Background/aims Optic nerve tortuosity and nerve and sheath thickening are observed on MRI in some patients with neurofibromatosis type 1 (NF-1). This study aimed to determine if tortuosity and thickening are associated with the development of optic pathway glioma (OPG) and subsequent vision loss.

Methods Children with NF-1 who underwent brain MRI between 1992 and 2005, and had at least 1 year of subsequent visual acuity (VA) follow-up, were identified retrospectively. The baseline MRI was independently reviewed by three neuroradiologists for consensus assessment. Tortuosity was identified using validated operational criteria. Optic nerve and sheath thicknesses and VA at last follow-up were directly measured.

Results Of 132 evaluable children, seven (5%) had tortuosity on baseline MRI. 20 subjects (15%) ultimately developed OPG at a median of 1.9 years (range 7 months–8.0 years) following the baseline MRI. Subjects with tortuosity were significantly more likely to develop OPG than those without tortuosity (57% vs 13%, p=0.01). In subjects who developed OPG, the prevalence of tumour-related vision loss was not significantly different between those with and without baseline tortuosity (14% vs 4%, p=0.28). No difference existed between mean baseline optic nerve (2.3 vs 2.2 mm) or sheath (5.2 vs 5.4 mm) thicknesses comparing subjects who did and did not develop OPG.

Conclusions Optic nerve tortuosity at baseline is associated with OPG development among patients with NF-1, but does not predispose to aggressive OPG with associated vision loss. Neither nerve nor sheath thickening at baseline is associated with OPG development.