Mariko Fujita

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 pre-operative MRI examinations. For tumours with liquid components, i.e. ameloblastomas and keratocystic odontogenic tumours (KCOTs), the signal intensity (SI) uniformity of their cystic components (UΣ) was calculated and then their UΣ values were compared. For tumours with solid components that had been examined using dynamic contrast-enhanced MRI (DCE-MRI), their CImax (maximum contrast index), Tmax (the time when CImax occurred), CIpeak (CImax × 0.90), Tpeak (the time when CIpeak 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 UΣ 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, CIpeak > 2.0 and Tpeak < 200 s; Type B, CIpeak < 2.0 and Tpeak < 200 s; Type C, CI300 > 2.0 and Tmax < 600 s; Type D, CI300 > 2.0 and Tmax > 600 s; Type E, CI300 < 2.0 and Tmax > 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.

Unusual MRI appearance of a lymphoepithelial cyst in the parotid gland

Lymphoepithelial cysts, which are also known as branchial cleft cysts, commonly occur in the lateral cervical region. Lymphoepithelial cysts arising in the parotid gland are rare and must be distinguished from parotid gland tumors. Magnetic resonance imaging (MRI) is useful for diagnosing parotid gland lesions, and MR images of lymphoepithelial cysts typically display a cystic mass that appears homogeneously hypointense on T1-weighted images and homogeneously hyperintense on T2-weighted images. However, some parotid gland tumors that retain fluid in their inner sections show similar MRI findings to lymphoepithelial cysts. Furthermore, lymphoepithelial cysts are sometimes modified by inflammation, and these cases are hard to diagnose. We report the case of a 59-year-old female with a lymphoepithelial cyst that arose in the parotid gland. The cyst had been affected by inflammation and displayed atypical imaging findings, i.e., heterogeneous signal intensity of the liquid component and the presence of a well-enhanced capsule-like structure surrounding the liquid component. In addition, we compare the MRI findings of this case with those of two other cervical lymphoepithelial cysts.