Orbital schwannomas: Findings from magnetic resonance imaging in 62 cases

Abstract

Purpose: To evaluate the diagnostic value of magnetic resonance imaging (MRI) and illustrate the common MRI features of orbital schwannoma. Methods: We reviewed 62 consecutive cases of pathologically proven orbital schwannoma investigated by MRI. All cases were examined using T1- and T2-weighted images. Enhanced T1-weighted images were obtained after administration of gadopentetate dimeglumine. The images were analysed and compared. Results: Cone-shaped lesions were the most frequent (16, 26%), followed by dumbbell-shaped (10, 16%), oval (9, 15%) and round lesions (8, 13%). The most common site was the superior aspect of the orbit (17, 27%), followed by the medial superior (12, 19%) and the orbital apex (12, 19%). On unenhanced T1-weighted images, 53 (85%) lesions showed isointensity or small patches of hypointensity. The patterns of enhancement seen on T1-weighted images correlated with the signal characteristics of unenhanced T2-weighted images. Five patterns emerged in our series. Among these patterns, the most common sign, found in 18 (29%) cases, was peripheral (ring) enhancement on enhanced T1-weighted images, which showed peripheral isointensity with central hyperintensity on T2-weighted images. Lesions with homogeneous or heterogeneous enhancement were seen in 16 (26%) and 26 (42%) cases, respectively. Conclusions: MRI is a valuable diagnostic method for orbital schwannoma, particularly when contrast is applied. The locations and shapes of tumours can be seen distinctly. T1-weighted images are relatively nonspecific. T2-weighted and enhanced T1-weighted images provide information about the pathology of tumours. In particular, peripheral enhancement should be considered a target sign of schwannoma.