OBJECTIVETo investigate magnetic resonance imaging (MRI) features of parotid malignant tumors and study their pathological basis.

METHODSForty-seven patients with parotid malignant tumors confirmed by surgery (41 patients) or biopsy (6 patients) were enrolled in this study. A comparative analysis was conducted of the pathological and MRI findings in 30 patients with the entire lesions available. Each of the MRI features was analyzed retrospectively and the typical MRI findings of common parotid malignant tumors were summarized.

RESULTSMRI allowed accurate diagnosis of parotid malignant tumors. Four patients with low-grade mucoepidermoid carcinoma showed well-defined tumor margin and were difficult to distinguish from benign tumors. Six patients with high-grade mucoepidermoid carcinoma had obscure margin of the tumor which easily underwent necrosis with liable lymph node involvement. The 8 cases of adenoid cystic carcinoma was characterized by extensive invasion surrounding the parotid gland. Most of 8 cases of malignant pleomorphic adenoma still showed high and heterogeneous signal on T2WI, with irregular shape and poorly defined margin. Nine cases of lymphoma all had secondary lesions characterized by extensive involvement and presence of multiple nodules. The 4 cases of acinic cell carcinoma showed either regular or irregular tumor morphology, presenting with high signal intensity on T1WI and T(2)WI.

CONCLUSIONMRI is an important modality for the diagnosis of parotid malignant tumors. Most of the common parotid malignant tumors have characteristic MRI and pathological features, which make possible their differential diagnosis.