Objective: The objective of this study was to investigate microstructural damage caused by pituitary macroadenomas by performing probabilistic tractography of the optic tracts and radiations using 7-T diffusion-weighted MRI (DWI). These imaging findings were correlated with neuro-ophthalmological results to assess the utility of ultra-high-field MRI for objective evaluation of damage to the anterior and posterior visual pathways.
Methods: Probabilistic tractography employing 7-T DWI was used to reconstruct the optic tracts and radiations in 18 patients with adenomas and in 16 healthy volunteers. Optic chiasm compression was found in 66.7% of the patients and visual defects in 61.1%. Diffusion indices were calculated along the projections and correlated with tumor volumes and results from neuro-ophthalmological examinations. Primary visual cortical thicknesses were also assessed.
Results: Fractional anisotropy was reduced by 21.9% in the optic tracts (p < 0.001) and 17.7% in the optic radiations (p < 0.001) in patients with adenomas. Patients showed an 8.5% increase in mean diffusivity of optic radiations compared with healthy controls (p < 0.001). Primary visual cortical thickness was reduced in adenoma patients. Diffusion indices of the visual pathway showed significant correlations with neuro-ophthalmological examination findings.
Conclusions: Imaging-based quantification of secondary neuronal damage from adenomas strongly correlated with neuro-ophthalmological findings. Diffusion characteristics enabled by ultra-high-field DWI may allow preoperative characterization of visual pathway damage in patients with chiasmatic compression and may inform prognosis for vision recoverability.
Keywords: DWI = diffusion-weighted MRI; FA = fractional anisotropy; FDR = false discovery rate; LGN = lateral geniculate nucleus; MD = mean diffusivity; OCT = optical coherence tomography; PSD = pattern standard deviation; RNFL = retinal nerve fiber layer; ROI = region of interest; T2-TSE = T2-weighted turbo spin echo; TSD = transsynaptic degeneration; V1 = primary visual cortex; VFD = visual field defect; aTSD = anterograde TSD; neuro-ophthalmology; neurosurgery; pituitary adenoma; pituitary surgery; tractography; ultra–high-field MRI; visual pathway.