Biomedical subjects
Publications and source records attributed to Mark G Burnett.
Decisions regarding the return of injured athletes to contact sports after spinal surgery can be complicated. The authors offer a brief overview of the return-to-play guidelines used successfully at their institution for the past two decades when caring for professional and amateur athletes after spinal surgery.
BACKGROUND AND PURPOSE: Functional stimulation is accompanied by increases in regional cerebral blood flow which exceed metabolic demands under normal circumstances, but it is unknown whether functional stimulation is beneficial or detrimental in the setting of acute ischemia. The aim of this study was to determine the effect of forepaw stimulation during temporary focal ischemia on neurological and tissue outcome in a rat model of reversible focal forebrain ischemia. METHODS: Sprague-Dawley rats were prepared for temporary occlusion of the right middle cerebral artery (MCA) using the filament model. Cerebral blood flow in the MCA territory was continuously monitored with a laser-Doppler flowmeter. Subdermal electrodes were inserted into the dorsal forepaw to stimulate either the forepaw ipsilateral or contralateral to the occlusion starting 1 minute into ischemia and continuing throughout the ischemic period. A neurological evaluation was undertaken after 24 hours of reperfusion, and animals were then euthanized and brain slices stained with 2,3,5-triphenyltetrazolium chloride. Cortical and striatal damage was measured separately. RESULTS: The cortical and striatal infarct volumes were both significantly reduced in the contralateral stimulated group compared with the ipsilateral stimulated group (48% total reduction). There were no statistically significant differences in the neurobehavioral scores between the 2 groups, or in the laser-Doppler flow measurements from the MCA core. CONCLUSIONS: Functional stimulation of ischemic tissue may decrease tissue damage and improve outcome from stroke. Although the precise mechanism of this effect remains to be determined, functional stimulation could readily be translated to clinical practice.
Systemic hemangiomatosis is extremely rare in adolescents and adults. The authors describe a 37-year-old man with a history of hepatic, splenic, cerebral, and multiple recurring osseous hemangiomas since age 14. After a 9-year period without disease progression, the patient presented with an acute bilateral lower extremity myelopathy. This was secondary to a T11 vertebral hemangioma that compressed the spinal cord. A 2-week course of radiation therapy failed to alleviate the patient's symptoms. Successful T11 vertebrectomy was then performed to decompress the spinal cord. The many organs and serially involved bones may represent a distinct variant of hemangiomatosis not previously described in the literature.
BACKGROUND: There is considerable uncertainty about the indications for cranial computed tomography (CT) scanning in patient with minor traumatic brain injury (TBI). This analysis involves an evidence-based comparison of several strategies for selecting patients for CT with regard to effectiveness and cost. METHODS: We performed a structured literature review of mild traumatic brain injury and constructed a cost-effectiveness model. The model estimated the impact of missed intracranial lesions on longevity, quality of life and costs. Using a 20-year-old patient for primary analysis, we compared the following strategies to screen for the need to perform a CT scan: observation in the emergency department or hospital floor, skull radiography, Selective CT based on the presence of additional risk factors and scanning all. RESULTS: Outcome measures for each strategy included average years of life, quality of life and costs. Selective CT and the CT All policy performed significantly better than the alternatives with respect to outcome. They were also less expensive in terms of total direct health care costs, although the differences did not reach statistical significance. The model yielded similar, but smaller, differences between the selective imaging and other strategies when run for older patients. CONCLUSIONS: Although the incidence of intracranial lesions, especially those that require surgery, is low in mild TBI, the consequences of delayed diagnosis are forbidding. Adverse outcome of an intracranial hematoma is so costly that it more than balances the expense of CT scans. In our cost-effectiveness model, the liberal use of CT scanning in mild TBI appears justified.
/Late cerebral radiation necrosis usually occurs within 3 years of stereotactic radiosurgery. The authors report on a case of recurrent radiation necrosis with rapid clinical deterioration and imaging findings resembling those of a malignant glioma. This 68-year-old man, who had a history of a left posterior temporal and thalamic arteriovenous malformation (AVM) treated with linear accelerator radiosurgery 13 years before presentation and complicated by radiation necrosis 11 years before presentation, exhibited new-onset mixed aphasia, right hemiparesis, and right hemineglect. Imaging studies demonstrated hemorrhage and an enlarging, heterogeneously enhancing mass in the region of the previously treated AVM. The patient was treated medically with corticosteroid agents, and stabilized temporarily. Unfortunately, his condition worsened precipitously soon thereafter, requiring the placement of a shunt for relief of obstructive hydrocephalus. Further surgical intervention was offered, but the patient's family opted for hospice care instead. The patient died 10 weeks after initially presenting to the authors' institution, and the results of an autopsy demonstrated radiation necrosis. Symptomatic radiation necrosis can occur more than a decade after stereotactic radiosurgery, necessitating patient follow up during a longer period of time than currently practiced. Furthermore, there is a need for more careful reporting on the natural history of such cases to clarify the pathogenesis of very late and recurrent radiation necrosis after radiosurgery and to define patient groups with a higher risk for these entities.
Most functional neuroimaging techniques rely on activation-flow coupling (AFC) to detect changes in regional brain function, but AFC responses may also be altered during pathophysiological conditions such as ischemia. To define the relationship between progressive ischemia and the AFC response, graded levels of cerebral blood flow reduction were produced using a rat compression ischemia model, and the cerebral hemodynamic response to forepaw stimulation was measured. Graded levels of cortical ischemia of the somatosensory cortex were induced in male Sprague-Dawley rats (n = 16) by compressing the intact dura with a 4-mm-diameter cylinder equipped with a laser-Doppler probe, combined with ipsilateral common carotid artery occlusion. At each level of CBF reduction, electric forepaw stimulation was conducted, and signal-averaged laser Doppler and evoked potential responses were recorded. A visible AFC response was present at all levels of CBF reduction (0-90% reduction from baseline), and the temporal characteristics of the response appeared largely preserved. However, the amplitude of the AFC response began to decline at levels of mild ischemia (10% flow reduction) and progressively decreased with further CBF reduction. The amplitude of the evoked response appeared to decrease in concert with the AFC amplitude and appeared to be equally sensitive to ischemia. AFC appears to be a sensitive marker for cerebral ischemia, and alterations in the AFC response occur at CBF reductions above the accepted thresholds for infarction. However, the AFC response is also preserved when flow is reduced below ischemic thresholds.
BACKGROUND: Capillary hemangiomas are benign vascular lesions that commonly present at birth or in early infancy on the face, scalp, back, or chest. The authors present an exceedingly rare case of an intracranial capillary hemangioma arising in an adult. Only 4 biopsy-proven cases have been reported in the pediatric population previous to this case report. CASE DESCRIPTION: A 31-year-old pregnant woman presented at 38 weeks of gestation with severe headaches, nausea, and vomiting. Imaging revealed an extra-axial mass lesion arising from the tentorium with both supra- and infratentorial components. The patient underwent a resection of her tumor, which was diagnosed as a capillary hemangioma by histopathologic examination. The patient required 2 further resections after the lesion exhibited a rapid regrowth from residual tumor in the left transverse sinus. The patient has remained free of disease 41 months out from her third surgery. CONCLUSIONS: Intracranial capillary hemangiomas are exceedingly rare entities, with a capability for rapid growth. When gross total resection cannot be achieved, these patients should be observed closely, and the use of adjuvant radiotherapy should be considered.
OBJECTIVE: We sought to determine the most efficient perioperative prophylactic strategy for deep venous thrombosis (DVT) in craniotomy patients by use of a decision analysis model. METHODS: We conducted a structured review of the relevant literature and compiled the reported incidences of DVT, pulmonary embolism, and postoperative intracranial hemorrhage (ICH) in craniotomy patients. We also obtained from the literature estimates of the likelihood and the impact of various outcomes of these complications. Data from 810 craniotomies performed at our own institution were also examined. The decision analytic model was then used to compare the effectiveness of pneumatic compression boots with pneumatic compression boots combined with either unfractionated or low-molecular-weight heparin. The model dealt with variability by using both sensitivity analysis and Monte Carlo simulation. RESULTS: As expected, the addition of heparin lowered the incidence of both DVT and pulmonary embolism, but at the cost of increasing ICH. Because the deleterious effects of ICH were so much greater than the benefits from heparinization, overall outcomes were best with mechanical prophylaxis alone. This was especially true for low-molecular-weight heparin, which is associated with a relatively high risk of ICH. Our own institutional data support the findings in the literature. Although the differences are modest, they reach statistical significance in the case of low-molecular-weight heparin. CONCLUSION: Using decision analytic modeling, we have shown that mechanical prophylaxis yields outcomes in craniotomy patients superior to those of either unfractionated or low-molecular-weight heparin.
OBJECTIVE: There has never been a large, randomized controlled trial to assess the impact of intraoperative imaging on the success of carotid endarterectomy (CEA). This comparison involves cost-effectiveness analysis. METHODS: We constructed a decision-analytic model to compare effectiveness and costs of intraoperative ultrasound (IUS) and completion angiography as adjuncts to CEA. Data on procedural mortality, morbidity, and costs were obtained from the English-language literature. The review included a total of 52 reports, encompassing more than 22,000 patients. The main components of costs were those of the monitoring interventions and the care of perioperative stroke. RESULTS: Mean perioperative outcome without completion imaging is approximately 96.7% of what it would be in the absence of perioperative stroke or death. IUS and completion angiography each result in approximately 2% improvement in expected outcome. Mean perioperative costs are 396.50 dollars for IUS, 721.30 dollars for no monitoring, and 840.90 dollars for completion angiography. Because IUS is significantly more effective at detecting technical errors that would likely result in perioperative stroke than no imaging and is significantly less costly than angiography, this strategy dominates the other two (i.e., it provides greater effectiveness at lower cost). CONCLUSION: Although surgical complications are uncommon, IUS substantially lowers the rate of perioperative stroke and mortality and thus is significantly more cost-effective than either completion angiography or no operative imaging.
Deep venous thrombosis (DVT) remains a source of significant morbidity and mortality in patients who undergo craniotomy procedures. Despite several studies in which the safety and efficacy of various prophylactic strategies were examined, there is still no consensus among clinicians. In this paper the authors review the literature with regard to epidemiological and pathophysiological features, screening methods, and prophylactic measures for DVT.
We combine diffuse optical and correlation spectroscopies to simultaneously measure the oxyhemoglobin and deoxyhemoglobin concentration and blood flow in an adult human brain during sensorimotor stimulation. The observations permit calculation of the relative cerebral metabolic rate of oxygen in the human brain, for the first time to our knowledge, by use of all-optical methods. The feasibility for noninvasive optical measurement of blood flow through the skull of an adult brain is thus demonstrated, and the clinical potential of this hybrid, all-optical noninvasive, methodology can now be explored.
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.
Despite widespread investigational and clinical usage of the calcium channel blocker nimodipine, its effects on cerebral physiology in normal and ischemic brain remain poorly understood. In order to gain insight into this subject we examined the effects of nimodipine on glucose metabolism and cerebral blood flow-metabolism coupling in the rat during conditions of reproducible focal ischemia. Nimodipine-treated animals were then matched with vehicle-treated controls for both study conditions. Animals were subjected to permanent occlusion of the middle cerebral artery (MCA) along with occlusion of the common carotid arteries. Five minutes into ischemia, an intravenous infusion of nimodipine (1 micro g/kg per min, n=9) or vehicle ( n=9) was initiated and continued until the end of the study. Seventy-five minutes after the occlusion, [14C]2-deoxyglucose was injected into the venous catheter for the measurement of the local cerebral metabolic rate for glucose (LCMRgl), followed 25 min later by the injection of N-isopropyl-[123I] p-iodoamphetamine for the measurement of local cerebral blood flow (LCBF). The animals were killed at the end of 2 h of ischemia, and the brains were processed for double-labeled autoradiography. In all animals, permanent MCA occlusion produced significant decrements in LCBF, LCMRgl, and LCBF/LCMRgl ratio in both the core of the ischemia as well as regions peripheral to the ischemia within the same cerebral hemisphere when compared with non-ischemic brain. There were no significant differences between the nimodipine-treated and vehicle-treated groups. In conclusion, nimodipine does not appear to alter cerebral blood flow or cerebral metabolism in ischemic brain.
Laser-speckle flowmetry was used to characterize activation flow coupling after electrical somatosensory stimulation of forepaw and hindpaw in the rat. Quantification of functional activation was made with high transverse spatial (microm) and temporal (msec) resolution. Different activation levels and duration of stimulation were quantitatively investigated, and were in good agreement with previous laser-Doppler measurements. Interestingly, the magnitude but not the overall shape of the response was found to scale with stimulus amplitude and the distance from the activation centroid. The results provide new insights about the spatial characteristics of cerebral blood flow response to functional activation, and the method should lead to improved understanding of the coupling of neuronal activity and hemodynamics under normal and pathologic conditions.
OBJECT: The goal of this study was to create a searchable database of research manuscripts authored by members of the American Association of Neurological Surgeons and the Congress of Neurological Surgeons (AANS/CNS) to describe the nature and character of the research currently being undertaken by neurosurgeons. METHODS: Manuscripts published by all physician members listed in the 2001 AANS/CNS Membership Directory (6921 physicians) were gathered into a database through individual literature searches of the author name for the calendar year 2001. Duplicate publications were purged and the database was reviewed for accuracy. An internal verification of the database revealed a 4% underreporting rate. Statistics from the database were compiled and displayed with information about AANS/CNS members and their clinical activities. The AANS/CNS members published a total of 2748 research the manuscripts in 479 different journals during 2001. Thirty-eight percent of the manuscripts (1042 of 2748) were authored by US members and 62% (1706 of 2748) by non-US members. The focus of the majority of manuscripts included the areas of brain tumor (26%; 707 of 2748), vascular disease (20%; 558 of 2748), spine (10%; 282 of 2748), and trauma (8%; 233 of 2748). Sixty-nine percent of manuscripts (1897 of 2748) were retrospective and technical clinical studies, and of these 39% (744 of 1897) were case reports. Laboratory investigations made up 15% (414 of 2748) of all manuscripts, whereas prospective randomized clinical trials represented 1% (34 of 2748). CONCLUSIONS: The majority of AANS/CNS member manuscripts are authored by non-US members despite their small AANS/CNS representation. Most research is clinical, based on retrospective data, and includes a large number of case reports. A disparity exists between what neurosurgeons do clinically and both the quantity and subject of their research.
Medical decisions often depend, in part, on cost-effectiveness concerns. Decision analysis is frequently used to help resolve these questions. Unfortunately, this technique has received little attention in neurosurgery. Using an example of moderate head injury, the authors illustrate the utility of this powerful tool in estimating the cost effectiveness of neurosurgical management options.