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Mark G. Burnett and Eric L. Zager

Clinicians caring for patients with brachial plexus and other nerve injuries must possess a clear understanding of the peripheral nervous system's response to trauma. In this article, the authors briefly review peripheral nerve injury (PNI) types, discuss the common injury classification schemes, and describe the dynamic processes of degeneration and reinnervation that characterize the PNI response.

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Reduction of cellular energy requirements

Screening for agents that may protect against CNS ischemia

Eric L. Zager and Adelbert Ames III

✓ Protection of the brain and spinal cord against ischemia is a goal of vast clinical importance. One approach to this objective is to reduce the tissue's functional activity in order to preserve energy for the metabolic processes that are essential to viability. Experiments to explore ways of reducing function-related energy demands were performed on isolated rabbit retina, a well-characterized model of organized adult mammalian central nervous system (CNS) tissue. The retina was maintained in a nearly physiological state in a miniature “heart-lung” apparatus. Energy metabolism (oxygen consumption and glycolysis) and electrophysiological function (determined by electroretinogram) of the in vitro retina were monitored, and their responses to a series of agents that may reduce energy requirements were determined.

Large reversible reductions in O2 consumption, glycolysis, and electrophysiological function were seen in response to mild hypothermia ( −3° to −6°C), phenytoin (Dilantin, 100 to 200 mg/kg), chlordiazepoxide (Librium, 200 µM), lithium (1 to 4 mM), Mg++ (6 to 20 mM), strophanthidin (0.15 to 0.25 µM), CO2 (25% to 30%), 2-amino-5-phosphonovaleric acid (APV, 500 µM), amiloride (1 mM), and dantrolene (1 mM). One retina was exposed simultaneously to a combination of six of these agents, which reduced its oxidative and glycolytic metabolism to less than 50% of the control level. The retina recovered metabolic and electrophysiological function after a 2½-hour exposure period. Other agents tested (diphenhydramine, midazolam, nifedipine, nimodipine, and quercetin) had effects on energy metabolism and electrophysiological function that were poorly reversible. Surprisingly little effect was seen in response to general anesthetic agents (thiopental and Althesin) and other CNS depressants (chlorpromazine, ethanol, lidocaine, paraldehyde, valproic acid, and baclofen). The presumed mechanisms through which these agents reduce cellular energy requirements, as well as their potential roles in the treatment of CNS ischemia, are discussed.

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Eric L. Zager, Daniel A. Del Vecchio and Scott P. Bartlett

✓ Temporal muscle asymmetry is a common sequela of pterional craniotomies. The authors describe a simple technique of restoring the temporal muscle to its origin by microscrew fixation. This technique provides reliable preservation of temporal muscle bulk and function with little additional operating time and no compromise of operative exposure.

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Acute presentations of syringomyelia

Report of three cases

Eric L. Zager, Robert G. Ojemann and Charles E. Poletti

✓ Three unusual cases are reported in which communicating syringomyelia presented acutely. The first patient presented with paraplegia, the second with acute respiratory distress secondary to bilateral vocal cord paralysis, and the third with symptoms of acute brain-stem ischemia. Each patient had a communicating spinal cord syrinx associated with a posterior fossa and foramen magnum region anomaly (a huge posterior fossa arachnoid cyst in one and Chiari malformations in two). The mechanisms of craniospinal pressure dissociation and hindbrain herniation are discussed, along with other reported emergency presentations of syringomyelia.

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Eric L. Zager, Ellen G. Shaver, Robert W. Hurst and Eugene S. Flamm

✓ Aneurysms of the distal anterior inferior cerebellar artery (AICA) are rare; fewer than 100 cases have been reported. The authors detail their experience with four cases and present endovascular as well as microsurgical management options.

The medical records and neuroimaging studies obtained in four patients who were treated at a single institution were reviewed. Clinical presentations, neuroimaging and intraoperative findings, and clinical outcomes were analyzed.

There were three men and one woman; their mean age was 43 years. Two patients presented with acute subarachnoid hemorrhage (SAH), and two presented with ataxia and vertigo (one with tinnitus, the other with hearing loss). Angiographic studies demonstrated aneurysms of the distal segment of the AICA. In one patient with von Hippel—Lindau syndrome and multiple cerebellar hemangioblastomas, a feeding artery aneurysm was found on a distal branch of the AICA. Three of the patients underwent successful surgical obliteration of their aneurysms, one by clipping, one by trapping, and one by resection along with the tumor. The fourth patient underwent coil embolization of the distal AICA and the aneurysm. All patients made an excellent neurological recovery.

Patients with aneurysms in this location may present with typical features of an acute SAH or with symptoms referable to the cerebellopontine angle. Evaluation with computerized tomography, magnetic resonance (MR) imaging, MR angiography, and digital subtraction angiography should be performed. For lesions distal to branches coursing to the brainstem, trapping and aneurysm resection are viable options that do not require bypass. Endovascular obliteration is also a reasonable option, although the possibility of retrograde thrombosis of the AICA is a concern.

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