Larger tumor volume is associated with visual acuity loss and axonal degeneration in children with optic pathway gliomas secondary to neurofibromatosis type 1

Background. We investigated whether volumetric magnetic resonance imaging (MRI) measures of the anterior visual pathway (AVP) in optic pathway gliomas secondary to Neurofibromatosis type 1 (NF1-OPG) are associated with visual acuity (VA) loss and axonal loss, as measured using optical coherence tomography (OCT).Methods. Children with NF1-OPGs enrolled in a prospective study of VA and OCT measures of the circumpapillary retinal nerve fiber layer (cpRNFL) thickness were eligible if they had undergone 3-Tesla MRI that included a T1-weighted volumetric sequence. The linear dimension and volume of the optic nerves, chiasm, and optic tracts were measured using our semi-automated algorithm. The combined volume of these components comprising the proximal AVP was used as a surrogate of total tumor burden. Regression models for VA and cpRNFL thickness were reported on a per-eye basis.Results. Fifty-two study eyes (26 children, mean 7.1 years) met inclusion criteria, of which 40% (N = 21 eyes) had abnormal VA. In regression analysis, only total AVP volume demonstrated a significant relationship to axonal loss, such that for every 1 mL increase in AVP volume, cpRNFL declined by 5.4 microns (P = .01). Total AVP volume > 1.75 mL predicted both axonal loss and abnormal VA (positive predictive value of 83.3% and 70.8%, respectively; negative predictive value of 80.0% and 88.0%, respectively).Conclusions. Volumetric measures of NF1-OPGs identified children with VA loss and axonal degeneration. Total tumor burden, as measured by AVP volume, had the strongest relationship with axonal injury. NF1-OPG volumetric measures may be helpful in making treatment decisions.