A New MRI-Based Malignancy Grading System for Parotid Mucoepidermoid Carcinoma.

PURPOSE: To improve the diagnosis of malignancy grade in parotid mucoepidermoid carcinoma using preoperative MRI. PATIENTS AND METHODS: Among 46 cases of parotid mucoepidermoid carcinoma, MRI findings were compared between low/intermediate malignancy and high malignancy. Primary lesions were assessed based on eight parameters. The scores were assigned to create criteria for diagnosing the malignancy grades on MRI. MRI diagnosis was compared with the diagnosis of malignancy grade using fine needle aspiration cytology and frozen section. RESULTS: High-grade malignancy showed distinctive changes in the maximum tumor diameter, shape, cystic component, margin, and necrotic areas. The MRI score of ≥ 6 was graded as a high-grade malignancy, the diagnostic accuracy was 89%. In contrast, the accuracy of fine needle aspiration cytology, and frozen section for the grade of malignancy was 52% and 22%, respectively. CONCLUSION: MRI scoring was found to be useful for determining the grade of malignancy of parotid mucoepidermoid carcinoma.