Role of corpus callosum in unconscious vision.

The existence of unconscious visually triggered behavior in patients with cortical blindness (e.g., homonymous hemianopia) has been amply demonstrated and the neural bases of this phenomenon have been thoroughly studied. However, a crosstalk between the two hemispheres as a possible mechanism of unconscious or partially conscious vision has not been so far considered. Thus, the aim of this study was to assess the relationship between structural and functional properties of the corpus callosum (CC), as shown by probabilistic tractography (PT), behavioral detection/discrimination performance and level of perceptual awareness in the blind field of patients with hemianopia. Twelve patients were tested in two tasks with black-and-white visual square-wave gratings, one task of movement and the other of orientation. The stimuli were lateralized to one hemifield either intact or blind. A PT analysis was carried out on MRI data to extract fiber properties along the CC (genu, body, and splenium). Compared with a control group of participants without brain damage, patients showed lower FA values in all three CC sections studied. For the intact hemifield we found a significant correlation between PT values and visual detection/discrimination accuracy. For the blind hemifield the level of perceptual awareness correlated with PT values for all three CC sections in the movement task. Importantly, significant differences in all three CC sections were found also between patients with above-vs. chance detection/discrimination performance while differences in the genu were found between patients with and without perceptual awareness. Overall, our study provides evidence that the properties of CC fibers are related to the presence of unconscious stimulus detection/discrimination and to hints of perceptual awareness for stimulus presentation to the blind hemifield. These results underline the importance of information exchange between the damaged and the healthy hemisphere for possible partial or full recovery from hemianopia.

Clinical Reasoning: An 80-Year-Old Woman With a Homonymous Hemianopsia.

An 80-year-old woman who was experiencing visual symptoms for 2 years was found to have a left homonymous hemianopsia (HH). On further evaluation the following month, she was noted to have simultanagnosia and alexia. MRI of the brain did not reveal a structural etiology for the symptoms. [18F]-fluorodeoxyglucose (FDG) PET-CT was performed to aid in the diagnostic investigation. This case of posterior cortical atrophy highlights the differential diagnosis of a HH in the absence of a structural lesion on MRI and the role of FDG PET-CT imaging in such patients.

Detection of post-stroke visual field loss by quantification of the retrogeniculate visual pathway.

Visual field loss is associated with poor post-stroke functional outcomes. However, early detection of visual field loss is often challenging in patients with disabling stroke. This study explored the association between the microstructural integrity of the retrogeniculate pathway and visual field loss in disabling stroke patients undergoing inpatient rehabilitation. Thirty patients with stroke lesions involving the retrogeniculate visual pathway were included. The degree of visual field loss was determined by the visual field index and mean deviation using automated perimetry. The fractional anisotropy (FA) values were obtained for the lateral geniculate nucleus and optic radiation; the FA laterality indices, representing the degree of degeneration, were calculated. The FA values were compared between the affected and unaffected hemispheres. The patients were categorized into complete and incomplete hemianopia groups, and their FA values were compared. The relationship between the FA laterality index and the degree of visual field loss was assessed. FA values of the lateral geniculate nucleus and optic radiation were lower on the affected side than on the unaffected side (P < 0.001 and P < 0.001, respectively). The affected optic radiation in the complete hemianopia group showed a lower FA value than in the incomplete group (P = 0.006). The FA laterality index of the optic radiation was positively correlated with the degree of visual field loss (visual field index, ρ = 0.629; mean deviation, ρ = 0.568). The quantification of the retrogeniculate visual pathway may aid in detecting post-stroke visual field loss. The microstructural integrity of the optic radiation is associated with the severity of visual field loss.

Avoidance and Improvement in Visual Field Defect After Surgery for Metastatic Brain Tumors in the Parietal and the Occipital Lobe.

OBJECTIVE: Visual field defects occasionally occur secondary to tumors in the parietal and the occipital lobes. The aim of this study was to analyze the efficacy of improvement in hemianopsia after surgery for metastatic brain tumors involving or adjacent to the optic radiation (OR). METHODS: The study included 49 patients with brain metastasis in the parietal and occipital lobes in the present study. Preoperative and postoperative neurological assessments included visual field, Mini-Mental State Examination, and Karnofsky performance scale. RESULTS: Of 49 patients, 33 (67.3%) presented with preoperative homonymous hemianopsia. Of these 33 patients, the visual field was improved postoperatively in 17 patients (51.5%). In all patients regardless of preoperative hemianopsia, postoperative visual fields did not deteriorate. Tractography demonstrated that the OR was split by the tumor (n = 6) and fanning of fibers expanded along the lateral side of the tumor (n = 11). All tumors were removed via surgical access toward the medial side of the tumor. Gross total resection was achieved in most tumors in the group with visual improvement (n = 16/17; 94.1%). Improvement in the visual field was attributed to tumor location in the subcortical white matter, removal rate of the tumor, and higher postoperative Karnofsky performance scale score. CONCLUSIONS: The OR tended to deviate to the lateral side of the tumor in the parieto-occipital junction. The postoperative visual field improved even in cases of an occipital tumor. Based on the present study, total resection via an appropriate surgical route should be considered to preserve the OR, leading to improvement in the postoperative visual field.

Traumatic chiasmal syndrome. Case report / Síndrome quiasmática traumática. Relato de caso

ABSTRACT Traumatic chiasmal syndrome is one of the rare etiologies of chiasmal syndrome, characterized by optic chiasm injury following head trauma. The main visual defect associated is bitemporal hemianopia with macular splitting; however, it can present with a variety of other visual defects and neurologic signs. The authors report a case of complete bitemporal hemianopia after head trauma, with multiple frontal and skull base fractures and no other neurologic deficits, or hypothalamic-pituitary abnormality. Most cases of traumatic chiasmal syndrome are caused by mechanical stretch or compression of the chiasma. Nevertheless, in this case, the radiologic findings excluded macroscopic disruption or external compression of the chiasma, raising the possibility of a contusion necrosis associated with functional impairment of the optic chiasma. Traumatic chiasmal syndrome must be considered in the differential diagnosis of patients presenting with complete bitemporal hemianopia after head injury caused by frontal and skull base fracture.

RESUMO A síndrome quiasmática traumática é uma das raras etiologias da síndrome do quiasma óptico, que se caracteriza pela presença de lesão do quiasma óptico causada por traumatismo craniencefálico. O principal defeito visual associado é a hemianopsia bitemporal com macular splitting. No entanto, pode se manifestar por uma variedade de outros defeitos visuais e sinais neurológicos. Os autores relatam um caso de hemianopsia bitemporal completa após traumatismo craniencefálico com múltiplas fraturas frontais e da base do crânio na ausência de outros défices neurológicos ou alterações do eixo hipotálamo-hipofisário. A maioria dos casos de síndrome quiasmática traumática é causada por estiramento mecânico ou compressão do quiasma. No entanto, no caso apresentado, os achados radiológicos excluíram lesão macroscópica ou compressiva do quiasma, levantando a possibilidade de uma necrose após contusão associada ao compromisso funcional do quiasma óptico. A síndrome quiasmática traumática deve ser considerada no diagnóstico diferencial de doentes que apresentam hemianopsia bitemporal completa após traumatismo craniencefálico, especialmente em casos de fratura do osso frontal e da base do crânio.

Visuo-spatial attention to the blind hemifield of hemianopic patients: Can it survive the impairment of visual awareness?

The general aim of this study was to assess the effect produced by visuo-spatial attention on both behavioural performance and brain activation in hemianopic patients following visual stimulus presentation to the blind hemifield. To do that, we tested five hemianopic patients and six age-matched healthy controls in an MRI scanner during the execution of a Posner-like paradigm using a predictive central cue. Participants were instructed to covertly orient attention toward the blind or sighted hemifield in different blocks while discriminating the orientation of a visual grating. In patients, we found significantly faster reaction times (RT) in valid and neutral than invalid trials not only in the sighted but also in the blind hemifield, despite the impairment of consciousness and performance at chance. As to the fMRI signal, in valid trials we observed the activation of ipsilesional visual areas (mainly lingual gyrus - area 19) during the orientation of attention toward the blind hemifield. Importantly, this activation was similar in patients and controls. In order to assess the related functional network, we performed a psychophysiological interactions (PPI) analysis that revealed an increased functional connectivity (FC) in patients with respect to controls between the ipsilesional lingual gyrus and ipsilateral fronto-parietal as well as contralesional parietal regions. Moreover, the shift of attention from the blind to the sighted hemifield revealed stronger FC between the contralesional visual areas V3/V4 and ipsilateral parietal regions in patients than controls. These results indicate a higher cognitive effort in patients when paying attention to the blind hemifiled or when shifting attention from the blind to the sighted hemfield, possibly as an attempt to compensate for the visual loss. Taken together, these results show that hemianopic patients can covertly orient attention toward the blind hemifield with a top-down mechanism by activating a functional network mainly including fronto-parietal regions belonging to the dorsal attentional network.

The Chiasmal Compression Index: An Integrative Assessment Tool for Visual Disturbances in Patients with Pituitary Macroadenomas.

OBJECTIVE: Visual status is routinely evaluated by neuro-ophthalmologic examination and computerized visual field (VF) tests in patients with chiasmal compression secondary to pituitary macroadenoma. Currently, no relevant data exists to accurately quantify the extent of optic apparatus compromise to further guide clinical decision-making. We aimed to assess for a possible quantitative correlation between optic chiasm geometric properties on magnetic resonance imaging (MRI) and VF deficits. METHODS: Visual assessments and concurrent MRI scans were retrospectively reviewed from patients treated for pituitary macroadenoma in a single medical institution. Chiasm width, chiasm minimal and maximal height, and chiasm angle were measured on MRI coronal plane images by 3 independent reviewers (for the sake of variability analysis). VF numerical summary parameters were also retrieved. RESULTS: A total of 30 patients were included in the final analysis. Average VF index was 70% (±30), and averaged mean deviation was 10.0 db (±9). Chiasm angle and width (which together represents the bending and stretching of the chiasm by the upward directed compression; both of which demonstrated high inter- and intraobserver agreement) showed strong correlation with VF loss. Chiasmal compression index derived from those parameters showed even stronger correlation. CONCLUSIONS: The strong correlation demonstrated by our results of this relatively simple radiologic measurement with VF status, despite the relatively small cohort, calls for further investigation in this promising direction, and may facilitate with basic assessment and clinical decision-making for patients with equivocal neuro-ophthalmologic evaluation, as well as with poor compliance.

Signo de la arteria cerebral posterior hiperdensa migratoria tras trombólisis intravenosa / Migratory hyperdense posterior cerebral artery sign following intravenous thrombolysis

INTRODUCCIÓN: La tomografía computarizada cerebral sigue siendo la modalidad de imagen básica en la fase aguda del ictus. El signo de la arteria cerebral posterior hiperdensa es un hallazgo radiológico precoz e infrecuente con valor topográfico y pronóstico que hay que tener en cuenta en las tomografías computarizadas iniciales. CASO CLÍNICO: Mujer de 79 años, que presenta de forma brusca una hemianopsia homónima izquierda, leve paresia facial inferior izquierda, hemiparesia izquierda 3/5 y grave hipoestesia izquierda. En la tomografía computarizada cerebral inicial se objetiva hiperdensidad cálcica del segmento P1 de la arteria cerebral posterior derecha. Se administra fibrinolítico intravenoso. Presenta mejoría clínica, y en la tomografía computarizada cerebral de control 24 horas después de la fibrinólisis se observa hiperdensidad del segmento P3 de la arteria cerebral posterior derecha. CONCLUSIONES: La evidencia de una hiperdensidad de la arteria cerebral posterior es un hallazgo radiológico infrecuente asociado a un mayor volumen de infarto isquémico. La tomografía computarizada cerebral en fase aguda resulta fundamental para tratar de dilucidar su etiología. Los émbolos cálcicos son una causa infradiagnosticada de ictus y ocurren de forma espontánea en una gran proporción. Ante la sospecha de embolismo cálcico, es necesario realizar un estudio en busca de una patología carotídea, valvular o del arco aórtico. La migración de la hiperdensidad arterial hacia distal en la tomografía computarizada se relaciona con un mejor pronóstico. Este caso presentó una buena evolución frente al mal pronóstico descrito en la bibliografía en casos de hiperdensidad arterial como marcador precoz de ictus en fase aguda

INTRODUCTION: Computed tomography (CT) scanning of the brain continues to be the basic imaging mode in the acute phase of stroke. The hyperdense posterior cerebral artery sign is an early and infrequent radiological finding with topographic and prognostic value that must be taken into account in the initial CT scans. CASE REPORT: We report the case of a 79-year-old woman who suddenly presented with severe left homonymous hemianopsia, mild lower left facial paresis, 3/5 left hemiparesis and severe left hypaesthesia. In the initial brain CT scan, calcium hyper¬density of the P1 segment is observed in the right posterior cerebral artery. Intravenous fibrinolytic therapy is administered. The patient shows clinical improvement, and in the follow-up brain CT scan at 24 hours after fibrinolysis, hyperdensity of the P3 segment is observed in the right posterior cerebral artery. CONCLUSIONS: Evidence of posterior cerebral artery hyperdensity is a rare radiological finding associated with an increased volume of ischaemic stroke. A computed tomography scan of the head in the acute phase is essential to try to clarify its causation. Calcium emboli are an under-diagnosed cause of stroke and occur spontaneously in a large proportion of cases. If calcium embolism is suspected, a study must be conducted in search of a carotid, valvular or aortic arch pathology. Migration of the arterial hyperdensity towards distal is associated with a better prognosis. This case presented good progress in contrast to the poor prognosis described in the literature in cases of arterial hyperdensity as an early marker of stroke in the acute phase

Reduced Peripapillary and Macular Vessel Density in Unilateral Postgeniculate Lesions With Retrograde Transsynaptic Degeneration.

BACKGROUND: Retrograde transsynaptic degeneration (RTSD) of the retinal ganglion cells and retinal nerve fiber layer after postgeniculate injury has been well documented, but to the best of our knowledge, associated retinal microvascular changes have not been examined. The purpose of our study was to assess vessel density (VD) at macular and peripapillary regions in patients with RTSD. METHODS: Cross-sectional study including 16 patients with homonymous visual field defects secondary to unilateral postgeniculate visual pathway injury and 18 age-matched controls. All participants were examined with AngioVue optical coherence tomography angiography to measure the peripapillary vessel density and macular vessel density (pVD/mVD) as well as the peripapillary retinal nerve fiber layer (pRNFL) and macular ganglion cell complex (GCC) thicknesses. The pRNFL and macular ganglion cell-inner plexiform layer (GCIPL) thicknesses also were evaluated using Cirrus OCT. A normalized asymmetry score (NAS) was calculated for GCIPL and GCC thickness, and mVD. RESULTS: Average pRNFL and macular GCIPL/GCC thicknesses were significantly thinner in both eyes of patients compared with control eyes (all P ≤ 0.05). Eight patients (50%), who showed a RTSD of the GCIPL map, had a relative thinning of the GCIPL/GCC ipsilateral to the brain lesion in both eyes (represented by a positive GCIPL-NAS/GCC-NAS). The mean pVD and mVD also were significantly reduced in patients (all P ≤ 0.05). There was a strong correlation between GCIPL-NAS/GCC-NAS and mVD-NAS index in both eyes (all r > 0.7, P = 0.001). Furthermore, there was a similar spatial pattern of damage for the macular GCC thickness and VD values. CONCLUSIONS: We demonstrated a significant VD decrease in peripapillary and macular areas of patients with RTSD because of postgeniculate lesions. The structural and microvascular asymmetry indexes were significantly correlated. These findings provide new insights regarding transsynaptic degeneration of the visual system.

Usefulness of MRI Slices Parallel to the Optic Chiasma in a Case with Traumatic Optic Nerve Avulsion after a Bear Attack.

Optic nerve avulsion is an exceedingly rare condition. Here, we describe a case of optic nerve avulsion in a 74-year-old man with temporal hemianopia in the contralateral eye after a bear attack. Magnetic resonance imaging (MRI) revealed separation of the optic nerve distal to the optic chiasma, whereas the high signal in diffusion-weighted imaging suggested nerve injury from the left side of the optic chiasma to the left optic tract. MRI slices parallel to the optic chiasma were obtained and used for evaluating the site of optic nerve avulsion and nerve injury, which were responsible for temporal hemianopia in the contralateral eye.

Neuronal mechanisms of motion detection underlying blindsight assessed by functional magnetic resonance imaging (fMRI).

Brain imaging offers a valuable tool to observe functional brain plasticity by showing how sensory inputs reshape cortical activations after a visual impairment. Following a unilateral post-chiasmatic lesion affecting the visual cortex, patients may suffer a contralateral visual loss referred to homonymous hemianopia. Nevertheless, these patients preserve the ability to unconsciously detect, localize and discriminate visual stimuli presented in their impaired visual field. To investigate this paradox, known as blindsight, we conducted a study using functional magnetic resonance imaging (fMRI) to evaluate the structural and functional impact of such lesion in a 33-year old patient (ML), who suffers a complete right hemianopia without macular sparing and showing strong evidences of blindsight. We thus performed whole brain and sliced thalamic fMRI scan sequences during an event-related motion detection task. We provided evidence of the neuronal fingerprint of blindsight by acquiring and associating neural correlates, specific structures and functional networks of the midbrain during blindsight performances which may help to better understand this condition. Accurate performance demonstrated the presence of residual vision and the ability to unconsciously perceive motion presented in the blind hemifield, although her reaction time was significantly higher in her blind-field. When the normal hemifield was stimulated, we observed significant contralateral activations in primary and secondary visual areas as well as motion specific areas, such as the supramarginal gyrus and middle temporal area. We also demonstrated sub-thalamic activations within the superior colliculi (SC) and the pulvinar. These results suggest a role of secondary subcortical structures in normal spontaneous motion detection. In a similar way, when the lesioned hemifield was stimulated, we observed contralateral activity in extrastriate areas with no activation of the primary lesioned visual cortex. Moreover, we observed activations within the SC when the blind hemifield was stimulated. However, we observed unexpected ipsilateral activations within the same motion specific areas, as well as bilateral frontal activations. These results highlight the importance of abnormal secondary pathways bypassing the primary visual area (V1) in residual vision. This reorganization in the structure and function of the visual pathways correlates with behavioral changes, thus offering a plausible explanation for the blindsight phenomenon. Our results may potentially impact the development of rehabilitation strategies to target subcortical pathways.

Petroclival Meningioma Presenting With an Ipsilateral Sixth Nerve Palsy and a Contralateral Homonymous Quadrantanopia: A Unique and Topographically Localizing Syndrome.

An 84-year-old woman reported onset of headaches, diplopia, and blurred vision. On examination, she was found to have a left sixth nerve palsy and an incongruous right homonymous hemianopia. Brain MRI demonstrated a left petroclival meningioma, causing this unusual combination of clinical findings. The patient was treated with radiation therapy and has remained stable over 4 years of follow-up.

Nomogram Using Optical Coherence Tomography and Visual Field Parameters to Predict Brain Lesions in Patients with Bitemporal Hemianopia.

PURPOSE: This study aims to develop a nomogram to predict brain lesions in patients with complete or incomplete bitemporal hemianopia by combining results from optical coherence tomography (OCT) and visual field (VF) testing. MATERIAL AND METHODS: We reviewed the medical records of patients who underwent magnetic resonance imaging (MRI) to identify brain lesions due to bitemporal hemianopia between January 2010 and March 2017, retrospectively. The patients were divided into two groups based on MRI findings: brain-lesion (+) group that had brain lesions on MRI (n = 63), and brain-lesion (-) group without brain lesions on MRI (n = 16). We compared OCT and VF findings between the two groups to find factors that could predict a brain lesion. Multiple logistic regression analysis was performed to select prognostic factors, and we constructed a nomogram to predict brain lesions on MRI. RESULT: The VF mean deviation was lower (p = 0.011) and all sectors of peripapillary retinal nerve fiber layer thickness except the temporal region were thicker in the brain-lesion (+) group. However, there was no statistically significant difference in macular ganglion cell-inner plexiform layer between the two groups. The area under the receiver operating characteristic curve of the nomogram for predicting brain lesions on MRI was 0.916. CONCLUSION: We developed a nomogram using VF and OCT examinations as a novel and accurate screening method to predict brain lesions in patients with bitemporal hemianopia and aid ophthalmologists and other clinicians in deciding whether to further evaluate a patient by MRI.

Action blindsight and antipointing in a hemianopic patient.

Blindsight refers to the observation of residual visual abilities in the hemianopic field of patients without a functional V1. Given the within- and between-subject variability in the preserved abilities and the phenomenal experience of blindsight patients, the fine-grained description of the phenomenon is still debated. Here we tested a patient with established "perceptual" and "attentional" blindsight (c.f. Danckert and Rossetti, 2005). Using a pointing paradigm patient MS, who suffers from a complete left homonymous hemianopia, showed clear above chance manual localisation of 'unseen' targets. In addition, target presentations in his blind field led MS, on occasion, to spontaneous responses towards his sighted field. Structural and functional magnetic resonance imaging was conducted to evaluate the magnitude of V1 damage. Results revealed the presence of a calcarine sulcus in both hemispheres, yet his right V1 is reduced, structurally disconnected and shows no fMRI response to visual stimuli. Thus, visual stimulation of his blind field can lead to "action blindsight" and spontaneous antipointing, in absence of a functional right V1. With respect to the antipointing, we suggest that MS may have registered the stimulation and subsequently presumes it must have been in his intact half field.

Visual rehabilitation training alters attentional networks in hemianopia: An fMRI study.

OBJECTIVE: Hemianopia is a visual field defect following post-chiasmatic damage. We now applied functional magnetic resonance imaging (fMRI) in hemianopic patients before and after visual rehabilitation training (VRT) to examine the impact of VRT on attentional function networks. METHODS: Seven chronic hemianopic patients with post- chiasmatic lesions carried out a VRT for five weeks under fixation control. Before vs. after intervention, we assessed the area of residual vision (ARV), contrast sensitivity function (CSF) and functional MRI data and correlated them with each other. RESULTS: VRT significantly improved the visual function of grating detection at the training location. Using fMRI, we found that the training led to a strengthening of connectivity between the right temporoparietal junction (rTPJ) to the insula and the anterior cingulate cortex (ACC), all of which belong to the cortical attentional network. However, no significant correlation between alterations of brain activity and improvements of either CSF or ARV was found. CONCLUSION: Visual rehabilitation training partially restored the deficient visual field sectors and could improve attentional network function in hemianopia. SIGNIFICANCE: Our MRI results highlight the role of attention and the rTPJ activation as one, but not the only, component of VRT in hemianopia.