Diagnostic value of MRI for odontogenic tumours

Objectives: To evaluate the diagnostic value of MRI for odontogenic tumours. Materials and methods: 51 patients with odontogenic tumours were subjected to preoperative MRI examinations. For tumours with liquid components, i.e. ameloblastomas and keratocystic odontogenic tumours (KCOTs), the signal intensity (SI) uniformity of their cystic components (US) was calculated and then their US values were compared. For tumours with solid components that had been examined using dynamic contrast-enhanced MRI (DCEMRI), their CI _max (maximum contrast index), Tmax (the time when CI_max occurred), CI_peak (CI_max×0.90), Tpeak (the time when CI_peak occurred) and CI₃₀₀ (i.e. the CI observed at 300 s after contrast medium injection) values were determined from CI curves. We then classified the odontogenic tumours according to their DCE-MRI parameters. Results: Significant differences between the US values of the ameloblastomas and KCOT were observed on T₁ weighted images, T₂ weighted images and short TI inversion recovery images. Depending on their DCE-MRI parameters, we classified the odontogenic tumours into the following five types: Type A, CI_peak > 2.0 and T_peak < 200 s; Type B, CI_peak < 2.0 and T_peak < 200 s; Type C, CI ₃₀₀ > 2.0 and T_max < 600 s; Type D, CI₃₀₀ > 2.0 and T_max > 600 s; Type E, CI₃₀₀ < 2.0 and T_max > 600 s. Conclusion: Cystic component SI uniformity was found to be useful for differentiating between ameloblastomas and KCOT. However, the DCE-MRI parameters of odontogenic tumours, except for odontogenic fibromas and odontogenic myxomas, contributed little to their differential diagnosis.