Diffusion-tensor MR imaging of optic pathway in idiopathic intracranial hypertension

To investigate the role of diffusion tensor imaging (DTI) of optic pathway in patients with idiopathic intracranial hypertension (IIH).

This study included 41 IIH patients and 22 controls. They underwent DTI of the optic nerve (ON) and optic radiation (OR). Their fractional anostrophy (FA) and mean diffusivity (MD) were calculated by two reviewers and correlated with papilledema grade.

The optic nerve mean FA and MD of patients for reviewer-1 were 0.21 ± 0.047 and 2.189 ± 0.52 ×10^-3 mm²/s and for reviewer-2 were 0.216 ± 0.047 and 2.17 ± 0.54 ×10^-3 mm²/s. The mean ON FA and MD of controls for reviewer-1 were 0.33 ± 0.048 and 1.29 ± 0.26 ×10^-3 mm²/s and for reviewer-2 were 0.34 ± 0.05 and 1.3 ± 0.26 ×10^-3 mm²/s. There was significant difference in FA and MD between patients and controls (p < 0.00001). The OR mean FA and MD of patients for reviewer-1 were 0.61 ± 0.03 and 2.26 ± 0.55 ×10^-3 mm²/s and for reviewer-2 were 0.6 ± 0.03 and 2.24 ± 0.57 ×10^-3 mm²/s The mean OR FA and MD of controls for reviewer-1 were 0.6 ± 0.03 and 2.19 ± 0.49 ×10^-3 mm²/s and for reviewer-2 were 0.6 ± 0.03 and 2.18 ± 0.49 ×10^-3 mm²/s. There was no significant difference in FA and MD obtained in patients and controls. Both the FA and the MD of the ON showed strong correlation with the papilledema grade (r = -0.8 and 0.951, respectively).

Our findings suggest that, IIH is associated mainly with pre-chiasmatic or ON involvement rather than post-chiasmatic parenchymal or OR involvement. DTI MD and FA parameters of the ON may be a reliable imaging biomarker for diagnosis of IIH and well correlated with papilledema grades.