The Evaluation of Optic Nerves Using 7 Tesla "Silent" Zero Echo Time Imaging in Patients with Leber's Hereditary Optic Neuropathy with or without Idebenone Treatment

Neuroimaging changes in the pregeniculate visual pathway and chiasmal enlargement in Leber hereditary optic neuropathy

PURPOSE

To describe the pattern of MRI changes in the pregeniculate visual pathway in Leber hereditary optic neuropathy (LHON).

METHOD

This retrospective observational study enrolled 60 patients with LHON between January 2015 and December 2021. The abnormal MRI features seen in the pregeniculate visual pathway were investigated, and then correlated with the causative mitochondrial DNA (mtDNA) mutation, the distribution of the MRI lesions and the duration of vision loss.

RESULT

The cohort included 48 (80%) males and 53 (88%) had bilateral vision loss. The median age of onset was 17.0 years (range 4.0-58.0). 28 (47%) patients had the m.11778G>A mutation. 34 (57%) patients had T2 hyperintensity (HS) in the pregeniculate visual pathway and 13 (22%) patients with chiasmal enlargement. 20 patients (71%) carrying the m.11778G>A mutation had T2 HS, significantly more than the 14 patients (44%) with T2 HS in the other LHON mutation groups (p=0.039). Furthermore, significantly more patients in the m.11778G>A group (16 patients (57%)) had T2 HS in optic chiasm (OCh)/optic tract (OTr) than the other LHON mutation groups (7 patients (22%), p=0.005). Optic chiasmal enlargement was more common in patients with vision loss duration <3 months compared with those ≥3 months (p=0.028).

CONCLUSION

T2 HS in the pregeniculate visual pathway is a frequent finding in LHON. Signal changes in the OCh/OTr and chiasmal enlargement, in particular within the first 3 months of visual loss, were more commonly seen in patients carrying the m.11778G>A mtDNA mutation, which may be of diagnostic significance.

Abnormal cerebral blood flow in patients with Leber's hereditary optic neuropathy

PURPOSE

The study aimed to unravel abnormal cerebral blood flow (CBF) in patients with Leber's hereditary optic neuropathy (LHON) using arterial spin labeling (ASL) and to investigate the associations among disrupted CBF, disease duration, and neuro-ophthalmological impairment.

METHODS

ASL perfusion imaging data was collected from 20 patients with acute LHON, 29 patients with chronic LHON, and 37 healthy controls. We used a one-way analysis of covariance to test the intergroup differences in CBF. Linear and nonlinear curve fit models were applied to explore the associations among CBF, disease duration, and neuro-ophthalmological metrics.

RESULTS

Brain regions differed in LHON patients, including the left sensorimotor and bilateral visual areas (p < 0.05, cluster-wise family-wise error correction). Acute and chronic LHON patients demonstrated lower CBF in bilateral calcarine than the healthy controls. Chronic LHON had lower CBF in the left middle frontal gyrus and sensorimotor cortex, and temporal-partial junction than the healthy controls and acute LHON. A significant logarithmic negative correlation was shown between CBF of left middle frontal gyrus and disease duration. A significant linear positive correlation was found between retinal nerve fiber layer thickness and CBF in left middle frontal gyrus, and negative correlations between loss of variance and CBF in left middle frontal gyrus and sensorimotor cortex (p < 0.05, Bonferroni correction).

CONCLUSION

LHON patients exhibited reduced CBF in the visual pathway, sensorimotor and higher-tier cognitive areas. Disease duration and neuro-ophthalmological impairments can influence the metabolism of non-visual areas.

Optic nerve lesion length is a biomarker of visual disability in the pre-chronic phase of Leber's hereditary optic neuropathy

OBJECTIVE

The current research aims to investigate relationships between the optic nerve (ON) lesion length with visual function in the pre-chronic phase ( illness duration < 12 months) of LHON.

METHODS

Orbital MRI was retrospectively analyzed for 45 patients with LHON in the pre-chronic phase. ON lesion length was measured by 2 trained independent readers and it was recorded as multiplication of the number of abnormal MRI slices and slice thickness on T2-STIR sequence in the coronal plane. Decimal visual acuity was converted to the logarithm of minimum angle of resolution. Intra-class correlation coefficients (ICCs) were used to assess intra- and inter-observer agreements. Pearson's correlation analysis and multivariate linear regression models were performed to analyze the correlations of the lesion length with best corrected visual acuity (BCVA) and visual field parameters.

RESULTS

81 afflicted eyes were selected. The ICCs for intra-observer and inter-observer analyses were 0.989 and 0.980 respectively. Both Pearson's correlation analysis and multivariate linear regression models indicated a significant positive correlation between the BCVA or mean deviation (MD) and ON lesion length (r_BCVA=0.368, P_BCVA=0.001; r_MD=-0.269, P_MD=0.045) with a coefficient of determination (R²) of 0.152 and 0.114 respectively adjusted for patients' sex, age of onset, onset of vision loss to performance of MRI, mitochondrial DNA mutations.

CONCLUSION

ON length with T2-STIR hyperintensities was positively associated with both BCVA and MD, and it was suspected to be a biomarker of visual disability in the pre-chronic phase of LHON.

Magnetic Resonance Imaging Findings in the Pregeniculate Visual Pathway in Leber Hereditary Optic Neuropathy

BACKGROUND

Current research has not provided a consistent and qualitative description of MRI features in Leber hereditary optic neuropathy (LHON). Our study aims to investigate the MRI findings in the pregeniculate visual pathway and discuss their clinical significance in LHON.

METHODS

Orbital MRI was retrospectively analyzed for 53 patients with LHON (101 afflicted eyes) admitted to the Department of Neurology, Beijing Tongren Hospital, Capital Medical University, from 2014 to 2019. We described the imaging abnormalities and discussed their associations with the time interval from the onset of vision loss to the performance of MRI (TIOVP), prevalence of m.11778G>A, and best-corrected visual acuity (BCVA).

RESULTS

T2 hyperintense signal (HS) was determined in 82 afflicted eyes, with 34 located in the intraorbital segment (IO) of the optic nerve (ON), 26 in the IO concurrent with intracanalicular segment (ICn), 14 in the IO and ICn concurrent with intracranial segment (ICr) of the ON, 4 in the IO, ICn, and ICr concurrent with optic chiasm (OCh), and 4 in the IO, ICn, ICr, and OCh concurrent with optic tract (OTr). MRI was normal in the remaining 19 afflicted eyes. Among the 6 groups, no statistical differences were found in the TIOVP (P = 0.071), prevalence of m.11778G>A (P = 0.234), and BCVA (P = 0.076). As T2 HS extended, the BCVA gradually decreased. Nineteen of the 54 afflicted eyes revealed contrast enhancement, with the TIOVP ranging from 0.25 to 6 months.

CONCLUSIONS

T2 HS was common in the pregeniculate visual pathway in LHON. It was not correlated with the prevalence of m.11778G>A and did not benefit in disease staging. As it extended, the BCVA gradually decreased. Contrast enhancement was relatively rare, always occurring in the subacute stage.

Application of advanced magnetic resonance imaging in glaucoma: a narrative review

Glaucoma is a group of eye diseases characterized by progressive degeneration of the optic nerve head and retinal ganglion cells and corresponding visual field defects. In recent years, mounting evidence has shown that glaucoma-related damage may not be limited to the degeneration of retinal ganglion cells or the optic nerve head. The entire structure of the visual pathway may be degraded, and the degradation may even extend to some non-visual brain regions. We know that advanced morphological, functional, and metabolic magnetic resonance technologies provide a means to observe quantitatively and in real time the state of brain function. Advanced magnetic resonance imaging (MRI) techniques provide additional diagnostic markers for glaucoma, which are related to known potential histopathological changes. Many researchers in China and globally have conducted clinical and imaging studies on glaucoma. However, they are scattered, and we still need to systematically sort out the advanced MRI related to glaucoma. We reviewed literature published in any language and included all studies that were able to be translated into English from 1 January 1980 to 31 July 2021. Our literature search focused on emerging magnetic resonance neuroimaging techniques for the study of glaucoma. We then identified each functional area of the brain of glaucoma patients through the integration of anatomy, image, and function. The aim was to provide more information about the occurrence and development of glaucoma diseases. From the perspective of neuroimaging, our study provides a research basis to explain the possible mechanism of the occurrence and development of glaucoma. This knowledge gained from these techniques enables us to more clearly observe the damage glaucoma causes to the whole visual pathway. Our study provides new insights into glaucoma-induced changes to the brain. Our findings may enable the progress of these changes to be analyzed and inspire new neuroprotective therapeutic strategies for patients with glaucoma in the future.

Neuroimaging in Leber Hereditary Optic Neuropathy: State-of-the-art and future prospects

Leber Hereditary Optic Neuropathy (LHON) is an inherited mitochondrial retinal disease that causes the degeneration of retinal ganglion cells and leads to drastic loss of visual function. In the last decades, there has been a growing interest in using Magnetic Resonance Imaging (MRI) to better understand mechanisms of LHON beyond the retina. This is partially due to the emergence of gene-therapies for retinal diseases, and the accompanying expanded need for reliably quantifying and monitoring visual processing and treatment efficiency in patient populations. This paper aims to draw a current picture of key findings in this field so far, the challenges of using neuroimaging methods in patients with LHON, and important open questions that MRI can help address about LHON disease mechanisms and prognoses, including how downstream visual brain regions are affected by the disease and treatment and why, and how scope for neural plasticity in these pathways may limit or facilitate recovery.

Retinal morphological and functional response to Idebenone therapy in Leber hereditary optic neuropathy

Leber hereditary optic neuropathy (LHON) is a mitochondrial disease leading to optic atrophy due to degeneration of the retinal ganglion cell. A curative treatment is not available at the moment, but a new antioxidant drug, Idebenone, is expected to reduce the progression of the disorder. Two male patients, genetically confirmed with LHON, were clinically, morphologically, and electrophysiologically evaluated, before and three, six, nine and 12 months after starting the treatment. The patient with 3460G>A mutation in mitochondrially-encoded nicotinamide adenine dinucleotide, reduced form (NADH):ubiquinone oxidoreductase core subunit (mtND)1 gene showed an improvement in visual acuity, visual field, and visual evoked potentials with no effect on morphological examinations, while the patient with 11778G>A mutation in mtND4 gene showed no functional, nor morphological recovery after one year of treatment. This study demonstrates that Idebenone, depending on the genetic profile of the disease, may be effective in functional improvement in patients with LHON.

Silent zero TE MR neuroimaging: Current state-of-the-art and future directions

Magnetic Resonance Imaging (MRI) scanners produce loud acoustic noise originating from vibrational Lorentz forces induced by rapidly changing currents in the magnetic field gradient coils. Using zero echo time (ZTE) MRI pulse sequences, gradient switching can be reduced to a minimum, which enables near silent operation.Besides silent MRI, ZTE offers further interesting characteristics, including a nominal echo time of TE = 0 (thus capturing short-lived signals from MR tissues which are otherwise MR-invisible), 3D radial sampling (providing motion robustness), and ultra-short repetition times (providing fast and efficient scanning).In this work we describe the main concepts behind ZTE imaging with a focus on conceptual understanding of the imaging sequences, relevant acquisition parameters, commonly observed image artefacts, and image contrasts. We will further describe a range of methods for anatomical and functional neuroimaging, together with recommendations for successful implementation.

Recent advances on optic nerve magnetic resonance imaging and post-processing

The optic nerve is known to be one of the largest nerve bundles in the human central nervous system. There have been many studies of optic nerve imaging and post-processing that have provided insights into pathophysiology of optic neuritis related to multiple sclerosis and neuromyelitis optica spectrum disorder, glaucoma, and Leber's hereditary optic neuropathy. There are many challenges in optic nerve imaging, due to the morphology of the nerve through its course to the optic chiasm, its mobility due to eye movements and the high signal from cerebrospinal fluid and orbital fat surrounding the optic nerve. Recently, many advanced and fast imaging sequences have been used with post-processing techniques in attempts to produce higher resolution images of the optic nerve for evaluating various diseases. Magnetic resonance imaging (MRI) is one of the most common imaging methodologies for the optic nerve. This review paper will focus on recent MRI advances in optic nerve imaging and explain several post-processing techniques being used for analysis of optic nerve images. Finally, some challenges and potential for future optic nerve studies will be discussed.

Decreased Volume of Lateral and Medial Geniculate Nuclei in Patients with LHON Disease-7 Tesla MRI Study

Leber’s hereditary optic neuropathy (LHON) is a maternally inherited genetic disorder leading to severe and bilateral loss of central vision, with a young male predilection. In recent years, multiple studies examined structural abnormalities in visual white matter tracts such as the optic tract and optic radiation. However, it is still unclear if the disease alters only some parts of the white matter architecture or whether the changes also affect grey matter parts of the visual pathway. This study aimed at improving our understanding of morphometric changes in the lateral (LGN) and medial (MGN) geniculate nuclei and their associations with the clinical picture in LHON by the application of a submillimeter surface-based analysis approach to the ultra-high-field 7T magnetic resonance imaging data. To meet these goals, fifteen LHON patients and fifteen age-matched healthy subjects were examined. A quantitative analysis of the LGN and MGN volume was performed for all individuals. Additionally, morphometric results of LGN and MGN were correlated with variables covering selected aspects of the clinical picture of LHON. In comparison with healthy controls (HC), LHON participants showed a significantly decreased volume of the right LGN and the right MGN. Nevertheless, the volume of the right LGN was strongly correlated with the averaged thickness value of the right retinal nerve fiber layer (RNFL). The abnormalities in the volume of the LHON patients’ thalamic nuclei indicate that the disease can cause changes not only in the white matter areas constituting visual tracts but also in the grey matter structures. Furthermore, the correlation between the changes in the LGN volume and the RNFL, as well as the right optic nerve surface area located proximally to the eyeball, suggest some associations between the atrophy of these structures. However, to fully confirm this observation, longitudinal studies should be conducted.