Journal of neurosurgery
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Journal of neurosurgery · Feb 1996
Microvascular anatomy of dural arteriovenous abnormalities of the spine: a microangiographic study.
Although most vascular abnormalities of the spinal cord are now ascribed to an abnormal communication between a dural artery and a medullary vein on the dura near a sensory nerve root, these lesions are too small for their anatomy to be demonstrated directly by spinal arteriography. Thus, it is unknown whether the site of dural arteriovenous shunting is an arteriovenous malformation (AVM), implying a congenital origin, or is a direct arteriovenous fistula (AVF), implying an acquired etiology. The authors treated six patients by en bloc resection of the involved dural root sleeve, proximal nerve root, and adjacent spinal dura. ⋯ Several medium-to-small collateral vessels arising from adjacent intercostal or lumbar arteries were commonly present in the dura and converged at the site of the AVF to join a single medullary vein. These results show that spinal dural AVMs are direct AVFs that link the dural branch of the radiculo-medullary-dural artery with the intradural medullary vein. They also provide an anatomical explanation for the presence of a multiple segmental arterial supply and a single draining medullary vein of spinal dural AVFs, and the propensity for reestablishment of flow through the arteriovenous shunt after embolic occlusion.
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Journal of neurosurgery · Feb 1996
Effects of spinal cord stimulation on the flexor reflex and involvement of supraspinal mechanisms: an experimental study in mononeuropathic rats.
The physiological mechanisms responsible for pain relief caused by spinal cord stimulation (SCS) are essentially unknown and recent experimental data are sparse. In the present study the authors explored the possible involvement of supraspinal mechanisms in the effects of SCS applied in rats with experimental mononeuropathy produced by sciatic nerve ligation according to the method of Bennett and Xie or that of Seltzer, et al. Confirming results of a previous study undertaken by the authors, the thresholds of the early component of the flexor reflex (latency 8-12 msec), which is mediated by A fibers, were significantly lower in the nerve-ligated than in the intact leg. ⋯ There was no effect on the late component of the reflex in either leg. The results indicate that this effect of SCS in mononeuropathic rats does not necessarily involve supraspinal mechanisms; instead SCS is operative at a spinal, segmental level. In view of the similarities between the effects of therapeutic SCS on cutaneous hypersensibility in patients with peripheral neuropathic pain and the effects demonstrated in neuropathic rats, the clinical pain relief achieved with SCS may be produced, at least partially, by intraspinal mechanisms.
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Journal of neurosurgery · Feb 1996
Case ReportsMiddle cerebral artery dissecting aneurysm with persistent patent pseudolumen. Case report.
The extremely rare condition of an ischemic right middle cerebral artery dissecting aneurysm with persistent patent pseudolumen is described. In the majority of cases of dissecting aneurysms, the pseudolumen persists for a very short time, probably because reentry from the pseudolumen is minimal or nonexistent. In contrast, the present case was assumed to have sufficient reentry from the bypass flow in the pseudolumen. Endothelial formation both in the true lumen and the pseudolumen was suggested as the possible mechanism of the stabilized double lumen.
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To determine the incidence of, and risk factors for, the occurrence of rebleeding between admission and early operation (ultra-early rebleeding) in patients with spontaneous subarachnoid hemorrhage (SAH), the authors reviewed the cases of 179 patients admitted within 24 hours after their last attack of SAH. Thirty-one (17.3%) of these patients had ultra-early rebleeding despite scheduling of early operation (within 24 hours after admission). The incidence of rebleeding significantly decreased as the time interval between the last attack and admission increased. ⋯ Multivariate analysis revealed that the following three factors were independently associated with ultra-early rebleeding: the level of enhancement of platelet sensitivity; the time interval between the last attack and admission; and the level of thrombin-antithrombin complex. On the basis of these findings, the authors suggest that many of the risk factors for ultra-early rebleeding are interrelated. A particularly high risk of ultra-early rebleeding was observed in those patients 1) who had platelet hypoaggregability; 2) who were admitted shortly after their last SAH; and 3) whose thrombin-antithrombin complex levels were extremely high and were thus in severe clinical condition.
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Journal of neurosurgery · Jan 1996
Relationship between transcranial Doppler-determined pulsatility index and cerebrovascular resistance: an experimental study.
Clinical studies with transcranial Doppler suggest that the pulsatility of the flow velocity (FV) waveform increases when the distal cerebrovascular resistance (CVR) increases. To clarify this relationship, the authors studied animal models in which the resistance may be decreased in a controlled manner by an increase in arterial CO2 tension, or by a decrease in cerebral perfusion pressure (CPP) in autoregulating animals. Twelve New Zealand white rabbits were anesthetized, paralyzed, and ventilated. ⋯ During the hypercapnic challenge the correlation between the cortical resistance and Doppler flow pulsatility was positive (r = 0.77, p<0.001). In all three groups in which cerebral perfusion pressure was reduced a negative correlation between pulsatility index and cerebrovascular resistance was found (r = -0.84, p<0.001). The authors conclude that PI cannot be interpreted simply as an index of CVR in all circumstances.