Shiraz Qureshi Shafi
Introduction
Optic nerve gliomas which are a part of a broader category of optic pathway gliomas, are low grade astrocytic tumours arising along the optic nerve, chiasm or tract. They represent approximately 1.5% to 4% of all orbital tumours and constitute a significant proportion of primary optic nerve neoplasms (1). Histologically, most optic nerve gliomas are classified as a pilocytic astrocytoma, with generally idle behaviours, although rare malignant forms exist.
Epidemiology
Optic pathway gliomas account for 3-5% of paediatric central nervous system tumours and are the most common intrinsic optic nerve tumour in children (2). Most cases present in the first decade of life, with a mean age at diagnosis around 8 years old.(1) A strong association with neurofibromatosis type 1 (NF1) exists with approximately 15-20% of individuals with NF1 develop an optic pathway glioma, often with a relatively benign clinical course compared with sporadic cases (3). The NF1 gene encodes neurofibromin, a tumour suppressor that downregulates RAS signalling. The loss of this results in increased cell proliferation. In contrast, sporadic cases of optic nerve gliomas frequently involve a BRAF-KIAA1549 fusion, activating the MAPK pathway (4).
Pathophysiology
Pilocytic astrocytomas arise from astrocyte progenitors along the optic nerve and pathway. These tumours typically exhibit slow growth but may extend locally, compressing adjacent neural structures (5). Histopathological features include a biphasic architecture with piloid and microcystic areas, Rosenthal fibres, and eosinophilic granular bodies. Malignant gliomas of the optic nerve and chiasm are exceedingly rare and are usually high grade astrocytomas such as glioblastoma, presenting with rapid clinical deterioration, particularly in adults (6).
Clinical presentation
The clinical manifestations of optic nerve gliomas are primarily visual. Symptoms range from subtle visual acuity reduction and field defects to more overt signs such as proptosis and afferent pupillary defects. Presentations depend on tumour location. Orbital optic nerve tumours often produce progressive visual loss and forward displacement of the globe. Whereas chiasmal lesions may present with bitemporal field defects and endocrine disturbances due to hypothalamic-pituitary involvement. In many children, visual loss may not be voluntarily reported, necessitating vigilance and formal visual assessments. Systemic signs in chiasmal and hypothalamic involvement include headaches, growth abnormalities, and precocious puberty (7).
Diagnostic evaluation
Magnetic resonance imaging of the brain and orbits with contrast remains the gold standard for diagnosis and monitoring. Optic nerve gliomas typically appear fusiformly enlarged with isointense to hypointense T1 and hyperintense T2 signals, with variable enhancement (8). Neuroimaging also helps differentiate optic nerve gliomas from other optic nerve lesions such as optic nerve sheath meningiomas, which show distinct radiographic features. Genetic testing for NF1 is indicated in all paediatric cases given the high prevalence and implications for surveillance (9). Histological confirmation via biopsy is generally unnecessary and avoided due to surgical risk, however, it may be considered when imaging is atypical or diagnosis remains uncertain (10).
Management
Management is tailored to symptom severity, tumour progression, age of the patient, NF1 status and visual function. Approaches include observation, chemotherapy, radiotherapy and surgery (11). Many optic nerve gliomas in children, especially NF1 associated lesions, follow an idle course. Periodic imaging and formal visual testing are central to this conservative management strategy (12). Chemotherapy is the first line therapy for progressive or symptomatic lesions in young children. Regimens often include carboplatin-based combinations (13). Radiotherapy can be considered in older children and adults with progressive disease, particularly when chemotherapy fails. Long term radiation toxicity, especially in the developing brain, limits its used in young children. Lastly, surgery is reserved for cases with severe proptosis, comprehensive symptoms or where tissue diagnosis is required.
Prognosis & Follow-up
The long-term prognosis for optic nerve glioma varies. Most paediatric cases demonstrate slow progression with stabilisation of vision, particularly in NF1 associated disease. Regular interval imaging and functional assessment are essential, as tumour growth may not correlate directly with visual decline. A comprehensive literature review across all patients with optic pathway gliomas and various treatment modalities has shown a tumour recurrence or progression in 38% of cases (14). Tumour related mortality with a mean follow-up of 11 years is 36%. Unfortunately, all patients with malignant optic nerve gliomas progress to complete vision loss within months of presentation. The mortality rate is 100%, with a mean survival period of less than 12 months.
Conclusion
Optic nerve gliomas are uncommon, primarily paediatric tumours with distinct clinical and radiographic profiles. Recent advancements in molecular understanding and treatment options have enhanced personalised care, balancing tumour control with visual preservation and quality of life. Multidisciplinary coordination and long-term surveillance remain critical to improving outcomes.
References
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