The signal intensity ratio of the optic nerve to ipsilateral frontal white matter is of value in the diagnosis of acute optic neuritis

Optic Nerve T2 Signal Intensity and Caliber Reflect Clinical Severity in Genetic Optic Atrophy

BACKGROUND

Genetic optic atrophies comprise phenotypically heterogenous disorders of mitochondrial function. We aimed to correlate quantitative neuroimaging findings of the optic nerves in these disorders with clinical measures.

METHODS

From a retrospective database of 111 patients with bilateral optic atrophy referred for genetic testing, 15 patients diagnosed with nonglaucomatous optic atrophy of genetic origin (7 patients with pathogenic variants in OPA1, 3 patients with Wolfram syndrome, and 5 patients with Leber hereditary optic neuropathy) who had accessible magnetic resonance (MR) images of the orbits and/or brain were analyzed. The primary outcome measures of T2 short Tau inversion recovery (STIR) signal and optic nerve caliber were quantified according to a standardized protocol, normalized to internal standards, and compared between cases and controls. Inter-rater reliability was assessed and clinical features were analyzed according to MRI features.

RESULTS

Compared with control patients, the 15 genetic optic atrophy patients demonstrated significantly increased T2 STIR signal (fold-change 1.6, P = 0.0016) and decreased optic nerve caliber (fold-change 0.72, P = 0.00012) after internal normalization. These metrics were reliable (inter-reader reliability correlation coefficients of 0.98 [P = 0.00036] and 0.74 [P = 0.0025] for normalized STIR and nerve caliber, respectively) and significantly correlated with visual acuity, cup-to-disc ratio, and visual field testing.

CONCLUSION

Normalized optic nerve STIR signal and optic nerve caliber significantly correlate with visual acuity, cup-to-disc ratio, and perimetric performance in patients with genetic optic atrophy. A formalized protocol to characterize these differences on MRI may help to guide accurate and expedient diagnostic evaluation.

A Comparative Review of Typical and Atypical Optic Neuritis: Advancements in Treatments, Diagnostics, and Prognosis

Optic neuritis (ON) is a debilitating condition that through various mechanisms, including inflammation or demyelination of the optic nerve, can result in partial or total permanent vision loss if left untreated. Accurate diagnosis and promptly initiated treatment are imperative related to the potential of permanent loss of vision if left untreated, which can lead to a significant reduction in the quality of life in affected patients. ON is subtyped as "typical" or "atypical" based on underlying causative etiology. The etiology of ON can be differentiated when appropriate diagnostic testing is performed. Using history taking, neuroimaging, and visual testing to localize the underlying pathology of ON in a time-sensitive manner is critical in mitigating these unsatisfactory outcomes. Herein, we examine the differences in presentation, pathophysiology, and treatments of typical ON causes, like multiple sclerosis (MS), and atypical causes such as neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein (MOG)-immunoglobulin G (IgG) ON. The present investigation places focus on both neuroimaging and visual imaging in the differentiation of ON. Additionally, this review presents physicians with a better understanding of different presentations, treatments, and prognoses of ON.

Diagnostic value of contrast-enhanced 3D FLAIR sequence in acute optic neuritis

PURPOSE

Contrast-enhanced fluid-attenuated inversion recovery (FLAIR) sequence of the brain has the potential for detecting optic nerve abnormality. This study aimed to compare the diagnostic value of whole-brain contrast-enhanced three-dimensional FLAIR with fat suppression (CE 3D FLAIR FS) sequence in detecting acute optic neuritis to dedicated orbit MRI and clinical diagnosis.

MATERIALS AND METHODS

Twenty-two patients with acute optic neuritis who underwent whole-brain CE-3D-FLAIR FS and dedicated orbit MRI were retrospectively included. The hypersignal FLAIR of the optic nerve on whole-brain CE-3D-FLAIR FS, enhancement, and hypersignal T2W on orbit images were assessed. The optic nerve to frontal white matter signal intensity ratio on CE-FLAIR FS was calculated as maximum signal intensity ratio (SIR) and mean SIR.

RESULTS

Twenty-six hypersignals of optic nerves were found on CE-FLAIR FS from 30 pathologic nerves. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of CE FLAIR FS brain and dedicated orbital images for diagnosing acute optic neuritis were 77%, 93%, 96%, 65%, and 82% and 83%, 93%, 96%, 72%, and 86%, respectively. Optic nerve to frontal white matter SIR of the affected optic nerves was higher than that of normal optic nerves. Using a cutoff maximum SIR of 1.24 and cutoff mean SIR of 1.16, the sensitivity, specificity, PPV, NPV, and accuracy were 93%, 86%, 93%, 80%, and 89% and 93%, 86%, 93%, 86%, and 91%, respectively.

CONCLUSION

The hypersignal of the optic nerve on whole-brain CE 3D FLAIR FS sequence has qualitative and quantitative diagnostic potential in patients with acute optic neuritis.

Structure-function relationship between magnetic resonance imaging lesion areas and visual field defects in initial optic neuritis with altitudinal hemianopsia

PURPOSE

To study the spatial association of magnetic resonance imaging (MRI) contrast enhancement (CE) areas with visual field defect (VFD) asymmetry in initial cases of optic neuritis (ON) with altitudinal hemianopsia (AH) with reference to nonarteritic anterior ischemic optic neuropathy (NAION) with AH.

STUDY DESIGN

Multicenter, cross-sectional study.

METHODS

The present study comprised 19 ON patients and 20 NAION patients with AH who underwent orbital contrast fat-suppressed MRI. The signal-to-intensity ratio (SIR) was calculated by dividing the maximum CE of the optic nerve by the mean CE of the cerebral white matter in 11 coronal sections at 3-mm intervals from immediately posterior to the eyeball to the optic chiasm. Sections in ON patients with an SIR exceeding the mean plus 2 standard deviations of the SIR at the corresponding section in the NAION group were considered abnormal. The correlation between upper-to-lower CE asymmetry in the maximum SIR section and VFD counterpart was determined.

RESULTS

The ON group had significantly higher maximum SIR than that of the NAION group (1.77 ± 0.88 vs. 1.25 ± 0.32; P < .01). Seven of the 19 patients had sections with abnormally high CE extending posteriorly beyond the orbital apex. Significant spatial correspondence was observed between CE and VFD asymmetry (rs = 0.563; P = .015) in the ON group but not in the NAION group (rs = - 0. 048; P = .850).

CONCLUSIONS

ON patients with AH frequently show CE even in the intracerebral optic nerve, maintaining a moderate structure-function correspondence.

Reproducibility and feasibility of optic nerve diffusion MRI techniques: single-shot echo-planar imaging (EPI), readout-segmented EPI, and reduced field-of-view diffusion-weighted imaging

Background

Diffusion-weighted imaging (DWI) is an essential technique for optic nerve diseases. However, the image quality of optic nerve DWI is decreased by the distortions and artifacts associated with conventional techniques. In order to establish this method as a critical tool in optic nerve diseases, reproducibility and feasibility of new technical and conventional approaches of DWI need to be systematically investigated.

Methods

DWIs were acquired using ss-EPI, readout-segmented EPI (rs-EPI) DWI, and reduced field-of-view (rFOV) DWI. 26 volunteers (mean age 31.2 years) underwent repeated MRI examinations in order to assess scan–rescan reproducibility and accuracy. The apparent diffusion coefficient (ADC) values (three ROIs were measured on each side) were determined to evaluate the reproducibility of each sequence and the differences between the three techniques. To quantify the geometric distortion artifacts, the length of optic nerve and the maximum angle of optic nerve were defined and compared to T2-weighted imaging. In addition, two readers evaluated four different aspects of image quality on 5-point Likert scales.

Results

rs-EPI DWI (ICCs: 0.916, 0.797 and 0.781) and rFOV DWI (ICCs: 0.850, 0.595 and 0.750) showed higher reproducibility (ICCs: ROI₁, ROI₂ and ROI₃) of mean ADC value in all three ROIs than ss-EPI DWI (ICCs: 0.810, 0.442 and 0.379). The quantitative analysis of geometric distortion yielded a higher agreement of both rs-EPI DWI and rFOV DWI with T2-weighted imaging than ss-EPI. rs-EPI DWI (2.38 ± 0.90) and rFOV DWI (2.46 ± 0.58) were superior to ss-EPI DWI (1.58 ± 0.64) with respect to overall image quality and other aspects of image quality, each with P < 0.05. The mean ADC values of rFOV DWI were significantly lower than those of rs-EPI DWI and ss-EPI DWI in all three ROIs (P < 0.001).

Conclusions

Both rs-EPI DWI and rFOV-EPI DWI are suitable techniques for the assessment of diffusion restriction and provide significantly improved image quality compared with ss-EPI DWI. For methods using the same acquisition time, rFOV DWI is superior to ss-EPI DWI, while rs-EPI showed an overall superiority, although this technique took 47% longer to perform.

Fractional anisotropy helps to differentiate the optic nerve impairment between neuromyelitis optica spectrum disorders and multiple sclerosis

OBJECTIVES

To assess the characteristics of optic nerve impairment between neuromyelitis optica spectrum disorders (NMOSD) and multiple sclerosis (MS) patients by fractional anisotropy (FA).

METHODS

Thirty-one NMOSD patients, 25 MS patients, and 17 heathy controls (HC) who underwent optic nerve DTI were included. The optic nerves of the NMOSD and MS patients were divided into vision-impaired (VI) subgroups and normal-appearing (NA) subgroups according to visual status, respectively. FA values were measured in the anterior, middle, and posterior segments of each intraorbital optic nerve.

RESULTS

FA values in VI NMOSD were significantly decreased in the whole optic nerve, especially the posterior segment of the optic nerve (p < 0.001). FA values measured in the anterior and middle segments of the optic nerve in VI MS were significantly decreased as compared to those in the HC (p < 0.05). Between NMOSD and MS, FA values in the posterior segment of the optic nerve showed significant differences (VI NMOSD vs. VI MS, 0.458 ± 0.097 vs. 0.568 ± 0.098, p < 0.001; NA NMOSD vs. NA MS, 0.568 ± 0.098 vs. 0.600 ± 0.085, p = 0.041, respectively). The signal intensity ratio (SIR) in the posterior segment of the optic nerve was significantly increased in VI NMOSD as compared with VI MS (p = 0.002). The combination of SIR and FA for distinguishing VI NMOSD from VI MS resulted in sensitivity, specificity, and positive and negative predictive values of 86.49%, 80.00%, 88.9%, and 76.2%, respectively.

CONCLUSION

FA could quantify the characteristics of NMOSD- and MS-related optic nerve impairment. DTI was a simple and effective imaging tool to differentiate between the two.

KEY POINTS

• NMOSD-related optic nerve impairment is extensive, often greater than half of the optic nerve, with the most significant involvement of the posterior segment of the optic nerve. • MS-related optic nerve impairment is more limited than NMOSD, and anterior and middle optic nerve involvement is common. • Optic nerve DTI is a convenient and effective imaging tool that can help characterize NMOSD and MS.

Evaluating the Utility of a Postprocessing Algorithm for MRI Evaluation of Optic Neuritis

BACKGROUND AND PURPOSE

MR imaging is useful for the detection and/or confirmation of optic neuritis. The objective of this study was to determine whether a postprocessing algorithm selectively increases the contrast-to-noise ratio of abnormal optic nerves in optic neuritis, facilitating this diagnosis on MR imaging.

MATERIALS AND METHODS

In this retrospective case-control study, coronal FLAIR images and coronal contrast-enhanced T1WI from 44 patients (31 eyes with clinically confirmed optic neuritis and 28 control eyes) underwent processing using a proprietary postprocessing algorithm designed to detect and visually highlight regions of contiguous increases in signal intensity by increasing the signal intensities of regions that exceed a predetermined threshold. For quantitative evaluation of the effect on image processing, the contrast-to-noise ratio of equivalent ROIs and the contrast-to-noise ratio between optic nerves and normal-appearing white matter were measured on baseline and processed images. The effect of image-processing on diagnostic performance was evaluated by masked reviews of baseline and processed images by 6 readers with varying experience levels.

RESULTS

In abnormal nerves, processing resulted in an increase in the median contrast-to-noise ratio from 17.8 to 85.0 (P < .001) on FLAIR and from 19.4 to 93.7 (P < .001) on contrast-enhanced images. The contrast-to-noise ratio for control optic nerves was not affected by processing (P = 0.13). Image processing had a beneficial effect on radiologists' diagnostic performance, with an improvement in sensitivities for 5/6 readers and relatively unchanged specificities. Interobserver agreement improved following processing.

CONCLUSIONS

Processing resulted in a selective increase in the contrast-to-noise ratio for diseased nerves and corresponding improvement in the detection of optic neuritis on MR imaging by radiologists.