Fig. 1

Methotrexate induced encephalopathy. A 64-year-old immunocompetent female has been diagnosed with primary central nervous system (CNS) lymphoma. High dose of methotrexate-based chemotherapy was administered. In the second week of treatment, she complained of bilateral upper limb weakness and numbness, as well as dysphagia. Axial FLAIR images (a, b) show hyperintensities in bilateral centrum semiovale and corona radiata sparing the subcortical U-fibers. Axial diffusion-weighted images (DWI) (c, d) show corresponding increased signal and low apparent diffusion coefficient (ADC) (not shown). The aforementioned areas with FLAIR and diffusion abnormalities do not show any post-contrast enhancement, and they represent methotrexate-induced leukoencephalopathy. Axial contrast-enhanced T1-weighted images (e, f) show enhancing lesions in both lateral ventricles including the ependymal and subependymal regions (arrows, f) as well as the left thalamus (red outlined arrowhead, f) are consistent with lymphomatous lesions