign and malignant tumors were increased to 100%,90.00%,88.89%,100%,and 94.44%.Conclusions:1.There was a lot of overlap and differential diagnosis limit on conventional MRI signs of different types of parotid tumors.2.ADCmean value,peripheral gland ADC value,ratio of tumor ADC value and peripheral gland ADC value and ADCmin value provide more reference for the differential diagnosis of parotid tumors.The ADC value of peripheral gland has high diagnostic efficacy in differentiating benign tumor from malignant tumor,malignant tumor and adenolymphoma.3.The TIC curves of different pathological types of parotid tumors overlap,and the diagnostic efficiency can be improved by combining ADC values.