Diffusion-weighted MRI in the differential diagnosis of parotid malignancies and pleomorphic adenomas: can the accuracy of dynamic MRI be enhanced?

Objectives (1) To verify whether appropriate selection of cutoff values for dynamic and diffusion-weighted magnetic resonance imaging (MRI) parameters optimizes the accuracy of preoperative differential diagnosis of parotid malignancies and pleomorphic adenomas. (2) To define the role of preoperative MRI in the differential diagnosis of parotid tumors. Study Design The retrospective analysis included 221 surgical patients with parotid tumors. Aside from ultrasonography-guided fine-needle biopsy, the preoperative protocol included dynamic and diffusion-weighted MRI. Final diagnoses were based on histopathologic examination of surgical specimens. Receiver operating characteristic analysis was conducted to determine the sensitivity and specificity of preoperative MRI with various combinations of cutoff values. Results Twenty-four patients with parotid malignancies (10.8%) and 57 with pleomorphic adenomas (25.8%) were identified. Parotid malignancies had significantly lower values of apparent diffusion coefficient and T peak , as well as significantly higher values of T max and washout rate. An apparent diffusion coefficient ≤1.267 × 10 3  mm/s 2 yielded optimum accuracy in identification of parotid malignancies (95.8% sensitivity and 93% specificity). Conclusion Diffusion-weighted MRI is effective in differential diagnosis of parotid malignancies. Optimization of preoperative diagnosis of parotid tumors should include preselection identification of Warthin tumors on the basis of dynamic MRI, followed by identification of pleomorphic adenomas based on diffusion-weighted MRI and cytologic examination of the remaining lesions.