Early diffusion-weighted MRI at 3 Tesla detects ischemic changes of the optic nerve in anterior ischemic optic neuropathy

To assess the impact of timing from visual symptoms' onset to diffusion-weighted (DW) 3 T MRI completion to detect ischemic changes of the optic disc and optic nerve in AION patients. This IRB-approved retrospective single-center study included 3 T MRI data from 126 patients with AION and 111 controls with optic neuritis treated between January 2015 and May 2020. Two radiologists blinded to all data individually analyzed imaging. A senior neuroradiologist resolved any discrepancies by consensus. The primary judgment criterion was the restricted diffusion of the optic disc and/or the optic nerve assessed subjectively on the ADC maps. ADC values were also measured. Spearman rank correlations were used to examine the relationships between timing from visual symptoms' onset to MRI completion and both the restricted diffusion and the ADC values. One hundred twenty-six patients (47/126 [37.3%] women and 79/126 [62.7%] men, mean age 69.1 ± 13.7 years) with AION were included. Restricted diffusion of the optic disc in AION eyes was more frequent in the early MRI group than in the late MRI group: 35/49 (71.4%) eyes versus 3/83 (3.6%) eyes, p < 0.001. ADC values of the pathological optic discs and optic nerves were lower in the early MRI group than in the late MRI group: 0.61 [0.52-0.94] × 10${}^{-3}$ mm${}^2$/s versus 1.28 [1.01-1.44] × 10${}^{-3}$ mm${}^2$/s, p < 0.001, and 0.74 [0.61-0.88] × 10${}^{-3}$ mm${}^2$/s versus 0.89 [0.72-1.10] × 10${}^{-3}$ mm${}^2$/s, p < 0.001, respectively. DWI MRI showed good diagnostic performance to detect AION when performed early after the onset of visual symptoms. Restricted diffusion of the optic disc in eyes affected by AION was significantly more likely to be observed in patients who had undergone MRI within 5 days after onset of visual symptoms. ADC values of the pathological optic discs and optic nerves were significantly lower in patients who had undergone MRI within 5 days after onset of visual symptoms of AION: 0.61 × 10${}^{-3}$ mm${}^2$/s versus 1.28 × 10${}^{-3}$ mm${}^2$/s, p < 0.001, and 0.74 × 10${}^{-3}$ mm${}^2$/s versus 0.89 × 10${}^{-3}$ mm${}^2$/s, p < 0.001, respectively. The optimal threshold for timing from visual symptoms' onset to MRI completion to detect restricted diffusion of the optic disc and/or optic nerve was 5 days, with an AUC of 0.88 (CI${}_{95\%}$: 0.82-0.94).