Publications by authors named "Zofia H Czosnyka"

25 Publications

  • Page 1 of 1

The Role of Cerebrospinal Fluid Dynamics in Normal Pressure Hydrocephalus Diagnosis and Shunt Prognostication.

Acta Neurochir Suppl 2021 ;131:359-363

Division of Neurosurgery, Department of Clinical Neuroscience, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.

Background: Over the years, there have been several reports and trials of the resistance to cerebrospinal fluid (CSF) outflow (Rout) in normal pressure hydrocephalus (NPH). This work aimed to revisit the utility of testing CSF circulation in a large population of patients clinically presenting with NPH.

Materials And Methods: We retrospectively analyzed the data of 369 NPH patients-either shunted or with endoscopic third ventriculostomy (ETV)-in Cambridge between 1992 and 2018. We determined the patients' outcomes (improvement versus no improvement at 6 months) by applying a threshold on R values and compared our results with those of existing literature. We also conducted a correlation analysis between all variables and calculated Chi-Statistics (as a measure of separability between improvement and no improvement outcomes) to determine a subset of variables which achieved the highest accuracy in prediction of outcome.

Results: In our dataset, R of 18 mmHg*min/mL achieved the highest Chi-statistics of 9.7 with p-value <0.01 when adjusted for age. In addition to R , intracranial pressure (ICP) values at the baseline and plateau, CSF production rate and ICP amplitude to slope ratio showed significant Chi-Statistics values (more than 5). Using these variables, an overall accuracy of 0.70 ± 0.09 was achieved for prediction of the shunt outcome.

Conclusion: Rout can be used for selecting patients for shunt surgery but not for excluding patients from treatment. Critical, multivariable approaches are required to comprehend CSF dynamics and pressure-volume compensation in NPH. Outcome definition and assessment could also be brought to question.
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http://dx.doi.org/10.1007/978-3-030-59436-7_69DOI Listing
June 2021

Comparison of Assessment for Shunting with Infusion Studies Versus Extended Lumbar Drainage in Suspected Normal Pressure Hydrocephalus.

Acta Neurochir Suppl 2021 ;131:355-358

Division of Neurosurgery, Department of Clinical Neuroscience, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.

Introduction: Tools available for diagnosis of normal pressure hydrocephalus (NPH) and prediction of shunt-response are overnight ICP monitoring, infusion studies, and extended lumbar drainage (ELD). We investigated the shunt-response predictive value by infusion tests versus ELD.

Material And Methods: We retrospectively recruited 83 patients who had undergone both infusion study and ELD assessments and compared infusion study hydrodynamics with improvement at clinic follow-up after ELD and after shunting.

Results: 62 patients had Rout >11 mmHg/mL/min. 28 Showed physiotherapy-documented improvement following ELD, and were selected for shunting, of which 21 were shunted. Of these, 19 showed improvement. Eight patients with Rout >20 mmHg/mL/min showed no response to ELD and were not shunted.There were 21 patients with Rout <11 mmHg/mL/min: five were shunted, showed improvement at follow-up, and had Rout >6 mmHg/mL/min. ICP amplitude did not differ at baseline or plateau between responders and non-responders.

Conclusions: ELD response and CSF dynamics differed remarkably. All patients with Rout <6 mmHg/mL/min showed no improvement with ELD, indicating that ELD and shunting might be contraindicated in these subjects. High Rout patients with no response to ELD could merit further consideration.
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http://dx.doi.org/10.1007/978-3-030-59436-7_68DOI Listing
June 2021

Global Cerebral Autoregulation, Resistance to Cerebrospinal Fluid Outflow and Cerebrovascular Burden in Normal Pressure Hydrocephalus.

Acta Neurochir Suppl 2021 ;131:349-353

Neurosurgery Unit, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.

Introduction: We previously examined the relationship between global autoregulation pressure reactivity index (PRx), mean arterial blood pressure (ABP), Resistance to cerebral spinal fluid (CSF) outflow (Rout) and their possible effects on outcome after surgery on 83 shunted patients. In this study, we aimed to quantify the relationship between all parameters that influence Rout, their interaction with the cerebral vasculature, and their role in shunt prognostication.

Methods: From 423 patients having undergone infusion tests for possible NPH, we selected those with monitored ABP and calculated its mean and PRx. After shunting, 6 months patients' outcome was marked using a simple scale (improvement, temporary improvement, and no improvement). We explored the relationship between age, different CSF dynamics variables, and vascular parameters using multivariable models.

Results: Rout had a weaker predictive value than ABP (Fisher Discrimination Ratio of 0.02 versus 0.42). ABP > 98 was an independent predictor of shunt outcome with odd ratio 6.4, 95% CI: 1.8-23.4 and p-value = 0.004. There was a strong and significant relationship between the interaction of age, PRx, ABP, and Rout (R = 0.53 with p = 7.28 × 10). Using our linear model, we achieved an AUC 86.4% (95% CI: 80.5-92.3%) in detecting shunt respondents. The overall sensitivity was 94%, specificity 75%, positive predictive value (PPV) of 54%, and negative predictive value of 97%.

Conclusion: In patients with low Rout and high cerebrovascular burden, as described by high ABP and disturbed global autoregulation, response to shunting is less likely. The low PPV of high resistance, preserved autoregulation and absence of hypertension could merit further exploration.
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http://dx.doi.org/10.1007/978-3-030-59436-7_67DOI Listing
June 2021

Differences in Cerebrospinal Fluid Dynamics in Posttraumatic Hydrocephalus Versus Atrophy, Including Effect of Decompression and Cranioplasty.

Acta Neurochir Suppl 2021 ;131:343-347

Division of Neurosurgery, Department of Clinical Neuroscience, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.

Introduction: Challenges in diagnosing post-traumatic hydrocephalus (PTH) have created a need for an accurate diagnostic tool. We aim to report CSF dynamics in PTH and atrophy, along with differences before and after cranioplasty.

Methods: We retrospectively analyzed traumatic brain injury patients with ventriculomegaly who had infusion studies. We divided patients depending on CSF dynamics into two groups: 'likely PTH' (A) and 'likely atrophy' (B). A group of idiopathic normal pressure hydrocephalus shunt-responsive patients was used for comparison (C).

Results: Group A consisted of 36 patients who were non-decompressed or had a cranioplasty in situ for over 1 month. Group B included 16 patients with low Rout, AMP, and dAMP, 9 of whom were decompressed. Rout and dAMP were significantly higher in Group A than B, but significantly lower than Group C (45 iNPH patients). RAP change during infusion in group A indicated depleted compensatory reserve compared to ample reserve in group B. Repeat studies in five decompressed patients post-cranioplasty showed all parameters increased.

Conclusions: Infusion tests are not useful in decompressed patients, whilst cranioplasty allowed differentiation between possible PTH and atrophy. Rout and AMP were significantly lower in PTH compared to iNPH and did not always reflect the degree of hydrocephalus reported on imaging.
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http://dx.doi.org/10.1007/978-3-030-59436-7_66DOI Listing
June 2021

Single Center Experience in Cerebrospinal Fluid Dynamics Testing.

Acta Neurochir Suppl 2021 ;131:311-313

Division of Neurosurgery, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.

Normal pressure hydrocephalus is more complex than a simple disturbance of the cerebrospinal fluid (CSF) circulation. Nevertheless, an assessment of CSF dynamics is key to making decisions about shunt insertion, shunt malfunction, and for further management if a patient fails to improve. We summarize our 25 years of single center experience in CSF dynamics assessment using pressure measurement and analysis. 4473 computerized infusion tests have been performed. We have shown that CSF infusion studies are safe, with incidence of infection at less than 1%. Raised resistance to CSF outflow positively correlates (p < 0.014) with improvement after shunting and is associated with disturbance of cerebral blood flow and its autoregulation (p < 0.02). CSF infusion studies are valuable in assessing possible shunt malfunction in vivo and for avoiding unnecessary revisions. Infusion tests are safe and provide useful information for clinical decision-making for the management of patients suffering from hydrocephalus.
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http://dx.doi.org/10.1007/978-3-030-59436-7_58DOI Listing
June 2021

Lower Breakpoint of Intracranial Amplitude-Pressure Relationship in Normal Pressure Hydrocephalus.

Acta Neurochir Suppl 2021 ;131:307-309

Academic Neurosurgery, Cambridge University Hospital, Cambridge, UK.

The relationship between intracranial pulse amplitude (AMP) and mean intracranial pressure (ICP) has been previously described. Generally, AMP increases proportionally to rises in ICP. However, at low ICP a lower breakpoint (LB) of amplitude-pressure relationship can be observed, below which pulse amplitude stays constant when ICP varies. Theoretically, below this breakpoint, the pressure-volume relationship is linear (good compensatory reserve, brain compliance stays constant); above the breakpoint, it is exponential (brain compliance decreases with rising ICP).Infusion tests performed in 169 patients diagnosed for idiopathic normal pressure hydrocephalus (iNPH) during the period 2004-2013 were available for analysis. A lower breakpoint was observed in 62 patients diagnosed for iNPH. Improvement after shunt surgery in patients in whom LB was recorded was 77% versus 90% in patients where LB was absent (p < 0.02). There was no correlation between improvement and slope of amplitude-pressure line above LB.The detection of a lower breakpoint is associated with less frequent improvement after shunting in NPH. It may be interpreted that cerebrospinal fluid dynamics of patients working on the flat part of the pressure-volume curve and having a 'luxurious' compensatory reserve, are more frequently caused by brain atrophy, which is obviously not responding to shunting.
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http://dx.doi.org/10.1007/978-3-030-59436-7_57DOI Listing
June 2021

Analysis of Intracranial Pressure Pulse-Pressure Relationship: Experimental Validation.

Acta Neurochir Suppl 2021 ;131:279-282

Faculty of Electronics and Information Technology, Institute of Electronic Systems, Warsaw University of Technology, Warsaw, Poland.

The slope of linear relationship between the amplitude of pulsations in intracranial pressure (ICP) versus mean ICP has recently been suggested as a useful guide for selecting patients for shunt surgery in normal pressure hydrocephalus (NPH). To better understand how the pathophysiology of cerebral circulation influences this parameter, we aimed to study the relationship between mean pressure and pulsation amplitude in a wide range of conditions affecting cerebrovascular tone and ICP in experimental conditions.We retrospectively analysed experimental material collected previously. Three physiological manoeuvres were studied in 29 New Zealand white rabbits: lumbar infusion with an infusion rate ≤0.2 mL/min to induce mild intracranial hypertension (n = 43), sympathetic blockade to induce arterial hypotension (n = 19), and modulation of the ventilator tidal volume, simultaneously influencing arterial carbon dioxide partial pressure (PaCO) to induce hypocapnia or hypercapnia (n = 17). We investigated whether the slope of the pulse amplitude (AMP)-ICP line depended on PaCO and arterial blood pressure (ABP) changes.We found a linear correlation between AMP-ICP and ICP with positive slope. Regression of slope against mean ABP showed a negative dependence (p = 0.03). In contrast, the relationship between slope and PaCO was positive, although not reaching statistical significance (p = 0.18).The slope of amplitude-pressure line is strongly modulated by systemic vascular variables and therefore should be taken as a descriptor of cerebrospinal fluid dynamics with great care.
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http://dx.doi.org/10.1007/978-3-030-59436-7_52DOI Listing
June 2021

External Hydrocephalus After Traumatic Brain Injury: Retrospective Study of 102 Patients.

Acta Neurochir Suppl 2021 ;131:35-38

Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neuroscience, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK.

Introduction: External hydrocephalus (EH) refers to impairment of extra-axial cerebrospinal fluid flow with enlargement of the subarachnoid space (SAS) and concomitant raised intracranial pressure (ICP). It is often confused with a subdural hygroma and overlooked, particularly when there is no ventricular enlargement. In this study, we aimed to describe the epidemiology of EH in a large population of adults with traumatic brain injury (TBI).

Methods: This observational, retrospective cohort study was conducted in adult patients who were admitted with TBI to the Department of Clinical Neuroscience at Addenbrooke's Hospital (Cambridge, UK) over a period of 3 years (2014-2017). Patients were included in the study if they had ICP monitoring and at least three CT scans within the first 21 days to assess SAS evolution. Patients who underwent a decompressive craniectomy were excluded. SAS was assessed individually on each CT scan by two independent investigators. ICP data were analysed with ICM+ software (Cambridge Enterprise Ltd., Cambridge, UK). Short-term and 6-month outcomes were examined. The groups of patients with and without EH were compared.

Results: Of the 102 patients included in the study, 30.4% developed EH after a delay of 2.98 ± 2.4 days. The initial Glasgow Coma Scale (GCS) scores did not differ between patients with and without EH. Subarachnoid haemorrhage was found to be the main risk factor for EH. Patients with EH required a significantly longer period of mechanical ventilation (+6.9 days), were more likely to have a tracheostomy (55% versus 33%), and had a longer stay in the intensive care unit (+8.5 days). ICP was higher during the 48 h after diagnosis of EH than during the previous 48 h. EH survivors had a lower mean Glasgow Outcome Scale Extended (GOS-E) score (4.6 versus 5.9, P = 0.031) and were more likely to receive a permanent shunt for secondary hydrocephalus (17.4% versus 1.8%, odds ratio 7.1).

Conclusion: In adults with TBI, EH remains insufficiently understood and probably underdiagnosed. This study showed that it is a frequent complication of TBI, with significant clinical consequences.
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http://dx.doi.org/10.1007/978-3-030-59436-7_8DOI Listing
June 2021

Development of normal pressure hydrocephalus following post-traumatic external hydrocephalus in an adult patient.

Br J Neurosurg 2020 Mar 12:1-4. Epub 2020 Mar 12.

Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.

We report the case of 74-year-old patient suspected of post-traumatic external hydrocephalus (EH) following a mild traumatic brain injury with a progressive neurological decline and a concomitant enlargement of subarachnoid spaces without ventriculomegaly on CT scan. A lumbar puncture revealed raised ICP and a careful CSF withdrawal was performed, resulting in an immediate neurological improvement, confirming the diagnosis of EH. During the 20-month follow-up, the patient presented progressive signs of normal pressure hydrocephalus (NPH): gait and cognitive decline, ventriculomegaly and the lumbar infusion study confirmed disturbed CSF dynamics. The patient underwent a ventriculoperitoneal shunt surgery, resulting in a long-lasting improvement.
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http://dx.doi.org/10.1080/02688697.2020.1738340DOI Listing
March 2020

Correlation between the total number of features of paediatric pseudotumour cerebri syndrome and cerebrospinal fluid pressure.

Childs Nerv Syst 2020 09 2;36(9):2003-2011. Epub 2020 Mar 2.

Paediatric Neurology, Department of Paediatrics, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge, CB2 0QQ, UK.

Purpose: Accurate diagnosis of pseudotumour cerebri syndrome (PTCS) in children is challenging. We aimed to see if the clinical and radiological assessment that is carried out before lumbar puncture could predict subsequently recorded CSF pressures, and thus whether it could be used to increase diagnostic certainty of paediatric PTCS.

Methods: We used internationally recognised diagnostic criteria to derive a list of clinical, brain neuroimaging and venography features that were accepted to be associated with a diagnosis of PTCS. We performed a retrospective cohort study of children referred to our centre with suspected PTCS, identifying the presence or absence of those features for each child at initial presentation. The sum total scores of the features that were present were correlated with the child's recorded CSF pressure.

Results: The sum total scores were significantly positively correlated with recorded CSF pressures. The positive correlation was seen when clinical and brain neuroimaging features were included alone, and the correlation was slightly stronger when venography features were included in addition.

Conclusion: Calculating the sum total of clinical, brain neuroimaging and venography features (where venography is performed) present at initial presentation can help in the management of children under investigation for PTCS. Children with high scores are more likely to have severely raised CSF pressures and thus may warrant more urgent LP investigations. By contrast, in children with subtle abnormalities in optic disc appearance such that disc oedema cannot be ruled out, a low score may add further reassurance and less urgency to proceed to LP.
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http://dx.doi.org/10.1007/s00381-020-04537-2DOI Listing
September 2020

Coupling of CSF and sagittal sinus pressure in adult patients with pseudotumour cerebri.

Acta Neurochir (Wien) 2020 05 12;162(5):1001-1009. Epub 2019 Dec 12.

Department of Radiology, Addenbrooke's Hospital, Cambridge, UK.

Objective: Pseudotumour cerebri syndrome (PTCS including idiopathic intracranial hypertension) is characterised by the symptoms and signs of raised cerebrospinal fluid pressure (CSFp) in the absence of ventricular dilatation or an intracranial mass lesion. Its aetiology is unknown in the majority of cases but there is much evidence for impaired CSF absorption. Traditionally, sagittal sinus pressure has been considered to be independent of CSF pressure in adults. However, the discovery of stenoses of intracranial venous sinuses and introduction of venous sinus stenting has highlighted the importance of the venous drainage in PTCS. In this study, we have explored the relationship between CSFp and SSp before and during a CSF infusion test and during CSF drainage.

Materials And Methods: Ten patients (9 females:1 male) with PTCS underwent infusion studies in parallel with direct retrograde cerebral venography. Both SSp and CSFp were recorded at a baseline and during CSFp elevation in a course of a CSF infusion test. The drainage of CSF after the CSF infusion was performed in 7 patients. In 5 cases, jugular venous pressure was also measured.

Results: CSFp and SSp including their amplitudes correlated significantly and strongly both at baseline (R = 0.96; p = 0.001) and during infusion (R = 0.92; p = 0.0026). During drainage, this correlation was maintained until SSp reached a stable value, whereas CSFp continued to decrease.

Conclusions: In this series of ten patients with PTCS, CSFp and SSp were coupled, both at baseline and during infusion. The implications of such coupling for the calculation of CSF outflow resistance are discussed.
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http://dx.doi.org/10.1007/s00701-019-04095-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7156361PMC
May 2020

Cerebrospinal fluid dynamics in pediatric pseudotumor cerebri syndrome.

Childs Nerv Syst 2020 01 19;36(1):73-86. Epub 2019 Jul 19.

Department of Clinical Neurosciences, Division of Neurosurgery, University of Cambridge, Hills Road, Cambridge, CB20QQ, UK.

Purpose: There is a growing body of evidence highlighting the importance of comprehensive intracranial pressure (ICP) values in pseudotumor cerebri syndrome (PTCS). Due to the highly dynamic nature of ICP, several methods of ICP monitoring have been established, including the CSF infusion study. We have performed a retrospective review of the CSF dynamics measurements for all pediatric patients investigated for PTCS in our center and examined their diagnostic value compared with clinical classification.

Methods: We retrospectively recruited 31 patients under 16 years of age investigated for PTCS by CSF infusion test. We used the clinically provided Friedman classification 13/31 patients with definite PTCS (group A), 13/31 with probable PTCS (group B), and 5/31 not PTCS (group C), to compare CSF dynamics in the 3 groups.

Results: CSF pressure (CSFp) was significantly increased in group A (29.18 ± 7.72 mmHg) compared with B (15.31 ± 3.47 mmHg; p = 1.644e-05) and C (17.51 ± 5.87; p = 0.01368). The amplitude (AMP) was higher in the definite (2.18 ± 2.06 mmHg) than in group B (0.68 ± 0.37; p = 0.01382). There was no in either CSFp or AMP between groups B and C. No lower breakpoint of the AMP-P line was observed in group A but was present in 2/13 and 2/5 patients in groups B and C. In group A, sagittal sinus pressure (SSp) and elasticity were the only parameters above threshold (p = 4.2e-06 and p = 0.001953, respectively), In group B, only the elasticity was significantly higher than the threshold (p = 004257). Group C did not have any of the parameters raised. The AUC of CSFp, elasticity, and SSp for the 3 groups was 93.8% (84.8-100% CI).

Conclusions: Monitoring of CSFp and its dynamics, besides providing a more precise methodology for measuring CSFp, could yield information on the dynamic parameters of CSFp that cannot be derived from CSFp as a number, accurately differentiating between the clinically and radiologically derived entities of PTCS.
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http://dx.doi.org/10.1007/s00381-019-04263-4DOI Listing
January 2020

Cerebral autoregulation, cerebrospinal fluid outflow resistance, and outcome following cerebrospinal fluid diversion in normal pressure hydrocephalus.

J Neurosurg 2018 03;130(1):154-162

1Division of Neurosurgery, University of Cambridge Department of Clinical Neuroscience, Addenbrooke's Hospital, Cambridge, United Kingdom; and.

Objective: Normal pressure hydrocephalus is not simply the result of a disturbance in CSF circulation, but often includes cardiovascular comorbidity and abnormalities within the cerebral mantle. In this study, the authors have examined the relationship between the global autoregulation pressure reactivity index (PRx), the profile of disturbed CSF circulation and pressure-volume compensation, and their possible effects on outcome after surgery.

Methods: The authors studied a cohort of 131 patients in whom a clinical suspicion of normal pressure hydrocephalus was investigated. Parameters describing CSF compensation and circulation were calculated during the CSF infusion test, and PRx was calculated from CSF pressure and mean arterial blood pressure (MAP) recordings. A simple scale was used to mark the patients’ outcome 6 months after surgery (improvement, temporary improvement, and no improvement).

Results: The PRx was negatively correlated with resistance to CSF outflow (R = -0.18; p = 0.044); patients with normal CSF circulation tended to have worse autoregulation. The correlation for patients who were surgically treated (n = 83) was R = -0.28; p = 0.01, and it was stronger in patients who experienced sustained improvement after surgery (n = 48, R = -0.43; p = 0.002). In patients who did not improve, the correlation was not significantly different from zero (n = 19, R = -0.07; p = 0.97). There was a trend toward higher values for PRx in nonresponders than in responders (0.16 ± 0.04 vs 0.09 ± 0.02, respectively; p = 0.061), associated with higher MAP values (107.2 ± 8.2 in nonresponders vs 89.5 ± 3.5 in responders; p = 0.195). The product of MAP × (1 + PRx), which was proposed as a measure of combined arterial hypertension and deranged autoregulation, showed a significant association with outcome (greater value in nonresponders; p = 0.013).

Conclusion: Autoregulation proves to associate with CSF circulation and appears strongest in shunt responders. Outcome following CSF diversion is possibly most favorable when CSF outflow resistance is increased and global cerebral autoregulation is intact, in combination with arterial normotension.
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http://dx.doi.org/10.3171/2017.7.JNS17216DOI Listing
March 2018

Brain pulsations enlightened.

Acta Neurochir (Wien) 2018 02 22;160(2):225-227. Epub 2017 Dec 22.

Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Box 167, Addenbrookes Hospital, Cambridge, Cb20QQ, UK.

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http://dx.doi.org/10.1007/s00701-017-3436-1DOI Listing
February 2018

Overdrainage of cerebrospinal fluid and hydrocephalus shunts.

Acta Neurochir (Wien) 2017 08 25;159(8):1387-1388. Epub 2017 Jun 25.

Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, Cambridge University Hospitals, Cambridge, cb2 0qq, UK.

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http://dx.doi.org/10.1007/s00701-017-3251-8DOI Listing
August 2017

Shunt Testing In Vivo: Observational Study of Problems with Ventricular Catheter.

Acta Neurochir Suppl 2016 ;122:353-6

Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.

Most shunt obstructions happen at the inlet of the ventricular catheter. Three hundred six infusion studies from 2007 to 2011 were classified as having a typical pattern of either proximal occlusion or patency. We describe different patterns of shunt ventricular obstruction.Solid block: Cerebrospinal fluid (CSF) aspiration was impossible. Baseline pressure was without pulse waveform (respiratory waveform may be visible). A quick increase of pressure to a level compatible with the shunt's setting was recorded in response to infusion. Distal occlusion of the shunt via transcutaneous compression resulted in a rapid increase in pressure to levels above 50 mmHg. This pattern was attributed to a solid ventricular block.Slit ventricles: At baseline, a pattern similar to that of the solid block was observed. After compression, the pressure increases, the pulse waveform appears, and the intracranial pressure is often stabilized at 25-40 mmHg. It is probable that previously slit ventricles were opened during the test.Partial block: In a partial block of the ventricular catheter by an in-growing choroid plexus, the pulse waveform at baseline was observed and CSF aspiration was possible. During infusion, the pressure increased, but the pulse amplitude disappeared. During the increase in the pressure in the shunt prechamber, the connection with the ventricles is disturbed by repositioning of the plexus.Infusion study via the shunt prechamber is able to visualize ventricular obstruction of the hydrocephalus shunt.
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http://dx.doi.org/10.1007/978-3-319-22533-3_69DOI Listing
July 2017

Waveform Analysis of Intraspinal Pressure After Traumatic Spinal Cord Injury: An Observational Study (O-64).

Acta Neurochir Suppl 2016 ;122:335-8

Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.

Following a traumatic brain injury (TBI), intracranial pressure (ICP) increases, often resulting in secondary brain insults. After a spinal cord injury, here the cord may be swollen, leading to a local increase in intraspinal pressure (ISP). We hypothesised that waveform analysis methodology similar to that used for ICP after TBI may be applicable for the monitoring of patients with spinal cord injury.An initial cohort of 10 patients with spinal cord injury, as presented by the first author at a meeting in Cambridge in May 2012, were included in this observational study. The whole group (18 patients) was recently presented in the context of clinically oriented findings (Werndle et al., Crit Care Med, 42(3):646-655, 2014, PMID: 24231762). Mean pressure, pulse and respiratory waveform were analysed along slow vasogenic waves.Slow, respiratory and pulse components of ISP were characterised in the time and frequency domains. Mean ISP was 22.5 ± 5.1, mean pulse amplitude 1.57 ± 0.97, mean respiratory amplitude 0.65 ± 0.45 and mean magnitude of slow waves (a 20-s to 3-min period) was 3.97 ± 3.1 (all in millimetres of mercury). With increasing mean ISP, the pulse amplitude increased in all cases. This suggests that the ISP signal is of a similar character to ICP recorded after TBI. Therefore, the methods of ICP analysis can be helpful in ISP analysis.
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http://dx.doi.org/10.1007/978-3-319-22533-3_66DOI Listing
July 2017

Intraspinal pressure and spinal cord perfusion pressure after spinal cord injury: an observational study.

J Neurosurg Spine 2015 Dec 14;23(6):763-71. Epub 2015 Aug 14.

Division of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Cambridge;

Object: In contrast to intracranial pressure (ICP) in traumatic brain injury (TBI), intraspinal pressure (ISP) after traumatic spinal cord injury (TSCI) has not received the same attention in terms of waveform analysis. Based on a recently introduced technique for continuous monitoring of ISP, here the morphological characteristics of ISP are observationally described. It was hypothesized that the waveform analysis method used to assess ICP could be similarly applied to ISP.

Methods: Data included continuous recordings of ISP and arterial blood pressure (ABP) in 18 patients with severe TSCI.

Results: The morphology of the ISP pulse waveform resembled the ICP waveform shape and was composed of 3 peaks representing percussion, tidal, and dicrotic waves. Spectral analysis demonstrated the presence of slow, respiratory, and pulse waves at different frequencies. The pulse amplitude of ISP was proportional to the mean ISP, suggesting a similar exponential pressure-volume relationship as in the intracerebral space. The interaction between the slow waves of ISP and ABP is capable of characterizing the spinal autoregulatory capacity.

Conclusions: This preliminary observational study confirms morphological and spectral similarities between ISP in TSCI and ICP. Therefore, the known methods used for ICP waveform analysis could be transferred to ISP analysis and, upon verification, potentially used for monitoring TSCI patients.
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http://dx.doi.org/10.3171/2015.3.SPINE14870DOI Listing
December 2015

Hydrocephalus shunt technology: 20 years of experience from the Cambridge Shunt Evaluation Laboratory.

J Neurosurg 2014 Mar 3;120(3):697-707. Epub 2014 Jan 3.

Department of Neurosurgery, Cambridge University Hospital National Health Service Trust, Cambridge, United Kingdom.

Object: The Cambridge Shunt Evaluation Laboratory was established 20 years ago. This paper summarizes the findings of that laboratory for the clinician.

Methods: Twenty-six models of valves have been tested long-term in the shunt laboratory according to the expanded International Organization for Standardization 7197 standard protocol.

Results: The majority of the valves had a nonphysiologically low hydrodynamic resistance (from 1.5 to 3 mm Hg/[ml/min]), which may result in overdrainage related to posture and during nocturnal cerebral vasogenic waves. A long distal catheter increases the resistance of these valves by 100%-200%. Drainage through valves without a siphon-preventing mechanism is very sensitive to body posture, which may result in grossly negative intracranial pressure. Siphon-preventing accessories offer a reasonable resistance to negative outlet pressure; however, accessories with membrane devices may be blocked by raised subcutaneous pressure. In adjustable valves, the settings may be changed by external magnetic fields of intensity above 40 mT (exceptions: ProGAV, Polaris, and Certas). Most of the magnetically adjustable valves produce large distortions on MRI studies.

Conclusions: The behavior of a valve revealed during testing is of relevance to the surgeon and may not be adequately described in the manufacturer's product information. The results of shunt testing are helpful in many circumstances, such as the initial choice of shunt and the evaluation of the shunt when its dysfunction is suspected.
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http://dx.doi.org/10.3171/2013.11.JNS121895DOI Listing
March 2014

Monitoring of spinal cord perfusion pressure in acute spinal cord injury: initial findings of the injured spinal cord pressure evaluation study*.

Crit Care Med 2014 Mar;42(3):646-55

1Academic Neurosurgery Unit, St. George's, University of London, London, United Kingdom. 2Department of Neurosurgery, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom. 3National Spinal Injuries Centre, Stoke Mandeville Hospital, Stoke Mandeville, United Kingdom. 4Department of Anaesthesia, St. George's Hospital, London, United Kingdom.

Objectives: To develop a technique for continuously monitoring intraspinal pressure at the injury site (intraspinal pressure) after traumatic spinal cord injury.

Design: A pressure probe was placed subdurally at the injury site in 18 patients who had isolated severe traumatic spinal cord injury (American Spinal Injuries Association grades A-C). Intraspinal pressure monitoring started within 72 hours of the injury and continued for up to a week. In four patients, additional probes were inserted to simultaneously monitor subdural pressure below the injury and extradural pressure. Blood pressure was recorded from a radial artery catheter kept at the same horizontal level as the injured segment of the spinal cord. We determined the effect of various maneuvers on spinal cord perfusion pressure and spinal cord function and assessed using a limb motor score and motor-evoked potentials.

Setting: Neurosurgery and neuro-ICU covering a 3 million population in London.

Subjects: Patients with severe traumatic spinal cord injury. Control subjects without spinal cord injury (to monitor spinal cerebrospinal fluid signal and motor evoked potentials).

Interventions: Insertion of subdural spinal pressure probe.

Measurements And Main Results: There were no procedure-related complications. Intraspinal pressure at the injury site was higher than subdural pressure below the injury or extradural pressure. Average intraspinal pressure from the 18 patients with traumatic spinal cord injury was significantly higher than average intraspinal pressure from 12 subjects without traumatic spinal cord injury. Change in arterial PCO2, change in sevoflurane dose, and mannitol administration had no significant effect on intraspinal pressure or spinal cord perfusion pressure. Increase in inotrope dose significantly increased spinal cord perfusion pressure. Bony realignment and laminectomy did not effectively lower intraspinal pressure. Laminectomy was potentially detrimental by exposing the swollen spinal cord to compression forces applied to the skin. By intervening to increase spinal cord perfusion pressure, we could increase the amplitude of motor-evoked potentials recorded from below or just above the injury level in nine of nine patients with traumatic spinal cord injury. In two of two patients with American Spinal Injuries Association grade C traumatic spinal cord injury, higher spinal cord perfusion pressure correlated with increased limb motor score.

Conclusions: Our findings provide proof-of-principle that subdural intraspinal pressure at the injury site can be measured safely after traumatic spinal cord injury.
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http://dx.doi.org/10.1097/CCM.0000000000000028DOI Listing
March 2014

Magnetic field interactions in adjustable hydrocephalus shunts.

J Neurosurg Pediatr 2008 Sep;2(3):222-8

United Kingdom Shunt Evaluation Laboratory, University of Cambridge, Cambridge, United Kingdom.

Object: Exposing patients with ventricular shunts to magnetic fields and MR imaging procedures poses a significant risk of unintentional changes in shunt settings. Shunt valves can also generate considerable imaging artifacts. The purpose of this study was to determine the magnetic field safety and MR imaging compatibility of 5 adjustable models of hydrocephalus shunts.

Methods: The Codman Hakim (regular and with SiphonGuard), Miethke ProGAV, Medtronic Strata, Sophysa Sophy and Polaris programmable valves were tested in a low-intensity magnetic field, and then translational attraction (TA), magnetic torque (MT), and volume of artifacts on T1-weighted spin echo (SE) and gradient echo (GE) pulse sequences in a 3-T MR imaging unit were measured.

Results: The ProGAV and Polaris valves were immune to unintentional reprogramming by magnetic fields up to 3 T. Other valves randomly changed settings, starting from the intensity of field: Sophy valve 24 mT, Strata valve 30 mT, and both Codman Hakim programmable valves from 42 mT. Shunt performances in the 3-T MR imaging unit are reported in the order of compatibility: 1) Codman Hakim regular, TA = 0.005 N, MT = 0.000 Nm, GE = 30 cm(3), SE = 2 cm(3); 2) Miethke ProGAV, TA = 0.001 N, MT = 1.4 x 10(3) Nm, GE = 231 cm(3), SE = 13 cm(3); 3) Codman Hakim with SiphonGuard, TA = 0.005 N, MT = 2.3 x 10(3) Nm, GE = 233 cm(3), SE = 19 cm(3); 4) Medtronic Strata, TA = 0.27 N, MT = 18.0 x 10(3) Nm, GE = 484 cm(3), SE = 86 cm(3); 5) Sophysa Sophy, TA = 0.82 N, MT = 38.9 x 10(3) Nm, GE = 758 cm(3), SE = 72 cm(3); and 6) Sophysa Polaris, TA = 0.80 N, MT = 39.6 x 10(3) Nm, GE = 954 cm(3), SE = 100 cm(3).

Conclusions: All valves, with the exception of the Polaris and ProGAV models, are prone to unintentional reprogramming when exposed to heterogeneous magnetic fields stronger than 40 mT. All tested valves can be considered safe for 3-T MR imaging. All valves generated a distortion of the MR image, especially the GE sequences.
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http://dx.doi.org/10.3171/PED/2008/2/9/222DOI Listing
September 2008

Investigation of the hydrodynamic properties of a new MRI-resistant programmable hydrocephalus shunt.

Cerebrospinal Fluid Res 2008 Apr 21;5. Epub 2008 Apr 21.

Shunt Evaluation Laboratory & Academic Neurosurgical Unit, Addenbrooke's Hospital, P,O, Box 167, Hills Road, Cambridge CB2 2QQ, UK.

Background: The Polaris valve is a newly released hydrocephalus shunt that is designed to drain cerebrospinal fluid (CSF) from the brain ventricles or lumbar CSF space. The aim of this study was to bench test the properties of the Polaris shunt, independently of the manufacturer.

Methods: The Polaris Valve is a ball-on-spring valve, which can be adjusted magnetically in vivo. A special mechanism is incorporated to prevent accidental re-adjustment by an external magnetic field. The performance and hydrodynamic properties of the valve were evaluated in the UK Shunt Evaluation Laboratory, Cambridge, UK.

Results: The three shunts tested showed good mechanical durability over the 3-month period of testing, and a stable hydrodynamic performance over 45 days. The pressure-flow performance curves, operating, opening and closing pressures were stable. The drainage rate of the shunt increased when a negative outlet pressure (siphoning) was applied. The hydrodynamic parameters fell within the limits specified by the manufacturer and changed according to the five programmed performance levels. Hydrodynamic resistance was dependant on operating pressure, changing from low values of 1.6 mmHg/ml/min at the lowest level to 11.2 mmHg/ml/min at the highest performance level. External programming proved to be easy and reliable. Even very strong magnetic fields (3 Tesla) were not able to change the programming of the valve. However, distortion of magnetic resonance images was present.

Conclusion: The Polaris Valve is a reliable, adjustable valve. Unlike other adjustable valves (except the Miethke ProGAV valve), the Polaris cannot be accidentally re-adjusted by an external magnetic field.
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http://dx.doi.org/10.1186/1743-8454-5-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2365935PMC
April 2008

In vitro hydrodynamic properties of the Miethke ProGAV hydrocephalus shunt.

Cerebrospinal Fluid Res 2006 Jun 29;3. Epub 2006 Jun 29.

Academic Neurosurgical Unit, Addenbrooke's Hospital, Cambridge CB2 2QQ, UK.

Background: Adjustable shunts are very popular in the management of hydrocephalus and are believed to help in minimizing the number of surgical revisions. The drawback with almost all constructions is that they may be accidentally readjusted in relatively weak magnetic fields (around 30-40 mTesla)

Materials And Methods: The ProGav Miethke shunt is composed of an adjustable balloon-spring valve unit and an integrated over-drainage compensating gravitational device (known as the shunt assistant). A mechanical 'brake' is intended to prevent changes to the valve's performance level in a strong magnetic field. We evaluated the performance and hydrodynamic properties of a sample of three valves in the UK Shunt Evaluation Laboratory.

Results: All the shunts showed good mechanical durability over the three-month period of testing, and good stability of hydrodynamic performance over a one-month period. The pressure-flow performance curves, operating, opening and closing pressures fell within the limits specified by the manufacturer, and changed according to the programmed performance levels. The operating pressure increased when the shunt assistant was in the vertical position, as specified. The valve has a low hydrodynamic resistance (0.53 mm mmHg ml(-1) min(-1)). External programming proved to be easy and reliable. Strong magnetic fields from a 3 Tesla MR scanner were not able to change the programming of the valve.

Conclusion: The ProGAV shunt is an adjustable, low resistance valve that is able to limit posture-related over-drainage. Unlike other adjustable valves, the ProGAV cannot be accidentally re-adjusted by external magnetic field such as a 3T MR scanner.
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http://dx.doi.org/10.1186/1743-8454-3-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1552084PMC
June 2006

Hydrodynamic properties of extraventricular drainage systems.

Neurosurgery 2003 Mar;52(3):619-23; discussion 623

Academic Neurosurgical Unit, Addenbrooke's Hospital, Cambridge, England.

Objective: Extraventricular drains (EVDs) are intended to control intracranial pressure for patients with acute disorders of the cerebrospinal fluid circulation. We tested five commercially available EVDs to assess their fundamental hydrodynamic properties, which determine the quality of this control.

Methods: The five most frequently used drainage systems were tested. The pressure responses to water flow from a computer-controlled infusion pump were studied in the rig constructed in the UK Shunt Evaluation Laboratory (Cambridge, England). EVDs were studied under normal conditions and after brief (20-s) contact of the vent located in the drip chamber with the test reagent. Pure water and water with 10% rat blood content were used for testing.

Results: All of the tested EVDs demonstrated low hydrodynamic resistance [<3.5 mm Hg/(ml/min)], indicating their ability to control intracranial pressure. When the drip chamber vents were in brief contact with the reagent, the hydrodynamic properties of two models were unaffected. For the three other EVDs, blockage of the drip chamber was observed, leading to increases in the inlet pressure to more than 150 mm Hg. All three models that demonstrated obstruction have the same vent configuration, which allows cerebrospinal fluid to accumulate close to the filter when the drip chamber is held horizontally. This feature was confirmed to be the cause of the blockage.

Conclusion: In clinical practice, special care should be taken to avoid contact of the drip chamber vents with cerebrospinal fluid, which causes obstruction and may lead to the development of gross intracranial hypertension. Specific configurations, as identified in this testing program, are safer than others in this respect.
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http://dx.doi.org/10.1227/01.neu.0000049956.11888.6dDOI Listing
March 2003

Cerebral autoregulation among patients with symptoms of hydrocephalus.

Neurosurgery 2002 Mar;50(3):526-32; discussion 532-3

Academic Neurosurgical Unit and Wolfson Brain Imaging Centre, Addenbrooke's Hospital, Cambridge, England.

Objective: To study the relationship between the resistance to cerebrospinal fluid (CSF) outflow and cerebral autoregulation.

Methods: We examined 35 patients who presented with ventricular dilation and clinical symptoms of communicating hydrocephalus. For all of these patients, CSF compensatory reserve was investigated by using a computerized infusion test, with simultaneous recording of blood flow velocity wave forms (by using transcranial Doppler ultrasonography) and arterial blood pressure (with a Finapress finger cuff). The resistance to CSF outflow was calculated as the absolute increase in intracranial pressure (interpolated over vasogenic waves) divided by the infusion rate (1.5 ml/min in most cases). The index of autoregulation was assessed as a correlation coefficient (moving time window of 5 min) between slow waves (with periods of 20 s to 2 min) in mean blood flow velocity and cerebral perfusion pressure.

Results: The mean intracranial pressure increased during the test, from 6 mm Hg (standard deviation, 6 mm Hg) to 20 mm Hg (standard deviation, 10 mm Hg) (P < 0.0001). The index of autoregulation was significantly correlated with the resistance to CSF outflow (r = -0.41, P < 0.03), indicating better autoregulation with greater resistance to CSF outflow.

Conclusion: Patients presenting with ventricular dilation may exhibit either decreased (atrophy) or increased (normal-pressure hydrocephalus) resistance to CSF outflow. Increased resistance is correlated with preserved autoregulation. Patients with low resistance, suggesting brain atrophy, more often have disturbed autoregulation in the middle cerebral artery territory, as assessed by transcranial Doppler ultrasonography.
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http://dx.doi.org/10.1097/00006123-200203000-00018DOI Listing
March 2002