Sildenafil improves scotoma after posterior cerebral infarctions: a case report.

A 65-year-old man had an embolic stroke of both posterior cerebral arteries in 2002. Two years later he noted rapid improvement of the residual bilateral inferior quadrant anopia whenever he took 25 mg sildenafil. The improvement of scotomas was verified by visual field examinations and persisted reproducibly for 3-7 days. An overlay of a subtraction of functional magnetic resonance imaging (MRI) during visual stimulation before and after medication onto a T1-weighted MRI of the patient revealed additional activations along the margins of the old cerebral infarctions. These findings and the additional results of a perfusion MRI suggest that phosphodiesterase 5 inhibitors may prove beneficial in the rehabilitative course after ischemic strokes.

Resistance of the internal mammary artery to restenosis: a histomorphologic study of various porcine arteries.

BACKGROUND/AIMS: Restenosis after percutaneous transluminal angioplasty (PTA) of the internal mammary artery (IMA) grafts is much less pronounced than in other arteries and venous grafts. The aim of the study was to test whether various arteries respond differently to dilatation. METHODS: PTA of the IMA, carotid, renal and circumflex coronary (RCx) arteries was performed in 9 pigs (balloon to artery ratio of 1:1.5). After 8 weeks, angiography was repeated and vessels prepared for histological analysis. Immunohistochemical staining was done to examine proliferative activity (Ki67) and to identify the vasa vasorum of the adventitia (F VIII-RA). RESULTS: The intima-media ratio after PTA was lowest in the IMA (0.06), followed by the carotid (0.27) and renal arteries (0.49) and the RCx (0.69). Proliferation of the intima was seen at 287 degrees of the vessel circumference in the RCx, at 286 degrees in the renal and at 166 degrees in the carotid artery. No proliferative activity was seen in the IMA. The intima-adventitia ratio was lower in the IMA than in the RCx and renal arteries (p < 0.05). CONCLUSION: Intima proliferation after PTA varies between the different vessels, with best results seen in the IMA. There are differences in remodeling after PTA between muscular, muscular/elastic and elastic arteries.

Evidence for cortical visual substitution of chronic bilateral vestibular failure (an fMRI study).

Bilateral vestibular failure (BVF) is a rare disorder of the labyrinth or the eighth cranial nerve which has various aetiologies. BVF patients suffer from unsteadiness of gait combined with blurred vision due to oscillopsia. Functional MRI (fMRI) in healthy subjects has shown that stimulation of the visual system induces an activation of the visual cortex and ocular motor areas bilaterally as well as simultaneous deactivations of multisensory vestibular cortex areas. Our question was whether the chronic absence of bilateral vestibular input (BVF) causes a plastic cortical reorganization of the above-described visual-vestibular interaction. We used fMRI to measure the differential effects of horizontal visual optokinetic stimulation (OKN) on activations and deactivations in 10 patients with BVF and compared their data directly to those of pairwise age- and sex-matched controls. We found that bilateral activation of the primary visual cortex (inferior and middle occipital gyri, Brodmann area BA 17, 18, 19), the motion-sensitive areas V5 in the middle and inferior temporal gyri (BA 37), and the frontal eye field (BA 8), the right paracentral and superior parietal lobule and the right fusiform and parahippocampal gyri was significantly stronger and the activation clusters were larger than that of the age-matched healthy controls. Small areas of BOLD signal decreases (deactivations), located primarily in the right posterior insula containing the parieto-insular vestibular cortex, were similar to those in the healthy controls. No other sensory brain areas showed unexpected activations or deactivations, e.g. the somatosensory or auditory cortex areas. Our finding of enhanced activations within the visual and ocular motor systems of BVF patients suggests that they might be correlated with an upregulation of visual sensitivity during tracking of visual motion patterns. Functionally, these enhanced activations are independent of optokinetic performance, since the mean slow-phase velocity of OKN in the BVF patients did not differ from that in normals. Although psychophysical and neurophysiological tests have provided various examples of how sensory loss in one modality leads to a substitutional increase of functional sensitivity in other modalities, this study presents the first evidence of visual substitution for vestibular loss by functional imaging.

Brainstem and cerebellar fMRI-activation during horizontal and vertical optokinetic stimulation.

Animal studies have shown that not only cortical, but also brainstem and cerebellar areas are involved in the initiation and generation of optokinetic nystagmus (OKN), e.g., cortico-(pretecto)pontine-olivo-cerebellar pathways. The aim of this fMRI study was to identify and differentiate brainstem and cerebellar areas involved in horizontal and vertical OKN (h/vOKN) in humans. In a group of nine healthy volunteers, hOKN and vOKN were statistically compared with a stationary control condition. There were common activated regions for hOKN and vOKN directions located in the transition zone between the posterior thalamus and the mesencephalon bilaterally covering the pretectal nucleus complex, which is known to be a major structure within the afferent branch of the optokinetic system. Furthermore, during hOKN, activation occurred bilaterally in the mediodorsal and dorsolateral ponto-medullary brainstem, which could be best attributed to the reticular formation, especially the paramedian pontine reticular formation (PPRF). For vOKN, additional activated areas in the dorsal mesencephalic brainstem could be best localized to the ocular motor nuclei and the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). For both OKN directions, the cerebellar activation was localized in the oculomotor vermis (declive VI, folium and tuber VIIA/B, in part pyramis VIIIA), and the flocculus bilaterally as well as widespread in the cerebellar hemispheres. In conclusion, fMRI allowed first attributions of neuronal substrates in the cerebellum and brainstem to hOKN and vOKN in humans. Consistent with the animal data, the dorsal ponto-medullary routes were involved bilaterally for hOKN, whereas the rostral mesencephalic routes were involved for vOKN.

Direction-dependent visual cortex activation during horizontal optokinetic stimulation (fMRI study).

Looking at a moving pattern induces optokinetic nystagmus (OKN) and activates an assembly of cortical areas in the visual cortex, including lateral occipitotemporal (motion-sensitive area MT/V5) and adjacent occipitoparietal areas as well as ocular motor areas such as the prefrontal cortex, frontal, supplementary, and parietal eye fields. The aim of this functional MRI (fMRI) study was to investigate (1) whether stimulus direction-dependent effects can be found, especially in the cortical eye fields, and (2) whether there is a hemispheric dominance of ocular motor areas. In a group of 15 healthy subjects, OKN in rightward and leftward directions was visually elicited and statistically compared with the control condition (stationary target) and with each other. Direction-dependent differences were not found in the cortical eye fields, but an asymmetry of activation occurred in paramedian visual cortex areas, and there were stronger activations in the hemisphere contralateral to the slow OKN phase (pursuit). This can be explained by a shift of the mean eye position of gaze (beating field) in the direction of the fast nystagmus phases of approximately 2.6 degrees, causing asymmetrical visual cortex stimulation. The absence of a significant difference in the activation pattern of the cortical eye fields supports the view that the processing of eye movements in both horizontal directions is mediated in the same cortical ocular motor areas. Furthermore, no hemispheric dominance for OKN processing was found in right-handed volunteers.

Metabolic changes in vestibular and visual cortices in acute vestibular neuritis.

Five right-handed patients with a right-sided vestibular neuritis were examined twice with fluorodeoxyglucose positron emission tomography while lying supine with eyes closed: once during the acute stage (mean, 6.6 days) and then 3 months later when central vestibular compensation had occurred. Regional cerebral glucose metabolism (rCGM) was significantly increased (p <0.001 uncorrected) during the acute stage in multisensory vestibular cortical and subcortical areas (parietoinsular vestibular cortex in the posterior insula, posterolateral thalamus, anterior cingulate gyrus [Brodmann area 32/24], pontomesencephalic brainstem, hippocampus). Simultaneously, there was a significant rCGM decrease in the visual (Brodmann area 17 to 19) and somatosensory cortex areas in the postcentral gyrus as well as in parts of the auditory cortex (transverse temporal gyrus). Fluorodeoxyglucose positron emission tomography thus allows imaging of the cortical activation pattern that is induced by unilateral peripheral vestibular loss. It was possible to demonstrate that the central vestibular system including the vestibular cortex exhibits a visual-vestibular activation-deactivation pattern during the acute stage of vestibular neuritis similar to that in healthy volunteers during unilateral labyrinthine stimulation. Contrary to experimental vestibular stimulation, the activation of the vestibular cortex was not bilateral but was unilateral and contralateral to the right-sided labyrinthine failure.