Optic pathway gliomas

General

Congenital WHO grade I astrocytoma of optic nerves or chiasm

Numbers

First decade of life

Aetiology

Aetiology	NF1	Sporadic
Frequency	30%	70%
Anatomical origin	- Optic nerve - Optic chiasm - Optic radiation - Geniculate ganglion.	- Chiasmatic-hypothalamic region - Other brain structures adjacent to, or involving the optic tract
Histology grade	1	2 (higher morbidity and even death)
Treatment	Radio surveillance	Chemo, Surgery
Rx	NO (risk of other cancer and moyamoya)	Yes

Genetic

NF-1 (50-60% of NF1 pt has it, comprise of 30% of all OPG)

Arise

In contrast, OPG associated with neurofibromatosis type 1 characteristically involve optic nerve, chiasm and optic radiation, including the geniculate ganglion.

Sporadic

Arise within the

Chiasmatic-hypothalamic region or
Other brain structures adjacent to, or involving the optic tract,

Not typically arise involve the optic nerves.

Clinical features

Usually discovered during first decade

Visual impairment

Afferent pupil defect
Pendular (monocular or seesaw) nystagmus
Optic disc abnormality

Proptosis if large intra-orbital component

Endocrine deficit

Focal neurological deficit

Hypothalamic behavioural disturbance (appetite, rage, obesity)

Stationary or progressive visual loss in one eye or both

Features of NF1

Pathology

PA (WHO grade l)

Solid and cystic components in MRI
Biphasic architecture with loose and compact areas, Rosenthal fibers

Pilomyxoid astrocytoma (WHO grade 2)

More aggressive , higher rate Of recurrence and CSF spread
More at hypothalamic/chiasmatic region

Diffuse fibrillary astrocytoma (WHO grade 2)

Prognostic markers

MIS-1 <1% associate with better outcome

B-K fusion gene

BRAF V600E point mutation

Management

Radiology surveillance

Indication

For grade 1 NF 1 associated

Biopsy

Indication

If imaging is non-diagnostic/atypical),

Biopsy cannot usually be justified if imaging is diagnostic

Useful vision is maintained ipsilateral to tumor debulking or resective surgery seems unnecessary.


---
title: Red means no and Green means yes
---
graph TD
    A[Chiasmatic-hypothalamic<br>tumor on MRI?] --> B[Presence of NF-1?]
    B --> C[It is justifiable not to<br>perform a biopsy, but<br>central neuroradiological<br>review of films is<br>recommended.]:::yes
    B --> D[Extensive contiguous<br>involvement of the visual<br>pathways?]:::no
    D --> E[It is justifiable not to<br>perform a biopsy, but<br>central neuroradiological<br>review of films is<br>recommended.]:::yes
    D --> F[Hypodensity on plain CT?]:::no
    F --> G[It is justifiable not to<br>perform a biopsy, but<br>central neuroradiological<br>review of films is<br>recommended.]:::yes
    F --> H[Biopsy recommended.]:::no

    classDef yes fill:#008000;
    classDef no fill:#FF0000;

Surgery

High risk

Due to their location morbidity associated with

Optic nerve or pathway
Risk to vascular supply to hypothalamus and pituitary

Indication

Resection

Unilateral failing or useless vision
OPG confined to the optic nerve
Optic nerve gliomas causing disfiguring proptosis in a blind eye (excision of optic nerve only).

Debulking

Exophytic growth
HCP
Failed chemo/radiotherapy

Aim

To protect vision on the good side

Potentially controlling hydrocephalus

Delaying radiotherapy in what is often a young patient group.

Operation note

Procedure

Right Pterional Craniotomy- Resection of Pre-Chiasmatic optic pathway Tumour- Joint Orbital Approach and Lateral Orbital. Enucleation of the Eye

Indication

Pre-chiasm right sided optic pathway lesion- blind in the right eye.
Discussed at MDT and decision for resection- goal for GTR of the lesion.
Parents aware high risk of having to remove the eyeball but would try to preserve if possible.

Findings

Pterional Approach first-lesion clearly identified and ICA, ACA chiasm and contralateral optic nerve all seen.
Small margin between tumour before it reached the chiasm seen and this was where the right optic nerve was divided.
Lesion mobilised from adherent arachnoid and around the rim of the optic canal. Lesion felt adherent deeper in the canal and likely around structures of the orbital.
Transorbital approach: Lateral orbit removed to improve access especially just behind the orbit after mobilising the lateral rectus. Optic nerve isolated as it joined the globe- this was clamped- noted dilation of the pupil as expected. Lesion resected as it entered the globe. Lesion however was large and very difficult to mobilise away from the orbital structure. Attempted resection and preservation of orbital musclers- lesion was too adherent to allow gross total resection. Attempted intracranial and orbital removal- too adherent to orbital musculature. decision therefore to remove the eye completely to improve exposure of the tumour. Subperiosteal resection removal of the muscles and preservation of part of the conjunctival. This was used to aid a layered closure of the orbit. Lesion removed from the orbit. Second look intracranial- inspection of optic canal, no lesion visible. Optic canal defect therefore packed with bone wax and surgical. GTR appeared to be achieved intra-operatively.

Procedure:

Ga, supine, Mayfield pins, malar prominence, standard prep and drape, pterional craniotomy with Midas Rex matchstick and craniotome. Sphenoid wing partial drilled to improve exposure. Dura reflected C-shaped fashion, hand held retractors and using microscope with suction, gentle aspiration CSF. Olfactory nerve identified and optic-carotid recess opened. Lesion seen as above and findings as above. Right CNII was divided with feather blade to ensure clean resection margin. Right epicanthus excision to expose zygoma, lateral orbital wall. Stryker saw to perform osteotomies- 7- straight KLS plates premeasured and drilled- 5mm screws utilised. Orbit entered and findings as above.

Closure:

Orbit: KLS straight plate, with 7, 5mm screws for orbital wall. Surgicel and bone was packed the orbital canal to minimise CSF leak. Residual layer conjunctiva used for layered eye closure with vicryl. Eye leashes removed, subcutaneous vicryl and interrupted monocryl for skin.
Cranial: Optic canal defect covered with Tissue patch, surgical and Tisseal. PDS running water tight closure dura with duraseal. Noted small defect in the inferior lateral orbital wall- likely secondary to orbital osteotomies- this was buttressed with Pericranium and gelfoam intracranially. BBraun cranifix set for bone. Temporalis opposed with vicryl, vicryl for galea and running monocryl for skin.

Post Op

PICU from recovery.
Tumour specimens sent to pathology and confirm tumour margin at orbit.
Analgesia, advance oral diet as tolerated.
CT scan overnight if concerns with neurology and contact on-call team please for review.

Chemotherapy

Indication

Patients < 9 yrs with glioma involving the chiasm and/or hypothalamus
Patients who have severe or worsening visual or hypothalamic dysfunction or
Signs of tumor growth

To delay radiotherapy and neurocognitive side effects
In NF-1 for additional risk of secondary moyamoya disease and intracranial tumors due to RT

Cranial radiation

Contraindicated in NF-1.

Vision sparing effect in sporadic tumors in older children and adults.

Outcome

Visual function often stable in untreated patients, but visual decline may result from tumor progression.