Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Optic Glioma (Pilocytic Astrocytoma of Optic Nerves or Chiasm)

Key Facts

•Congenital low-grade astrocytoma of optic nerves or chiasm • 30–50% of patients have neurofibromatosis type 1 • Usually discovered during first decade

• Vision ranges from normal to severely impaired • MRI may be diagnostic in showing intrinsic mass of anterior visual pathway • Biopsy reserved for cases in which imaging is not diagnostic • Chemotherapy and radiation are treatment options but no controlled study available to show efficacy

Clinical Findings

•Stationary or progressive visual loss in one eye or both • Iris hamartomas (Lisch nodules) and/or eyelid plexiform neurofibromas may be present • Visual acuity and/or visual field loss • Afferent pupil defect is common • Pendular (monocular or seesaw) nystagmus sometimes • Optic discs normal, swollen, or pale • Proptosis if large intraorbital component

Ancillary Testing

•MRI shows intrinsic mass of optic nerves, optic chiasm, optic tracts, or hypothalamus • Brain MRI may also show hamartomas elsewhere that are typical of neurofibromatosis type 1

Differential Diagnosis

•Optic nerve sheath meningioma, orbital neurofibroma or schwannoma

• Craniopharyngioma • Optic neuritis

Treatment

•Biopsy if imaging is not diagnostic • Ventriculoperitoneal shunt to relieve hydrocephalus • No treatment for patients with glioma confined to optic nerve unless there is disfiguring proptosis and eye is blind, in which case consider surgical excision of tumorous optic nerve with sparing of eye and extraocular muscles • Chemotherapy for patients under age 9 with glioma involving the chiasm and/or hypothalamus and who have severe or worsening visual or hypothalamic dysfunction or signs of tumor growth • Cranial radiation is contraindicated for patients with neurofibromatosis because of risks of occlusive vasculopathy and secondary tumors • There are no controlled trials

to affirm that any treatment option improves on the natural history

Prognosis

•Visual function often stable in untreated patients • Visual decline may result from tumor growth, tumor production of extracellular matrix, or reactive meningeal hyperplasia • Tumors confined to optic nerve have very low grade histology (grade 1 astrocytoma) and generally show little if any growth

• Intracranial extension of a tumor originally confined to the orbit has never been reliably documented • Tumors involving optic chiasm and hypothalamus are of a higher histologic grade (grade 2) than tumors confined to optic nerve and may cause considerable morbidity and even death

A

B

Fig. 3.29 Intracranial optic glioma. Postcontrast axial T1 MRI shows thickening and enhancement of the optic chiasm (arrow).

Fig. 3.28 Orbital optic glioma. (A) Postcontrast coronal T1 MRI

shows enlarged right optic nerve with enhancing (bright) cuff that represents meningeal reaction to the tumor (arrow).

(B) Postcontrast axial T1 MRI shows that the tumor is confi ned to the orbit (arrow). In a child, these imaging fi ndings are suffi ciently diagnostic of pilocytic (grade 1) astrocytoma (optic glioma) that biopsy is unnecessary.

Glioma Optic

Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Anterior Visual Pathway Intracranial Aneurysm

Key Facts

•Ballooning of a segment of the intracranial carotid artery because of a congenital media defect (saccular or berry aneurysm) or chronic arteriosclerosis and hypertension (fusiform aneurysm)

•Affects carotid–ophthalmic artery junction or supraclinoid carotid artery

•Causes visual acuity and/or visual field loss by compression of optic nerve or chiasm

•Coiling is as effective and safer than clipping but is an option only if the aneurysm has a relatively narrow neck

•Recovery of vision depends on preoperative degree of visual damage

Clinical Findings

•Chronic (rarely acute) visual loss, usually monocular

•May have headache or hypopituitary symptoms

•Visual acuity and/or visual field loss (nerve fiber bundle or hemianopic defects)

•Afferent pupil defect

•Optic disc appears normal or pale

Ancillary Testing

•Brain CT or MRI usually shows a mass in anterior middle fossa

•CT angiography or magnetic resonance angiography is necessary for more secure diagnosis

•Conventional catheter cerebral angiography is necessary for best definition, especially if non-invasive studies are equivocal or intervention is being considered

Differential Diagnosis

• Other sellar or presellar middle fossa mass lesions

Treatment

•Surgical treatment (clipping, wrapping) is challenging because these aneurysms are often large (supraclinoid) or hard to reach and patients often have arteriosclerosis

•Intravascular coiling is usually preferred unless the aneurysm has a very wide neck

Prognosis

•Without intervention, saccular (berry) aneurysms rupture at 3%/year if <25 mm diameter and at 8%/year if >25 mm diameter

•Intervention rarely produces substantial visual recovery—its purpose is to prevent further visual loss and death from rupture

•Morbidity and mortality of intervention depend on size of aneurysm and age and health of patient

A

B

Fig. 3.30 Supraclinoid carotid artery aneurysm. (A) Right carotid lateral cerebral angiogram shows large aneurysm (arrow) arising above the ophthalmic artery branch; it compressed and damaged the right optic nerve. (B) After coiling, the aneurysm no longer fi lls with contrast dye (arrow).

Aneurysm Intracranial Pathway Visual Anterior