Nonconventional Optic Nerve Imaging in Multiple Sclerosis
Section snippets
Optic nerve anatomy
The paired optic nerves, each 50 mm in length, serve to transmit visual information from the retina to the optic chiasm. Each optic nerve, from the globe to the chiasm, is composed of four parts: intraocular (optic nerve head, 1 mm), intraorbital (25 mm), intracanalicular (traversing the optic canal, 9 mm), and intracranial (stretching from the canal to the optic chiasm, 4 to 16 mm). Each is composed of a bundle of nerve fibers that maintain a topical arrangement along their course from the
Optic neuritis: clinical presentation
In the absence of other symptoms of MS, acute demyelinating ON is referred to as one of the clinically isolated syndromes (CIS) suggestive of MS. Young to middle-aged persons (second through fourth decade) are most commonly affected. ON is approximately three times more common in women than in men.3, 6, 7 Patients present with vision loss that is acute or subacute. In greater than 90% of patients, pain exacerbated by eye movements is reported. The degree of vision loss is variable, with median
Conventional MR imaging: lesions of the optic nerve
The diagnosis of acute, monosymptomatic ON is often based on the appropriate clinical history and supportive examination findings, without the need for neuroimaging. However, data from the Optic Neuritis Treatment Trial (ONTT)12 and the Longitudinal Optic Neuritis Study (LONS)13, 14 have highlighted the utility of brain MR imaging in predicting the subsequent risk of developing MS. In atypical cases, MR imaging of the orbits should be obtained to exclude an alternate diagnosis, such as a
Optic nerve atrophy
While classically considered an inflammatory-demyelinating process, both acute and chronic phases of MS have been shown to result in axonal injury;1 this is the basis for progressive and permanent neurologic dysfunction as a consequence of demyelinating disease. Following the acute phase of ON (when the inflammatory process results in edema of the optic nerve), ongoing demyelination results in axon loss and atrophy. This process was first documented using conventional optic nerve imaging in
Magnetization transfer MR imaging
Magnetization transfer MR imaging (MT MR imaging) provides an analysis of the degree of tissue damage, both within and surrounding demyelinating lesions. By measuring macromolecular density, MT MR imaging is superior to conventional MR imaging in its specificity for detecting irreversible demyelination and axonal injury. The studies completed to date suggest that MT MR imaging correlates with functional outcome measures, and may be a useful technique for the longitudinal monitoring of patients
Diffusion tensor MR imaging
Advances in image acquisition and post-processing have allowed the use of DT MR imaging in the longitudinal study of patients with MS. As with other quantitative MR imaging techniques, it is noninvasive and can both detect and quantify tissue changes within and around demyelinating lesions. Application of this technique allows for quantification of the structural integrity of axons; as a result, DT MR imaging represents another potential surrogate for monitoring disease progression in MS.
The
Optical coherence tomography
As a technique for detecting subtle but important tissue changes brought about as a consequence of demyelinating disease, OCT has received significant attention. OCT allows for the direct visualization of the relevant tissues themselves; thus, the integrity of the optic nerve fibers as they originate from the retinal ganglion cells can be assessed. OCT circumvents the barrier of the skull, providing a “window” into the disease process and a reflection of alterations occurring elsewhere in the
Summary
It is well recognized that conventional MR imaging is, at present, the most important paraclinical modality for assessing the risk of MS in patients with acute demyelinating ON, and for monitoring the progression of disease. However, there are several limitations that limit the utility of conventional MR in imaging the optic nerve. Furthermore, conventional MR imaging is inadequate as an outcome metric for clinical trials of neuroprotective agents. Newer strategies, including measurement of
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Cited by (21)
Recent advances on optic nerve magnetic resonance imaging and post-processing
2021, Magnetic Resonance ImagingCitation Excerpt :Similarly, Wang et al. also found that MTR reduction in diseased optic nerves was −9.24% after 3 months, −12.48% after 6 months, and −7.61% after 1 year, in which the percentage was measured on the interocular difference [56]. MTR can be measured in different segments along the whole optic nerve, which provides useful information on the progressive nature of the demyelination and remyelination over time [59]. The reduction in MTR is thought to be due to demyelination and Wallerian degeneration that causes the axonal damage.
Multiple sclerosis
2016, Handbook of Clinical NeurologyCitation Excerpt :Using these sequences, the causative lesion can be frequently identified (Glisson and Galetta, 2009). Additional typical findings include dilation of the optic nerve sheath immediately posterior to the globe on fat-saturated fast spin-echo sequences, and optic nerve sheath enhancement on T1-weighted postcontrast scans (Glisson and Galetta, 2009) (Fig. 20.8). In a study of patients with an initial episode of unilateral optic neuritis, the mean cross-sectional area of the intraorbital portion of the optic nerve was lower in diseased eyes than in the fellow eyes and in the eyes of healthy controls (Hickman et al., 2001).
Ophthalmic Manifestations of Systemic Diseases-Part 2: Metabolic, Infections, Granulomatoses, Demyelination, and Skeletal Dysplasias
2014, Current Problems in Diagnostic RadiologyMeasures of visual pathway structure and function in MS: Clinical usefulness and role for MS trials
2013, Multiple Sclerosis and Related DisordersCitation Excerpt :OCT is similar to B-mode ultrasound B-mode imaging, but uses light instead of sound to form images. An optical beam is scanned along the retina and the machine measures echo-time delays in order to synthesize a picture of the retinal structure (Jindahra et al., 2010; Lameril et al., 2009; Sakata et al., 2009; Glisson and Galetta, 2009). Advances in OCT, including the development of spectral- (Fourier) domain technology, provide increased sensitivity and capacity for careful analysis of pathologic changes in the retina in vivo.
Diffusion Magnetic Resonance Imaging in Multiple Sclerosis
2011, Neuroimaging Clinics of North AmericaCitation Excerpt :DTI is a surrogate marker of the structural integrity of the optic nerve, with increases in MD and reductions in FA in case of neuritis. DTI can also be applied to further detection of early optic nerve alterations, before abnormalities detected on conventional MR imaging.81 Despite the potential usefulness of DTI in the clinical scenario in the assessment of the optic nerve, its acquisition is still a technical challenge.
Lesions of the optic nerve
2011, Handbook of Clinical NeurologyCitation Excerpt :At present, MRI continues to be the most important paraclinical modality for assessing the risk of future MS and for monitoring disease progression in patients with acute demyelinating optic neuritis (Fig. 6.6B, C). However, newer imaging strategies, including magnetization transfer MRI, diffusion tensor MRI, and OCT, are being used alone and in combination for earlier detection of clinical impairment, monitoring disease progression, predicting disability, and ascertaining the effects of experimental neuroprotective therapies (Glisson and Galetta, 2009). OCT in particular can provide rapid, reproducible, high-resolution images of retinal anatomy, and is increasingly being used to model the axonal and neuronal degeneration that is now recognized as part of the disease process that contributes to permanent disability in MS (Frohman et al., 2008).