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Introduction

Focal cerebral ischemia

Fredric B. Meyer

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Fredric B. Meyer and Jeffrey N. Bruce

This edition of the Video Supplement entitled “Microsurgery of the Third Ventricle, Pineal Region, and Tentorial Incisura” highlights approaches to accessing the third ventricle for surgical resection of a variety of pathologies. The third ventricle has critical neurovascular anatomy that must always be respected to prevent patient harm. Visualization of critical anatomy in three dimensions from a surgeon' line of sight is important when planning the optimum surgical approach. Some of the keys to safely operating in this region include thoughtful head positioning, limitation of brain retraction, and the use of trajectories which capitalize on CSF cisterns and fissures. Some of the videos included in this volume illustrate standard operations while others depict more unique and innovative approaches that take advantage of these surgical windows. We hope you enjoy the videos included in this supplement.

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Fredric B. Meyer and Wanda L. Windschitl

Saphenous vein patch closure of carotid endarterectomies may decrease the risk of acute postoperative occlusion and recurrent stenosis. However, the disadvantages of a vein patch include postoperative rupture and pseudoaneurysm formation.

Object. The authors sought to assess the effectiveness of collagen-impregnated fabric grafts as substitutes for saphenous vein grafts.

Methods. In this report the authors prospectively analyzed 290 consecutive carotid endarterectomies in which a secondary closure was accomplished using a knitted double-velour graft. The 30-day major neurological morbidity and mortality rate was 1.7%. There were no postoperative occlusions or wound hematomas. The rate of recurrent carotid artery stenosis was less than 1%, and the graft site in one patient became infected.

Conclusions. For surgeons who prefer a secondary closure of carotid endarterectomies, the synthetic graft may prove to be a viable alternative to a saphenous vein.

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Fredric B. Meyer and Donald A. Muzzi

✓ A strategy for intraoperative cerebral protection is described in which intraoperative electroencephalography is used to titrate the level of inspired isoflurane given for anesthesia to obtain isoelectricity prior to temporary vessel occlusion during repair of difficult aneurysms. During temporary vessel occlusion, arterial blood pressure is maintained or increased with an inotropic or vasopressor agent. After clipping of the aneurysm, the concentration of isoflurane is reduced to allow the patient to awaken in the operating room for early postoperative neurological examination. The combination of a high concentration of isoflurane, temporary vessel occlusion, and maintenance of arterial blood pressure may be a useful protective regimen during neurovascular procedures.

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Michelle J. Clarke and Fredric B. Meyer

✓The mathematical modeling of hydrocephalus is a relatively young field. The discipline evolved from Hakim's initial description of the brain as a water-filled sponge. Nagashima and colleagues subsequently translated this description into a computer-driven model by defining five important system rules. A number of researchers have since criticized and refined the method, providing additional system constraints or alternative approaches. Such efforts have led to an increased understanding of ventricular shape change and the development of periventricular lucency on imaging studies. However, severe limitations exist, precluding the use of the mathematical model to influence the operative decisions of practicing surgeons. In this paper, the authors explore the history, limitations, and future of the mathematical model of hydrocephalus.

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Bernard A. Coert, Robert E. Anderson, and Fredric B. Meyer

Object. A nitric oxide (NO) donor that has been successfully used in the treatment of myocardial infarction, 3-morpholinosydnonimine (SIN-1), may be a potential neuroprotective agent. Production of NO in brain microsomes is dependent on the pH. The purpose of this study was to determine the efficacy of SIN-1 and its dependence on pH in vivo during periods of focal cerebral ischemia.

Methods. At 0.1 or 1 mg/kg, SIN-1 was administered to 54 Wistar rats 30 minutes before a 2-hour period of focal cerebral ischemia under moderate hypo-, normo-, and hyperglycemic conditions. Measurements of brain intracellular pH (pHi); regional cortical blood flow, and the redox state of nicotinamide adenine dinucleotide were obtained in three additional animals to confirm the effects of the serum glucose manipulations. The animals were killed at 72 hours after the ischemic period to obtain infarction volumes. Administration of SIN-1 significantly reduced infarction in normoglycemic animals and, to a lesser extent, in hyperglycemic animals, indicating that SIN-1 was less effective under hyperglycemic conditions. At either dose SIN-1 had no significant effect on infarction volume in moderately hypoglycemic animals because moderate hypoglycemia in itself significantly (p < 0.005) reduced infarction volume.

Conclusions. The NO donor SIN-1 may be a useful intraoperative cerebral protective agent. Furthermore, it is hypothesized that a mechanism that could explain the published discrepancies regarding the effects of NO donors in vivo may be affected by differences in ischemic brain acidosis.

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Brian A. Iuliano, Robert E. Anderson, and Fredric B. Meyer

✓ The authors examined the effects of both intermittent reperfusion and nitric oxide synthase (NOS) inhibition, caused by NG-nitro-l-arginine methyl ester (l-NAME) during episodes of focal cerebral ischemia induced to simulate the neurosurgical setting. Seventy-eight Wistar rats underwent single (60 minutes of ischemia) or repetitive (four 15-minute periods of ischemia separated by 5 minutes of reperfusion) episodes of middle cerebral artery occlusion while under anesthesia (1.0% halothane). Twenty-four hours after the procedure, the animals were given neurological examinations and then sacrificed for histological preparation and examination. The intermittent reperfusion groups tended to have smaller mean cortical infarctions. There was also a trend showing a decrease in infarction size in groups given l-NAME. The combination of intermittent reperfusion and preischemic administration ofl-NAME (10 mg/kg) resulted in a 65% reduction in infarction size (p < 0.05) when compared to that caused by 60 minutes of single occlusion without l-NAME. The use of NOS inhibition combined with intermittent reperfusion may be a technique to provide intraoperative cerebral protection during neurovascular procedures that require temporary vascular occlusion.