What is the role of MRI in the diagnosis of optic neuritis?

Updated: Feb 25, 2016
  • Author: Pil (Peter) S Kang, MD; Chief Editor: James G Smirniotopoulos, MD  more...
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Answer

Thin (2-3mm), fat-suppressed, T2-weighted images, such as short tau inversion recovery (STIR) sequences, through the optic nerves may show characteristic high-signal intensity foci in the minimally expanded or nonexpanded nerve. These lesions frequently enhance following intravenous contrast administration, which is not seen in a healthy optic nerve. Some studies have shown that certain findings, such as optic nerve lesions of greater length and in certain locations (within the optic canal), may be associated with a worse visual prognosis and may benefit from certain treatments, but other studies have not supported this conclusion.

The signal intensity ratio (SIR) of the optic nerve to the white matter (WM) on STIR was found to be of diagnostic value for acute optic neuritis (AON) in a study of 405 patients with suspected orbital diseases who underwent orbital MRI with  a 3-T scanner. SIRave and SIRmax were significantly (P<  0.001) higher in patients with acute optic neuritis than in control patients. At a cut-off SIRave value of 1.119, the sensitivity, specificity, and accuracy were 0.939, 0.840, and 0.870; and at a cut-off SIRmax value of 1.281,  sensitivity, specificity, and accuracy were 1.000, 0.720 and 0.806, respectively. [8]

Optic neuritis in neuromyelitis optica was found to have a distinct pattern on MRI, as compared to  relapsing-remitting multiple sclerosis. The majority of neuromyelitis optica lesions were longitudinally extensive, measuring at least 17.6 mm in length and involving at least 3 optic nerve segments. At a cutoff of 17.6 mm lesion length, the specificity for neuromyelitis optica was 76.9%; sensitivity, 80.8%; and positive likelihood, 3.50. Conversely, multiple sclerosis lesions were more commonly focal in one optic nerve segment localized anteriorly. [9]

In 25 patients with optic neuritis, multi-scale MRI texture analysis was used to assess optic nerve pathology. Retinal nerve fiber layer (RNFL) values were 20% thicker and lesion texture was 14% more heterogeneous in affected eyes than in nonaffected eyes. In addition, the lesion texture ratio of affected to nonaffected eyes was greater in patients than in controls. In the affected eyes, visual acuity recovered significantly over 6 months (18/23 patients) and 12 months (18/21 patients) when RNFL thickness and optic nerve area ratio decreased over time. Texture heterogeneity in the standard MRI of acute optic nerve lesions was the only measure that predicted functional recovery after optic neuritis. The authors concluded that tissue heterogeneity may be a potential measure of functional outcome in optic neuritis patients and that advanced analysis of the texture in standard MRI could provide insights into mechanisms of injury and recovery in patients with similar disorders. [10]

Diffusion-weighted and diffusion-tensor imaging may contribute more data that may prove to have some bearing on treatment and/or on prognosis. [11, 12, 13, 14] The thought is that the loss of anisotropy (manifested by an increase in the apparent diffusion coefficient or a decrease in fractional anisotropy) associated with demyelination and/or axonal damage may be more sensitive and/or yield more prognostic information than anatomic imaging findings (size, T2 signal intensity, and enhancement, which suggests loss of the blood-brain barrier due to the underlying pathologic process), which could manifest themselves much later than the findings associated with loss of anisotropy. However, with the current technology, diffusion-weighted and diffusion-tensor imaging of the optic nerves is too time- and labor-intensive for broad clinical application.

In a study of 31 patients with optic neuritis, 3-dimensional double inversion recovery (3D DIR) was found to provide improved detection of optic nerve signal abnormalities over 2-dimensional (2D) short tau inversion recovery (STIR) fluid-attenuated inversion recovery (FLAIR). Multiplanar DIR images had the best performance for the diagnosis of optic neuritis, with a sensitivity of 95% and a specificity of 94%. [15]


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