Isolated bilateral lateral geniculate body necrosis following acute pancreatitis: A rare cause of bilateral loss of vision in a young female.

Sudden bilateral visual loss because of bilateral lateral geniculate body (LGB) necrosis is a very rare entity. The mechanisms causing these isolated lesions have still not been fully understood. We report a case of sudden loss of vision in a 22-year-old female following an attack of acute pancreatitis, just after starting the paleo diet. Neuroimaging revealed bilateral LGB necrosis. Multidisciplinary approach was sought and she was subsequently managed successfully. On follow-up, her visual acuity showed improvement, and neuroimaging revealed resolution of hyperintensities in bilateral LGB with residual blooming suggestive of old hemorrhagic gliosis. The possible reasons for isolated lesions of the LGB are hemorrhagic infarction and osmotic demyelination. In the present case, we postulate a vascular pathology, possibly hypo-perfusion because of shock following acute pancreatitis.

Hemorrhagic Intracranial Cavernoma Presenting as a Homonymous Horizontal Sectoranopia.

ABSTRACT: Hemorrhagic lateral geniculate nucleus (LGN) insults are rare but have been reported in association with tumors, vascular malformations, and trauma. The localization of LGN lesions is facilitated by recognition of pathognomonic visual field defects. A 21-year old woman developed a sudden onset painless left homonymous horizontal sectoranopia. Magnetic resonance imaging revealed a hemorrhagic cavernous malformation of the right temporal lobe. Optical coherence tomography (OCT) and Humphrey perimetry findings localized the lesion to the right LGN. Specifically, OCT testing revealed a right homonymous sectoranopia pattern of hemi-retinal macular ganglion layer-inner plexiform layer (mGCIPL) thinning contralateral to the left sided visual field defect. The OCT pattern reflected retrograde neuroaxonal degeneration from the right LGN lesion. This case highlights a unique pattern of mGCIPL thinning characteristic for a posterior lateral choroidal artery injury, affecting the LGN. These findings illustrate how functional eloquence correlates with topographical elegance in the afferent visual pathway.

Arterial Supply of the Thalamus: A Comprehensive Review.

The thalamus is a deep cerebral structure that is crucial for proper neurological functioning as it transmits signals from nearly all pathways in the body. Insult to the thalamus can, therefore, result in complex syndromes involving sensation, cognition, executive function, fine motor control, emotion, and arousal, to name a few. Specific territories in the thalamus that are supplied by deep cerebral arteries have been shown to correlate with clinical symptoms. The aim of this review is to enhance our understanding of the arterial anatomy of the thalamus and the complications that can arise from lesions to it by considering the functions of known thalamic nuclei supplied by each vascular territory.

Incongruous, incomplete, homonymous hemianopia due to an infarction localized to the lateral geniculate body.

A 45-year-old male was admitted with an acute-onset visual field defect. Goldmann perimetry revealed an incongruent, incomplete right homonymous hemianopia. The left eye showed a wedge-shaped, horizontal right hemianopia, whereas the right eye showed constriction of the right visual hemifield. MRI showed acute infarction localized to the left lateral geniculate body (LGB). LGB has a dual blood supply: from the anterior choroidal artery and from the lateral posterior choroidal artery (LPChA). The LPChA territory of LGB receives projection from the retinal area around the macula and horizontal meridian. Therefore, an LPChA territory infarction of LGB can cause a wedge-shaped, horizontal visual field defect. The visual field defect in our patient would be caused by an LPChA territory infarction of LGB. Our patient showed an incongruent homonymous hemianopia. LGB has six laminae, with the ipsilateral retinal fibers terminating in layers two, three, and five and the crossed fibers terminating in layers one, four, and six. The laminar structure provides the anatomical basis for the incongruous visual field defects in a case of partial lesion of LGB. Based on the present data, we believe that an ischemic lesion localized to LGB should be considered in patients presenting with incongruous, incomplete homonymous hemianopia.

Controlled ultrasound-induced blood-brain barrier disruption using passive acoustic emissions monitoring.

The ability of ultrasonically-induced oscillations of circulating microbubbles to permeabilize vascular barriers such as the blood-brain barrier (BBB) holds great promise for noninvasive targeted drug delivery. A major issue has been a lack of control over the procedure to ensure both safe and effective treatment. Here, we evaluated the use of passively-recorded acoustic emissions as a means to achieve this control. An acoustic emissions monitoring system was constructed and integrated into a clinical transcranial MRI-guided focused ultrasound system. Recordings were analyzed using a spectroscopic method that isolates the acoustic emissions caused by the microbubbles during sonication. This analysis characterized and quantified harmonic oscillations that occur when the BBB is disrupted, and broadband emissions that occur when tissue damage occurs. After validating the system's performance in pilot studies that explored a wide range of exposure levels, the measurements were used to control the ultrasound exposure level during transcranial sonications at 104 volumes over 22 weekly sessions in four macaques. We found that increasing the exposure level until a large harmonic emissions signal was observed was an effective means to ensure BBB disruption without broadband emissions. We had a success rate of 96% in inducing BBB disruption as measured by in contrast-enhanced MRI, and we detected broadband emissions in less than 0.2% of the applied bursts. The magnitude of the harmonic emissions signals was significantly (P<0.001) larger for sonications where BBB disruption was detected, and it correlated with BBB permeabilization as indicated by the magnitude of the MRI signal enhancement after MRI contrast administration (R(2) = 0.78). Overall, the results indicate that harmonic emissions can be a used to control focused ultrasound-induced BBB disruption. These results are promising for clinical translation of this technology.

Homonymous hemianopia from infarction of the optic tract and lateral geniculate nucleus in deep cerebral venous thrombosis.

A 20-year-old man developed right homonymous hemianopia, hemiparesis, and hemisensory loss from deep cerebral venous thrombosis in the setting of high altitude. Approximately 3 months later, brain MRI showed encephalomalacia of the left optic tract and lateral geniculate nucleus, as well as signal abnormalities of the internal capsule and posterolateral thalamus. Homonymous hemianopia has previously been described in 1 case after deep cerebral venous thrombosis but without detailed neuroimaging features.

Unconscious response priming by shape depends on geniculostriate visual projection.

It has been suggested that unconscious visual processing of some stimulus features might occur without the contribution of early visual cortex (V1/V2). In the present study, the causal role of V1/V2 in unconscious processing of simple shapes in intact human brain was studied by applying transcranial magnetic stimulation (TMS) on early visual cortex or lateral occipital cortex (LO) while observers performed a metacontrast-masked response priming task with arrow figures as visual stimuli. Magnetic stimulation of V1/V2 impaired masked priming 30-90 ms after the onset of the prime. Stimulation of LO reduced the magnitude of masked priming at 90-120 ms, but this effect occurred only in the early parts of the priming experiment. A control task measuring the visibility of masked primes indicated that the orientation of masked primes could not be consciously discriminated and that TMS did not influence the conscious visibility of the primes indirectly by reducing the effectiveness of the mask in the critical time windows. We conclude that feedforward sweep of processing from V1/V2 (30-90 ms) to LO (90 ms and above) is necessary for unconscious priming of shape, whereas conscious perception requires also the contribution of recurrent (feedback) processing.

Neurometabolic coupling in the lateral geniculate nucleus changes with extended age.

Attempts have been made in various studies to identify and trace changes in function in the aging visual system. Some results are conflicting and we report here a unique approach in an attempt to resolve selected issues. We have estimated neurometabolic coupling in the central visual pathway in young and old cats. Our technique provides high resolution simultaneous measurements of neuronal activity and changes in concentration of tissue oxygen in the thalamus of young and old cats. Following visual stimulation, we find shorter latency and time to peak in tissue oxygen responses in old compared with young animals. Estimates of local activity induced initial negative oxygen response show substantial reductions in older animals. Measurements of neural activity in the form of multiple unit activity are similar in the two age groups. To investigate the mechanisms underlying the changes in tissue oxygen response in older animals, we measured vascular capillary density and found it to be substantially lower in old than that in young animals. Together, these findings suggest that the changes in metabolic responses with age may be largely accounted for by alterations in the cerebral microvasculature rather than by changes in neural activity.

High-resolution fMRI mapping of ocular dominance layers in cat lateral geniculate nucleus.

In this work, we exploited the superior capability of high-resolution functional magnetic resonance imaging (fMRI) for functional mapping of ocular dominance layer (ODL) in the cat lateral geniculate nucleus (LGN). The stimulus-evoked neuronal activities in the LGN ODLs associated with contralateral- and ipsilateral-eye visual inputs were successfully differentiated and mapped using both blood-oxygenation-level dependent (BOLD)-weighted and cerebral blood volume (CBV)-weighted fMRI methods. The morphology of mapped LGN ODLs was in remarkable consistency with histology findings in terms of ODL shape, orientation, thickness and eye-dominance. Compared with the BOLD signal, the CBV signal provides higher reproducibility and better spatial resolvability for function mapping of LGN because of improved contrast-to-noise ratio and point-spread function. The capability of fMRI for non-invasively imaging the functional sub-units of ODL in a small LGN overcomes the limitation of conventional neural-recording approach, and it opens a new opportunity for studying critical roles of LGN in brain function and dysfunction at the fine scale of ocular dominance layer.

Characterisation of the BOLD response time course at different levels of the auditory pathway in non-human primates.

Non-human-primate fMRI is becoming increasingly recognised as the missing link between the widely applied methods of human imaging and intracortical animal electrophysiology. A crucial requirement for the optimal application of this method is the precise knowledge of the time course of the Blood Oxygenation Level Dependent (BOLD) signal. We mapped the BOLD signal time course in the inferior colliculus (IC), medial geniculate body (MGB) and in tonotopically defined fields in the auditory cortex of two macaques. The results show little differences in the BOLD-signal time courses within the auditory pathway. However, we observed systematic differences in the magnitude of the change in the BOLD signal with significantly stronger signal changes in field A1 of the auditory cortex compared to field R. The measured time course of the signal was in good agreement with similar studies in human auditory cortex but showed considerable differences to data reported from macaque visual cortex. Consistent with the studies in humans we measured a peak in the BOLD response around 4 s after the onset of 2-s broadband noise stimuli while previous studies recorded from the primary visual cortex of the same species reported the earliest peaks to short visual stimuli several seconds later. The comparison of our results with previous studies does not support differences in haemodynamic responses within the auditory system between human and non-human primates. Furthermore, the data will aid optimal design of future auditory fMRI studies in non-human primates.

Anomalous medial origin of the anterior choroidal artery with associated aneurysm.

Injury to the anterior choroidal artery (AchA) can be devastating owing to the importance of the territory it supplies. The AchA is a known site of aneurysm formation, and is often exposed during various surgical and endovascular procedures. We report a patient with an aneurysm at the origin of the AchA, and an anomalous medial take off of the artery from the internal carotid artery, then a sharp lateral turn followed by a normal course toward the choroidal fissure, unreported to date to our knowledge. The aneurysm was treated successfully by endovascular therapy. The typical anatomy of the AchA, and reported variations in its origin are discussed. Thorough knowledge of the normal cerebrovascular anatomy and attention to variations play an important role in the successful management of patients with neurological vascular conditions.

Isolated homonymous hemianopsia due to lateral posterior choroidal artery region infarction: a case report.

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.

Deficient responses from the lateral geniculate nucleus in humans with amblyopia.

Amblyopia or lazy eye is the most common cause of uniocular blindness in adults. It is caused by a disruption to normal visual development as a consequence of unmatched inputs from the two eyes in early life, arising from a turned eye (strabismus), unequal refractive error (anisometropia) or form deprivation (e.g. cataract). Animal models based on extracellular recordings in anesthetized animals suggest that the earliest site of the anomaly in the primate visual pathway is the primary visual cortex (corresponding to the striate cortex, cytoarchitectonic area 17 and area V1), which is where inputs from the two eyes are first combined in an excitatory fashion, whereas more distal and monocular processing structures such as the retina and lateral geniculate nucleus (LGN) are normal. Using high-field functional magnetic resonance imaging in a group of human adults with amblyopia, we demonstrate that functional deficits are first observable at a thalamic level, that of the LGN. Our results suggest the need to re-evaluate the current models of amblyopia that are based on the assumption of a purely cortical dysfunction, as well as the role for the LGN in visual development.

Noninvasive measurement of the cerebral blood flow response in human lateral geniculate nucleus with arterial spin labeling fMRI.

To date, functional magnetic resonance imaging (fMRI) studies of the lateral geniculate nucleus (LGN) have primarily focused on measures of the blood oxygenation level dependent (BOLD) signal. Arterial spin labeling (ASL) is an MRI method that can provide direct measures of functional cerebral blood flow (CBF) changes. Because CBF is a well-defined physiological quantity that contributes to BOLD contrast, CBF measures can be used to improve the quantitative interpretation of fMRI studies. However, due in part to the low intrinsic signal-to-noise ratio of the ASL method, measures of functional CBF changes in the LGN are challenging and have not previously been reported. In this study, we demonstrate the feasibility of using ASL fMRI to measure the CBF response of the LGN to visual stimulation on a 3 T MRI system. The use of background suppression and physiological noise reduction techniques allowed reliable detection of LGN activation in all five subjects studied. The measured percent CBF response during activation ranged from 40 to 100%, assuming no interaction between the left and right LGN.

Bilateral isolated lateral geniculate body lesions in a patient with pancreatitis and microangiopathy.

An 18-year-old woman developed pancreatitis and a thrombotic microangiopathy but no electrolyte abnormalities. She required intubation hours after admission and was not able to communicate for 8 days. Upon recovering consciousness, she reported severely impaired vision in both eyes, but ophthalmologic evaluation and neuroimaging were not obtained until several days later. Ophthalmologic examination documented retinal infarcts and profound binocular vision loss with hourglass bilateral homonymous hemianopic visual field loss. MRI showed signal abnormalities restricted to the area of the lateral geniculate bodies (LGBs) with characteristics most suggestive of hemorrhagic infarction. Very few cases of isolated bilateral LBG lesions have been reported. Damage has been attributed to myelinolysis from osmotic demyelination or to infarction from microvascular occlusion. This case conforms more to microvascular infarction. The vulnerability of the LGB to selective microvascular infarction may be based on a combination of its unique architecture and high metabolic demand.

Activation of superior colliculi in humans during visual exploration.

BACKGROUND: Visual, oculomotor, and - recently - cognitive functions of the superior colliculi (SC) have been documented in detail in non-human primates in the past. Evidence for corresponding functions of the SC in humans is still rare. We examined activity changes in the human tectum and the lateral geniculate nuclei (LGN) in a visual search task using functional magnetic resonance imaging (fMRI) and anatomically defined regions of interest (ROI). Healthy subjects conducted a free visual search task and two voluntary eye movement tasks with and without irrelevant visual distracters. Blood oxygen level dependent (BOLD) signals in the SC were compared to activity in the inferior colliculi (IC) and LGN. RESULTS: Neural activity increased during free exploration only in the SC in comparison to both control tasks. Saccade frequency did not exert a significant effect on BOLD signal changes. No corresponding differences between experimental tasks were found in the IC or the LGN. However, while the IC revealed no signal increase from the baseline, BOLD signal changes at the LGN were consistently positive in all experimental conditions. CONCLUSION: Our data demonstrate the involvement of the SC in a visual search task. In contrast to the results of previous studies, signal changes could not be seen to be driven by either visual stimulation or oculomotor control on their own. Further, we can exclude the influence of any nearby neural structures (e.g. pulvinar, tegmentum) or of typical artefacts at the brainstem on the observed signal changes at the SC. Corresponding to findings in non-human primates, our data support a dependency of SC activity on functions beyond oculomotor control and visual processing.

Sectoranopia: a stroke in the lateral geniculate nucleus or optic radiations?

BACKGROUND: The lateral geniculate nucleus (LGN) is the site at which ganglion cell axons of the optic tract synapse with neurons that form the optic radiations. Lesions of the perigeniculate visual pathway are characterized by distinct pupillary, visual field, and ophthalmoscopic findings. Such findings, combined with results from neuroimaging, enable one to precisely locate the area of the visual pathway that is involved. CASE REPORT: A patient who presented to our clinic with a complaint of narrowly missing several motor vehicle accidents recently was found to have a left horizontal sectoranopia on a screening visual field. Magnetic resonance imaging confirmed the presence of an old infarct involving the optic radiations. The patient's medical history was significant for high homocysteine levels that likely contributed to his having had several cerebral vascular accidents in the past, one of which affected the optic radiations. CONCLUSIONS: Damage to the LGN and optic radiations can produce sectoranopic visual field defects. Although it may not be possible to specify the exact location of a lesion, understanding the blood supply of the visual pathway and retinotopic organization of the LGN aids in the localization of infarcts that cause characteristic visual field defects.