Optic chiasm, optic tract and deep white demyelination: an unusual distribution of myelin oligodendrocyte glycoprotein-associated demyelination (MOGAD), case report and review of literature
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Abstract:
A preschool girl presented with sudden-onset bilateral painless loss of vision from 2 days prior. Child’s examination showed light perception vision, sluggishly reacting pupils, otherwise normal anterior segment, healthy optic disc and retina in both eyes. MRI of brain and orbit with contrast revealed thickened left part of the optic chiasm with contrast enhancement extending proximally to bilateral optic tract and hyperintensities in the left thalamus and periventricular white mater. Considering the topographical distribution of lesions in the brain, neuromyelitis optica spectrum disorder was suspected. The child was started on intravenous methylprednisolone followed by tapering oral steroids. Serological testing was positive for myelin oligodendrocyte glycoprotein (MOG) and negative for aquaporin-4 antibodies. This case represents an unusual case of MOG associated demyelination disorder where the distribution of lesions showed chiasmal involvement along with optic tract, thalamus and deep white mater lesions.Keywords:
Optic tract
Optic chiasm
Neuromyelitis Optica
Decussation
A preschool girl presented with sudden-onset bilateral painless loss of vision from 2 days prior. Child’s examination showed light perception vision, sluggishly reacting pupils, otherwise normal anterior segment, healthy optic disc and retina in both eyes. MRI of brain and orbit with contrast revealed thickened left part of the optic chiasm with contrast enhancement extending proximally to bilateral optic tract and hyperintensities in the left thalamus and periventricular white mater. Considering the topographical distribution of lesions in the brain, neuromyelitis optica spectrum disorder was suspected. The child was started on intravenous methylprednisolone followed by tapering oral steroids. Serological testing was positive for myelin oligodendrocyte glycoprotein (MOG) and negative for aquaporin-4 antibodies. This case represents an unusual case of MOG associated demyelination disorder where the distribution of lesions showed chiasmal involvement along with optic tract, thalamus and deep white mater lesions.
Optic tract
Optic chiasm
Neuromyelitis Optica
Decussation
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Background The axons of ganglion cells in the nasal retina decussate at the optic chiasm. It is unclear why tumours cause more injury to crossing nasal fibres, thereby giving rise to temporal visual field loss in each eye. To address this issue, the course of fibres through the optic chiasm was examined following injection of a different fluorescent tracer into each eye of a monkey. Methods Under general anaesthesia, cholera toxin subunit B—Alexa Fluor 488 was injected into the right eye and cholera toxin subunit B—Alexa Fluor 594 was injected into the left eye of a single normal adult male rhesus monkey. After a week’s survival for anterograde transport, serial coronal sections through the primary optic pathway were examined. Results A zone within the core of the anterior and mid portions of the optic chiasm was comprised entirely of crossing fibres. This zone of decussation was delineated by segregated, interwoven sheets of green (right eye) and red (left eye) fibres. It expanded steadily to fill more of the optic chiasm as fibres coursed posteriorly towards the optic tracts. Eventually, crossed fibres became completely intermingled with uncrossed fibres, so that ocular separation was lost. Conclusions A distinct, central compartment located within the anterior two-thirds of the optic chiasm contains only crossing fibres. Sellar tumours focus their compressive force on this portion of the structure, explaining why they so often produce visual field loss in the temporal fields.
Optic chiasm
Optic chiasma
Decussation
Optic tract
Alexa Fluor
Optic cup (embryology)
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Abstract Components of the peripheral visual pathway were examined in two bottlenose dolphins, Tursiops truncatus, each with unilateral ocular degeneration and scarring of 3 or more years' duration. In both animals, the optic nerve associated with the blind eye right eye in Tg419 and left eye in Tt038 had a translucent, gel‐like appearance upon gross examination. This translucency was also evident in the optic tract contralateral to the affected eye. In Tg419, myelinated axons of varying diameters were apparent in the left optic nerve, whereas the right optic nerve, serving the blind eye, appeared to be devoid of axons. In Tt038, myelinated axons were associated with the right optic nerve (serving the functional eye) and left optic tract but were essentially absent in the left optic nerve and right optic tract. Examined by light microscopy in serial horizontal sections, the optic chiasm of Tt038 was arranged along its central plane in segregated, alternating pathways for the decussation of right and left optic nerve fibers. Ventral to this plane, the chiasm was comprised of fibers from the left optic nerve, whereas dorsal to the central plane, fibers derived from the right optic nerve. Because of this architectural arrangement, the right and left optic nerves grossly appeared to overlap as they crossed the optic chiasm with the right optic nerve coursing dorsally to the left optic nerve. At the light and electron microscopic levels, the optic nerves and tracts lacking axons were well vascularized and dominated by glial cell bodies and glial processes, an expression of the marked glial scarring associated with postinjury axonal degeneration. The apparent absence of axons in one of the optic tract pairs (right in Tt038 and left in Tg419) supports the concept of complete decussation of right and left optic nerve fibers at the optic chiasm in the bottlenose dolphin. © 1994 Wiley‐Liss, Inc.
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In addition to the retinofugal fibers from theganglion cells of the retina and the supraoptic commissural fibers (Gudden''s commissure), the optic tracts, chiasm, and nerves of the rhesus monkey contain centrifugal (retinopetal, optic efferent) fibers to the retina. The centrifugal fibers were identified in the optic nerves, chiasm, and tracts of bilaterally enucleated monkeys on the basis of the principle that, following enucleation, the retinofugal fibers within the optic nerves, chiasm, and tracts degenerate and fragment months before the centrifugal fibers to the retina.Normally stained axons are present in the optic tracts; chiasm, and nerves of adult rhesus monkeys 5 or more months following bilateral enucleation. Many of these fibers, revealed by the Romanes silver technique, are present in those regions which exhibit the intense glial reactions associated with the axonal degeneration of the retinofugal fibers.The axons located centrally in the optic nerves appear to be centrifugal fibers to the retina. The cells of origin of these fibers are probably in the superior collicular region, from which their axons course successively through the midbrain reticular formation, crus cerebri (and capsule of the lateral geniculate body), optic tract, chiasm and optic nerve before terminating in the retina. Some of these fibers decussate and some remain uncrossed in their passage through the optic chiasm.
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Lateral geniculate nucleus
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Optic chiasm
Optic tract
Eye Enucleation
Optic chiasma
Monocular
Decussation
Saimiri sciureus
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Abstract: A 39-year-old woman presented with acute visual loss in her right eye. Brain and orbit MRI demonstrated T2 hyperintensity along a long section of her right optic nerve, chiasm, and tract with no evidence of decussation of the inflammation. Subsequent seropositivity for the aquaporin 4 antibody confirmed a diagnosis of neuromyelitis optica. Posterior pathway involvement is typical in neuromyelitis optica and supports the hypothesis that the condition is an astrocytopathy. Furthermore, the absence of decussation in the condition may be a function of astrocyte localization within the chiasm.
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Neuromyelitis Optica
Optic chiasm
Aquaporin 4
Gliogenesis
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Vision loss early in life has dramatic consequences on the organization of the visual system and hence on structural plasticity of its remnant components. Most of the studies on the anatomical changes in the brain following visual deprivation have focused on the re-organization of the visual cortex and its afferent and efferent projections. In this study, we performed a quantitative analysis of the volume and size of the optic chiasm, optic nerve, optic tract and the lateral geniculate nucleus (LGN), the retino recipient thalamic nucleus. Analysis was carried out on structural T1-weighted MRIs from 22 congenitally blind (CB), 14 late blind (LB) and 29 age -and sex-matched sighted control (SC) subjects. We manually segmented the optic nerve, optic chiasm and optic tract, while LGN volumes were extracted using in-house software. We also measured voxel intensity of optic nerve, optic chiasm and optic tract. Mean volumes of the optic nerve, optic tract and optic chiasm were reduced by 50 to 60% in both CB and LB participants. No significant differences were found between the congenitally and late-onset blind participants for any of the measures. Our data further revealed reduced white matter voxel intensities in optic nerve, optic chiasm and optic tract in blind compared to sighted participants, suggesting decreased myelin content in the atrophied white matter. The LGN was reduced by 50% and 44% in CB and LB, respectively. In LB, optic nerve volume correlated negatively with the blindness duration index; no such correlation was found for optic chiasm, optic tract and LGN. The observation that despite the absence of visual input about half of the subcortical retinofugal projections are structurally preserved raises the question of their functional role. One possibility is that the surviving fibers play a role in the maintenance of circadian rhythms in the blind through the intrinsically photosensitive melanopsin-containing retinal ganglion cells.
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Optic chiasm
Optic chiasma
Optic radiation
Lateral geniculate nucleus
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Optic chiasm
Decussation
Optic tract
Optic chiasma
Trochlear nerve
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Optic chiasm
Optic tract
Optic chiasma
Axonal Degeneration
Degeneration (medical)
Decussation
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Decussation
Optic chiasm
Optic tract
Optic chiasma
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