Fig. 1

Comparison of the appearance of metastasis and demyelinating lesion in this patient. a The patient was treated by stereotaxic radiotherapy in January 2018 for several brain metastases, the largest being located at the cortico-subcortical junction of the left precentral gyrus. The lesion appeared hypointense with central necrosis and large perilesional oedema on T2-weighted images, had complete ring enhancement on post-contrast T1-weighted images, and increased normalized cerebral blood volume (nrCBV = 1.2) and cerebral blood flow (nrCBF = 1.7) ratios on perfusion weighted images. b In June 2018, he developed several demyelinating lesions, the largest being located in the left superior frontal gyrus. Contrary to the brain metastasis, the lesion was juxtacortical, had little perilesional oedema, partial ring enhancement (i.e. open ring sign), and low nrCBV and nrCBF