Estimation of in vivo human brain-to-skull conductivity ratio from simultaneous extra- and intra-cranial electrical potential recordings.

OBJECTIVE: The present study aims to accurately estimate the in vivo brain-to-skull conductivity ratio by means of cortical imaging technique. Simultaneous extra- and intra-cranial potential recordings induced by subdural current stimulation were analyzed to get the estimation. METHODS: The effective brain-to-skull conductivity ratio was estimated in vivo for 5 epilepsy patients. The estimation was performed using multi-channel simultaneously recorded scalp and cortical electrical potentials during subdural electrical stimulation. The cortical imaging technique was used to compute the inverse cortical potential distribution from the scalp recorded potentials using a 3-shell head volume conductor model. The brain-to-skull conductivity ratio, which leads to the most consistent cortical potential estimates with respect to the direct intra-cranial measurements, is considered to be the effective brain-to-skull conductivity ratio. RESULTS: The present estimation provided consistent results in 5 human subjects studied. The in vivo effective brain-to-skull conductivity ratio ranged from 18 to 34 in the 5 epilepsy patients. CONCLUSIONS: The effective brain-to-skull conductivity ratio can be estimated from simultaneous intra- and extra-cranial potential recordings and the averaged value/standard deviation is 25+/-7. SIGNIFICANCE: The present results provide important experimental data on the brain-to-skull conductivity ratio, which is of significance for accurate brain source localization using piece-wise homogeneous head models.

High-resolution EEG: cortical potential imaging of interictal spikes.

BACKGROUND: It is of clinical importance to localize pathologic brain tissue in epilepsy. Noninvasive localization of cortical areas associated with interictal epileptiform spikes may provide important information to facilitate presurgical planning for intractable epilepsy patients. METHODS: A cortical potential imaging (CPI) technique was used to deconvolve the smeared scalp potentials into the cortical potentials. A 3-spheres inhomogeneous head model was used to approximately represent the head volume conductor. Five pediatric epilepsy patients were studied. The estimated cortical potential distributions of interictal spikes were compared with the subsequent surgical resections of these same patients. RESULTS: The areas of negativity in the reconstructed cortical potentials of interictal spikes in 5 patients were consistent with the areas of surgical resections for these patients. CONCLUSIONS: The CPI technique may become a useful alternative for noninvasive mapping of cortical regions displaying epileptiform activity from scalp electroencephalogram recordings.

A single-incision laparoscopic technique for retrieval and replacement of disconnected ventriculoperitoneal shunt tubing found in the peritoneum.

A 7-year-old girl presented with signs and symptoms of increased intracranial pressure 2 years after insertion of a ventriculoperitoneal (VP) shunt. Evaluation revealed disconnection of the distal shunt catheter and migration into the peritoneal cavity. A single-incision laparoscopic procedure was performed to locate and remove the disconnected shunt tubing, and the new shunt catheter was inserted through the laparoscopic port site. Laparoscopy is being used more frequently for evaluation and repair of distal VP shunt malfunctions, but generally still requires multiple incisions for port placement and insertion of the new shunt catheter. The single-incision technique used here is technically feasible, allows excellent visualization of the peritoneal cavity and does not require any incisions beyond the previous one used for initial shunt insertion.

Measurements of intraventricular pressure in a patient shunted from the ventricle to the internal jugular vein against the direction of blood flow (the El-Shafei shunt).

OBJECT: After demonstrating the anti-siphoning properties of a distensible tube in vitro, El-Shafei constructed a shunting system that directs CSF flow into the internal jugular vein against the flow of blood. Though clinically effective, the in vivo pressure dynamics of this type of shunt system have not been investigated. METHODS: After failure at multiple other extracranial absorptive sites, an 18-year-old woman was shunted from the lateral ventricle to the internal jugular vein against the direction of blood flow. The shunt system contained an in-line noninvasive telemonitor allowing examination of postural intracranial pressure dynamics in the awake state. This shunt system demonstrated postural pressure dynamics that were consistent with a stringent nonsiphoning shunting system. CONCLUSIONS: These observations validate the use of the El-Shafei shunt placement as a biologically nonsiphoning CSF absorptive system. In addition, the stringency of the anti-siphoning properties of the internal jugular vein open the possibility of preferentially using this shunting system in patients who clearly exhibit symptoms of shunt overdrainage.

Intraventricular pressure dynamics in ventriculocholecystic shunting: a telemetric study.

Extracranial cerebrospinal fluid shunting is the current mainstay of therapy for hydrocephalus. The generally preferred extracranial site for cerebrospinal fluid absorption is the peritoneal space; however, the cardiac atrium and the pleura are also commonly used. On occasion other CSF recipient sites, such as the gallbladder, are used secondarily when the more common absorptive spaces are unavailable or unsuitable. The gallbladder, though, exhibits its own pressure dynamics in response to physiological stimuli. The effects of gallbladder contraction on intraventricular pressure (IVP) in the presence of a ventriculocholecystic (VGB) shunt are unknown. We had the opportunity to place a VGB shunt in a 4-year-old child who was coupled to a noninvasive telemonitor. After a period of acclimation, we examined the IVP dynamics of that shunting system both pre- and postprandially. We found that before ingestion of food, the gallbladder provides a CSF recipient site similar to that of the peritoneal space. However, after ingestion of a meal containing fat, we found that IVP rose more than 10 cm water in a stereotypic fashion consistent with postprandial gallbladder contraction. The increase in IVP lasted for several hours reaching a peak at approximately 75 min postprandially. We conclude that the VGB shunt is a viable alternative for extracranial cerebrospinal fluid shunting; however, one must be aware of the peculiar dynamics of this shunt in relation to food ingestion and the potential for unusually high IVPs.

A theoretical model of benign external hydrocephalus that predicts a predisposition towards extra-axial hemorrhage after minor head trauma.

INTRODUCTION: There is controversy over whether there exists a predisposition towards bleeding into the subdural space in infants with benign external hydrocephalus (BEH) or other enlargement of the extra-axial space (e.g. subdural hygroma). The presumed etiology implicates shear forces in over-stretching the extra-axial blood vessels. We have created a model of the intracranial space that approximates certain aspects of BEH. Using this model, we predict situations where children with BEH will bleed into the extra-axial space when normal infants will not. METHODS: The cranial model consists of two spheres representing the brain and the skull. The distance between them represents the width of the extra-axial space. The spheres are concentric (with interspheric distance equal to N) in the normal condition and nonconcentric in BEH. In BEH, the distance between the two spheres varies from N to Q (0 < N

The selective toxicity of 1-methyl-4-phenylpyridinium to dopaminergic neurons: the role of mitochondrial complex I and reactive oxygen species revisited.

1-Methyl-4-phenylpyridinium (MPP(+)) is selectively toxic to dopaminergic neurons and has been studied extensively as an etiologic model of Parkinson's disease (PD) because mitochondrial dysfunction is implicated in both MPP(+) toxicity and the pathogenesis of PD. MPP(+) can inhibit mitochondrial complex I activity, and its toxicity has been attributed to the subsequent mitochondrial depolarization and generation of reactive oxygen species. However, MPP(+) toxicity has also been noted to be greater than predicted by its effect on complex I inhibition or reactive oxygen species generation. Therefore, we examined the effects of MPP(+) on survival, mitochondrial membrane potential (DeltaPsim), and superoxide and reduced glutathione levels in individual dopaminergic and nondopaminergic mesencephalic neurons. MPP(+) (5 microM) selectively induced death in fetal rat dopaminergic neurons and caused a small decrease in their DeltaPsim. In contrast, the specific complex I inhibitor rotenone, at a dose (20 nM) that was less toxic than MPP(+) to dopaminergic neurons, depolarized DeltaPsim to a greater extent than MPP(+). In addition, neither rotenone nor MPP(+) increased superoxide in dopaminergic neurons, and MPP(+) failed to alter levels of reduced glutathione. Therefore, we conclude that increased superoxide and loss of DeltaPsim may not represent primary events in MPP(+) toxicity, and complex I inhibition alone is not sufficient to explain the selective toxicity of MPP(+) to dopaminergic neurons. Clarifying the effects of MPP(+) on energy metabolism may provide insight into the mechanism of dopaminergic neuronal degeneration in PD.

In vivo intracranial pressure dynamics in patients with hydrocephalus treated by shunt placement.

OBJECT: With the commercial availability of a variety of shunt systems, there is considerable controversy over the choice of the most appropriate shunt valve for each individual with hydrocephalus. Although the performance characteristics of all shunt systems are well documented in the laboratory setting, there is little description of the in vivo dynamics of intracranial pressure (ICP) after implantation of commonly used shunt systems in humans. The authors coupled telemonitoring devices to several different shunt systems to measure the performance characteristics of these valve systems with respect to intraventricular pressure (IVP) at increments of head elevation. METHODS: Twenty-five patients with different shunt systems and three control patients without shunts were studied for IVP at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees of head elevation, and the resultant curves were analyzed for the best-fit regression coefficient. For purposes of analysis the authors grouped shunt valve systems by design characteristics into three groups: differential-pressure valves (r = -0.321 +/- 0.061; 11 patients), nonsiphoning systems (r = -0.158 +/- 0.027; 10 patients), and flow-regulated valves (r = -0.16 +/- 0.056; four patients); there were three control patients without shunts (r = -0.112 +/- 0.037). CONCLUSIONS: The authors found that differential-pressure valves always caused ICP to drop to 0 by 30 degrees of head elevation, whereas all other valve systems caused a more gradual drop in ICP, more consistent with pressures observed in the control patients without shunts. Not surprisingly, the differential-pressure valve group was found to have a significant difference in mean regression coefficient when compared with those in whom nonsiphoning shunts (p < 0.023) or no shunts were placed (p < 0.049). These data provide a basis for evaluating shunt valve performance and for predicting valve appropriateness in patients in whom characteristics such as pressure and flow dynamics are weighed in the choice of a specific valve for implantation.

A child with neurofibromatosis-1 and a lumbar epidural arteriovenous malformation.

A 10-year-old child with neurofibromatosis-1 was evaluated for progressive lumbar scoliosis, back pain, and foot numbness. Magnetic resonance imaging showed several lumbar intraspinal and extraspinal masses consistent with neurofibromas. The mass at L3-L5 compressed the thecal sac and was thought to be the source of the symptoms. On operative exploration, a lumbar epidural arteriovenous malformation was found, which was removed in its entirety. The child's back pain and foot numbness resolved. Epidural arteriovenous malformations in patients with neurofibromatosis-1 are rare and have been reported only in the cervical spine. Our finding of a lumbar epidural arteriovenous malformation in a child with neurofibromatosis-1 demonstrates that vascular anomalies can be present throughout the spine of patients with neurofibromatosis-1 and should be considered in the differential diagnosis of any neurofibromatosis-1-related epidural mass.

Telemetric assessment of intracranial pressure changes consequent to manipulations of the Codman-Medos programmable shunt valve.

INTRODUCTION: Noninvasive manipulation of programmable shunt valves may allow customization of intracranial pressure (ICP) dynamics in individual shunted patients. Manipulations of the recently FDA-approved Codman-Medos variable pressure valve (VPV) are monitored by radiographic changes in the valve mechanism, necessitating a skull radiograph with each pressure change. We wished to assess the in vivo impact of VPV manipulations on ICP changes using a noninvasive telemonitor as an alternative to radiographic confirmation and as a method for validating the ICP changes. METHODS: TeleSensor devices (Radionics) were implanted in-line with 12 VPV shunt systems. ICP was assessed telemetrically in the supine position whenever the valve pressure was adjusted (both before and 2-5 min after the manipulation). RESULTS: Valve manipulation was confirmed by radiograph for the initial manipulations only and matched the telemetric pressure changes observed in all cases. Confirmed manipulations of the valve were generally followed by a near equivalent relative change in ICP (

Management of cavernous malformations in the pediatric population.

The management of cavernous malformations (CMs) in a child is similar in many ways to that of CMs in an adult. There are specific general principles that need to be considered when approaching these lesions in children, however. The long life span anticipated in the pediatric patient may favor an aggressive surgical approach for single, small asymptomatic cavernous malformations or for certain symptomatic lesions in eloquent locations. The observed history of a given malformation may be the best guide to determine its treatment. The authors discuss some of these principles and review their experience with a series of children who have presented for management of cerebral CM.

Delayed repair of open depressed skull fracture.

INTRODUCTION: Elevation and repair of an open depressed skull fracture is often thought of as an emergency procedure. Common indications for emergent elevation of a depressed skull fracture have been dural tear, seizure, gross contamination or mass effect from bone or a sizable underlying intracerebral hematoma. As treatment of head injury moves towards management of cerebral perfusion pressure (CPP) rather than intracranial pressure (ICP), we sought a way to maximize CPP in the initial treatment of head-injured patients with depressed skull fractures that would eventually require surgery by delaying surgery, when possible, until after the initial period of elevated ICP. METHODS: Over a 12-month period, 7 patients (all male, ages 1-15 years) were admitted to our institution with the diagnosis of open depressed skull fracture without significant mass effect requiring urgent decompression. All had significant head trauma with altered mental status and a Glasgow Coma Score of 3-12. Patients were treated with antibiotic prophylaxis (nafcillin, ceftriaxone, metronidazole), seizure prophylaxis (phenytoin) and underwent CPP management in an intensive care unit setting as indicated by intracranial pressure monitoring or clinical assessment. Length of medical management of CPP ranged from 4 to 12 days. Upon stabilization of CPP, patients were operated for repair of their dural, bone and scalp injuries. RESULTS: All 7 patients treated in the above manner suffered no ill effects from their delayed surgery: there was no meningitis, no late seizures, and no cerebrospinal fluid leak. Complications attributable to delay were not present at follow-up ranging from 12 to 24 months. CONCLUSIONS: We have delayed surgery for repair of open depressed skull fractures in order to maximize medical management of CPP in the setting of acute trauma. Among other considerations, the risk of intraoperative hypotension occurring at a time of acutely raised ICP was avoided by this delay. We conclude that there is a role, in this specifically defined subset of head trauma patients, for delayed surgical repair of open depressed skull fractures.

Endoscopic approach to noncommunicating fluid spaces in the shunted patient.

INTRODUCTION: It is well known that shunted hydrocephalic patients can, over time, develop entrapped ventricles or cystic spaces not in communication with the remaining ventricles. This situation has traditionally been treated with placement of an additional catheter or shunt system in the noncommunicating fluid space. With the advent of minimally invasive endoscopic techniques, it has become possible to fenestrate trapped fluid spaces into the shunted ventricular system, thus preventing the need for additional catheters. METHODS: Fifteen shunted patients presented with noncommunicating fluid spaces over a 4-year period at our two institutions. We attempted fenestration procedures in 14 of those patients. The various procedures included: septum pellucidum fenestration, cyst fenestration, third ventriculocisternostomy and a combination of the above. RESULTS: Thirteen of 16 (81%) endoscopic fenestrations successfully prevented the need for a complicated shunting system. There were 3 technical failures (3/16, 19%) in which an additional catheter was added to the existing shunt system at the time of the endoscopic procedure. There were no adverse neurologic effects from the endoscopic procedures; however, in 4 of the 14 patients (29%) a shunt revision was performed between 2 and 30 days following the fenestration. CONCLUSIONS: These results show that the endoscopic approach to establishing communication between noncommunicating CSF spaces in the shunted patient is safe and efficacious in preventing the need for additional CSF catheters. Though we encountered failures, the majority of cases are technically feasible. In these patients early shunt malfunction may occur, most likely due to intraoperative bleeding and will require shunt revision.

Intraventricular pressure dynamics in patients with ventriculopleural shunts: a telemetric study.

Extracranial CSF shunting to the pleural absorptive surface is sometimes used as an alternative to ventriculoperitoneal shunting. The pressure dynamics of this type of shunt would be expected to differ from peritoneal shunting due to active changes in pleural pressures caused by the ventilatory cycle. We have had opportunity to examine the in vivo intraventricular pressure (IVP) dynamics of ventriculopleural shunts utilizing a commercially available implantable telemonitor (Telesensor; Radionics, Burlington, Mass.). Four patients with ventriculopleural shunts were monitored telemetrically while supine and at increments of head elevation to 90 degrees. Two patients with 'medium' grade differential pressure valves exhibited IVPs which were never greater than zero. One patient with an in-line antisiphoning device in the shunt system appeared to have IVPs closely resembling those seen in shunting to the peritoneal space. Another patient with valve opening pressure set at 19 cm of water consistently had supine intraventricular pressures less than 10 cm of water that readily fell to zero with minimal head elevation. We conclude that the negative intrapleural pressures generated by the ventilatory cycle tend to cause IVPs in ventriculopleural shunts to be lower than those expected in peritoneal shunting. This observation suggests that ventriculopleural shunts may be appropriate for patients requiring very low intraventricular pressures in order to resolve their hydrocephalic symptoms.

C2/3 instability in a child with Down's syndrome . case report and discussion.

Down's syndrome patients are prone to cervical ligamentous laxity, the vast majority of which is at the C1/2 level. We describe the case of a 2-year-old girl with Down's syndrome who was found to have cervical instability at the C2/3 level on screening cervical spine radiographs with 9 mm of anterolisthesis of C2 on C3. She was without clinically evident neurological deficit from this condition; however, T2-weighted magnetic resonance imaging of her cervical spine revealed high intensity signal changes within the spinal cord at and above that level. She underwent posterior fusion that was complicated by poor tolerance of her Minerva-type cervical brace. She eventually developed a stable fusion with 5 mm of anterolisthesis at the C2/3 level. This is the only Down's syndrome patient with instability at the C2/3 level that we have found reported. Our experience suggests that Down's syndrome patients can have instability at C2/3 that can be successfully treated with posterior fusion.

Surgical management of neonatal hydrocephalus.

Maintenance of normal intracranial pressure is crucial to the development of the neonatal brain. Certainly, neonatal hydrocephalus will perturb cerebral development and calls for careful and timely intervention. Many competing factors must be taken into account when evaluating the neonate with hydrocephalus. A neurosurgical approach to the management of neonatal hydrocephalus is presented with emphasis on practical treatment paradigms.

Telemetric intraventricular pressure measurements after third ventriculocisternostomy in a patient with noncommunicating hydrocephalus.

OBJECTIVE: To examine and document intraventricular pressure (IVP) dynamics in an adult after endoscopic third ventriculocisternostomy performed as treatment for hydrocephalus associated with aqueductal stenosis. METHODS: A 30-year-old man who had undergone ventriculoperitoneal shunting at age 21 years for aqueductal stenosis caused by a tectal mass presented with symptoms and imaging studies consistent with shunt malfunction. He underwent urgent ventriculoscopic third ventricular ventriculocisternostomy, which resolved his symptomatology. The existing shunt was not revised. At the time of surgery, a catheter connected to an intracranial pressure TeleSensor device (Radionics, Burlington, MA) was inserted into the ventricular system. Postoperatively, the patient's recovery was assessed by IVP recordings. This system allowed us to record IVP in an awake patient with a functioning third ventriculocisternostomy. RESULTS: We observed an initial postoperative IVP of 17 cm H2O in the supine position, which decreased to 0 cm H2O at 90 degrees of head elevation. The IVP decreased during the first 48 hours postoperatively to 0 to 2 cm H2O when supine. By 1 week postoperatively, the patient's IVP had returned to a baseline of 15 to 17 cm H2O when supine, with a gradual decrease to 0 cm H2O at 30 degrees of head elevation. Three months postoperatively, the patient's IVP in the supine position was 8 cm H2O, with IVP decreasing to 0 cm H2O at 45 degrees of head elevation. Magnetic resonance (MR) imaging performed at that time revealed evidence of flow through the third ventriculocisternostomy. CONCLUSION: We conclude that after an initial period of adjustment, the IVP in this patient returned to an unremarkable baseline despite the novel fluid pathway into the prepontine cistern. This may represent maturation of the breach through the third ventricular floor or brain recovery from a period of high pressure. Also, the shape of the postural IVP curve closely resembled that observed in patients who are not hydrocephalic. These data represent the first documentation of the intraventricular pressure response to ventriculocisternostomy and suggest possible intracerebral responses to this alteration in cerebrospinal fluid flow.

The use of clinical practice guidelines (CPGs) to evaluate practice and control costs in ventriculoperitoneal shunt management.

BACKGROUND: As a step toward maximizing the quality and cost-effectiveness of neurosurgical care, we designed clinical practice guidelines (CPGs) for the management of VP shunt malfunctions and infections at a tertiary care pediatric teaching institution. The detailed CPGs determine the use of radiographic studies, laboratory tests, and invasive procedures in the management of this problem. One purpose of the CPGs is to provide clear clinical guidelines for the medical trainee, thereby reducing variability in care and unnecessary utilization of resources. METHODS: The CPGs were developed in stages over a 2-year period. The practice patterns in our institution for the management of shunt malfunctions and infections were articulated. They were compared with those published in the neurosurgical literature, and areas of clinical decision-making variability were identified. Preliminary guidelines were formulated, and data regarding patient care were prospectively collected. Based on this data, final CPGs were formulated and implemented. Total and itemized hospital charges for patients managed according to the CPGs were compared with those for patients in the 3 years before CPG implementation. RESULTS: CPG-managed patients had generally lower total and itemized charges as compared with control patients. Decreased charges per hospital day and charges for shunt films in the CPG group were statistically significant. CONCLUSIONS: The process by which the CPGs were developed and implemented, as well as the CPGs themselves, are described. We also present the clinical, demographic, and financial data that were prospectively collected for all patients managed within the CPGs over an initial 1-year period and compare it with data obtained for control groups of shunt malfunction patients admitted during the 3 years before implementation of the CPGs. We find a trend toward reduction of charges after implementation of the CPG.

Surgery of the spine in myelodysplasia. An overview.

Significant spinal deformity is particularly common in nonambulatory patients with myelodysplasia. Progressive deformity may be caused by congenital anomalies, paralytic collapse, hip contractures, or spinal cord tethering. Existing or projected functional impairment should be the principle indication for treatment. Surgical treatment is complicated by poor soft tissue coverage, associated contractures, lack of sensation, weak bone, and absence of posterior elements. Successful fusion can be achieved by circumferential (anterior and posterior) fusion and current rigid segmental instrumentation. The unique deformities and bony anatomy require individualized techniques to achieve fixation.

Hydrocephalus requiring urgent external ventricular drainage in a patient with diabetic ketoacidosis and cerebral edema: case report.

OBJECTIVE AND IMPORTANCE: Neurological deterioration, typically attributed to cerebral edema, is a rare but life-threatening complication in the treatment of diabetic ketoacidosis (DKA). We report the case of a child with DKA who became comatose but demonstrated acute obstructive hydrocephalus, instead of cerebral edema. CLINICAL PRESENTATION: An 11-year-old male patient presented with new-onset insulin-dependent diabetes mellitus and DKA. He was initially responsive but, after several hours of treatment, became unresponsive, with dilated pupils and decerebrate posturing. Cranial computed tomographic scanning demonstrated obstructive hydrocephalus resulting from focal cerebellar and brain stem edema. INTERVENTION: The patient was initially managed with medical treatment but ultimately required urgent ventricular drainage to arrest a progressive herniation syndrome. To our knowledge, this report describes only the second such case reported and the first requiring urgent ventriculostomy. CONCLUSIONS: These observations emphasize the importance of recognizing hydrocephalus as a potentially reversible cause of coma in DKA and of initiating prompt neurosurgical intervention, if warranted.