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Optic nerve neuritis


Key points

  • Definition: Optic nerve neuritis (ONN) is inflammation of the optic nerve (ON), which may cause sudden painful, partial or complete visual loss, for a variety of reasons.

  • Classic clue: Young woman presenting with painful eye movement, decreased visual acuity showing enlarged, enhancing ON, and periventricular white matter lesions suggesting multiple sclerosis (MS).

  • ONN usually develops in association with an autoimmune disorder, which may be initiated by infection.

Imaging

Computed tomography features

  • Typically shows an enlarged, enhancing ON.

  • Normal examination in approximately 50% of cases with clinical ONN.

  • May be difficult to distinguish from early optic nerve meningioma (ONM) on computed tomography (CT).

  • Need to look outside the orbit to see signs of MS (see Figure 37-1 , D and E ).

    FIGURE 37-1 ■, A, Axial CT shows avid ON enhancement extending from the right orbital apex to the globe. B, Axial T1 Gd with fat-suppression displays avid enhancement of the right ON. Left ON is not involved. C, Coronal T1 Gd with fat-suppression displays avid enhancement of enlarged right optic nerve. No enhancement of left ON. D, T1 with Gd finds focal enhancement of tiny lesions involving central white matter of corona radiata secondary to MS. E, Axial T2WI through upper cord shows focal lesion on right, secondary to MS. A combination of bilateral optic neuritis and transverse myelitis would suggest Devic disease.

Magnetic resonance imaging features

  • Preferred modality for evaluation of ONN.

  • Gd enhanced fat-saturation (fat-sat) images show enlarged ON with areas of focal enhancement.

  • Normal examination in approximately 50% of cases with clinical ONN.

  • Short tau inversion recovery (STIR) sequences show increased signal intensity (SI) in the substance of the nerve, sometimes in multiple segments.

  • Entire brain can be concurrently examined looking for MS.

  • While the approximately 50% sensitivity seems low, the main function of magnetic resonance imaging (MRI) is to exclude other causes of ON compromise, such as tumor. ,

  • In some patients, the pattern of Gd enhancement is clearly different, affecting only the ON sheath. This condition is commonly called perioptic neuritis or optic perineuritis. ,

Clinical issues

Presentation

  • ONN indicates its inception with decreased visual acuity and pain, particularly with eye movement.

  • Sudden onset of monocular blindness is seen in 20% of cases.

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