Optic pathway glioma: correlation of imaging findings with the presence of neurofibromatosis

Abstract

Background and purpose: Despite the benign histology of optic pathway glioma (OPG) (low-grade astrocytoma), its biological behavior is unpredictable, and it is unclear whether specific morphologic or anatomic patterns may be predictive of prognosis. It is also unclear whether OPG associated with neurofibromatosis (NF) is a distinct entity from non-NF-OPG. Our purpose was to describe the MR imaging features of OPG, compare the findings between patients with and those without NF, and identify prognostic imaging signs.

Methods: MR examinations of 91 patients with OPG (47 with NF and 44 without) were reviewed at presentation and during follow-up. The images were evaluated for size and extension of tumor, and imaging parameters. Statistical bivariate analysis was used to compare the patients with and those without NF, and Pearson correlation was used to evaluate the correlation between the different imaging parameters and prognosis. Kappa values were calculated to determine intraobserver and interobserver variability.

Results: The most common site of involvement in the NF group was the orbital nerve (66%), followed by the chiasm (62%). In the non-NF group, the chiasm was the most common site of involvement (91%); the orbital nerves were involved in only 32%. Extension beyond the optic pathway at diagnosis was uncommon in the NF group (2%) but frequent in the non-NF group (68%). In the NF group, the tumor was smaller and the original shape of the optic pathways was preserved (91% vs. 27% in the non-NF group). The presence of cystic components was significantly more common in the non-NF patients (66% vs. 9% in the NF group). During follow-up, half the NF patients remained stable, in contrast to 5% of the non-NF group. No statistical correlation was found between imaging features and biological behavior of the tumor.

Conclusion: NF-OPG is a separate entity from non-NF-OPG, with different imaging features and prognosis, thereby warranting a specific diagnostic, clinical, and therapeutic approach.

fig 1.

14-year-old boy with NF. A and B, Sagittal unenhanced (A) and coronal contrast-enhanced (B) T1-weighted MR images show typical findings of OPG in patients with NF: thickened retroorbital optic nerves and chiasm, with preservation of original contour. The tumor is small and homogeneous, without any cystic components

fig 2.

4-year-old girl without NF. Axial contrast-enhanced T1-weighted image shows typical findings of optic glioma in patients with NF: a large mass, with cystic components, that does not respect the boundaries of the optic pathways. The temporal horns are enlarged, and the right middle cerebral artery courses in a fissure of the mass (arrow)