暂无摘要。

Impairment of the geniculostriate pathway results in scotomas in the corresponding part of the visual field. Here, we present a case of patient IB with left eye microphthalmia and with lesions in most of the left geniculostriate pathway, including the Lateral Geniculate Nucleus (LGN). Despite the severe lesions, the patient has a very narrow scotoma in the peripheral part of the lower-right-hemifield only (beyond 15° of eccentricity) and complete visual field representation in the primary visual cortex. Population receptive field mapping (pRF) of the patient\'s visual field reveals orderly eccentricity maps together with contralateral activation in both hemispheres. With diffusion tractography, we revealed connections between superior colliculus (SC) and cortical structures in the hemisphere affected by the lesions, which could mediate the retinotopic reorganization at the cortical level. Our results indicate an astonishing case for the flexibility of the developing retinotopic maps where the contralateral thalamus receives fibers from both the nasal and temporal retinae.

暂无摘要。

Injury to the primary visual cortex (V1, striate cortex) and the geniculostriate pathway in adults results in cortical blindness, abolishing conscious visual perception. Early studies by Larry Weiskrantz and colleagues demonstrated that some patients with an occipital-lobe injury exhibited a degree of unconscious vision and visually-guided behaviour within the blind field. A more recent focus has been the observed phenomenon whereby early-life injury to V1 often results in the preservation of visual perception in both monkeys and humans. These findings initiated a concerted effort on multiple fronts, including nonhuman primate studies, to uncover the neural substrate/s of the spared conscious vision. In both adult and early-life cases of V1 injury, evidence suggests the involvement of the Middle Temporal area (MT) of the extrastriate visual cortex, which is an integral component area of the dorsal stream and is also associated with visually-guided behaviors. Because of the limited number of early-life V1 injury cases for humans, the outstanding question in the field is what secondary visual pathways are responsible for this extraordinary capacity? Here we report for the first time a case of a child (B.I.) who suffered a bilateral occipital-lobe injury in the first two weeks postnatally due to medium-chain acyl-Co-A dehydrogenase deficiency. At 6 years of age, B.I. underwent a battery of neurophysiological tests, as well as structural and diffusion MRI and ophthalmic examination at 7 years. Despite the extensive bilateral occipital cortical damage, B.I. has extensive conscious visual abilities, is not blind, and can use vision to navigate his environment. Furthermore, unlike blindsight patients, he can readily and consciously identify happy and neutral faces and colors, tasks associated with ventral stream processing. These findings suggest significant re-routing of visual information. To identify the putative visual pathway/s responsible for this ability, MRI tractography of secondary visual pathways connecting MT with the lateral geniculate nucleus (LGN) and the inferior pulvinar (PI) were analysed. Results revealed an increased PI-MT pathway in the left hemisphere, suggesting that this pulvinar relay could be the neural pathway affording the preserved visual capacity following an early-life lesion of V1. These findings corroborate anatomical evidence from monkeys showing an enhanced PI-MT pathway following an early-life lesion of V1, compared to adults.

We report a case of a 55-year-old man who developed acute-onset narrowing of his visual field. He showed right homonymous hemianopsia without any other neurological symptoms and signs. Brain CT and MRI showed localized hemorrhage (about 1.6 ml) in the left lateral geniculate body (LGB). A cerebral angiography showed no vascular anomalies of cerebral vessels, and the left anterior choroidal artery and left lateral posterior choroidal artery could be visualized well. He had hypertension, polycythemia and dyslipidemia and was a habitual smoker and an alcoholic. In the literature, various kinds of visual field defects including hemianopsia, upper quadrant hemianopsia, lower quadrant hemianopsia, and horizontal sectoranopia have been reported in eight cases of LGB hemorrhage. Localized LGB hemorrhage was found in only one case out of 2,763 cerebral hemorrhage patients enrolled in our stroke registry for 11 years from 2005 to 2016. Localized hemorrhage of LGB very rarely occurred.

A 40-year-old man was diagnosed with pancreatitis following cholecystectomy. During hospitalisation, he reported bilateral acute vision loss. His best-corrected visual acuity (BCVA) was counting fingers in the right eye and 20/200 in the left eye. Ocular fundus examination and optical coherence tomography revealed a slight alteration in the retinal nerve fibres in the nasal macular region. Automated perimetry revealed bilateral visual field defects affecting both temporal and nasal hemifields in a predominantly nasal distribution, and brain MRI confirmed symmetrical lesions within both lateral geniculate nuclei. BCVA was gradually recovered, reaching 20/20 within 6 weeks.

Pre-operative tractography of the optic radiation (OR) has been advised to assess the risk for postoperative visual field deficit (VFD) in certain candidates for resective epilepsy surgery. Diffusion tensor imaging (DTI) tractography relies on a precise anatomical determination of start and target regions of interest (ROIs), such as the lateral geniculate nucleus (LGN) and the primary visual cortex (V1). The post-chiasmal visual pathway and V1 show considerable inter-individual variability, and in epilepsy patients parenchymatous lesions might further complicate this matter. A functionally based tractography (FBT) seems beneficial for precise OR identification. We assessed practicability of FBT for OR identification in a patient with occipital lobe epilepsy due to a temporo-occipital maldevelopmental tumor. The MRI protocol at 3T included a T1-weighted sagittal 3D scan, a T2-weighted axial 2D scan and a DTI scan using an echo planar spin echo sequence. ROIs for fiber tracking of OR (LGN & V1) were determined with T2*-weighted fMRI-based retinotopic assessment. After DTI pre-processing and fiber tracking, paths with similar properties were combined in clusters for visual presentation and OR localization. Retinotopic phase maps allowed for the identification of V1 and LGN for a precise DTI-based reconstruction of OR, which was distant to the patient\'s tumor. Location and structure of ORs were comparable in each hemisphere. FBT could thus influence the human research of the extrastriate visual pathway and the risk management of post-operative VFD in epilepsy surgery.

暂无摘要。

A 41-year-old woman presented with progressive hemianopsia caused by compression of the lateral geniculate body by the dilated basal vein draining a contralateral frontal arteriovenous malformation (AVM). Magnetic resonance (MR) imaging revealed left frontal AVM and right lateral geniculate body compression due to the dilated basal vein. Emergent presurgical transarterial embolization and surgical removal were performed. Left hemianopsia completely recovered 3 months after surgery and MR imaging indicated improvement of the compression of the lateral geniculate body. Direct mechanical compression of the enlarged drainage vein is one of the causes of homonymous hemianopsia. Early surgical treatment is recommended to obtain a rapid recovery.

An 86-year-old, right-handed, hypertensive man suddenly experienced blurring of vision predominating in the left visual field. Neurological examinations were normal, except for left homonymous hemianopsia. Goldmann visual field testing revealed a left congruent incomplete homonymous hemianopsia with macular splitting. Brain MRI, with a T2-weighted image, demonstrated a lesion of high intensity in the right lateral geniculate body (LGB), as well as the posterior part of the caudate nucleus, posterolateral thalamus, and dorsolateral thalamus. MRA revealed severe stenosis at the second segment of right posterior cerebral artery (PCA). SPECT revealed significantly decreased blood perfusion in the striate cortex. To the best of our knowledge, this is the first case of an isolated, congruent, incomplete, homonymous hemianopsia due to lateral posterior choroidal artery (LPChA) region infarction. The LPChA possibly supplied the LGB through the PCA system. A horizontal, homonymous sectoranopia is typically the hallmark of an LPChA region infarction. However, a homonymous hemianopsia may also occur when the entire LGB has been affected. In the case of homonymous hemianopsia, LGB damage due to LPChA region infarction should be considered, in addition to lesions of the visual pathway, such as the optic tract, optic radiations, and occipital cortex.