Optic Pathway Gliomas in Neurofibromatosis Type 1: An Update: Surveillance, Treatment Indications, and Biomarkers of Vision

Abstract

Optic pathway gliomas (OPGs) occur in 15%-20% of children with neurofibromatosis type 1 (NF1), leading to visual deficits in fewer than half of these individuals. The goal of chemotherapy is to preserve vision, but vision loss in NF1-associated OPG can be unpredictable. Determining which child would benefit from chemotherapy and, equally important, which child is better observed without treatment can be difficult. Unfortunately, despite frequent imaging and ophthalmologic evaluations, some children experience progressive vision loss before treatment. Indications for chemotherapy usually are based on a comprehensive, quantitative assessment of vision, but reliable vision evaluation can be challenging in young children with NF1-OPG. The ability to identify and predict impending vision loss could potentially improve management decisions and visual outcomes. To address this challenge, ophthalmologic, electrophysiologic, and imaging biomarkers of vision in NF1-OPG have been proposed. We review current recommendations for the surveillance of children at risk for NF1-OPG, outline guidelines for initiating therapy, and describe the utility of proposed biomarkers for vision.

FIG. 1.

A 7-year-old girl with NF1-OPG involving the optic nerves (A), optic chiasm and hypothalamus (B), and optic tracts (C) shown on T2 sequences. Focal areas of T2 signal intensity are demonstrated in the midbrain and thalamus (B–D) and may abut tumor margins. NF1, neurofibromatosis type 1; OPG, optic pathway glioma.

FIG. 2.

Indications for treatment and factors affecting decision-making in patients with NF1-OPG. logMAR, logarithm of the minimal angle of resolution; NF1, neurofibromatosis type 1; OPG, optic pathway glioma; S/Sx, signs and symptoms; VA, visual acuity; VF, visual fields; *VA compared with age-based norms ** including change in color vision, new afferent pupillary defect, strabismus, optic disc swelling/pallor.

FIG. 3.

Diffusion tractography of the optic radiations (in red) superimposed on axial (A), sagittal (B), and 3-dimensional composite (C) b = 0 sec/mm² images of a child with NF1-OPG. Decreased diffusion along these tracts may reflect white matter damage. NF1, neurofibromatosis type 1; OPG, optic pathway glioma.

FIG. 4.

Axial T1 brain MRI (A) with segmentation in red (B) of a patient with bilateral NF1-OPG. Volumetric rendering of the NF1-OPG involving both sides of the anterior visual pathway (C) with 2D slices through the tumor (D). The irregular tumor shape is not amenable to traditional (i.e., 2D) measures. NF1, neurofibromatosis type 1; OPG, optic pathway glioma; 2D, 2 dimensional.