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Per Kristian Eide

OBJECTIVE

The objective of this study was to examine how pulsatile and static intracranial pressure (ICP) scores correlate with indices of intracranial pressure-volume reserve capacity, i.e., intracranial elastance (ICE) and intracranial compliance (ICC), as determined during ventricular infusion testing.

METHODS

All patients undergoing ventricular infusion testing and overnight ICP monitoring during the 6-year period from 2007 to 2012 were included in the study. Clinical data were retrieved from a quality registry, and the ventricular infusion pressure data and ICP scores were retrieved from a pressure database. The ICE and ICC (= 1/ICE) were computed during the infusion phase of the infusion test.

RESULTS

During the period from 2007 to 2012, 82 patients with possible treatment-dependent hydrocephalus underwent ventricular infusion testing within the department of neurosurgery. The infusion tests revealed a highly significant positive correlation between ICE and the pulsatile ICP scores mean wave amplitude (MWA) and rise-time coefficient (RTC), and the static ICP score mean ICP. The ICE was negatively associated with linear measures of ventricular size. The overnight ICP recordings revealed significantly increased MWA (> 4 mm Hg) and RTC (> 20 mm Hg/sec) values in patients with impaired ICC (< 0.5 ml/mm Hg).

CONCLUSIONS

In this study cohort, there was a significant positive correlation between pulsatile ICP and ICE measured during ventricular infusion testing. In patients with impaired ICC during infusion testing (ICC < 0.5 ml/mm Hg), overnight ICP recordings showed increased pulsatile ICP (MWA > 4 mm Hg, RTC > 20 mm Hg/sec), but not increased mean ICP (< 10–15 mm Hg). The present data support the assumption that pulsatile ICP (MWA and RTC) may serve as substitute markers of pressure-volume reserve capacity, i.e., ICE and ICC.

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Per Kristian Eide

OBJECTIVE

The pathophysiology of chronic noncommunicating hydrocephalus (ncHC) is poorly understood. This present study explored whether lessons about the pathophysiology of this clinical entity might be retrieved from results of overnight monitoring of pulsatile and static intracranial pressure (ICP) and ventricular infusion testing.

METHODS

The study cohort included adult patients (> 20 years of age) with chronic ncHC due to aqueductal stenosis in whom symptoms had lasted a minimum of 6 months. A reference cohort consisted of age- and sex-matched patients managed for communicating HC (cHC). Information about symptoms and clinical improvement following surgery was retrieved from a quality register, and results of overnight ICP recordings and ventricular infusion testing were retrieved from the hospital ICP database.

RESULTS

The cohort with ncHC consisted of 61 patients of whom 6 (10%) were managed conservatively, 34 (56%) by endoscopic third ventriculostomy (ETV), and 21 (34%) using ETV and subsequent shunt surgery. In patients responding to surgery, pulsatile ICP (mean ICP wave amplitude) was significantly increased to a similar magnitude in patients with ncHC and the reference cohort (cHC). Furthermore, intracranial compliance (ICC) was reduced in clinical responders. The results of ventricular infusion testing provided evidence that patients responding to ETV have impaired ventricular CSF absorption, while those requiring shunt placement after ETV present with impaired CSF absorption both in the intraventricular and extraventricular compartments.

CONCLUSIONS

The study may provide some lessons about the pathophysiology of chronic ncHC. First, increased pulsatile ICP and impaired ICC characterize patients with chronic ncHC who respond clinically to CSF diversion surgery, even though static ICP is not increased. Second, in patients responding clinically to ETV, impaired ventricular CSF absorption may be a key factor. Patients requiring shunt placement for clinical response appear to have both intraventricular and extraventricular CSF absorption failure. A subgroup of patients with ncHC due to aqueductal stenosis has normal ventricular CSF absorption and normal ICC and may not be in need of surgical CSF diversion.

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Per Kristian Eide and Tryggve Lundar

Arne Torkildsen was a pioneering Norwegian neurosurgeon who introduced the ventriculocisternal shunt, the first clinically successful shunt for CSF diversion in hydrocephalus. The procedure, usually referred to as ventriculocisternostomy (VCS), Torkildsen’s operation, orTorkildsen’s shunt, became internationally recognized as an efficient operation for the treatment of noncommunicating hydrocephalus. The operation gained widespread use in the 1940s and 1950s before the introduction of extracranial shunts. In this paper, the authors look more closely at Torkildsen’s development of the VCS and examine how this surgical approach differed from other procedures for treating hydrocephalus before World War II. Long-term results of the VCS are presented.

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Terje Sæhle and Per Kristian Eide

OBJECT

In patients with hydrocephalus and shunts, lasting symptoms such as headache and dizziness may be indicative of shunt failure, which may necessitate shunt revision. In cases of doubt, the authors monitor intracranial pressure (ICP) to determine the presence of over- or underdrainage of CSF to tailor management. In this study, the authors reviewed their experience of ICP monitoring in shunt failure. The aims of the study were to identify the complications and impact of ICP monitoring, as well as to determine the mean ICP and characteristics of the cardiac-induced ICP waves in pediatric versus adult over- and underdrainage.

METHODS

The study population included all pediatric and adult patients with hydrocephalus and shunts undergoing diagnostic ICP monitoring for tentative shunt failure during the 10-year period from 2002 to 2011. The patients were allocated into 3 groups depending on how they were managed following ICP monitoring: no drainage failure, overdrainage, or underdrainage. While patients with no drainage failure were managed conservatively without further actions, over- or underdrainage cases were managed with shunt revision or shunt valve adjustment. The ICP and ICP wave scores were determined from the continuous ICP waveforms.

RESULTS

The study population included 71 pediatric and 75 adult patients. There were no major complications related to ICP monitoring, but 1 patient was treated for a postoperative superficial wound infection and another experienced a minor bleed at the tip of the ICP sensor. Following ICP monitoring, shunt revision was performed in 74 (51%) of 146 patients, while valve adjustment was conducted in 17 (12%) and conservative measures without any actions in 55 (38%). Overdrainage was characterized by a higher percentage of episodes with negative mean ICP less than −5 to −10 mm Hg. The ICP wave scores, in particular the mean ICP wave amplitude (MWA), best differentiated underdrainage. Neither mean ICP nor MWA levels showed any significant association with age.

CONCLUSIONS

In this cohort of pediatric and adult patients with hydrocephalus and tentative shunt failure, the risk of ICP monitoring was very low, and helped the authors avoid shunt revision in 49% of the patients. Mean ICP best differentiated overdrainage, which was characterized by a higher percentage of episodes with negative mean ICP less than −5 to −10 mm Hg. Underdrainage was best characterized by elevated MWA values, indicative of impaired intracranial compliance.

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Radek Frič and Per Kristian Eide

OBJECTIVE

Several lines of evidence suggest common pathophysiological mechanisms in Chiari malformation Type I (CMI) and idiopathic intracranial hypertension (IIH). It has been hypothesized that tonsillar ectopy, a typical finding in CMI, is the result of elevated intracranial pressure (ICP) combined with a developmentally small posterior cranial fossa (PCF). To explore this hypothesis, the authors specifically investigated whether ICP is comparable in CMI and IIH and whether intracranial volumes (ICVs) are different in patients with CMI and IIH, which could explain the tonsillar ectopy in CMI. The authors also examined whether the symptom profile is comparable in these 2 patient groups.

METHODS

The authors identified all CMI and IIH patients who had undergone overnight diagnostic ICP monitoring during the period from 2002 to 2014 and reviewed their clinical records and radiological examinations. Ventricular CSF volume (VV), PCF volume (PCFV), and total ICV were calculated from initial MRI studies by using volumetric software. The static and pulsatile ICP scores during overnight monitoring were analyzed. Furthermore, the authors included a reference (REF) group consisting of patients who had undergone ICP monitoring due to suspected idiopathic normal-pressure hydrocephalus or chronic daily headache and showed normal pressure values.

RESULTS

Sixty-six patients with CMI and 41 with IIH were identified, with comparable demographics noted in both groups. The occurrence of some symptoms (headache, nausea, and/or vomiting) was comparable between the cohorts. Dizziness and gait ataxia were significantly more common in patients with CMI, whereas visual symptoms, diplopia, and tinnitus were significantly more frequent in patients with IIH. The cranial volume measurements (VV, PCFV, and ICV) of the CMI and IIH patients were similar. Notably, 7.3% of the IIH patients had tonsillar descent qualifying for diagnosis of CMI (that is, > 5 mm). The extent of tonsillar ectopy was significantly different between the CMI and IIH cohorts (p < 0.001) but also between these 2 cohorts and the REF group. Pulsatile ICP was elevated in both cohorts without any significant between-group differences; however, static ICP was significantly higher (p < 0.001) in the IIH group.

CONCLUSIONS

This study showed comparable and elevated pulsatile ICP, indicative of impaired intracranial compliance, in both CMI and IIH cohorts, while static ICP was higher in the IIH cohort. The data did not support the hypothesis that reduced PCFV combined with increased ICP causes tonsillar ectopy in CMI. Even though impaired intracranial compliance seems to be a common pathophysiological mechanism behind both conditions, the mechanisms explaining the different clinical and radiological presentations of CMI and IIH remain undefined.

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Per Kristian Eide and Wilhelm Sorteberg

Object

In this study, the authors compare simultaneous measurements of static and pulsatile pressure parameters in the epidural space and brain parenchyma of hydrocephalic patients.

Methods

Simultaneous intracranial pressure (ICP) signals from the epidural space (ICPEPI) and the brain parenchyma (ICPPAR) were compared in 12 patients undergoing continuous ICP monitoring as part of their diagnostic workup for hydrocephalus. The static ICP was characterized by mean ICP and the frequency of B waves quantified in the time domain, while the pulsatile ICP was determined from the cardiac beat–induced single ICP waves and expressed by the ICP pulse pressure amplitude (dP) and latency (dT; that is, rise time).

Results

The 12 patients underwent a median of 22.5 hours (range 5.9–24.8 hours) of ICP monitoring. Considering the total recording period of each patient, the mean ICP (static ICP) differed between the 2 compartments by ≥ 5 mm Hg in 8 patients (67%) and by ≥ 10 mm Hg in 4 patients (33%). In contrast, for every patient the ICP pulse pressure readings from the 2 compartments showed near-identical results. Consequently, when sorting patients to shunt/no shunt treatment according to pulsatile ICP values, selection was independent of sensor placement. The frequency of B waves also compared well between the 2 compartments.

Conclusions

The pulsatile ICP is measured with equal confidence from the ICPEPI and ICPPAR signals. When using the pulsatile ICP for evaluation of hydrocephalic patients, valid measurements may thus be obtained from pressure monitoring in the epidural space. Recorded differences in the mean ICP between the epidural space and the brain parenchyma are best explained by differences in the zero setting of different sensors.

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Geir Ringstad, Kyrre Eeg Emblem and Per Kristian Eide

OBJECT

The objective of this study was to assess the net aqueductal stroke volume (ASV) and CSF aqueductal flow rate derived from phase-contrast MRI (PC-MRI) in patients with probable idiopathic normal pressure hydrocephalus (iNPH) before and after ventriculoperitoneal shunt surgery, and to compare observations with intracranial pressure (ICP) scores.

METHODS

PC-MRI at the level of the sylvian aqueduct was undertaken in patients undergoing assessment for probable iNPH. Aqueductal flow in the craniocaudal direction was defined as positive, or antegrade flow, and net ASV was calculated by subtracting retrograde from antegrade aqueductal flow. Aqueductal flow rate per minute was calculated by multiplying net ASV by heart rate. During the same hospital admission, clinical examination was performed using NPH score and overnight continuous ICP monitoring. Twelve patients were followed prospectively 12 months after shunt placement with clinical assessment and a second PC-MRI. The study also included 2 healthy controls.

RESULTS

Among 21 patients examined for iNPH, 17 (81%) received a shunt (shunt group), and 4 were treated conservatively (conservative group). Among the patients with shunts, a clinical improvement was observed in 16 (94%) of the 17. Net ASV was negative in 16 (76%) of 21 patients before shunt placement and in 5 (42%) of 12 patients after shunt placement, and increased from a median of −5 μl (range −175 to 27 μl) to a median of 1 μl (range −61 to 30 μl; p = 0.04). Among the 12 patients with PC-MRI after shunt placement, 11 were shunt responders, and in 9 of these 11 either a reduced magnitude of retrograde aqueductal flow, or a complete reversal from retrograde to antegrade flow, occurred. Net ASV was significantly lower in the shunt group than in the conservative group (p = 0.01). The aqueductal flow rate increased from −0.56 ml/min (range −12.78 to 0.58 ml/min) to 0.06 ml/min (range −4.51 to 1.93 ml/min; p = 0.04) after shunt placement.

CONCLUSIONS

In this cohort of patients with iNPH, retrograde net aqueductal flow was observed in 16 (76%) of 21 patients. It was reversed toward the antegrade direction after shunt placement either by magnitude or completely in 9 (75%) of 12 patients examined using PC-MRI both before and after shunt placement (p = 0.04); 11 of the 12 were shunt responders. The study results question previously established concepts with respect to both CSF circulation pathways and CSF formation rate.

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Tiril Sandell, Jostein Holmen and Per Kristian Eide

Object

Although essential arterial hypertension (AH) represents a major health issue, its underlying causes remain unknown. An intriguing hypothesis is that AH in some cases may be caused by vascular compression of the rostral ventrolateral medulla (RVLM). Because hemifacial spasms (HFSs) are caused by vascular compression of the seventh cranial nerve in close proximity to the RVLM, one would, if this hypothesis is correct, expect to find a positive association between the occurrence of AH and chronic HFSs. Such a positive association would not be expected in patients with trigeminal neuralgia (TN), since TN is caused by vascular compression of the fifth cranial nerve, which is not close to the RVLM.

Methods

In view of this background, the authors conducted a retrospective population-based study to investigate how the occurrence of AH in patients with either HFSs or TN compares with the prevalence of AH in the general population, when adjusted for sex and age. The general population was represented by participants of the Nord-Trøndelag Health Study 3 (HUNT3).

Results

The prevalence of AH in the authors' patients with HFSs was significantly higher than in a sex- and age-adjusted sample from the general population; this was not true for the patients with TN.

Conclusions

The authors suggest that the data provide supporting evidence to the theory that compression of the RVLM may be one cause of AH.

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Erlend Aambø Langvatn, Radek Frič, Bernt J. Due-Tønnessen and Per Kristian Eide

OBJECTIVE

Reduced intracranial volume (ICV) and raised intracranial pressure (ICP) are assumed to be principal pathophysiological mechanisms in childhood craniosynostosis. This study examined the association between ICV and ICP and whether ICV can be used to estimate the ICP.

METHODS

The authors analyzed ICV and ICP measurements from children with craniosynostosis without concurrent hydrocephalus and from age-matched individuals without craniosynostosis who underwent diagnostic ICP measurement.

RESULTS

The study included 19 children with craniosynostosis (mean age 2.2 ± 1.9 years) and 12 reference individuals without craniosynostosis (mean age 2.5 ± 1.6 years). There was no difference in ICV between the patient and reference cohorts. Both mean ICP (17.1 ± 5.6 mm Hg) and mean wave amplitude (5.9 ± 2.6 mm Hg) were higher in the patient cohort. The results disclosed no significant association between ICV and ICP values in the patient or reference cohorts, and no association was seen between change in ICV and ICP values after cranial vault expansion surgery (CVES) in 5 children in whom ICV and ICP were measured before and after CVES.

CONCLUSIONS

In this cohort of children with craniosynostosis, there was no significant association between ICV and ICP values prior to CVES and no significant association between change in ICV and ICP values after CVES in a subset of patients. Therefore, ICV could not reliably estimate the ICP values. The authors suggest that intracranial hypertension in childhood craniosynostosis may not be caused by reduced ICV alone but rather by a distorted relationship between ICV and the volume of intracranial content (brain tissue, CSF, and blood).

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Eun-Hyoung Park, Per Kristian Eide, David Zurakowski and Joseph R. Madsen

Object

The pathophysiology of normal pressure hydrocephalus (NPH), and the related problem of patient selection for treatment of this condition, have been of great interest since the description of this seemingly paradoxical condition nearly 50 years ago. Recently, Eide has reported that measurements of the amplitude of the intracranial pressure (ICP) can both positively and negatively predict response to CSF shunting. Specifically, the fraction of time spent in a “high amplitude” (> 4 mm Hg) state predicted response to shunting, which may represent a marker for hydrocephalic pathophysiology. Increased ICP amplitude might suggest decreased brain compliance, meaning a static measure of a pressure-volume ratio. Recent studies of canine data have shown that the brain compliance can be described as a frequency-dependent function. The normal canine brain seems to show enhanced ability to absorb the pulsations around the heart rate, quantified as a cardiac pulsation absorbance (CPA), with properties like a notch filter in engineering. This frequency dependence of the function is diminished with development of hydrocephalus in dogs. In this pilot study, the authors sought to determine whether frequency dependence could be observed in humans, and whether the frequency dependence would be any different in epochs with high ICP amplitude compared with epochs of low ICP amplitude.

Methods

Systems analysis was applied to arterial blood pressure (ABP) and ICP waveforms recorded from 10 patients undergoing evaluations of idiopathic NPH to calculate a time-varying transfer function that reveals frequency dependence and CPA, the measure of frequency-dependent compliance previously used in animal experiments. The ICP amplitude was also calculated in the same samples, so that epochs with high (> 4 mm Hg) versus low (≤ 4 mm Hg) amplitude could be compared in CPA and transfer functions.

Results

Transfer function analysis for the more “normal” epochs with low amplitude exhibits a dip or notch in the physiological frequency range of the heart rate, confirming in humans the pulsation absorber phenomenon previously observed in canine studies. Under high amplitude, however, the dip in the transfer function is absent. An inverse relationship between CPA index and ICP amplitude is evident and statistically significant. Thus, elevated ICP amplitude indicates decreased performance of the human pulsation absorber.

Conclusions

The results suggest that the human intracranial system shows frequency dependence as seen in animal experiments. There is an inverse relationship between CPA index and ICP amplitude, indicating that higher amplitudes may occur with a reduced performance of the pulsation absorber. Our findings show that frequency dependence can be observed in humans and imply that reduced frequency-dependent compliance may be responsible for elevated ICP amplitude observed in patients who respond to CSF shunting.