In contmdistinction to the widespread use of imaging ultrasound in exmnining many other l'egions of the body, ultrasonography of the centralnervow; system has been seriously limited because high· frequency ultrasound dues not readily penetrate the bon y covering of this organ system. The difl'iculty in using ultrasound to visualize lm1in and spinal cord structm·es is a paradox in the history of medical ultr:•sonogmphy hecause much of the interest in the early days of this field of diagnostic imaging was in the central nervous system. ~lore than 30 years ago, French et a!. used A-mode s<:anning to localize il subcortical brain tumor in an e:\+ cised postmortem specimen. U! Advances in central nervous system ultrasonography have been made, however, in applic.ltions in which the skull or vertebral bodies have not impeded the pasage of ultrasound waves. There have been three pl'incipal areas of such applkations: postoperative scanning through craniectomy portals, : l .~ imaging through the fontanels of infants,5·6 and intraoperative ultrasonography.Operative use of imaging ultrasound for brain disease was first employed in the 1960s. ' :' "-II However, the A-mode scanning available then presented problems of interpretation which prevented widespread applkation of this dia~nostic tool. ~lore recent adnmces in ultrasound technology, particularly the development of high-resolution real-time B-mode scanners, have eliminated manv of the em~ lier difHculties in operative imaf,ting. This IHL'i re· suited in u renewed trial of ultrasonic scanning in various types of operations on the hrain 1 :2 -:H and spinal cord. ~. 2l iAs part of a pro~ra m to assess the utility of op· erative ultrasonography in a number of surgical dis· ciplines. we employed ultrasound imaging during brain and spinal cord surgery. \Ve have reviewed our experience of spedfic applications in terms of the impact of ultrasonography on management during opemtion. From this analysis we have de· termined the situations in which ultrasonograph~· during neurosurgery can be most helpful. This analvsis has enabled us to establish criteria for the most productive use of ultrasound during brain and spinal cord surgery and is the basis of this report. METHODSOperative ultrasonography during neurosurgical procedures was performed with real-time B-mode instruments employing mechanically driven sectorscanning transducers. High Stoy. Philips, and Dia-155

SUMMARY: Does the world need another ICA classification scheme? We believe so. The purpose of proposed angiography-driven classification is to optimize description of the carotid artery from the endovascular perspective. A review of existing, predominantly surgically-driven classifications is performed, and a new scheme, based on the study of NYU aneurysm angiographic and cross-sectional databases is proposed. Seven segments -cervical, petrous, cavernous, paraophthlamic, posterior communicating, choroidal, and terminus -are named. This nomenclature recognizes intrinsic uncertainty in precise angiographic and cross-sectional localization of aneurysms adjacent to the dural rings, regarding all lesions distal to the cavernous segment as potentially intradural. Rather than subdividing various transitional, ophthalmic, and hypophyseal aneurysm subtypes, as necessitated by their varied surgical approaches and risks, the proposed classification emphasizes their common endovascular treatment features, while recognizing that many complex, trans-segmental, and fusiform aneurysms not readily classifiable into presently available, saccular aneurysm-driven schemes, are being increasingly addressed by endovascular means. We believe this classification may find utility in standardizing nomenclature for outcome tracking, treatment trials and physician communication.

No abstract

Platelet deposition in the microcirculation may play a role in focal cerebral ischemia. We investigated platelet deposition in selected parts of the cat brain after temporary middle cerebral artery occlusion. Ten anesthesized cats were given autologous indium-lll-labeled platelets and chromium-51-labeled erythrocytes. The right middle cerebral artery was occluded with miniature aneurysm clips for 3 hours via a transorbital approach; blood pressure was reduced concomitantly to decrease the collateral circulation. Removal of the clips initiated a 45-minute period of normotensive reperfusion. After sacrifice, the brain was removed and sectioned for comparison of right-versus left-hemisphere platelet deposition. Platelets were selectively deposited in the territory of the occluded right middle cerebral artery. Significant deposition was found in the caudate nucleus, internal capsule, parietal cortex, and the centrum semiovale. Our findings support the evidence that platelets are deposited in the microvasculature during temporary severe focal cerebral ischemia. (Stroke 1989;20:664-667) P latelet deposition in the cerebral microcirculation may play a role in focal cerebral ischemia. Morphologic techniques failed to implicate erythrocytes in microcirculatory obstruction during focal cerebral ischemia.1 Few studies have focused on the role of platelets in microcirculatory changes during cerebral infarction.2 -5 No study has used an experimental model analogous to clinical focal cerebral ischemia.We undertook this study to evaluate platelet deposition induced by temporary occlusion of the right middle cerebral artery (MCA) followed by reperfusion in cats. Materials and MethodsBlood (30 ml) from adult cats was collected through a catheter inserted into the femoral vein with citrate-phosphate-dextrose (CP-NIH formulation) as the anticoagulant. Lactated Ringer's solution (20 ml) was administered intravenously to augment vascular volume. The blood was treated with 50 nmol prostaglandin E] to prevent platelet activation and was centrifuged at 280g for 20 minutes at 25° C to separate platelet-rich plasma from the erythrocytes. The platelets were pelleted by centrifugation at l,500g for 15 minutes, and the From the Departments of Neurosurgery (J.J.J., R.M., R.M.C.)

A young Mexican female developed neurocysticercosis presenting as a lymphocytic meningoencephalitis with eosinophilia. Parasitic cysts in the fourth ventricle and pre-pontine cistern were well visualized by magnetic resonance imaging but not by computerized tomography. The meningoencephalitis recurred despite treatment with praziquantel and dexamethasone, and obstructive hydrocephalus eventually developed. The patient remains well one year after excision of the intraventricular cyst. This case emphasizes the distinct advantages of magnetic resonance imaging in the diagnosis of intraventricular neurocysticercosis, and the potential need for surgical rather than medical intervention in this condition.

Subcentimeter arteriovenous malformations (AVMs) located in deep or eloquent cortex can be difficult to localize intraoperatively and safely remove with surgery. Nevertheless, surgical resection may be the optimal definitive treatment option available for select patients. In this communication, we describe our experience using a framed-based stereotactic approach for resecting these AVMs. The operative records of all AVMs treated at our institution over an 8-year period (1996-2004) were reviewed. 180 surgically treated AVMs were identified. From this group of patients, frame-based stereotaxy was used for 8 AVMs (4.4%) in 7 patients. The angiograms, operative reports, and medical records for these 7 patients were retrospectively reviewed with attention to neurological outcome, extent of AVM obliteration, and anatomic factors that impacted the decision to employ a frame-based stereotactic approach. All AVMs removed with this technique were less than 1 cm in diameter. Angiography confirmed complete resection in all cases. No new neurological deficits occurred in any patient. By providing highly accurate three-dimensional nidus localization and minimizing approach-related brain manipulation, frame-based stereotaxy reduces the morbidity associated with resection of subcentimeter AVMs located in deep or eloquent regions of the brain. This technique makes a definitive surgical cure available to patients who otherwise would only be considered for radiosurgery.

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To Fuse or Not to Fuse? To THE EDITOR: I read with interest the article on internal fixation of the lumbar spine by Dickman, et al. (Dickman CA, Fessler RG, MacMillan M, et al: Transpedicular screw-rod fixation of the lumbar spine: operative technique and outcome in 104 cases. J Neurosurg 77:860-870, December, 1992). I wish to commend the authors for an interesting piece of work. However, this article is just another "how we do it and our results" paper and I submit that this retrospectively retrieved information adds very little to the totally inadequate literature existing to date on lumbar spine fusion.Technology continues to offer better methods of catalyzing a desired result, but we have failed to respond to the most pertinent question that has remained unanswered for decades: "What are the indications for lumbar spine fusion?" A recent review of the literature by Turner, et at., I reinforces this question and suggests that few real guidelines currently exist. They state, "No advantage has been demonstrated for surgery with fusion over surgery without fusion for several low back disorders, and the complications of fusion are common." The role of lumbar fusion needs to be defined for specific lumbar disorders with prospective randomized trials. When this is accomplished, the time, expense, and added morbidity associated with this technology will be justified to our patients and our peers. 1. Turner JA, Ersek M, Herron L, et aI: Patient outcomes after spinal fusions. JAMA 268:907-911. 1992RESPONSE: We appreciate Dr. Atkinson's interest in our manuscript. He is 100% correct that one of the most important unanswered questions regarding lumbar fusions is "what are the indications?" At this time, we have relatively good data for these indications in trauma.' In addition, prospective randomized evaluations have clearly answered this question for intervertebral disc disease. 2 Similar data exist for spondylolisthesis. 1 However, degenerative disease of the spine remains an area in which we have very few answers. The breadth and complexity of disease processes which are encompassed under the title "degenerative disease" makes the establishment of definitive indications for fusion an extremely difficult question to answer. Nonetheless, prospective randomized trials that will address these questions are currently being established.In the meantime, we are left with a retrospective analysis of our own results. At this time, analysis of large case loads of lumbar fusions utilizing instrumentation for augmentation of the fusion rate is relatively sparse in the neurosurgical literature. Neurosurgeons J. Neurosurg. / Volume 79/ July, 1993 have been, and remain, leaders in the field of spinal surgery, and it is imperative that we critically analyze our operative results and discuss new techniques. Our paper was not intended to address specific indications for fusion. It was intended to: 1) educate the neurosurgical community regarding the surgical techniques for pedicle screw fixation; 2) review the operative anatomy, morp...