Intraoperative MR at 1.5 Tesla--experience and future directions.

The objective of this report is to present and contrast the development of the different intraoperative MR systems that are currently in use. The manuscript focuses on the design and clinical experience of a 1.5 Tesla MR system, based on a movable magnet. This configuration is similar to the operating microscope and other surgical adjuncts, with MR technology moved to and from the patient as needed. The system has been used to monitor 294 neurosurgical procedures. including CNS neoplasia. epilepsy, cervical spine disorders, arteriovenous malformations, cavernomas and aneurysms. In many cases the surgical procedure was significantly altered by intraoperatively acquired MRI. Future developments include the construction of a 3 Tesla intraoperative MR system and an ambidextrous MR-compatible robot. This seamless integration of robotic technology into an intraoperative MR environment may well revolutionize neurosurgery.

A brief history of aneurysm clips.

In this communication the authors outline the development of aneurysm clips from those originally used by Walter Dandy to those currently in use. The history is rich in contributions from neurosurgical pioneers and innovators. As a result, the modern neurosurgeon has a wide selection of biocompatible aneurysm clips with known closing pressure, of variable sizes and shapes, and a selection of clip applicators that do not obstruct the surgical field.

The effect of delta-9-tetrahydrocannabinol on forebrain ischemia in rat.

The purpose of the study was to evaluate the effect of delta-9-tetrahydrocannabinol (THC), the major psychoactive constituent of marijuana, on ischemic neuronal injury. A 12-min ischemic insult was induced by a reduction in systolic blood pressure to a mean of 50 mm Hg, followed by bilateral carotid artery occlusion at a middle ear temperature of 37.5 degrees C. THC at either a low (0.1 mg/kg; n=8) or high (10 mg/kg; n=8) dose was injected i.p. every 12 h for 7 days prior to ischemia. Non-treated ischemic (n=8) animals formed the control group. The animals were sacrificed 3 weeks post-ischemia for quantitative histopathology. THC at either dose did not significantly reduce ischemic neuronal damage in the hippocampus. The high dose THC-treated group showed significantly less neocortical injury, compared to either the control or low-dose THC groups (p<0.05). The striatum was markedly protected by both low and high dose THC (p<0.001). This regionally specific protection implies that either the hippocampus undergoes suprathreshold ischemic injury or that mechanisms of ischemic injury vary in different brain regions.

Ischemic neuronal injury is ameliorated by astrocyte activation.

BACKGROUND: The motivation of this study was to more precisely define the in vivo role of astrocytes in forebrain ischemia. Controversy exists in the literature as to whether they protect or injure neurons in this setting. METHODS: Astrocytes in the rat hippocampus were disabled with stereotactic administration of a gliotoxin, ethidium bromide, 3 days prior to induction of forebrain ischemia. The extent of neuronal injury in this group was compared to a control category receiving intrahippocampal saline only. RESULTS: Saline-injected animals demonstrated decreased hippocampal CA1 sector injury, and increased gliosis on the side of the injection compared to the contralateral side (P < 0.01) or ethidium bromide-treated animals (P < 0.05). CONCLUSIONS: The results suggest that activated astrocytes are protective to neurons subjected to an ischemic insult. This may result from their ability to elaborate neurotrophic factors, buffer potassium and metabolize a variety of neurotransmitters.

Ablative therapy for movement disorders. Complications in the treatment of movement disorders.

Presently, there is a renaissance in the surgical treatment of movement disorders. Prompted by the growing recognition of the limitations of drug therapy, this resurgence has been further promoted by progress in neuronal transplantation, advances in neuroimaging and stereotactic surgical techniques, and innovative therapies, such as deep brain stimulation for abnormal movements. Mortality associated with thalamotomy and pallidotomy is rare, but morbidity is not inconsiderable, particularly in the elderly and those with preexisting brain damage. Judicious patient selection and physiologic confirmation of stereotactic targets are cornerstones to complication avoidance.

Evidence for a high free radical state in low-grade astrocytomas.

OBJECTIVE: It is postulated that reactive oxygen species may play an inductive role in neuro-oncogenesis. However, data pertaining to the redox state of astrocytomas are limited, which prompted us to undertake this study. METHODS: Intraoperative snap-frozen samples were obtained from the surface and core of 8 low-grade and 11 high-grade astrocytomas. Small portions of each specimen were fixed in 10% neutral formalin or cacodylate-buffered glutaraldehyde. Lipid peroxidation was estimated by measuring thiobarbituric acid-reactive substances, and total glutathione levels were determined. Light microscopy was performed to define the relevant histopathology, and electron microscopy was used to quantitate peroxisomal content. RESULTS: Thiobarbituric acid-reactive substance values for low-grade astrocytomas were significantly elevated compared to those for malignant lesions, as was the case for total glutathione. This discrepancy was especially marked at the tumor surface. Peroxisomes predominated in the low-grade category. CONCLUSION: We speculate regarding malignant transformation as a possible consequence of this decline in antioxidant capacity, as well as regarding the role of seizures and astrocytoma glutamate receptors in the initiation of free radical cascades. The therapeutic and teleological implications are considerable.

Epidemiology of childhood brain tumors.

BACKGROUND: Brain tumors comprise more than 20% of all childhood malignancies, and constitute the greatest number of solid pediatric cancers. Incidence rates reported have varied from 2.4 to 3.5/100,000 children, reflecting the impact of modern imaging techniques, the application of diverse investigative methodologies, and the accessibility of the community to health care. METHODS: Material from patients < 18 years of age was collated from the Manitoba Cancer Foundation Tumor Registry, the personal records of Winnipeg pediatric neurologists, and autopsy data. Patient data were also obtained from hospital charts and operating room log books. Histological sections were examined and classified according to the American Cancer Society by a single neuropathologist. The chi-square test was used for statistical evaluation. RESULTS: During the seven-year study period, the diagnosis of brain tumor was made in 89 pediatric patients, of which 88 were diagnosed premortem. The overall average annual incidence rate for both sexes was 4.03/100,000 child-years, higher than that previously reported. The male and female average annual incidence rates were 4.2 and 3.7/100,000 child-years, respectively. Tumor type and location were relatively unremarkable, with an expected peak of medulloblastoma occurring in young males. The yearly incidence of tumor occurrence was fairly stable, and the geographic distribution of cases within Manitoba, homogeneous. CONCLUSION: The highest incidence rates of pediatric brain tumors have been recorded in countries possessing sophisticated universal health care systems, possibly reflecting their efficacy in disease surveillance.

The immediate effects of peripheral denervation on inhibitory mechanisms in the somatosensory thalamus.

Multiunit recordings were made in the ventroposterior lateral nucleus of the thalamus in anesthetized raccoons. During recording from cells responding to cutaneous stimulation of a forepaw digit, the corresponding digit was denervated permanently (by cutting its four digital nerves) or temporarily (by injecting lidocaine into the base of the digit). Both procedures resulted in immediate increases in the inhibition that could be induced by stimulation of the adjacent digits when the original cutaneous receptive field was on the glabrous skin. In each case with temporary denervation, this enhanced off-focus inhibition decreased when the excitatory responses returned to normal. In contrast, temporary denervation of the digit during recording at sites in the hairy skin representation did not reveal this increased inhibition from adjacent digits. When capsaicin was applied to the digital nerves in two animals, the excitatory receptive fields of thalamic neurons increased in area, but were still restricted to the same part of the digit. These data indicate that the immediate unmasking of inhibitory responses, previously reported in primary somatosensory cortex of the raccoon, is also present in the thalamus. The capsaicin-induced expansion of excitatory receptive fields confirms previous experiments in other species, and suggests that C fibers play a role in modulating the size of cutaneous receptive fields. However, the enlargement of excitatory receptive fields by capsaicin is much less than the unmasking of inhibitory fields induced by digit denervation, and indicates that different mechanisms are involved in controlling these various inputs to thalamic neurons.

Incidence and clinicopathological features of meningioma.

The incidence of intracranial meningioma in Manitoba, Canada, was reviewed from 1980 through 1987. During that time, 193 tumors were diagnosed, with a male:female ratio of 1:2. This occurrence corresponded to crude incidence rates of 2.3/100,000 for all meningiomas and 0.17/100,000 for malignant meningiomas. Among malignant meningiomas, the male:female ratio was 1:1. The age-specific annual incidence rate increased with age up to the eighth decade where it peaked at 8.4/100,000. The distribution of histopathological subtypes was: 74 meningotheliomatous (38%), 64 transitional (33%), 14 malignant (7%), 14 fibroblastic (7%), seven psammomatous (4%), four angioblastic (2%), and 16 unknown (8%). The diagnosis of malignant meningioma was based on the World Health Organization criteria, with only Grade III and IV tumors included in this subtype. Clinical features did not allow for differentiation of benign from malignant neoplasms. Individuals with malignant tumors were, however, more likely to suffer paresis (50%) and less likely to be without deficit (14%) than their benign counterparts. The radiographic appearance of "mushrooming" was observed only in patients with malignant meningioma. All malignant tumors showed evidence of peritumoral edema; however, none exhibited calcification. During the 8-year study interval, the tumor recurred in 10 (71%) of the 14 patients with malignant meningioma. Tumor recurrence was accompanied by dedifferentiation from a more benign histology in four patients (2% of the total material).