Fig. 3

Case 2, radiological findings. a MRI brain at presentation. The right optic nerve is thicker than the left one (red arrow). Abnormal enhancement of the optic nerve sheath (tram-track sign) (yellow arrows) extends to the intraorbital and intracanalicular segments of the nerve. There is abnormal enhancement and stranding of the perioptic fat. Axial (i) and coronal (ii) T1-weighted post-contrast fat-saturated images are shown. b MRI brain at clinical progression. Newly developed multiple lesions in the periventricular white matter are noted. Two representative axial T1-weighted post-contrast fat-saturated images are shown