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PURPOSE: Dural arteriovenous fistulas (dAVF) account for approximately 10-15% of all intracranial arteriovenous abnormalities. dAVFs carry a significant risk of mortality, particularly in cases of acute hemorrhage, of up to 10%. A small proportion of these dAVFs are found in the anterior cranial fossa (ACF), of which the rate of hemorrhage can be as high as up to 91%. The Scepter Mini (SM) is the smallest dual-lumen micro-balloon (MB) available for neurointerventional practice. It consists of a 2.8 French outer diameter, with a 2.2 mm × 9 mm semi-compliant balloon providing a working length of 165 cm. The SM is navigated with a 0.008-inch wire making it a particularly attractive tool accessible to the pedicles normally reached with liquid embolization micro-catheters. METHODS: Five consecutive patients over a 1-year period between 2020 and 2021 were evaluated and treated for ACF dAVF using a liquid embolization approach using the SM balloon. All patients were treated using ethylene-vinyl alcohol copolymer (EVOH), of which Squid 18 and/or Squid 12 were the chosen viscosities. Control angiograms were performed for all patients post-embolization. RESULTS: All patients demonstrated complete occlusion of the ACF dAVF on immediate post-treatment angiography. No immediate complications were encountered; particularly, there were no reports of visual field deficit in any of the patients. CONCLUSION: The MB is a valuable adjunctive tool that can enhance the safety and efficacy of trans-ophthalmic embolization of ACF dAVFs, providing additional protection to the retinal and posterior ciliary arteries against unwanted reflux of liquid embolic agent.

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We report a case of a 64-year-old man with a fusiform right extracranial vertebral artery aneurysm, spanning over half the extra-cranial V2 (foraminal) segment, presenting with recurrent multi-focal posterior circulation embolic ischaemic stroke. The patient was treated with endovascular embolisation of the right vertebral artery to prevent further thrombo-embolic events. Distal and proximal occlusion of the aneurysmal vertebral artery was performed with a micro-vascular plug with partial aneurysm sack embolisation to aid thrombosis and reduce the risk of recanalisation. Two months post procedure MR angiography confirmed successful aneurysm occlusion with no post-procedural complication. The patient returned to his normal independent life. Endovascular treatment with vessel sacrifice is an effective treatment with low morbidity and we believe the MVP device to be a efficacious option in the vertebral artery.

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PURPOSE: There is overwhelming evidence for the clinical benefits that are derived following mechanical thrombectomy in large-vessel acute ischaemic stroke. The risk of stroke is elevated in pregnancy due to many factors. To date, there have been two reports, totalling five patients, who have undergone mechanical thrombectomy in pregnancy, thus demonstrating the feasibility of the procedure; however, there is no data on the radiation exposure to the mother or foetus related to this therapy. METHODS: We highlight the important technical considerations to minimise the risk of the procedure and report the estimated dose received by mother and foetus. We also compare these doses with those received during whole-body CT in trauma and CT pulmonary angiogram (CTPA) examinations. RESULTS: Three cases of mechanical thrombectomy were performed at separate tertiary referral neuroscience centres in the UK. Following diagnostic CT and mechanical thrombectomy, the total whole-body effective dose to the pregnant patient was significantly higher than in patients undergoing CTPA (p < 0.05), but not significant different compared to whole-body CT imaging in trauma patients. The estimated dose received by the foetus following diagnostic CT and mechanical thrombectomy was significantly lower than in whole-body imaging in trauma patients at p < 0.05, with no difference in estimated foetal dose compared to CTPA imaging. CONCLUSION: The estimated doses received by the foetus during diagnostic stroke imaging and mechanical thrombectomy are equivalent to, or less than, purely diagnostic imaging in emergency situations.

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A persistent hypoglossal artery was first described in 1889 and is one of the more common anatomical variations arising from aberration in normal development. Endovascular coiling has been recognised as a robust treatment for acutely ruptured intracranial arterial aneurysms, although specific data regarding an aneurysm arising from a persistent hypoglossal artery is lacking due to the low incidence. Here we report both the oldest patient reported to be treated with a persistent hypoglossal artery-associated aneurysm and also explicitly report endovascular treatment of a persistent hypoglossal artery aneurysm arising at the posterior inferior cerebellar artery origin. Qualitative systematic review of the available medical literature demonstrates limited evidence regarding treatment of persistent hypoglossal artery-associated aneurysms with the majority being carried out via open surgery. Ruptured posterior inferior cerebellar artery aneurysm arising from a persistent hypoglossal artery can be successfully and safely treated by endovascular therapy via the persistent hypoglossal artery. Randomised study of this situation is unlikely to be feasible; however, qualitative review of the literature reveals six such aneurysms that have been treated surgically, and this case appears to be the first via an endovascular means.

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Going into space is a disorienting experience. Many studies have looked at sensory functioning in space but the multisensory basis of orientation has not been systematically investigated. Here, we assess how prolonged exposure to microgravity affects the relative weighting of visual, gravity, and idiotropic cues to perceived orientation. We separated visual, body, and gravity (when present) cues to perceived orientation before, during, and after long-term exposure to microgravity during the missions of seven astronauts on the International Space Station (mean duration 168 days) and measuring perceived vertical using the subjective visual vertical and the perceptual upright. The relative influence of each cue and the variance of their judgments were measured. Fourteen ground-based control participants performed comparable measurements over a similar period. The variance of astronauts' subjective visual vertical judgments in the absence of visual cues was significantly larger immediately upon return to earth than before flight. Astronauts' perceptual upright demonstrated a reduced reliance on visual cues upon arrival on orbit that re-appeared long after returning to earth. For earth-bound controls, the contributions of body, gravity, and vision remained constant throughout the year-long testing period. This is the first multisensory study of orientation behavior in space and the first demonstration of long-term perceptual changes that persist after returning to earth. Astronauts showed a plasticity in the weighting of perceptual cues to orientation that could form the basis for future countermeasures.

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Arteriovenous fistulation between the vertebral arteries to extradural (epidural) veins, termed vertebro-vertebral arteriovenous fistulae, are uncommon diagnoses without established diagnostic algorithms or treatment options. Minimal evidence exists describing the management of this pathology. Endovascular treatment was performed under general anaesthesia by coil occlusion of the vertebral artery from the point of the fistula to the mid-vertebral artery. Repeat magnetic resonance angiographic imaging one week following the procedure confirmed an 80% reduction in the size of the epidural vein and decompression of the cervical spinal cord. At four-week follow-up there was significant qualitative improvement in the myelopathic symptoms including walking distance and pain. Normal physiological filling of the collapsed extradural vein was observed on follow-up digital subtraction angiography at five months. Catheter angiography by an experienced interventional neuro-radiologist is critical in defining the anatomy and providing minimally invasive treatment.

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The perceived orientation of objects, gravity, and the body are biased to the left. Whether this leftward bias is attributable to biases in sensing or processing vestibular, visual, and body sense cues has never been assessed directly. The orientation in which characters are most easily recognized--the perceived upright (PU)--can be well predicted from a weighted vector sum of these sensory cues. A simple form of this model assumes that the directions of the contributing inputs are coded accurately and as a consequence participants tilted left- or right-side-down relative to gravity should exhibit mirror symmetric patterns of responses. If a left/right asymmetry were present then varying these sensory cues could be used to assess in which sensory modality or modalities a PU bias may have arisen. Participants completed the Oriented Character Recognition Test (OCHART) while manipulating body posture and visual orientation cues relative to gravity. The response patterns showed systematic differences depending on which side they were tilted. An asymmetry of the PU was found to be best modeled by adding a leftward bias of 5.6° to the perceived orientation of the body relative to its actual orientation relative to the head. The asymmetry in the effect of body orientation is reminiscent of the body-defined left-leaning asymmetry in the perceived direction of light coming from above and reports that people tend to adopt a right-leaning posture.

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Bispectral index (BIS) is a monitoring modality designed and used for monitoring depth of anaesthesia. We wish to report a case where BIS monitoring may have alerted us to a potential adverse neurological event during angiographic coiling of a cerebral aneurysm.

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Establishing our orientation in the world is necessary for almost all aspects of perception and behavior. Gravity usually defines the critical reference direction. The direction of gravity is sensed by somatosensory detectors indicating pressure points and specialized organs in the vestibular system and viscera that indicate gravity's physical pull. However, gravity's direction can also be sensed visually since we see the effects of gravity on static and moving objects and also deduce its direction from the global structure of a scene indicated by features such as the sky and ground. When cues from either visual or physical sources are compromised or ambiguous, perceptual disorientation may result, often with a tendency to replace gravity with the body's long axis as a reference. Orientation cues are compromised while floating in the weightlessness of space (which neutralizes vestibular and somatosensory cues) or while suspended at neutral buoyancy in the ocean (which neutralizes somatosensory cues) and the ability to sense orientation cues may also be compromised in the elderly or in clinical populations. In these situations, enhancing the visual cues to orientation may be beneficial. In this chapter, we review research using specially constructed virtual and real environments to quantify the contribution of various visual orientation cues. We demonstrate how visual cues can counteract disorientation by providing effective orientation information.

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The perceived direction of up depends on both gravity and visual cues to orientation. Static visual cues to orientation have been shown to be less effective in influencing the perception of upright (PU) under microgravity conditions than they are on earth (Dyde et al., 2009). Here we introduce dynamic orientation cues into the visual background to ascertain whether they might increase the effectiveness of visual cues in defining the PU under different gravity conditions. Brief periods of microgravity and hypergravity were created using parabolic flight. Observers viewed a polarized, natural scene presented at various orientations on a laptop viewed through a hood which occluded all other visual cues. The visual background was either an animated video clip in which actors moved along the visual ground plane or an individual static frame taken from the same clip. We measured the perceptual upright using the oriented character recognition test (OCHART). Dynamic visual cues significantly enhance the effectiveness of vision in determining the perceptual upright under normal gravity conditions. Strong trends were found for dynamic visual cues to produce an increase in the visual effect under both microgravity and hypergravity conditions.

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Chuck Oman has been a guide and mentor for research in human perception and performance during space exploration for over 25 years. His research has provided a solid foundation for our understanding of how humans cope with the challenges and ambiguities of sensation and perception in space. In many of the environments associated with work in space the human visual system must operate with unusual combinations of visual and other perceptual cues. On Earth physical acceleration cues are normally available to assist the visual system in interpreting static and dynamic visual features. Here we consider two cases where the visual system is not assisted by such cues. Our first experiment examines perceptual stability when the normally available physical cues to linear acceleration are absent. Our second experiment examines perceived orientation when there is no assistance from the physically sensed direction of gravity. In both cases the effectiveness of vision is paradoxically reduced in the absence of physical acceleration cues. The reluctance to rely heavily on vision represents an important human factors challenge to efficient performance in the space environment.

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We measured the effect of the orientation of the visual background on the perceptual upright (PU) under different levels of gravity. Brief periods of micro- and hypergravity conditions were created using two series of parabolic flights. Control measures were taken in the laboratory under normal gravity with subjects upright, right side down and supine. Participants viewed a polarized, natural scene presented at various orientations on a laptop viewed through a hood which occluded all other visual cues. Superimposed on the screen was a character the identity of which depended on its orientation. The orientations at which the character was maximally ambiguous were measured and the perceptual upright was defined as half way between these orientations. The visual background affected the orientation of the PU less when in microgravity than when upright in normal gravity and more when supine than when upright in normal gravity. A weighted vector sum model was used to quantify the relative influence of the orientations of gravity, vision and the body in determining the perceptual upright.

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Eye, head, and body movement are intimately linked. During self-motion, the eyes track objects by a combination of vestibular reflexes and smooth pursuit eye movements but although the world appears stable during saccadic gaze changes, it does not appear stable during physical self-motion. We determined the amount by which a fixated object needed to be moved in space in order to appear earth stationary to a linearly moving observer. Observers were oscillated sinusoidally either passively or under their own control, under lit and fully darkened conditions. The visual targets always needed to move (in space) in the same direction as the observer to be judged as earth stationary. Targets needed to be moved more in order to be judged as earth stationary when movement was in the dark, rather than in the light, and also when movement was passive rather than when it was active. Efference copy motor signals, visual movement, and non-visual cues all contribute significantly and approximately additively to the estimate of self-motion. Errors in perceived self-motion can produce subsequent illusory visual motion.

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The direction of 'up' has traditionally been measured by setting a line (luminous if necessary) to the apparent vertical, a direction known as the 'subjective visual vertical' (SVV); however for optimum performance in visual skills including reading and facial recognition, an object must to be seen the 'right way up'--a separate direction which we have called the 'perceptual upright' (PU). In order to measure the PU, we exploited the fact that some symbols rely upon their orientation for recognition. Observers indicated whether the symbol 'horizontal P' presented in various orientations was identified as either the letter 'p' or the letter 'd'. The average of the transitions between 'p-to-d' and 'd-to-p' interpretations was taken as the PU. We have labelled this new experimental technique the Oriented CHAracter Recognition Test (OCHART). The SVV was measured by estimating whether a line was rotated clockwise or counter-clockwise relative to gravity. We measured the PU and SVV while manipulating the orientation of the visual background in different observer postures: upright, right side down and (for the PU) supine. When the body, gravity and the visual background were aligned, the SVV and the PU were similar, but as the background orientation and observer posture orientations diverged, the two measures varied markedly. The SVV was closely aligned with the direction of gravity whereas the PU was closely aligned with the body axis. Both probes showed influences of all three cues (body orientation, vision and gravity) and these influences could be predicted from a weighted vectorial sum of the directions indicated by these cues. For the SVV, the ratio was 0.2:0.1:1.0 for the body, visual and gravity cues, respectively. For the PU, the ratio was 2.6:1.2:1.0. In the case of the PU, these same weighting values were also predicted by a measure of the reliability of each cue; however, reliability did not predict the weightings for the SVV. This is the first time that maximum likelihood estimation has been demonstrated in combining information between different reference frames. The OCHART technique provides a new, simple and readily applicable method for investigating the PU which complements the SVV. Our findings suggest that OCHART is particularly suitable for investigating the functioning of visual and non-visual systems and their contributions to the perceived upright of novel environments such as high- and low-g environments, and in patient and ageing populations, as well as for normal observers.

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In order to test whether the control of eye movement in response to head movement requires an internal model of head orientation or instead can rely on directly sensing information about head orientation and movement, perceived gravity was separated from physical gravity to see which dominated the eye-movement response. Internal model theory suggests that the oculomotor response should be driven by perceived, internalized gravity, whereas the direct sensing theory predicts it should always be driven by vestibularly sensed gravity. Subjects lay on an airbed either supine or on their side and were sinusoidally translated along their dorsoventral body axis. The direction of perceived gravity was separated from physical gravity by performing the experiments in a room built on its side with the direction of its "floor" orthogonal to both physical gravity and the subject's translation. The swinging sum of the imposed sinusoidal acceleration with physical gravity was thus in a plane orthogonal to its sum with perceived gravity. Oculomotor responses to these swinging vectors were looked for and responses were found only to the sum of the acceleration with physical gravity, not perceived gravity. It was concluded that an internal model is not used to drive these compensatory eye movements.

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The perception of shading-defined form results from an interaction between shading cues and the frames of reference within which those cues are interpreted. In the absence of a clear source of illumination, the definition of 'up' becomes critical to deducing the perceived shape from a particular pattern of shading. In our experiments, twelve subjects adjusted the orientation of a planar disc painted with a linear luminance gradient from one side to the other, until the disc appeared maximally convex-that is, until the luminance gradient induced the maximum perception of a three-dimensional shape. The vision, gravity, and body-orientation cues were altered relative to each other. Visual cues were manipulated by the York Tilted Room facility, and body cues were altered by simply lying on one side. The orientation of the disc that appeared maximally convex varied in a systematic fashion with these manipulations. We present a model in which the direction of perceptual 'up' is determined from the sum of three weighted vectors corresponding to the vision, gravity, and body-orientation cues. The model predicts the perceived direction of 'up', contributes to our understanding of how shape-from-shading is deduced, and also predicts the confidence with which the 'up' direction is perceived.

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In a series of three separate experiments, we studied two different orientation illusions, in both of which vertical lines appear tilted as a result of being set against a tilted background pattern. The 'simultaneous tilt illusion' (STI), in which a target grating is viewed within an abutting tilted grating surround, is thought to originate early in the cortical processing of visual contours. In contrast, the 'rod-and-frame' illusion (RFI), which is induced by a distant tilted frame, is thought to originate much later in the perceptual processing system. In the first two experiments we found that orientation-guided action was virtually impervious to the RFI, whereas both perceptual experience and action were equally influenced by the STI. In the third experiment, in which the two illusions were pitted one against the other, an opposite pattern of effects emerged, such that visuomotor performance was now deceived by the illusion much more than was perceptual experience. This pattern of association and dissociation in the effects of visual illusions on perception versus action can best be explained within a two-visual-systems model of cortical processing.

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