Representative CT and MRI of patient 4. (A) CT image acquired 3 days after intoxication showing obliteration of the fourth ventricle and sulcal marking in the posterior fossa suggesting swelling of intracranial structures. (B) CT image taken at 6 months showing widening of the cisterns and mild cerebellar atrophy. (C, D) T1-weighted sagittal MRI (TR = 500, TE = 30) and T2-weighted axial image (TR = 2500, TE = 80) taken 1 year later reveal severe atrophy of the cerebellar vermis and hemispheres. (E, F) T2-weighted axial images showing no abnormality in the basal ganglia. Cortical atrophy was very mild in comparison with the cerebellar atrophy. Diffuse subcortical white matter lesions were also found but are less prominent than those of CO poisoning (supplementary fig 1).