MR imaging features of spinal schwannomas and meningiomas

Spinal schwannomas and meningiomas are mostly benign, intra-dural extramedullary tumours. We retrospectively reviewed the Magnetic Resonance Imaging (MRI) examinations of 52 spinal schwannomas and meningiomas operated on at our institution since 1998. The series included 28 schwannomas and 24 meningiomas. We compared MRI features of schwannomas and meningiomas and evaluated statistical features that would allow differentiation. Tumours with extraspinal extension were excluded. Concerning the cranio-caudal distribution, half of the cervical tumours were schwannomas, 72% of thoracic lesions were meningiomas and all lumbar tumours were schwannomas. Meningiomas were significantly located at the upper and mid thoracic levels and schwannomas in the lumbar area. On T1-weighted images, MRI signal intensity and heterogeneity were not statistically different between meningiomas and schwannomas. On T2-weighted images, the signal intensity appeared significantly hyperintense and heterogeneous for schwannomas. After Gd-DTPA, we observed a significant difference between meningiomas and schwannomas, the enhancement being intense and heterogeneous in cases of schwannomas, and moderate and homogeneous in cases of meningiomas. The last significant qualitative item was the "dural tail sign", a dural enhancement or thickening near the tumour. It was found in only 16 cases of meningiomas. A simple diagnostic test was built for schwannomas by processing a multiple agreement analysis with the 6 significant items: cranio-caudal location, T2 signal intensity, T2 signal heterogeneity, Gd-DTPA enhancement intensity and heterogeneity, and the "dural tail sign". This test allowed diagnosis of schwannomas with a sensitivity of 96.4%, a specificity of 83.3%, a positive predictive value of 87.1%, and a negative predictive value of 95.7%. In conclusion, we consider that a diagnosis of schwannoma should be made when a spinal intradural extramedullary tumour shows hyperintensity on T2W images or intense enhancement without dural tail sign; otherwise meningioma is more probable.