Section Editor: Sandy Cheng-Yu Chen, M.D.
Taipei Medical University Hospital, Taipei, Taiwan
Chronic nitrous oxide use, in this case inhalation of 100 canisters daily for 1 year, leads to irreversible inactivation of vitamin B12, which can lead to subacute combined degeneration of the spinal cord. The classic pattern as demonstrated here is T2 hyperintensity in the dorsal columns of the cervical cord on sagittal images (arrows), seen as the “inverted V” sign on axial images (quiz image).