Teaching Case

A 15-year-old male presented with recurring episodes of severe headaches for a period of 6 months and insidious onset loss of vision. He presented with complete loss of vision. On ophthalmologic examination, there was vision field loss and nystagmus.

On MRI, diffuse thickening with lobulated mass lesion is seen involving the optic chiasma, bilateral intracranial optic nerves and optic tracks, which shows hypointense on T1W images and hyperintense signal on the T2W, FLAIR images. The lesion also involves the infundibular stalk and tuber cinereum. Mild enhancement is seen in the optic chiasma on post-contrast images. There is preservation of the optic chiasma contour, although swollen.

Background

Optic pathway gliomas are relatively uncommon tumours, with a variable clinical course and usually seen in the setting of neurofibromatosis type I (NF1). In spite of being commonly associated with NF1, isolated cases that are not associated with NF1 are also seen. According to studies, The most common site of involvement in the NF group was the orbital nerve (66%), followed by the chiasma (62%). In the non-NF group, the chiasma 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%) [1].

Clinical Perspective

Clinical presentation largely depends on the extent and location of the tumour. Decreased vision (63%) is the common presenting symptom [2]. In larger tumours, mass effects result in proptosis. Involvement of the hypothalamus may result in polyuria/polydipsia [3]. Other symptoms of involvement of hypothalamus include obesity and endocrine dysfunction (e.g., short stature). In large intracranial tumours, symptoms of raised intracranial pressure, focal neurological deficits and hydrocephalus from distortion of the midbrain are seen.

Imaging Perspective

On MRI, optic pathway gliomas are usually hypo- to isointense on T1, and hyperintense on T2 images [4,5]. 50% of the cases show bright enhancement on post-contrast images. These tumours can be confined to specific areas of the optic pathway, such as the optic nerve or the chiasma. They can show more diffuse development along the optic tracts. When a tumour is confined to the optic nerves, imaging demonstrates well-circumscribed enlargement along with a tortuous or kinked appearance of the nerves. Tumours developed from the chiasma may present as non-enhancing enlargement of the chiasma or as bulky suprasellar enhancing lesions. They may present with or without an exophytic component. Patients with sporadic tumours predominantly have chiasmatic lesions with optic nerve involvement in a third of cases, while NF1 patients most commonly have optic nerve lesions, which may or may not extend to the chiasma [6,7]. An anatomical classification was proposed in the late 1950s by Dodge et al., defining tumours according to their location, as involving either the optic nerves alone (stage 1), the chiasma with or without nerve involvement (stage 2), and the hypothalamus or other adjacent structures (stage 3).

Outcome

Optic gliomas show variable clinical and radiological progression and therefore require a multi-disciplinary approach. In patients with NF1, the tumours are usually quiescent, with little progression demonstrated over some years. In others, the tumours are more aggressive with extension along the optic pathways [2]. Initial management involves serial MRI scans and visual acuity testing. Treatment is only initiated following disease progression with either reduction in visual acuity or enlargement of tumour on neuroimaging [8]. Management options include surgery, radiotherapy and chemotherapy. Chemotherapy is the first-line treatment and initially involves treatment with carboplatin and vincristine [9]. Surgery is rarely curative, as the borders of the tumour tend to extend beyond MRI findings. Surgery invariably leads to visual loss, endocrine deficits and cerebrovascular accidents. It is therefore reserved for cases with minimal visual potential, severe disfiguring proptosis or corneal exposure [3,10].

Overall optic pathway gliomas carry a 5-year survival rate of >90% [9].

Take Home Message / Teaching Points

Optic pathway gliomas account for 3–5% of all pediatric CNS tumours and represent the most common intrinsic optic nerve tumours. These tumours are particularly frequent in children with neurofibromatosis type 1 but isolated tumours in patients without NF1 are also seen. Although optic pathway gliomas are low-grade tumours, their behaviour can be aggressive, and their management is often challenging. Their management includes observation, surgery, chemotherapy and radiation.