Enhancement and demyelination of the intraorbital optic nerve. Fat suppression magnetic resonance imaging.

Conventional spin-echo magnetic resonance imaging (MRI) of intraorbital optic neuritis is hampered by the adjacent high signal and chemical shift artifact of orbital fat. Frequency-selective saturation pulse MRI reduces these problems and was used to determine its utility in evaluation of intraorbital optic neuritis. Eight consecutive patients with optic neuritis underwent MRI within 1 week of the onset of visual loss. Conventional MRI with T1, proton density, and T2 weighting and frequency-selective saturation pulse MRI with T1, proton density, and T2 weighting were performed. After administration of intravenous gadopentetate dimeglumine, T1-weighted conventional and frequency-selective saturation pulse MRI were performed. Frequency-selective saturation pulse MRI showed gadopentetate dimeglumine enhancement in the intraorbital optic nerve in 7 patients and the intracranial optic nerve in 3 patients. Conventional MRI failed to show optic nerve gadopentetate dimeglumine enhancement in patients with intraorbital lesions, but did show intracranial lesions. Frequency-selective saturation pulse MRI showed bilateral optic nerve enhancement in 3 patients with unilateral visual signs and symptoms. Proton density and T2-weighted conventional MRI of the brain showed no convincing signal aberrations in the optic nerves. In the MRI evaluation of intraorbital optic neuritis: (1) frequency-selective saturation pulse fat suppression MRI is superior to T1-weighted conventional MRI in the detection of gadopentetate dimeglumine enhancement; (2) frequency-selective saturation pulse proton density and T2-weighted MRI is superior to proton density and T2-weighted conventional MRI; (3) frequency-selective saturation pulse MRI showed gadopentetate dimeglumine enhancement as well as proton density/T2-weighted signal aberration in exactly the same portion of the intraorbital optic nerve.