MR diffusion tensor imaging of optic radiation in chronic Leber's hereditary optic neuropathy

Abstract

Objective To observe quantitatively the optic radiation alterations in chronic Leber's hereditary optic neuropathy (LHON) using MR diffusion tensor imaging at 3.0 T. Methods Twenty-five patients with chronic LHON and twenty-eight sex- and age-matched disease-free control subjects were enrolled from March 2011 to December 2014. The whole brain DTI examination and retinal optical coherence tomography were performed in all the subjects. The parameters values of optic radiation including fractional anisotropy(FA),mean diffusivity(MD),principal eigenvalue(λ//),orthogonal eigenvalue(λ⊥) and average retinal nerve fiber layer (RNFL) thickness and temporal retinal nerve fiber layer(RNFL) thickness were measured. For DTI and OCT parameters, differences between patients and controls and differences right and left of the patient group were evaluated using independent-samples t test and paired t test respectively. Results In LHON patients, the DEC maps showed that the bilateral optic radiation fibers were obviously sparse and slender. The values of FA, MD, λ// and λ⊥ in the right optic radiation were 0.523±0.050, (0.903±0.061) ×10-9 mm2/s, (4.999±0.097) ×10-9 mm2/s and (4.126±0.065) ×10-9 mm2/s respectively, and the corresponding values of left optic radiation were 0.537±0.041, (1.057±0.573)×10-9 mm2/s,(5.052±0.119)×10-9 mm2/s and (4.138±0.072)×10-9 mm2/s. Compared with optic radiation in the control group, the bilateral FA was significant reduced, the bilateral λ⊥ value and right MD value were significant increased (t=-6.524, -6.045, 6.932, 6.454, 3.471, P 0.05) .There were no significant differences in FA, MD, λ// and λ⊥ between the left and right eyes in LHON patients(P>0.05). The values of average RNFL thickness and temporal RNFL thickness in right eyes were (59.36±10.94) and (41.72±9.43) μm respectively, and the corresponding values of left eyes were (60.12±9.81), (44.72±9.43) μm. The average and temporal RNFL thickness were significantly thinned in LHON patients compared with the control group (t=-16.357, -10.398,-17.169,-9.672, P 0.05), temporal RNFL thickness between the left and right eyes was statistically significant (t=2.645, P<0.05). Conclusion The bilateral optic radiation had significant degeneration and atrophy in chronic LHON. Key words: Optic nerve diseases; Magnetic resonance imaging; Comparative study