Cystic lesions of the parotid gland: radiologic-pathologic correlation according to the latest World Health Organization 2017 Classification of Head and Neck Tumours

To determine the value of adding diffusion-weighted (DW) magnetic resonance (MR) imaging to dynamic contrast material-enhanced MR imaging when distinguishing between benign and malignant parotid tumors. This retrospective study was approved by the institutional review board, and the informed consent requirement was waived. The authors analyzed MR images of 50 lesions (36 benign, 14 malignant) in 47 patients. DW MR imaging and dynamic contrast-enhanced MR imaging were performed in all patients. Time-intensity curve (TIC) patterns were categorized as follows: type A, time to peak was more than 120 seconds; type B, time to peak was 120 seconds or less with high washout ratio (> or = 30%); type C, time to peak was 120 seconds or less with low washout ratio (< 30%); and type D, flat. The apparent diffusion coefficient (ADC) values were measured on DW MR images. Sensitivity, specificity, accuracy, and positive and negative predictive values were calculated for type A, B, and D tumors regarded as benign and for type C tumors regarded as malignant. On the basis of DW MR imaging results, ADC threshold values between pleomorphic adenomas and carcinomas and between Warthin tumors and carcinomas were selected. Diagnostic accuracy was compared before and after modification diagnosis referring to the ADC value obtained with the McNemar test. P < .05 was considered to indicate a significant difference. ADC threshold values were 1.4 x 10(-3) mm(2)/sec between pleomorphic adenomas and carcinomas and 1.0 x 10(-3) mm(2)/sec between Warthin tumors and carcinomas. Accuracy (82% vs 94%) and positive predictive value (67% vs 92%) significantly improved with the addition of ADC values in the evaluation of patients with type B or C tumors. A persistent or flat TIC pattern on dynamic contrast-enhanced MR images indicates benign disease, but there is added value from including the ADC value in the evaluation of tumors that show a plateau or washout TIC pattern. RSNA, 2008

The surgical approach to parotid tumors is different for benign and malignant neoplasms, but the clinical symptoms do not correlate well with histology. Difficulties in tumor classification also arise in imaging modalities, in which sonography has the lowest and MR imaging, the highest accuracy. The purpose of this study was to review our experience using conventional MR imaging of the neck in the evaluation of parotid tumors and to evaluate which MR imaging findings are best able to predict malignant histology. Eighty-four consecutive patients (43 males, 41 females; median age, 56 years; range, 9-85 years) with parotid gland tumors who underwent MR imaging before surgery were prospectively included in the present study and retrospectively analyzed. Histology was available for all tumors. We analyzed the following MR imaging parameters: signal intensity, contrast enhancement, lesion margins (well-defined versus ill-defined), lesion location (deep/superficial lobe), growth pattern (focal, multifocal, or diffuse), and extension into neighboring structures, perineural spread, and lymphadenopathy. The 57 (68%) benign and 27 (32%) malignant tumors consisted of 29 pleomorphic adenomas, 17 Warthin tumors, 11 various benign tumors, 5 mucoepidermoid carcinomas, 3 adenoid cystic carcinomas, 1 acinic cell carcinoma, 1 carcinoma ex pleomorphic adenoma, 9 metastases, and 8 various malignant neoplasms. Specific signs predictive of malignancy were the following: T2 hypointensity of the parotid tumor (P = .048), ill-defined margins (P = .001), diffuse growth (P = .012), infiltration of subcutaneous tissue (P = .0034), and lymphadenopathy (P = .012). Low signal intensity on T2-weighted images and postcontrast ill-defined margins of a parotid tumor are highly suggestive of malignancy.

Our aim was to determine the value of echo-planar diffusion-weighted MR imaging (epiDWI) in differentiating various types of primary parotid gland tumors. One hundred forty-nine consecutive patients with suspected tumors of the parotid gland were examined with an epiDWI sequence by using a 1.5T unit. Image analysis was performed by 2 radiologists independently, and the intraclass correlation coefficient was computed. Histologic diagnosis was obtained in every patient. For comparison of apparent diffusion coefficients (ADCs), a paired 2-tailed Student t test with a Bonferroni correction was used. In 136 patients, a primary parotid gland tumor was confirmed by histology. Among the observers, a high correlation was calculated (0.98). ADC values of pleomorphic adenomas were significantly higher than those of all other entities, except for myoepithelial adenomas (P = .054). ADC values of Warthin tumors were different from those of myoepithelial adenomas, lipomas, and salivary duct carcinomas (P < .001, 0.013, and .037, respectively). Mucoepidermoid carcinomas, acinic cell carcinomas, and basal cell adenocarcinomas were not differentiable from Warthin tumors (P = .094, .396, and .604, respectively). epiDWI has the potential to differentiate pleomorphic adenoma and myoepithelial adenomas from all other examined entities. Due to an overlap not only within the group of benign and malignant lesions but also between groups, diagnoses should not be addressed on the basis of ADC values solely. Therefore, further studies combining DWI, morphologic criteria, and probably other MR imaging techniques seem warranted.