High-grade malignancies of the parotid gland: identification with MR imaging.

Most tumors in the parotid gland are either benign neoplasms or low-grade malignancies. The magnetic resonance (MR) images of 29 patients with such tumors were reviewed. These masses typically have low T1-weighted and high T2-weighted signal intensities and have clearly defined margins. The signal characteristics presumably reflect the serous and mucinous products that are characteristic of these lesions. The MR images of six patients with aggressive parotid tumors were reviewed and correlated with operative and pathologic findings. These high-grade parotid lesions are uncommon, usually have poorly defined margins, and have low T1- and T2-weighted signal intensities. These signal characteristics presumably reflect the lack of serous and mucinous products, the high mitotic ratio, and the high nuclear to cytoplasmic ratios that are characteristic of these lesions. The authors conclude that the findings of these tumors on MR images are characteristic and should be suggestive of their diagnosis. The preoperative diagnosis of these high-grade tumors allows a more radical surgical treatment to be well planned before surgery. The primary differential diagnoses of these aggressive tumors with MR imaging include fibrosis and sialolithiasis.