Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Traumatic Optic Neuropathy

Key Facts

•Most optic nerve trauma occurs indirectly from a forceful blow to the ipsilateral brow a few inches above the orbital rim (the sweet spot)

•A blow to the sweet spot is transmitted to the optic canal, where the nerve is bruised

•There need be no external evidence of trauma

•Optic canal fractures are uncommon and incidental

•Visual loss is sudden and non-progressive

•Some recovery may spontaneously occur within days to weeks

•There is no effective treatment

•Evidence that high-dose corticosteroid treatment or surgical decompression of the optic canal improves visual outcome is weak

•Direct trauma to optic nerve can also result from a blow or laceration of the orbit or eye

•Visual loss is then more likely due to retinopathy or choroidopathy

Clinical Findings

•History of blunt trauma to brow

•Acute loss of vision in ipsilateral eye

•Visual acuity and/or visual field loss (usually nerve fiber bundle but may be hemianopic if chiasm was bruised)

•No evidence of periocular or ocular soft tissue injury

•Eye appears structurally normal

•Afferent pupil defect

•Fundus appears normal acutely

Optic disc pallor appears ≥4 weeks after injury

Ancillary Testing

•Blows to cranium: brain and orbit imaging may be normal or show optic canal or other sphenoid fractures

•Blows or lacerations to eye or orbit: imaging may show soft tissue swelling and hemorrhage

Differential Diagnosis

•In the proper setting and with full findings, there is no differential diagnosis

•If globe was struck, visual loss may result from traumatic retinopathy or choroidopathy (choroidal rupture)

Treatment

•High-dose corticosteroid treatment (30 mg/kg loading dose followed by 5.4 mg/ kg per day for 3 days) has been used based on a small benefit of this treatment to the spinal cord if administered within 8 h in acute spinal cord injury

•No controlled clinical trial has been done of this regimen in traumatic optic neuropathy • An uncontrolled clinical trial showed no benefit • Experimental studies of optic nerve crush injury suggest that this treatment may be harmful

•If an optic canal fracture is present, it may be tempting to surgically decompress the canal because there are many case reports of postoperative visual improvement, but a single uncontrolled clinical trial showed no benefit of this procedure

•There is no effective treatment of direct contusion or avulsion injury of the optic nerve

Prognosis

• Some visual recovery may occur within weeks but is not the rule

Fig. 3.31 Traumatic optic neuropathy. Precontrast axial CT shows a left optic canal fracture (arrow) in a patient who sustained permanent and complete loss of vision in the left eye after being struck in the head. Caution: optic canal fractures are present in only a minority of patients who suffer traumatic optic neuropathy!

Hemorrhage

Tear

Fig. 3.32 Autopsy specimen of intracanalicular optic nerve in a patient who died after a strong blow to the forehead. The specimen shows a tissue cleft and hemorrhages. The pathology of traumatic optic neuropathy may look like this. (From Lindenberg R et al. Neuropathology of Vision. An Atlas. Philadelphia: Lea & Febiger; 1973: 167, with permission.)

Neuropathy Optic Traumatic

Disorders Chiasm• 3 SECTIONor Nerve Optic Acquired

Radiation Optic Neuropathy

Key Facts

•Sudden, often stepwise, and usually irreversible visual loss caused by infarction of intracranial optic nerve(s) or optic chiasm

•Occurs months to years after radiation treatment of paranasal sinus or cranial base tumors

•Rare event (<2%) except if:

•total dose >6000 cGy

•daily dose fraction >200 cGy

•patient has pre-existing arteriolar sclerosis or diabetes

•there has been a breach in delivery technique

•Eye and surrounding tissues appear structurally normal

•Afferent pupil defect is usually only objective sign

•No effective treatment (corticosteroids and hyperbaric oxygen have been tried but without benefit)

•Visual loss is irreversible

Clinical Findings

•Acute painless visual loss, usually monocular

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

•Eyes and surrounding tissues appear structurally normal

•Afferent pupil defect

Ancillary Testing

•Brain MRI shows enhancement and thickening of intracranial segment of affected optic nerve and sometimes optic chiasm

Differential Diagnosis

•Orbital or middle fossa tumor

•Orbital or middle fossa inflammation

•Optic neuritis

Treatment

•No effective treatment (corticosteroids and hyperbaric oxygen have been tried but without benefit)

Prognosis

•Minimal if any visual recovery

• Further visual loss is common, often in a step-wise (stroke-like) pattern

A B

Fig. 3.33 Radiation optic neuropathy. (A) Precontrast coronal T1 MRI of the prechiasmatic optic nerves (upper left) and optic chiasm (upper right) shows thickening on the right side (arrows). (B) Postcontrast coronal T1 MRI shows that these thickened areas enhance. Such fi ndings can also be seen in infl ammatory and infi ltrative (neoplastic) processes.

Neuropathy Optic Radiation