Jack M. Fein

Neurogenic Hypertension Related to Vascular Compression of the Lateral Medulla

Neurogenic hypertension may be reproduced consistently in experimental animals, although its clinical significance is unclear. An ectatic loop of the posterior inferior cerebellar (PICA) compressed the left vagus nerve root entry-exit zone in two patients with long-standing hypertension. When this loop was mobilized for occipital-PICA bypass, the hypertension resolved. These observations suggest that neurovascular compression of the area encompassing the nucleus tractus solitarius may be a sufficient cause of neurogenic hypertension in humans. The structural and functional relationships of these areas of the brain stem and their role in modulating blood pressure are reviewed.

Epidermoid tumor of the cerebellopontine angle: diagnostic value of computed tomographic metrizamide cisternography.

The extent of spread of an epidermoid tumor in the posterior fossa may be difficult to discern preoperatively. Conventional computed tomographic (CT) studies may not outline the tumor capsule, and the low attenuation of the tumor itself may not allow a distinction from cerebrospinal fluid. CT metrizamide cisternography was helpful in delineating the inferior pole of an epidermoid tumor, which could then be delivered through a transtentorial approach.

Bypass induced cerebral aneurysm

The development of aneurysm after EC-IC bypass was studied in 6 cases by angiography. Increase in blood flow and alteration of slow pattern are contributing factors. It is suggested that the difference in structure between cortical arteries and scalp arteries enhances their sensitivity to transcranial pressure difference. High TCP gradients may induce post-operative aneurysm, and careful management of blood flow through the bypass is recommended.

Angiographic Demonstration of Postoperative Cortical Artery Stenosis Induced by Biemer Temporary Clips

Five patients underwent cerebral revascularization operations during which Biemer clips were used to occlude temporarily a branch of the middle cerebral artery. Postoperative angiograms revealed stenoses at the sites where the clips were applied. Excessive clip closing forces may have caused significant endothelial injury, which then produced the stenoses. Clips that exert a minimal occlusive force would avoid this response and are recommended for temporary occlusion of cortical arteries.

Cortical nicotinamide adenine dinucleotide (NADH) kinetics in patients undergoing extracranial-intracranial bypass.

Nicotinamide adenine dinucleotide (NADH) kinetics were measured in 76 cortical areas in 26 patients with transient ischemic attacks (TIAs) undergoing extracranial-intracranial bypass. Direct cortical stimulation was utilized to induce changes in surface fluorescence corresponding to a brief oxidation and reduction of mitochondrial NADH. Preoperative studies of cerebral blood flow in gray matter (CBF)g) demonstrated normal perfusion in 11 patients and ischemic changes ((CBF)g less than 43.5 ml/100 g/minute) in 15 patients. In 30 normally perfused areas within the craniotomy, the mean half-time for reduction (t1/2(red)) of cortical NAD was 21.5 +/- 2.6 seconds. In 39 ischemic areas, the mean t1/2(red) was 5.6 +/- 1.2 seconds. These rapid reduction rates were associated with supernormal overshoots of the base line indicative of a transient oxygen debt. Kinetic responses could not be elicited from 7 areas adjacent to foci of decreased attenuation on compound tomography. Bypass resulted in normalization of the t1/2(red) in 24 of 28 areas of ischemia. The dependence of NADH kinetics on blood flow through the graft was demonstrated in 15 of 19 areas of mild ischemia by the reapplication of a clip to the donor artery. It is concluded that persistent reversible abnormalities of cortical mitochondrial metabolism exit in a significant number of patients with a history of TIAs who are suitable candidates for bypass surgery. In such patients bypass may effectively augment the nutrient supply to meet the bioenergetic demands associated with increased electrophysiological activity.

BRAIN ENERGETICS AND CEREBRAL DEATH

The energy‐charge potential of the brain, defined as the ratio of high‐ and low‐energy phosphate levels, may be correlated with brain viability after injury. Two different states of dysergic brain metabolism may be induced by subarachnoid hemorrhage, depending on the intracranial pressure. Simultaneous measurements of oxidative metabolism and ATP, ADP, and AMP levels were made in rats after cisternal injection of fresh arterial blood under high (>50 mm Hg) and normal (5‐10 mm Hg) intracranial pressure. The hyperbaric injections were uniformly associated with progressive and severe cerebral infarctions. These were correlated with low flow and depressed energy charge potential. A low rate of blood flow and metabolism persisted and the animals showed no signs of recovery postoperatively. Injections under normal pressure were associated with an equally severe suppression of brain blood flow and metabolic rates, but energy charge potential was preserved and clinical function, flow and metabolism were eventually recovered. Despite the cerebral dysfunction, which may appear similar in both cases, the prognosis for viability in the two instances is quite different. These paradigms are useful in formulating concepts of the energy state necessary for functional brain survival.

Reflow into a Thrombosed Giant Middle Cerebral Artery Aneurysm after Extracranial-Intracranial Bypass

This report graphically illustrates the consequences of flow augmentation through extracranial-intracranial bypass grafts. Propagation of clot from a thrombosed middle cerebral artery aneurysm into the middle cerebral artery produced transient ischemic attacks. Superficial temporal artery-middle cerebral artery bypass was performed to augment cerebral blood flow. Postoperative angiography demonstrated filling of the aneurysm through improved collateral channels. The role of bypass operation in the presence of an aneurysm and its contribution to collateral blood flow and clot lysis are discussed.

Cardiovascular Considerations in Cerebrovascular Surgery

The heart and the brain enjoy a mutual relationship and interdependency. Alterations of cardiac function may be anticipated in most patients requiring cerebrovascular surgery. Cardiovascular disease is an important risk factor in the management of occlusive cerebrovascular lesions, aneurysms, and hypertensive hemorrhage. This chapter describes the evaluation and management of patients with cardiac disease in anticipation of cerebrovascular surgery. A variety of acute neurologic changes such as those associated with subarachnoid hemorrhage have profound effects on the heart. Physiologic and pathologic neurogenic factors influencing cardiac function are described.

Acquisition of Technical Skills in Microvascular Neurosurgery

Microsurgical techniques have extended the ability of neurosurgeons to perform procedures that require greater than normal visual resolution. These techniques have been of particular value in cerebrovascular surgery. They have facilitated the management of patients with ischemic cerebrovascular disease, aneurysms, arteriovenous malformations, and other problems as well.