Optic Pathway Glioma and Cerebral Focal Abnormal Signal Intensity in Patients with Neurofibromatosis Type 1: Characteristics, Treatment Choices and Follow-up in 134 Affected Individuals and a Brief Review of the Literature

Abstract

Optic pathway glioma (OPG) is a rare neoplasm and a defining feature of neurofibromatosis type 1 (NF1), a tumor suppressor genetic disorder. OPG predominantly arises during childhood. In contrast to sporadic OPG, this neoplasm frequently appears to show a more favorable course. Outcome appears to depend on localization of tumor; however, the correlation of imaging findings and visual acuity is in general low. Treatment for symptomatic OPG is not well standardized. Furthermore, determination of visual acuity as the most important parameter of follow-up control is often difficult to determine, particularly in children. Focal abnormal signal intensity (FASI) is a characteristic finding on magnetic resonance imaging (MRI) of NF1 patients. The aim of this study was to evaluate clinical and imaging findings of NF1 patients affected with OPG.

Patients and methods: Data of 925 NF1 patients with appropriate MRI cranial sectional images (N=1,948) were evaluated. A further 50 patients with cranial computed tomograms were included in the study. We compared imaging and clinical findings with respect to localization of OPG. Furthermore, we compared follow-up in treated individuals to those who were only regularly re-examined. The presence of FASI on MRI was determined and correlated to the occurrence of OPG. Dodge classification was applied to categorize OPG location.

Results: OPG was diagnosed in 134 patients. The mean age of patients with symptomatic OPG was 7.6 years (n=57, 42.5%) and 11.6 years (n=77, 57.5%) in asymptomatic patients. The female to male ratio was about 1.1:1. In 48 symptomatic patients, the findings of initial ophthalmological investigations were available. In symptomatic patients, reduced visual acuity was the predominant finding. Strabismus (25%), exophthalmos (22.9%) and amblyopia (20.8%) were most frequently noticed, followed by endrocrinological abnormalities (14.6%). However, these findings did not differ between patients who were treated or who were subjected to a 'wait-and-see' policy. We could not verify an effect of therapy on vision in patients treated for OPG compared to symptomatic patients without treatment. OPG affecting the total optic pathway was more frequently diagnosed in symptomatic patients. FASI did not correlate with functional OPG status.

Conclusion: OPG in NF1 is symptomatic in slightly less than 50% of affected individuals. This neurological finding may show a wide range of symptoms. At present, no established treatment protocol emerges from the history of the patients of this study and also from the literature. Although the onset of symptomatic OPG is strongly associated with early childhood, late onset of symptomatic OPG is a feature of adult NF1. Research for association of FASI to neurological findings in these patients should be based on other issues than association with OPG.

Keywords: Neurofibromatosis type 1; brain tumor; focal areas of signal intensity; magnetic resonance imaging; optic pathway glioma; orbital tumor; skull base; skull base tumor; visual acuity.