How can MRI of the orbit and brain with contrast differentiate between neuroretinitis and optic neuritis?

MRI Differentiation of Neuroretinitis and Optic Neuritis

Contrast-enhanced MRI of the orbits and brain effectively differentiates neuroretinitis from optic neuritis by demonstrating optic nerve enhancement and T2 hyperintensity in optic neuritis, while neuroretinitis typically shows normal optic nerve imaging or only optic nerve sheath enhancement without intrinsic nerve involvement. 1

Key Imaging Distinctions

Optic Neuritis MRI Findings

• Intrinsic optic nerve abnormalities are the hallmark, with T2 hyperintensity, optic nerve swelling, and contrast enhancement present in 95% of cases 2, 3
• Coronal fat-suppressed T2-weighted sequences optimally visualize these optic nerve lesions 2, 3
• T1-weighted post-contrast images with fat suppression identify abnormal optic nerve enhancement in 95% of optic neuritis cases 3
• The presence of T2-hyperintense lesions within the nerve differentiates optic neuritis from ischemic and toxic optic neuropathies 2

Neuroretinitis MRI Findings

• Normal optic nerve imaging is typical, as neuroretinitis primarily affects the retina and optic disc rather than the optic nerve itself 4
• When MRI abnormalities occur, they show optic nerve sheath enhancement and perineural fat enhancement rather than intrinsic nerve involvement 5
• The pathology involves subretinal fluid accumulation and neurosensory retinal thickening visible on OCT, not MRI 4

Recommended Imaging Protocol

Both contrast-enhanced MRI of the orbits AND brain should be obtained together when evaluating suspected optic neuritis, as this dual approach is critical for:

• Evaluating abnormal enhancement and T2 signal changes within the optic nerve 1
• Assessing for intracranial demyelinating lesions that predict multiple sclerosis risk 1
• Even a single clinically silent T2 hyperintense brain lesion dramatically increases MS risk (hazard ratio 5.1 for 1-3 lesions) 3

Clinical Context for Differentiation

Optic Neuritis Presentation

• Subacute visual loss over hours to days with periocular pain worsening with eye movement 3
• Red-green color desaturation (dyschromatopsia) is characteristic 2, 3
• Central scotomas are the typical visual field defect 3
• Optic disc may be normal (retrobulbar neuritis in 2/3 of cases) or show mild edema 6

Neuroretinitis Presentation

• Unilateral optic neuropathy is typical, most commonly from cat scratch disease (Bartonella henselae) 4
• Swollen optic disc with eventual macular star formation is pathognomonic 4
• OCT shows flattening of the fovea and subretinal fluid, not visible on MRI 4

Critical Pitfalls to Avoid

• Do not rely on optic disc appearance alone: One-third of optic neuritis cases show disc edema, mimicking neuroretinitis clinically 6
• Optic perineuritis can coexist with neuroretinitis, showing nerve sheath enhancement that may be confused with optic neuritis 5
• Perioptic nerve sheath enhancement can occur in typical optic neuritis, but soft tissue enhancement extrinsic to the nerve indicates non-MS etiology such as granulomatous disease or infection 2
• Treatment delay beyond 2 weeks is an unfavorable prognostic factor in optic neuritis, making urgent MRI essential 2

Red Flags Requiring Antibody Testing

If MRI shows any of these features, immediately test for AQP4-IgG and MOG-IgG antibodies to exclude neuromyelitis optica spectrum disorders or MOG-antibody disease 2:

• Bilateral simultaneous involvement 2
• Posterior optic nerve involvement extending to chiasm 2
• Long optic nerve lesions 2
• Soft tissue enhancement extrinsic to the nerve affecting orbit, orbital apex, or cavernous sinus 2