Neurotoxicity of intrathecal methotrexate: MR imaging findings.

We report a case of intrathecal methotrexate neurotoxicity manifesting as left arm weakness and aphasia. Diagnostic imaging showed restricted diffusion and fluid-attenuated inversion recovery imaging findings were normal at presentation. Three weeks later, diffusion abnormalities resolved, and T2-weighted studies showed increased signal intensity of prolonged T2 changes in areas of prior restricted diffusion. We attribute the clinical and radiographic findings to cytotoxic edema secondary to intrathecal methotrexate.