Diagnostic Value Of Diffusion-weighted Imaging Combined With Dynamic Contrast-enhanced MR Imaging In Salivary Gland Tumors

Objective To evaluate the application value of diffusion-weighted imaging combined with dynamic contrast-enhanced MR imaging in salivary gland tumors.Materials and Methods Forty-five patients with salivary gland tumors were scanned with conventional MR imaging, diffusion-weighted imaging (DWI) and dynamic contrast-enhanced MR imaging (DCE-MRI). All patients were proved by surgery or biopsy.(1) T1-weighted imaging and T2-weighted imaging sequences were used in conventional MRI. The morphology, margin, capsule and signal intensity were observed for all tumors.(2) Diffusion-weighted Imaging (DWI) was obtained using single-shot, spin-echo, echo-planar imaging (SS-SE-EPI). We used2b factors (0and1000s/mm2) for the apparent diffusion coefficient (ADC) values.(3) GRE T1WI (VIBE) sequence was used in Dynamic contrast-enhanced MR images (DCE-MRI). Time of peak enhancement (Tpeak) and washout ratio (WR) were determined from time-signal intensity curve (TIC). Four TIC tumor types were classified as follows on the basis of a Tpeak of120seconds and a WR of30%. In type A, the Tpeak was longer than120seconds. This type was considered to have gradual enhancement. In type B, the Tpeak was shorter than or equal to120seconds and the WR was greater than or equal to30%. This type was considered to have early enhancement and high washout. In type C, the Tpeak was shorter than or equal to120seconds and the WR was less than30%. This pattern was considered to have early enhancement and low washout. In type D, the TIC was flat. This type was considered to be markedly non-enhanced or cystic.Results.(1) Forty-five patients with salivary gland tumors included thirty-four benign tumors (eighteen pleomorphic adenomas, thirteen Warthin tumors, one Schwannoma, one lymphangioma, one basal cell adenoma) and eleven malignant tumors (three acinic cell carcinomas, two mucoepidermoid carcinomas, one adenoid cystic carcinomas, one carcinoma ex pleomorphic adenoma, one invasive carcinoma, one low-differentiated adenocarcinoma, one bronchial cleft cyst malignant change, one sarcomatoid carcinoma). In conventional MR images, benign salivary gland tumors often showed well-defined and clear margins, and malignant tumors showed irregular margin or infiltration into the surrounding tissue.(2) we found significant differences in ADCs between any2of the3different types of the salivary gland tumors, and pleomorphic adenomas, Warthin tumors and malignant tumors were1.72±0.29×10-3mm2/s),0.74±0.05×10-3mm2/s and0.95±0.09×10-3mm2/s respectively. However, benign and malignant salivary tumors had no statistical differences in ADCs, which were1.33±0.52×10-3mm2/s and0.95±0.09×10-3mm2/s.(3) sixteen pleomorphic adenomas and one Schwannoma had type A curves; thirteen Warthin tumors, one basal cell adenoma, one acinic cell carcinoma and one mucoepidermoid carcinoma had type B curves; two acinic cell carcinomas, one mucoepidermoid carcinoma, one adenoid cystic carcinomas, one carcinoma ex pleomorphic adenoma, one invasive carcinoma, one low-differentiated adenocarcinoma, one bronchial cleft cyst malignant change, one sarcomatoid carcinoma and two pleomorphic adenomas had type C curves.one lymphangioma had a type D curve; In addition, Tpeak and WR were seen among the eleven malignant tumors and thirteen Warthin tumors, and the Tpeaks of malignant tumors and Warthin tumors were respectively42.5±15.5s and22.4±12.1s; the WR values were respectively17.2%±13.2and57.5%±8.1.(4) On the basis of TIC patterns alone, we regarded type A, B, and D TIC tumors as benign neoplasms and type C TIC tumors as malignant neoplasms, the sensitivity, specificity, accuracy, and positive and negative predictive values were82%、94%、91%、82%、94%; When we applied ADC values limited to type B and C tumors and modified the diagnosis with reference to the ADC values, the sensitivity, specificity, accuracy, and positive and negative predictive values were90%、97%、95%、90%、97%。Conclusion(1) The ADCs of Warthin tumors were significantly lower than those of malignant tumors, and the ADCs of malignant tumors were lower than those of pleomorphic adenomas. So the technique of DWI can be applied to the diagnosis of benign salivary gland tumors (Warthin tumors, pleomorphic adenomas) and malignant salivary gland tumors.(2) In DCE-MRI, A type A, type B or D TIC pattern indicated benign salivary tumors, and Warthin tumors mostly had a high WR of a type B TIC pattern; A type C TIC pattern indicated malignant salivary tumors.(3) On the basis of DCE-MRI, here is added diagnostic value from including the ADC value in the evaluation of benign and malignant salivary tumors with overlapping type B or C TIC pattern.