Pressure monitoring during neuroendoscopy: new insights

BACKGROUND

Significant increases in intracranial pressure (ICP) may occur during neuroendoscopic procedures. To detect and prevent serious and sustained increases, ICP should be monitored. At present, controversy exists on the optimal location of the monitoring sensor. Therefore, we conducted an in vitro study to estimate the pressure gradients between the ventricle, the 'gold standard' site, and the rinsing inlet and outlet.

METHODS

A head model and a standard endoscope were used. Rinsing was enforced by using a pressurized infusion bag. Using clinically relevant flow rates, pressure was measured at the rinsing inlet and outlet, in the ventricle, and at the distal end of the rinsing channel using a tip sensor or a capillary tube.

RESULTS

At a flow of 61 ml min(-1), the steady-state pressures measured at the rinsing inlet, in the ventricle, and at the rinsing outlet were 38, 26, and 12 mm Hg, respectively. At 135 ml min(-1), these increased to 136, 89, and 42 mm Hg. Transendoscopic pressure measurements were always within 1 mm Hg of the ventricular pressure.

CONCLUSIONS

During endoscopy, measurements at the rinsing inlet overestimated the ventricular pressure by ∼50 mm Hg during heavy rinsing, whereas measurements at the rinsing outlet underestimated the pressure by ∼50 mm Hg. An electronic tip sensor or a pressure capillary tube placed at the distal end of the lumen of the rinsing channel of the endoscope did not interfere with rinsing flow and produced measurements that were equal to ventricular pressures.

Intradural endoscopic closure of dural breaches in a case of post-traumatic tension pneumocephalus

INTRODUCTION

Post-traumatic tension pneumocephalus can become a life-threatening condition that urges the surgeon to repair the causal breach in the dura. Dural repair via craniotomy may be jeopardised by the fragility of the dura and by its firm adhesions to the bone, especially in aged patients. Transnasal sealing requires the opening of each of the paranasal sinuses or cells that line the frontal base.

METHOD

We present the case of a 92-year-old man, in whom an alternative, minimally invasive procedure was chosen. The patient was in a poor general condition and suffered from progressive obtundation till coma, because of a massive tension pneumocephalus, which was not reversed by drainage of the intracranial air via a burr hole, but even increased instead. Through the existing burr hole at the coronal suture, a rigid endoscope was introduced. Because of a massive backward compression of the brain, the endoscope could be passed in front of it to visualize the dural defects at the level of the ethmoidal roof. Pericranium, harvested from around the burr hole, was glued against the defects. The procedure was repeated at the contralateral side.

RESULT

After surgery, a gradual decrease of the amount of intracranial air was documented. The patient regained consciousness and was extubated. In spite of this favourable course, he suddenly died two weeks after surgery from combined pulmonary and renal dysfunction. Autopsy documented the efficacious endoscopic sealing of the skull base, which was the least invasive procedure in the given circumstances.

Neurosurgical aspects of temporal deep brain stimulation for epilepsy

Deep brain stimulation (DBS), which mimics the effect of ablative surgery in movement disorders, is considered by analogy as potentially useful in the epileptic temporal lobe as an alternative to resection. It could be applied to patients in whom resective surgery is less beneficial, e.g. cases without memory impairment or with bilateral hippocampal involvement. In patients who undergo invasive presurgical analysis, the necessary intrahippocampal leads can serve for the application of DBS, provided that they are suited for chronic use. The hippocampus, in which the focus of epilepsy is detected, is stimulated continuously using high-frequency square-wave pulses. The reduction of interictal spike activity during a period of acute stimulation is the criterion for deciding whether the leads will be connected to an internal pulse generator. We are conducting a pilot study, with 16 patients enrolled so far, ten of whom have been followed up for more than one year. Some theoretical considerations are dedicated to hippocampal DBS.

Value of Cushing reflex as warning sign for brain ischaemia during neuroendoscopy † †This work was performed at the Department of Anaesthesia, Ghent University Hospital, Ghent, Belgium

BACKGROUND

During an endoscopic neurosurgical procedure a sudden increase in intracranial pressure may occur at any time. We present a prospective study of haemodynamic changes during such procedures.

METHODS

Physiological data were recorded during the whole operative procedure in 17 consecutive patients who underwent an endoscopic neurosurgical procedure under general anaesthesia. Monitoring included invasive blood pressure, intracranial pressure, electrocardiogram, end-expired carbon dioxide, pulse oximetry and heart rate. Pressure and ECG waveforms were recorded at 100 Hz and evaluated in a subsequent offline analysis.

RESULTS

In almost every case, the occurrence of hypertension and tachycardia was clearly the result of an increase in intracranial pressure. Also, a Cushing reflex developed in almost every case where the cerebral perfusion pressure dropped below 15 mm Hg. The occurrence of bradycardia was not systematically associated with a low cerebral perfusion pressure.

CONCLUSION

In this study, we describe the haemodynamic effects of increased intracranial pressure during endoscopic neurosurgical procedures and their respective sequence of events at high temporal resolution. Although most clinicians rely on the occurrence of bradycardia to diagnose intracranial hypertension during endoscopic neurosurgical procedures, we show that a simultaneous onset of hypertension and tachycardia is a better indicator of impaired brain perfusion. Waiting for a persistent bradycardia to alert the surgeon during endoscopic neurosurgical procedures could allow severe bradycardia or even asystole to develop.

Unicoronal Suture Immobilization in the Fetal Rabbit

Pre-clinical evaluation of surgical procedures aimed to correct craniosynostosis is ideally performed in species of small animals characterized by perinatal brain development, early skeletal maturation, and genuine synostosis in all newborns. It would be nearly impossible to breed such a colony to homozygosity, so most researchers have resorted to artificial postnatal suture immobilization. Our aim was to test the hypothesis that artificial immobilization of a unicoronal suture in the fetal rabbit (25 days of gestation) would result in neurocranial growth alterations similar to those seen in the 9-day postnatally immobilized or congenital synostotic rabbit models. The advantages of prenatal immobilization are that rabbits can undergo the tested corrective procedure at postnatal day 9. This age corresponds to a human age of 6 months and allows the deformity and the effects of its correction to be more readily detected. The heads of 25-day-old fetuses of five time-dated pregnant New Zealand white rabbits were exposed by hysterotomy. The left unicoronal suture of 4 fetuses in each litter was immobilized with a polyglactin suture piercing the frontal and parietal bone plates. The remaining two fetuses were sham-operated. Nine days after spontaneous delivery, all rabbits were marked with four titanium screws close to the sagittal and coronal sutures. Growth was recorded with dorsoventral cephalograms at 9 and 90 days. The group with the immobilized suture showed a small increase in growth across the sagittal sutures. However, the decreases in growth at the unicoronal suture in both the immobilized (5.41-mm difference with sham-treated group) and nonimmobilized (1.17-mm difference with sham-treated group) were significant. Fetal immobilization results in growth alterations similar to those observed after postnatal immobilization.

Cardiovascular changes during endoscopic third ventriculostomy

During an endoscopic third ventriculostomy (ETV) a sudden increase in intracranial pressure (ICP) may occur at any time. In the literature little attention has been paid to the early detection of such an increase. In particular the occurrence of a 'Cushing reflex' has not been discussed in this context. Therefore, we have now analysed retrospectively the anesthesia charts of 88 patients with obstructive hydrocephalus who had undergone ETV under general anesthesia. Monitoring included invasive blood pressure, electrocardiogram, end-expired carbon dioxide, pulse oximetry and heart rate. These variables were now evaluated before and after the introduction of the endoscope and during and after the occurrence of any change. In 67 patients the procedure had been uneventful. In 6 patients the occurrence of tachycardia and hypertension followed by bradycardia and hypertension was clearly the result of an increase in ICP, which we call a Cushing reflex. In his classical description of this pressure response Cushing reported the occurrence of hypertension, bradycardia and apnoea. However, many investigators have shown that beside systemic hypertension, both tachycardia and bradycardia are essential components of the Cushing reflex. Waiting for a persistent bradycardia to alert the surgeon during ETV can allow a fatal asystole.

The pathophysiology of motor symptoms in Parkinson's disease

This review focuses on some of the known and hypothetical pathophysiological mechanisms underlying the motor symptoms in Parkinson's disease (PD). Current views on these mechanisms have largely been influenced by models of basal ganglia functioning and dysfunctioning. These models have allowed to explain some clinical findings and to predict a number of results of basal ganglia surgery in movement disorders. However, neurophysiological studies as well as neurochemical data have broadened our vision on basal ganglia functioning and dysfunctioning in PD. Moreover, these more fundamental insights in basal ganglia functioning allow new concepts on the development of treatment strategies, and on the prevention of motor fluctuations in PD.

Endovascular Treatment of a Giant Petrous Internal Carotid Artery Aneurysm

Expansive aneurysms of the petrous internal carotid artery are rare. Compressive and thrombembolic neurological deficits and occasionally extradural haemorrhage in combination with a pulsatile tinnitus are most important and alarming symptoms. Due to its extradural location, subarachnoid haemorrhage does not occur. Treatment is indicated since rupture may be devastating and recurrent ischaemic attacks severely disabling. Because direct neurosurgical access to the petrous internal carotid artery is very difficult, treatments consists of parent vessel occlusion with or without extra-intracranial bypass construction. We present a case of a young man with a giant petrous artery aneurysm provoking a thrombembolic event which was treated successfully with proximal balloon occlusion of the internal carotid artery after a temporary balloon occlusion test.

Vagus nerve stimulation for epilepsy, clinical efficacy of programmed and magnet stimulation

RATIONALE

Vagus nerve stimulation (VNS) by intermittent and programmed electrical stimulation of the left vagus nerve in the neck, has become widely available. It is an effective treatment for patients with refractory epilepsy. Patients can be provided with a magnet that allows to deliver additional stimulation trains. Since earlier studies have demonstrated the persistence of a stimulation effect after discontinuation of the stimulation train, we evaluated the clinical efficacy of VNS both in the programmed intermittent stimulation mode and magnet stimulation mode.

METHODS

A group of 30 patients (16 F, 14 M) with medically refractory partial epilepsy, who were unsuitable candidates for resective surgery, were included in the study. The patients, their companions and caregivers were instructed on how to administer additional stimulation trains using a hand-held magnet when an aura or a seizure onset occurred. Patients or caregivers could recognize habitual seizures and were able to evaluate sudden interruption of these seizures. Using seizure diaries, detailed accounts of magnet use and regular clinic follow-up visits, data on seizure frequency and severity and number of magnet applications were collected. Patients who provided unreliable information were excluded from the analysis.

RESULTS

Forty-seven percent of all patients had an improvement in seizure control with a reduction in seizure frequency of more than 50% during a mean follow-up of 33 months (range: 4-67 months). More than half of the patients used the magnet and provided reliable information. In 63% of patients who were able to self-administer or receive additional magnet stimulation, seizures could be interrupted, be it consistently or occasionally. More than half of the patients who reported a positive effect of magnet stimulation became responders. In most cases the magnet was applied by a caregiver.

CONCLUSIONS

To our knowledge, this study is the first to explore the efficacy of magnet-induced vagus nerve stimulation. Results suggest that the magnet is a useful tool that provides patients and mainly caregivers with an additional means of controlling refractory seizures. Additional controlled studies comparing programmed stimulation and magnet-induced stimulation in monitoring conditions are warranted.

Symptomatic pineal cysts: clinical manifestations and management

Between 1991 and 2000, seven patients presented with symptomatic pineal cysts at our hospital (6 females, 1 male). Average age was 22 years (range 4-33 years). Headache was present in 6 patients, who were subsequently operated on. A scotoma and a transient inferior visual field deficit were minor signs in two patients respectively. A Parinaud syndrome with vertical gaze paralysis was found in none. In one child, paroxysmal pupillary dilatations and contractions ('springing pupils') constituted the only signs and a conservative policy was adopted. Four patients presented with hydrocephalus and were treated by an endoscopic resection of their pineal cysts (one stereotactically, three free-hand). Two other patients presented with a prolonged history of symptoms and signs: headache alone in one, headache with discrete neurological deficits in the other. Ventricles in these two patients were not dilated and therefore an open cyst resection by infratentorial supracerebellar approach was performed. Average follow-up in the six "operated" patients was 29 months (range 12-108 months). All four patients treated by endoscopy, are symptom-free at follow-up, whereas the two who were approached by open surgery, are not. Clinical presentation, radiological evaluation and treatment modalities of pineal cysts are discussed and compared with experiences reported in the literature. It is concluded that pineal cysts in the presence of obstructive hydrocephalus are a clear indication for endoscopy with a rigid endoscope.

Direct medical costs of refractory epilepsy incurred by three different treatment modalities: a prospective assessment

PURPOSE

More than 20% of epilepsy patients have refractory seizures. Treatment options for these patients include continued polytherapy with/without novel antiepileptic drugs (AEDs), epilepsy surgery (ES), or vagus nerve stimulation (VNS). The purpose of this study was prospectively to compare epilepsy-related direct medical costs (ERDMCs) incurred by these different treatment modalities.

METHODS

Eighty-four patients underwent a complete presurgical evaluation protocol at our institution. As a result, 24 (29%) patients were treated with continued AED polytherapy only; 35 (40%) underwent ES; and 25 (30%) had VNS. In each patient, annual costs in the 2 years preceding the therapeutic decision (ERDMC-pre) and during the follow-up afterward (ERDMC-post) were prospectively calculated. Furthermore, frequency of complex partial seizures with/without secondary generalization (CPS+/-SG), dosage and number of AEDs, number of hospital admission days, clinic visits, and laboratory tests before and after the therapeutic decision also were prospectively assessed. ERDMC-pre and ERDMC-post were compared in and among the three treatment groups.

RESULTS

In patients conservatively treated with AEDs, mean frequency of CPSs decreased from 12 per month to nine per month, whereas mean ERDMCs decreased from $2,525 U.S. to $2,421 U.S. In surgical patients, mean seizure frequency decreased from six to fewer than one per month; mean ERDMCs per year decreased from $1,465 U.S. preoperatively to $1,186 U.S. postoperatively. In the VNS group, mean seizure frequency decreased from 21 per month to seven per month. ERDMCs in this subgroup decreased from $4,826 U.S. to $2,496 U.S. Mean seizure frequency changes were significant when conservatively treated patients were compared with surgically treated and VNS patient groups (chi2 test, p<0.001 and p=0.0019, respectively). ERDMC changes in conservatively treated patients also were statistically significant when compared with surgically treated and VNS patients (chi2 test, p=0.0007 and p=0.0036, respectively). No statistically significant differences were found in ERDMC changes between the surgical and VNS groups (chi2 test, p=0.387).

CONCLUSIONS

Ongoing daily treatment of patients who underwent resective surgery costs significantly less than conservative treatment. For patients in whom resective surgery is not an option, ERDMC show a significant decrease in VNS-treated patients compared with conservatively treated patients.

Programmed and magnet-induced vagus nerve stimulation for refractory epilepsy

Vagus nerve stimulation (VNS) is an effective alternative treatment for patients with refractory epilepsy. The generator produces intermittent stimulation trains and does not require patient intervention. Using currently available technology, continuous stimulation is incompatible with a reasonable battery life. Because earlier studies have demonstrated the persistence of a stimulation effect after discontinuation of the stimulation train, we intended to evaluate the clinical efficacy of VNS in both the programmed intermittent stimulation mode and the magnet stimulation mode. Patients, companions, and caregivers were instructed on how to administer additional stimulation trains when an aura or a seizure onset occurred. We assumed that patients or caregivers could recognize habitual seizures and were able to evaluate sudden interruption of these seizures. During a mean follow-up of 35 months, 46% of patients became responders, with a reduction in seizure frequency of more than 50%. Twenty-nine percent of patients stopped having convulsive seizures. In two thirds of patients who were able to self-administer or receive additional magnet stimulation, seizures could be interrupted consistently or occasionally. More than half of the patients who reported a positive effect of magnet stimulation became responders. Only three patients were able to use the magnet themselves. In most cases, support from caregivers was necessary. This study is the first to document the efficacy of magnet-induced VNS in a larger patient population during long-term follow-up. The magnet is a useful tool that provides patients who are treated with VNS and mainly caregivers of such patients with an additional means of controlling seizures. To further confirm the self-reported results from our patients, additional studies comparing programmed stimulation and magnet-induced stimulation during monitoring conditions are needed.

Vagus nerve stimulation for refractory epilepsy

Vagus nerve stimulation (VNS) is a neurophysiological treatment for patients with medically or surgically refractory epilepsy. Since the first human implant in 1989, more than 10 000 patients have been treated with VNS. Two randomized controlled studies have shown a statistically significant decrease in seizure frequency during a 12-week treatment period versus a baseline period when 'high stimulation' mode was compared with 'low stimulation' mode. The efficacy appears to increase over time. In general, one third of the patients show a >50% reduction of seizure frequency; one third show a 30-50% seizure reduction, and one third of patients show no response. Few patients become seizure-free. Side effects during stimulation are mainly voice alteration, coughing, throat paraesthesia and discomfort. When studied on a long-term basis, VNS is an efficacious, safe and cost-effective treatment not only in adults but also in children and the elderly. The precise mechanism of action remains to be elucidated. In recent years much progress has been made through neurophysiological, neuroanatomical, neurochemical and cerebral blood flow studies in animals and patients treated with VNS. Further elucidation of the mechanism of action of VNS may increase its clinical efficacy and our general understanding of some physiopathological aspects of epilepsy. Finally, VNS may become an alternative treatment for other conditions such as depression and pain.

The mechanism of action of vagus nerve stimulation for refractory epilepsy: the current status

Vagus nerve stimulation (VNS) is a neurophysiologic treatment for patients with medically or surgically refractory epilepsy. Since the first human implant in 1989, more than 10,000 patients have been treated with VNS. The precise mechanism of action remains to be elucidated. Animal experiments with VNS were initially performed to demonstrate efficacy and safety preceding the clinical trials in human patients. Mechanism of action research involving animal experiments can provide essential clues. Animal experiments are often labor-intensive even in the hands of experienced researchers, however, and the results remain only a reflection of the complicated pathophysiologic systems of the human brain. Mechanism of action research in human patients treated with VNS is particularly challenging because of safety concerns, the large number of patients required, and the heterogeneous nature of various small patient series. This study provides an overview of the progress that has been made in the past 10 years through neurophysiologic, neuroanatomic, neurochemical, and cerebral blood flow studies in animals and patients treated with VNS. Further elucidation of the mechanism of action of VNS may increase its clinical efficacy. It may also provide inspiration for the development of new therapeutic modalities for refractory epilepsy.

Deep brain stimulation of the globus pallidus pars interna in advanced Parkinson's disease

Pallidotomy is now widely performed for the treatment of advanced Parkinson's disease (PD). Preliminary reports of the effect of globus pallidus pars interna deep brain stimulation (GPi DBS) have also been promising. We have analyzed a cohort of 22 consecutive patients enrolled in a multicenter study. Surgery was bilateral in 17 and unilateral in five patients. At 6-month follow-up, the bilaterally GPi-implanted patients demonstrated a marked improvement when examined after drug withdrawal ("off") and under optimal medication ("on") using the Unified Parkinson's Disease Rating Scale (UPDRS). The benefit induced by the stimulation in the "off" medication condition in the total motor score was 31% and in the activities of daily living (ADL) scores was 39%. During the "on" medication period, the reduction in the total "on" dyskinesias score was 66% and in the ADL score was 32%. A similar pattern of improvement was seen in the group of patients with unilateral GPi stimulation, although a second cohort of 12 patients not included in the multicenter study showed greater improvements in "on" motor functioning. Although the effect of DBS is predominantly reversible, electrode insertion alone resulted in measurable clinical effects in the absence of stimulation. Thus, at 6-month follow-up, the benefit observed without stimulation was up to 44% in the "on" dyskinesias score and 29% in timed tapping scores undertaken in the "off" medication state. Complications among 34 patients from all centers included perioperative infection (n=3), hardware fracture (n=2), and premature battery failure (n=3). These results show a positive antiparkinsonian effect of pallidal DBS. No specific complications were observed with bilateral procedures.

99Tc(m)-ECD SPET perfusion changes by internal pallidum stimulation in Parkinson's disease

High-frequency stimulation of the internal pallidum is an effective surgical approach for patients with advanced Parkinson's disease suffering from motor fluctuations and L-dopa induced dyskinesia. To study the acute effects of internal pallidum stimulation, changes in cerebral blood flow were measured by means of a single-day split-dose protocol using 99Tc(m)-ECD SPET. Nine patients with advanced Parkinson's disease and with a clinical picture predominated by tremor and drug-induced dyskinesia, were imaged before and immediately after electrostimulation. Brain perfusion data were mirrored to the same electrode side (five left and four right implants), co-registered and analysed statistically on a voxel-by-voxel basis (Statistical Parametric Mapping) and by an automated volume-of-interest approach. Acute stimulation of the internal pallidum induced a significantly decreased perfusion in the ipsilateral thalamus and striatum, as well as in the right parietal cortex. For the subgroup of seven patients with effective motor score improvements, a significant correlation between thalamic and striatal perfusion changes and UPDRS III motor score was present (P = 0.04). These results suggest that effective stimulation of the internal globus pallidus may produce symptom relief through decreased activity in pallido-thalamo-cortical circuits.

Vagus nerve stimulation for medically refractory epilepsy; efficacy and cost-benefit analysis

INTRODUCTION

Vagus nerve stimulation is a novel treatment for patients with medically refractory epilepsy, who are not candidates for conventional epilepsy surgery, or who have had such surgery without optimal outcome. To date only studies with relatively short follow-up are available. In these studies efficacy increased with time and reached a maximum after a period of 6 to 12 months. Implantation of a vagus nerve stimulator requires an important financial investment but a cost-benefit analysis has not been published.

PATIENTS AND METHODS

Our own experience with VNS in Gent comprises 15 patients with mean age of 29 years (range: 17-44 years) and mean duration of epilepsy of 18 years (range: 4-32 years). All patients underwent a comprehensive presurgical evaluation and were found not to be suitable candidates for resective epilepsy surgery. Mean post-implantation follow-up is 24 months (range: 7-43 months). In patients with follow-up of at least one year, efficacy of treatment in terms of seizure control and seizure severity was assessed one year before and after the implantation of a vagus nerve stimulator. Epilepsy-related direct medical costs (ERDMC) before and after the implantation were also compared.

RESULTS

A mean reduction of seizure frequency from 14 seizures/month (range: 2-40/month) to 8 seizures/month (range: 0-30/month) was achieved (Wilcoxon signed rank test n = 14; p = 0.0016). Five patients showed a marked seizure reduction of > or = 50%; 6 became free of complex partial seizures, 3 of whom became entirely seizure free for more than 12 months; 2 patients had a worthwhile reduction of seizure frequency between 30-50%; in 2 patients seizure frequency reduction has remained practically unchanged. Seizure freedom or > or = 50% seizure reduction was achieved within the first 4 months after implantation in 6/11 patients. Before the implantation, the mean yearly epilepsy-related direct medical costs per patient were estimated to be 8830 US$ (n = 13; range: 1879-31,129 US$; sd = 7667); the average number of hospital admission days per year was 21 (range: 4-100; sd = 25.7). In the 12 months after implantation, ERDMC had decreased to 4215 US$ (range: 615-11,794 US$; sd = 3558) (Wilcoxon signed rank test n = 13; p = 0.018) and the average number of admission days to 8 (range: 0-35) (Wilcoxon signed rank test n = 13; p = 0.023).

CONCLUSION

VNS is an effective treatment of refractory epilepsy and remains effective during long-term follow-up. Cost-benefit analysis suggests that the cost of VNS is saved within two years following implantation.

[Methyl-11C]thymidine positron emission tomography in tumoral and non-tumoral cerebral lesions

BACKGROUND

No ideal radiopharmaceutical exists for positron emission tomography (PET) that fulfills all clinical requirements for the study of brain tumors.

PURPOSE

The usefulness of a recently developed PET tracer, [methyl-11C]thymidine ([methyl-11C]TdR) is explored in brain tumors.

PATIENTS AND METHODS

Twenty patients with confirmed tumoral and non-tumoral brain lesions were investigated with [methyl-11C] TdR PET. The 11C activity was visually and quantitatively assessed. In two patients, dynamic scans were performed. The PET findings were compared to those of magnetic resonance imaging (MRI) or computed tomography (CT) of the brain and to the final diagnosis.

RESULTS

Eight out of ten patients with confirmed tumoral lesions or tumor recurrence had increased 11C activity within the lesion. In ten non-tumoral lesions no increased 11C uptake was found. The dynamic PET studies showed that [methyl-11C] TdR first acts as a blood flow tracer, but that later on the uptake of 11C activity is due to labeled metabolites, crossing the blood-brain barrier. Increased tracer activity was only observed in tumoral and not in non-tumoral contrast-enhanced lesions on MRI or CT.

CONCLUSIONS

[Methyl-11C] TdR is not a selective PET radiopharmaceutical for brain tumors, but can be used as a tracer for tumoral blood-brain barrier disruption.

Accuracy of single-sequence MRI for investigation of the fluid-filled spaces in the inner ear and cerebellopontine angle

We prospectively studied 163 patients referred for MRI of the temporal bone. A presumed diagnosis was made using only one of three sequences: a single thick (12 mm) slice fast T2-sequence, 3D fourier transform constructive interference in steady state (3DFT-CISS) sequence and a gadolinium-enhanced T1-weighted sequence. The visibility of the cochlea, vestibule and superior, lateral and posterior semicircular canals of normal temporal bones was assessed on the T2-weighted images: they were almost always visible (98-100%), with exception of the superior semicircular canal, seen in only 35% of cases. The images were interpreted as abnormal in 34 patients (21%). Using only the fast T2-weighted, 3DFT-CISS and gadolinium-enhanced T1-weighted sequences a presumed false positive diagnosis was made in 5, 1 and 0 cases and a false negative diagnosis in 2, 2 and 4 cases respectively. The overall reliability of the thick-section fast T2-weighted images is limited. This study suggests that a combination of gadolinium-enhanced T1-weighted and 3DFT-CISS images can be considered the gold standard for temporal bone MRI and neither sequence performed separately is as accurate as both together.

A stereotaxic atlas of the forebrain of the bank vole (Clethrionomys glareolus)

In this article part of the forebrain of the bank vole (Clethrionomys glareolus) is presented in stereotaxic coordinates. The stereotaxic procedure was performed as follows. With the vole's head mounted in a stereotaxic adaptor, internal reference tracks were made with a 0.5-mm diameter microdialysis cannula and India ink, 2 mm in front and 2.6 mm behind the skull landmark bregma. Brains were fixed for 72 h in 4% commercial formaldehyde in sodiumcacodylate buffer containing 1% CaCl2. To determine shrinkage they were weighed before and after fixation. After embedding in paraffin they were sectioned at 25 microm and stained with Nissl. Photomicrographs were taken from the brain of one animal while its frontal (antero-posterior) coordinates of five neural structures were compared with those of 12 other voles. Variability was also checked in lateral and vertical directions at frontal level -1.0 mm (relative to bregma). The results show that the distance between the two skull landmarks bregma and lambda correlates significantly and negatively with the antero-posterior position of each of the brain areas. On the basis of these results an equation is proposed to improve accuracy in locating neural structures that deviate due to biological variability.

Changes in quality of life following unilateral pallidal stimulation in Parkinson's disease

Twenty patients with Parkinson's disease (age range 38-70 years) completed the Sickness Impact Profile (SIP) 2 months before and 3 months after long-term high-frequency electrostimulation of the globus pallidus internus to improve clinical symptoms. The SIP provides an estimate of perceived quality of life on 12 health-status categories. Neurological assessment with the Hoehn and Yahr scale and the Unified Parkinson's Disease Rating Scale revealed a significant postoperative reduction in clinical symptomatology (p<0.001). The patients experienced a general improvement in self-reported quality of life that exceeded the purely motor and physical aspects of quality of life. The significant postoperative drop in perceived impairment of communication skills can be considered the most important subjective improvement. Longitudinal research on a larger sample of patients is necessary to evaluate the durability of the subjective improvement in quality of life after unilateral pallidal stimulation.

Cognitive outcome after unilateral pallidal stimulation in Parkinson's disease

OBJECTIVES

Chronic high frequency electrostimulation of the globus pallidus internus mimics pallidotomy and improves clinical symptoms in Parkinson's disease. The aim of this study was to investigate the cognitive consequences of unilateral deep brain stimulation.

METHODS

Twenty non-demented patients with Parkinson's disease (age range 38-70 years) were neuropsychologically assessed 2 months before and 3 months after unilateral pallidal stimulation. The cognitive assessment included measures of memory, spatial behaviour, and executive and psychomotor function. In addition to group analysis of cognitive change, a cognitive impairment index (CII) was calculated for each individual patient representing the percentage of cognitive measures that fell more than 1 SD below the mean of a corresponding normative sample.

RESULTS

Neurological assessment with the Hoehn and Yahr scale and the unified Parkinson's disease rating scale disclosed a significant postoperative reduction in average clinical Parkinson's disease symptomatology (p<0.001). Repeated measures multivariate analysis of variance (using right/left side of stimulation as a between subjects factor) showed no significant postoperative change in cognitive performance for the total patient group (main effect of operation). The side of stimulation did not show a significant differential effect on cognitive performance (main effect of lateralisation). There was no significant operation by lateralisation interaction effect. Although the patients experienced significant motor symptom relief after pallidal stimulation, they remained mildly depressed after surgery. Analysis of the individual CII changes showed a postoperative cognitive decline in 30% of the patients. These patients were significantly older and took higher preoperative doses of levodopa than patients showing no change or a postoperative cognitive improvement.

CONCLUSIONS

Left or right pallidal stimulation for the relief of motor symptoms in Parkinson's disease seems relatively safe, although older patients and patients needing high preoperative doses of levodopa seem to be more vulnerable for cognitive decline after deep brain stimulation.

Primary sinonasal mucosal melanoma: three different therapeutic approaches to inoperable local disease or recurrence and a review of the literature

Sinonasal melanoma is an uncommon disease with a bad prognosis and a high local recurrence rate. The use of radiotherapy in such conditions remains controversial. A review of the literature is presented in an attempt to answer some of the questions regarding therapeutic options. Data on incidence, aetiology, pathology and prognosis are also provided. Case studies are reported of three patients with sinonasal melanoma referred to our department in a relatively short time period and needing radiotherapy as a single treatment modality, using a conformal three-dimensional treatment technique. One patient was also treated with temporary 1251 seeds, while another was treated using intensity modulation. Both intensity modulation and temporary 1251 seeds are feasible techniques, providing satisfactory dose distributions encompassing the tumour volume while sparing critical structures. Surgery remains the treatment of choice for sinonasal melanoma. Radiotherapy should be used postoperatively and is a good alternative in cases of inoperable disease. Adjacent critical structures limit the radiation dose to the tumour area, especially when high fraction doses are used. Therefore, beam intensity modulation and 1251 seeds can be used to increase the tumour dose without exceeding the radiation tolerance of the surrounding structures.

Single-voxel proton MR spectroscopy and positron emission tomography for lateralization of refractory temporal lobe epilepsy

PURPOSE

We compared the metabolic information obtained from single-voxel proton MR spectroscopy and positron emission tomography (PET) in patients with temporal lobe epilepsy.

METHODS

Twenty-nine patients with temporal lobe epilepsy were screened for metabolic abnormalities with both proton MR spectroscopy and PET. Lateralization with MR spectroscopy was possible by using NAA/(Cho+Cr) and an asymmetry index. Hypometabolism as determined by PET was classified as typical or complex.

RESULTS

Twenty-four (96%) of 25 patients whose seizure onset could be lateralized to one temporal lobe showed ipsilateral lateralization with either MR spectroscopy or PET, whereas concordant lateralization with both techniques was possible only in 14 (56%) of the 25 patients. MR spectroscopy showed 42 abnormal temporal lobes whereas PET showed only 25 lobes with decreased metabolism. All temporal lobes with hypometabolism at PET also had a low NAA/(Cho+Cr). Five patients (20%) with negative PET studies had seizures lateralized correctly with MR spectroscopy.

CONCLUSION

Proton MR spectroscopy is more sensitive in depicting metabolic abnormalities than is PET in patients with temporal lobe epilepsy. Patients with negative PET studies will benefit from MR spectroscopy for the purpose of lateralization.

Value of single-voxel proton MR spectroscopy in temporal lobe epilepsy

PURPOSE

To study the value of different parameters derived from single-voxel proton MR spectroscopy of the mesial temporal lobes in the lateralization of the epileptogenic zone in patients with temporal lobe epilepsy.

METHODS

We studied 12 healthy volunteers and 21 patients with temporal lobe epilepsy refractory to medical treatment, which was clearly lateralized with electroencephalography (EEG) and MR imaging. The mesial temporal lobes were investigated with single-voxel proton MR spectroscopy using a point-resolved spectroscopic sequence with an echo time of 135 milliseconds. The normalized concentration of N-acetylaspartate (NAA), creatine (Cr), and choline-containing compounds (Cho), and the metabolite ratios NAA/Cho+Cr, NAA/Cr, Cho/Cr, and NAA/Cho were calculated from the spectra. Using these values and an asymmetry index, we assigned the patients to one of five lateralization categories.

RESULTS

The most consistent MR spectroscopic parameter for clear lateralization was the NAA/Cho+Cr ratio, followed by the NAA ratio. But with an adequate asymmetry index, the epilepsy in 17 (81%) of 21 patients could be lateralized by EEG and MR imaging with both parameters concordantly. Symmetric bilateral abnormalities were found in four of the 21 patients with NAA/Cho+Cr and in only one of the 21 patients with NAA. With both parameters, no contradictory lateralization was found; however, this was indeed the case with the remaining ratios, NAA/Cr, Cho/Cr, and NAA/Cho, in two, three, and one of the patients, respectively. A statistically significant decrease in NAA was found on the epileptic side, but also on the contralateral side.

CONCLUSION

With an adequate asymmetry index, NAA/Cho+Cr and NAA are equally sensitive in predicting the side of involvement in patients with unilateral temporal lobe epilepsy.

A combined stereotaxic adaptor and anaesthesia apparatus for microdialysis studies in small rodents

Intracerebral microdialysis in the bank vole (Clethrionomys glareolus) challenges the accuracy and precision of the stereotaxic implantation technique because of the small brain size. In this paper, a miniaturized stereotaxic head holder is described that allows precise alignment of bone landmarks on the skull and prevents all movement after fixation by clamping the skull symmetrically at the os parietale and at the os nasale. In addition, the head holder is adapted for inhalation anaesthetic delivery in order to ensure stable anaesthetic depth over several hours. The system is not restricted to bank voles but can be readily applied to other small experimental animals, which could lead to a more widespread use of the microdialysis technique in mice.

Epilepsy surgery in Belgium, the Flemish experience

Between January 1992 and June 1995, 160 patients were presurgically evaluated for medically refractory epilepsy by the Epilepsy Monitoring and Surgery Team at the University Hospital of Gent. All these patients underwent a comprehensive presurgical evaluation, including extensive neurological history and examination, video-EEG monitoring of interictal EEG and habitual seizures, CT and optimum MR. In a large subgroup of these patients a comprehensive neuro-psychological examination and interictal 18FDG-PET were performed. After the non-invasive phase of the presurgical evaluation, a bilateral carotid angiography and intracarotid amytal procedure was planned in 27 patients to establish hemispheric language dominance and bilateral memory function. After proper selection, 14 patients underwent invasive video-EEG monitoring with intracranial implantation of parenchymal and/or subdural electrodes to further document the area of seizure onset. From the initial group of 160 potential surgical candidates, 40 patients (20 M, 20 F) with mean age of 31 years (range: 2 months-55 years) and mean duration of uncontrolled seizures of 16 years (range: 2 months-47 years) eventually underwent a surgical procedure. 30/40 patients were on high dose antiepileptic polytherapy. Optimum MR detected structural abnormalities, confined to a limited brain area, in 39 patients. These abnormalities were of space-occupying nature in 21 cases; an atrophic lesion was suspected in 17 patients. Structural abnormalities were most frequently located in the temporal lobe (n = 26) and the frontal lobe (n = 7). Video-EEG monitoring documented complex partial seizures in 32 patients with occasional secondary generalisation in 14. In most of these patients, seizures could be subclassified as being of temporal lobe origin based on clinical and EEG criteria. Two patients had only simple partial seizures. One patient with Sturge-Weber syndrome and a strictly unilateral angioma had hemiconvulsions. A mentally retarded patient with Lennox-Gastaut syndrome had different types of seizures. After non-invasive and invasive exploration, the area of seizure onset could be determined in all patients. Standard or modified temporal lobectomy +/- hippocampectomy were the most commonly performed procedures (n = 26). In 5 patients complete lesionectomies were performed for epileptogenic structural lesions in and outside the temporal lobe. In 2 patients only partial lesionectomies were possible; in 5 patients only biopsies could be performed. Anterior 2/3 callosotomy and hemispherectomy were each performed in one patient. Postsurgical seizure control, after average follow-up of 20 months (range: 6-40 months), was excellent in 27 patients who became seizure-free. In these patients antiepileptic therapy was tapered 2 years after surgery. An additional 4 patients continue to experience non-disabling simple partial seizures only. Patients in whom only biopsies or partial lesionectomies were performed have poor seizure control. Three patients died as a result of the intrinsic malignancy of their space-occupying lesion. Two patients who are seizure free experienced a moderate postoperative hemiparesis with subtotal recovery. Overall quality of life was substantially improved both in patients who became entirely seizure free or who experienced a very significant reduction in seizure frequency. Presurgical evaluation and epilepsy surgery are a labour intensive but rewarding therapeutic alternative for patients with medically refractory epilepsy. Besides providing therapeutic efficacy, comprehensive presurgical evaluation and epilepsy surgery allow for fruitful clinical neurological research.

Endoscopic management of craniopharyngiomas: a review of 3 cases

The authors describe the endoscopic management of cystic craniopharyngiomas in 3 cases. This method has been attempted in cystic craniopharyngiomas using a rigid endoscope. The instrument has been described earlier (7-9). All these operations were done under general anaesthesia. Criteria for endoscopic extirpation and removal included type D, E, F classification according to Yasargil (17). All 3 cases fitted in the F category. There were one female and two male patients. In the female patient an aspiration of cyst contents was performed as a first attempt to relieve her hydrocephalus. Two months later recurrent symptomology necessitated a larger intervention. All cysts were opened using the laser, drained by a Fogarthy balloon-catheter, and the capsule removed by forceps. This technique is safe and provides a reasonable alternative to open microsurgery, radioactive isotope instillation, or radiotherapy. In our series we achieved total removal in one case after the second intervention and partial removal in two cases. There was no mortality directly associated with this procedure and the female patient developed severe electrolyte disturbances after macroscopic total removal. Our results suggest that endoscopic of management of cystic craniopharyngiomas is a safe and effective procedure which could be considered as the initial management for cystic craniopharyngiomas of the intraventricular type.

Trans-sternal approach to intraspinal tumours in the upper thoracic region

The surgical management of ventrally located intraspinal tumours is often difficult, particularly in the upper thoracic region. The anterior approach to these tumours is hindered by anatomical structures. We report our experience using the trans-sternal approach. Three patients with intraspinal tumour between T1 and T4 underwent this approach. The surgical technique, the clinical presentation, the radiological features and the results are presented.

Clinical and neurophysiological correlations in patients with refractory partial epilepsy and intracranial structural lesions

Twenty patients (13 males, 7 females), who presented with refractory partial epilepsy and a CT and/or MR detected intracranial intra-axial structural lesion were admitted to the University of Gent Epilepsy Monitoring Unit. Mean duration of the epilepsy was 17 years (2-47 years). All patients were enrolled in a comprehensive presurgical protocol including neurological examination, video-scalp-EEG monitoring with prolonged interictal and ictal recording, neuropsychological assessment and positron emission tomography (PET). Intracranial EEG monitoring was performed in 5 patients in whom discrepancies between different tests were found during the non-invasive evaluation. Clinical neurological examination was normal in 16 patients; 4 patients had a mild contralateral hemiparesis. Lesions were mainly located in the temporal lobe (55%). Most patients presented with complex partial seizures (90%). Clinical seizure characteristics correlated well with the lesion location in 55% of patients. Interictal EEG showed focal epileptic activity and focal slowing in respectively 85% and 30% of patients. Interictal EEG lateralization was congruent with the side of the lesion in 17 patients (85%). Interictal EEG localization was congruent with the lobe of the lesion in 13 patients (65%). Ictal EEG lateralized correctly in 14 patients (70%) and localized correctly in 10 patients (50%). Neuropsychological assessment lateralized and localized congruently in respectively 8/17 (47%) and 7/17 (41%) of patients. Interictal PET showed focal interictal hypometabolism, congruent with the lesion, in 13/16 (81%) of patients. Intracranial EEG was congruent with the lesion location in 3 patients but non-congruent in 2 patients. All patients underwent surgical procedures: average follow-up was 14 months (6-24 months). Complete surgical removal of the lesion with free margins resulted in a more than 90% reduction of seizures without postoperative neurological deficit in 12/13 patients.

A large intracranial xanthoma in familial hypercholesterolemia

Intracranial xanthomata occurring in patients with familial hypercholesterolemia are very rare. We present a young woman with a large intracranial xanthoma. The patient was treated for a familial hyperlipoproteinemia type IIa. MRI and morphological features are shown and discussed on reviewing the literature.

A multipurpose cerebral endoscope and reflections on technique and instrumentation in endoscopic neurosurgery

We discuss our experiences concerning our cerebral endoscope with reflections on various techniques used since 1986. During this time we have had experience with four prototypes. This minimal invasive procedure has been successful to a certain extent both in paediatric and adult patients, stereotactically and by freehand method or both. Further modification for flexibility and manipulation of the optic element is under development.

Endoscopic diagnosis and treatment of para- and intra-ventricular cystic lesions

Different cystic lesions can be located in or around the ventricular system, eventually causing hydrocephalus. Twenty-one patients are described where endoscopic intervention, mainly large fenestration towards the ventricular cavity, has been performed. This treatment can sometimes replace open surgery or extracranial shunting. Most rewarding are the arachnoid and ependymal intra- and paraventricular cysts. With careful and adequate endoscopic technique this procedure is safe and much less invasive than other methods described.

Diagnostic and therapeutic stereotactic cerebral endoscopy

Modern neuro-imaging caused a renewed interest in endoscopic techniques. Several indications for stereotactic endoscopy are illustrated. A prototype of a new four channel endoscope is used. Lesions in the posterior part of the third ventricle an even the fourth ventricle are reachable for biopsy. Cystic intra- or paraventricular lesions can be approached stereotactically and treated. Continuous rinsing is mandatory to preserve a clear vision.

Transventricular endoscopic investigation and treatment of suprasellar arachnoid cysts

Three children with a suprasellar arachnoid cyst and characteristic neuropathological signs are presented. Through the use of CT scanning and NMR imaging the location, volume and attenuation factors of these cysts can be documented. Stereotactically guided endoscopic exploration of the third ventricle region with visualization and manipulation of the cyst have been performed. This technique should be considered a safe and accurate alternative to craniotomy.

Endoscopic treatment of suprasellar arachnoid cysts

Four cases of large suprasellar arachnoid cysts in children are described. The authors propose a large fenestration into the lateral ventricles and into the basal cisterns as the treatment of choice. A specific multipurpose cerebral endoscope has been designed by the first author. The endoscopic technique with different instruments and with the use of a laser is illustrated. Results and complications are discussed.

Leptomeningeal cyst: early diagnosis by color Doppler imaging

A newborn with a leptomeningeal cyst over the anterior fontanelle due to birth trauma is described. Color Doppler flow sonograms were helpful to diagnose the leptomeningocele in its early stages and to differentiate it from a cephalhematoma or subgaleal haemorrhage by demonstrating cerebro-fugal flow in an arterial connection between the extracranial fluid collection and the dural space.

Transesophageal echocardiography: a simple method for monitoring the patency of ventriculoatrial shunts. Technical note

A new method for evaluating the patency of a ventriculoatrial shunt is described, and early experience with it is reported. Transesophageal echocardiography can demonstrate a cerebrospinal fluid leak in the right atrium through the atrial tip of a shunting device. This capability was an incidental discovery, and since then the accuracy of the technique in evaluating the patency of a ventriculoatrial shunt has been prospectively studied in 20 observations of 16 patients. The method proved to be accurate in 90% to 100% of cases. It is concluded that transesophageal echocardiography offers a rapid and accurate assessment of ventriculoatrial shunt function, is well tolerated, and is easy to perform.

Spinal cord stimulation in chronic pain: evaluation of results, complications, and technical considerations in sixty-nine patients

Sixty-nine patients undergoing spinal cord stimulation (SCS) were studied for a period of up to 8 years. Indications, implantation techniques, and stimulation systems are presented in this article. Pain-suppressor effects of SCS are reviewed, assessing the clinical efficacy over time as well as complications with the stimulation device. Immediately following implantation, inadequate pain relief was noted in 20% of the patients. Decrease of the efficacy of pain alleviation occurs during the first 3 years after implantation. Most failures are noted in patients presenting with failed back surgery. This study also demonstrates that SCS systems should offer the capability of both monopolar and bipolar stimulation modes by the use of multipolar electrodes.

Spinal cord stimulation in chronic pain therapy

Spinal cord stimulation was undertaken in 45 patients referred to the University Hospital in Ghent. Failed back surgery was the major indication for implantation. Raynaud's phenomenon, causalgia, polyneuropathy, phantom limb pain, and diverse causes were the other indications. Before neurosurgical implantation of the system, a percutaneous epidural trial procedure was performed. The efficacy of the implanted stimulation system was estimated by considering the use of medication and the patients' personal appreciation of the obtained pain relief. Thirty-five patients experienced very good pain relief. Only two patients needed further narcotic analgesics. Eight patients stopped using the stimulation system. To ensure good results, strict selection criteria and many surgical reinterventions seemed to be necessary. Although spinal cord stimulation is a nonablative technique, many complications may occur.