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Optic Neuritis


KEY FACTS

Imaging

  • Focal or segmental T2 hyperintensity of optic nerve

    • Nerve normal in size or minimally enlarged

  • Central or diffuse nerve enhancement

    • ± peripheral sheath enhancement

Top Differential Diagnoses

  • Neuromyelitis optica

  • Ischemic optic neuropathy

  • Infectious optic neuritis (ON)

  • Idiopathic perineuritis (pseudotumor)

  • Granulomatous optic neuropathy (sarcoid)

  • Optic nerve sheath meningioma

  • Optic nerve glioma

Pathology

  • Presumed autoimmune process triggered by infection, systemic disease, or other stressor

Clinical Issues

  • Symptoms and signs

    • Acute loss of visual acuity

    • Relative afferent pupillary defect if unilateral

    • Impaired color vision

    • Eye pain

  • Optic disc acutely looks normal

    • About 1/3 demonstrate mild swelling

  • Distinct clinical profiles

    • Acute ON

    • Neuromyelitis optica (Devic syndrome)

    • Acute demyelinating encephalomyelitis

    • Pediatric ON

  • Spontaneous recovery of vision is characteristic

    • Corticosteroids accelerate acute recovery

    • Early interferon therapy mitigates risk of MS

Diagnostic Checklist

  • Identification of demyelinating lesions in CNS is most important neuroimaging task in setting of ON

    • High incidence of MS in patients with ON

    • Findings on MR strongly predictive of MS

  • Recommend brain and spinal cord imaging

Axial T1WI C+ FS MR in a woman with left eye pain and decreased color vision shows intense segmental enhancement of the left intraorbital optic nerve
. A component of peripheral nerve sheath enhancement is seen extending posteriorly
.

Axial FLAIR MR of the brain in the same patient shows multiple periatrial, capsular, callosal, and subcortical white matter lesions
. Cerebrospinal fluid (CSF) analysis yielded oligoclonal bands, and the patient was diagnosed with multiple sclerosis.

Coronal T1WI C+ FS MR in 22-year-old woman with right eye vision loss, pain, afferent pupillary defect shows enhancement of the intraorbital optic nerve
(compared with normal nonenhancing left nerve
).

Coronal STIR MR in the same patient shows increased signal in the right optic nerve
. Note that the hyperintense signal of the right nerve is similar to CSF in the optic nerve sheath, whereas the normal left nerve
is distinct from the surrounding CSF.

TERMINOLOGY

Abbreviations

  • Optic neuritis (ON)

IMAGING

General Features

  • Best diagnostic clue

    • Enhancement & mild enlargement of optic nerve

  • Location

    • Unilateral in 70%

    • Segment(s) of nerve involvement

      • –

        Anterior intraorbital: 45%

      • –

        Mid intraorbital: 60%

      • –

        Intracanalicular: 35%

      • –

        Prechiasmatic & chiasm: 10%

  • Size

    • Optic nerve diffusely mildly enlarged

CT Findings

  • CECT

    • Often normal, may show mild optic nerve enlargement or enhancement

MR Findings

  • T1WI

    • Optic nerve diffusely & mildly enlarged

  • T2WI

    • Focal or segmental hyperintensity of optic nerve

    • ± coexistent ↑ signal brain & spinal cord lesions

      • –

        Increase long-term disability risk

  • STIR

    • Hyperintensity of optic nerves similar to T2WI

  • FLAIR

    • ± coexistent ↑ signal white matter lesions in brain

      • –

        Presence is strong predictor for multiple sclerosis (MS)

      • –

        Especially if increased on early follow-up brain scan

  • DWI

    • Increased diffusivity in demyelinating plaques

      • –

        May temporarily show decreased diffusion acutely (uncommon)

      • –

        Differentiates acute ON from ischemic optic neuropathy

    • Decreased fractional anisotropy

  • T1WI C+

    • Nerve enhancement centrally or diffusely > 90%

      • –

        Consistent with active demyelination

    • Variant peripheral sheath enhancement pattern

      • –

        May simulate nerve sheath meningioma

      • –

        Less likely to be associated with MS

  • Functional MR

    • Reduced visual cortex activation

Ultrasonographic Findings

  • Grayscale ultrasound

    • Mild enlargement of optic nerve

  • Pulsed Doppler

    • ↑ peak systolic & end diastolic arterial velocities

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