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Gary G. Ferguson

✓ Preliminary experiments with glass model bifurcation aneurysms demonstrated that turbulent flow pattern occurs in the sac of an aneurysm at a low flow rate (critical Reynolds number, 400 ± 10 S.E.M.). A prediction that flow is turbulent in the sac of human intracranial saccular aneurysms was confirmed in a clinical study. Bruits, indicative of turbulence, were recorded with a phonocatheter from the sacs of 10 out of 17 intracranial aneurysms exposed at surgery where the mean arterial pressures were above 50 mm Hg. The amplitude of the bruits varied with the pressure. All of the patients in whom no bruit was found had profound Arfonad hypotension at the time of recording.

Turbulence causes vibration in the wall of a vessel. This vibration produces and accelerates degenerative changes in vascular tissue by a process similar to the structural fatigue of metals by vibration. The author proposes that the turbulent blood flow within an aneurysm contributes to the degeneration of the elastica, and the production of the atheromatous changes, characteristically seen in its wall. This weakens the wall causing continuing enlargement and eventual rupture.

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Gary G. Ferguson

✓ An investigation using glass models disclosed that the apex of a bifurcation is subjected to hemodynamic forces which may initiate the aneurysmal process by producing focal destruction of the internal elastic membrane. A prediction from model studies that turbulence occurs within intracranial aneurysms was confirmed in a clinical study. Bruits, indicative of turbulent blood flow, were recorded from the sacs of 12 of 19 cases studied at the time of craniotomy. Turbulence causes degenerative changes that weaken the wall of an aneurysm and allow it to enlarge. Measurement in four cases revealed that intra-aneurysmal pressure is the same as systemic arterial pressure. An in vitro study of the static elastic properties of human intracranial aneurysms demonstrated that they are relatively nondistensible in comparison to major intracranial arteries. This altered elasticity reflects the destruction of the elastic tissue in the wall of an aneurysm. An analysis of the physical factors influencing whether an aneurysm ruptures showed that the probability of rupture increases with an increase in intra-aneurysmal pressure, an increase in aneurysmal size, a decrease in the minimum wall thickness of an aneurysm, or a decrease in the strength of its structural components.

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Gary G. Ferguson

✓ Mean and pulsatile intra-aneurysmal blood pressures were recorded from four cases of human intracranial saccular aneurysms at the time of operative exposure. In each case the mean intra-aneurysmal pressure equalled the mean systemic arterial pressure, and the intra-aneurysmal pressure was pulsatile. The results demonstrate that, contrary to the findings of another report, intracranial aneurysms are subjected to the full force of systemic blood pressure.

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Brian D. Toyota and Gary G. Ferguson

✓ Recurrent subarachnoid hemorrhage (SAH) in the early period following successful clipping of a cerebral aneurysm is unusual. The authors report a unique case of distal basilar artery dissection and fatal SAH on the 6th day postoperatively. It is concluded that this complication was related to vascular trauma inflicted by repositioning the aneurysm clips during a seemingly uneventful procedure for a basilar artery tip aneurysm.

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J. Keith Farrar, Francis W. Gamache Jr., Gary G. Ferguson, John Barker, George P. Varkey and Charles G. Drake

✓ The progression of changes in cerebral blood flow (CBF) and neurological status were measured in 12 patients in whom profound hypotension (mean arterial blood pressure (MABP): 30 to 40 mm Hg) was used during intracranial aneurysm surgery. Nine patients (Group I) showed autoregulation of CBF to an MABP of 40 to 50 mm Hg during surgery. None of these patients had arterial spasm preoperatively. Postoperatively, mild flow disturbances were noted at the site of retraction. Three Group I patients developed arterial spasm postoperatively, but there was no associated neurological deterioration. The remaining three patients (Group II) had impaired autoregulation during surgery, and CBF decreased by 35% to 65% at an MABP of 50 mm Hg. Two of these patients had angiography immediately before surgery, and both showed moderate to severe arterial spasm. Relatively severe flow disturbances were noted postoperatively at the site of retraction, and two patients developed ischemic deficits of late onset. Brain retractor pressure and the degree and duration of hypotension were equivalent in the two patient groups. There was no correlation between intraoperative reductions in CBF (to as low as 20 ml/100 gm/min in the unretracted hemisphere) and immediate postoperative neurological deficits. The use of halothane and mannitol and the relatively short duration of the flow reductions were suggested as factors contributing to the protection from ischemia that was observed. Arterial spasm was found to produce hemodynamic instability and reduced CBF, although neurological status was unaffected in the majority of patients. Patients with impaired autoregulation during surgery were at increased risk of delayed ischemic complications postoperatively, and showed characteristic flow disturbances at all three stages of their clinical course.

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Charles G. Drake, Sydney J. Peerless and Gary G. Ferguson

✓ Hunterian proximal artery occlusion was used in the treatment of 160 of 335 patients harboring giant aneurysms of the anterior circulation. One hundred and thirty-three of these aneurysms arose from the internal carotid arteries, 20 from the middle cerebral arteries, and seven from the anterior cerebral arteries. Ninety percent of the patients had satisfactory outcomes. The safety of internal carotid artery occlusion has been greatly enhanced by preoperative flow studies and by test occlusion with an intracarotid balloon to identify those patients who require preliminary extracranial-to-intracranial bypass, which was used in all of the middle cerebral occlusions. The anterior cerebral artery had magnificent leptomeningeal collateral flow that prevented infarction even without cross flow. Obliteration of the aneurysm by thrombosis was complete, or nearly so, in all but four patients whose treatment was completed. Analysis of poor outcome in 16 patients revealed that hemodynamic ischemic infarction was known to occur after only two of the carotid occlusions.

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Andrew P. Gasecki, Michael Eliasziw, Gary G. Ferguson, Vladimir Hachinski, Henry J. M. Barnett and for the North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group

✓ The purpose of this study was to examine how the prognosis of patients who presented with a recent ischemic event referable to a 70% to 99% stenosis of one carotid artery (ipsilateral) was altered by stenosis and occlusion of the contralateral carotid artery. The benefit of performing carotid endarterectomy on the recently symptomatic artery, in the presence of contralateral artery disease, was also examined.

A total of 659 patients were grouped into one of three categories according to the extent of stenosis in the contralateral carotid artery: less than 70% (559 patients), 70% to 99% (57 patients), and occlusion (43 patients). Strokes that occurred during the follow-up period were designated as ipsilateral if they arose from the same carotid artery as the symptom for which the patient had been entered into the study. Medically treated patients with an occluded contralateral artery were more than twice as likely to have had an ipsilateral stroke at 2 years than patients with either severe (hazard ratio: 2.36; 95% confidence interval (CI): 1.00–5.62) or mild-to-moderate (hazard ratio: 2.65; 95% CI: 1.43–4.90) contralateral artery stenosis. The perioperative risk of stroke and death was higher in patients with an occluded contralateral artery (4.0% risk) or mild-to-moderate (5.1% risk) contralateral stenosis. Regression analyses indicated that the results were not affected by other risk factors.

An occluded contralateral carotid artery significantly increased the risk of stroke associated with a severely stenosed ipsilateral carotid artery. Despite higher perioperative morbidity in the presence of an occluded contralateral artery, the longer-term outlook for patients who had endarterectomy performed on the recently symptomatic, severely stenosed ipsilateral carotid artery was considerably better than for medically treated patients.

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David Pelz, Richard N. Rankin and Gary G. Ferguson

✓ Seventy-four consecutive patients who had undergone carotid endarterectomy procedures were examined with intravenous digital subtraction angiography (IV-DSA) and duplex ultrasonography (DUS) at intervals ranging from 1 to 14 months postoperatively. Ninety-one percent of the DUS and 74% of the DSA images were of diagnostic quality. The two modalities agreed in the assessment of the endarterectomy appearance in 84% of the arteries, with 85% showing no evidence of significant residual disease. There were no arteries with severe restenosis or complete occlusion. In the 10 vessels in which the two modalities disagreed in disease assessment, the IV-DSA images were often degraded by artifact or vessel overlap leading to underestimation of disease. The authors conclude that DUS is the examination of choice for routine follow-up studies of carotid endarterectomy.

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Stephen P. Lownie, Charles G. Drake, Sydney J. Peerless, Gary G. Ferguson and David M. Pelz

Object. The authors reviewed their 20-year experience with giant anterior communicating artery aneurysms to correlate aneurysm size with clinical presentation and to analyze treatment methods.

Methods. In 18 patients, visual and cognitive impairment were quantitated and clinical outcome was categorized according to the Rankin scale. Statistical analysis was performed using Fisher's exact test.

Conclusions. At least 3.5 cm of aneurysm mass effect was required to produce dementia in the patient (p = 0.0004). Dementia was usually caused by direct brain compression by the aneurysm rather than by hydrocephalus. Optic apparatus compression occurred with smaller aneurysms (2.7–3.2 cm) when they pointed inferiorly.

Aneurysm neck clipping was possible in half of the cases. Special techniques, including temporary clipping, evacuation of intraluminal thrombus, tandem and/or fenestrated clipping, and clip reconstruction were often required. Occlusion of or injury to the anterior cerebral artery (ACA) was the main cause of poor outcome or death.

Proximal ACA occlusion, even of dominant A1 segments with small or no contralateral A1 artery, was an effective treatment alternative and was well tolerated as a result of excellent leptomeningeal collateral circulation.