Non-arteritic anterior ischaemic optic neuropathy: evaluation of the brain and optic pathway by conventional MRI and magnetisation transfer imaging.

The purpose of the study was to examine the brain and the visual pathway of patients with non-arteritic anterior ischaemic optic neuropathy (NAION) by using conventional MRI (cMRI) and volumetric magnetisation transfer imaging (MTI). Thirty NAION patients, aged 67.5 +/- 8.14 years, and 28 age- and gender-matched controls were studied. MTI was used to measure the magnetisation transfer ratio (MTR) of the chiasm and for MTR histograms of the brain. The presence of areas of white matter hyperintensity (WMH) was evaluated on fluid-attenuated inversion recovery (FLAIR) images. Area of the optic nerves (ONs) and volume of the chiasm were assessed, as were coronal short-tau inversion recovery (STIR) and MTI images, respectively. More areas of WMH were observed in patients (total 419; mean 14.4; SD 19) than in controls (total 127; mean 4.7; SD 5.7), P < 0.001. Area (in square millimetres) of the affected ONs, volume(in cubic millimetres) and MTR (in percent) of the chiasm (10.7 +/- 4.6), (75.8 +/- 20.2), (56.4 +/- 6.5), respectively, were lower in patients than in controls (13.6 +/- 4.3), (158.2 +/- 75.3) (62.1 +/- 6.2), respectively, P < 0.05. Mean MTR of brain histograms was lower in patients (53.0 +/- 8.0) than in controls (58.0 +/- 5.6), P < 0.05. NAION is characterised by decreased ON and chiasmatic size. The low MTR of the chiasm and brain associated with increased areas of WMH may be suggestive of demyelination and axonal damage due to generalised cerebral vascular disease.