CSF Dynamics for Shunt Prognostication and Revision in Normal Pressure Hydrocephalus.

BACKGROUND: Despite the quantitative information derived from testing of the CSF circulation, there is still no consensus on what the best approach could be in defining criteria for shunting and predicting response to CSF diversion in normal pressure hydrocephalus (NPH). OBJECTIVE: We aimed to review the lessons learned from assessment of CSF dynamics in our center and summarize our findings to date. We have focused on reporting the objective perspective of CSF dynamics testing, without further inferences to individual patient management. DISCUSSION: No single parameter from the CSF infusion study has so far been able to serve as an unquestionable outcome predictor. Resistance to CSF outflow (Rout) is an important biological marker of CSF circulation. It should not, however, be used as a single predictor for improvement after shunting. Testing of CSF dynamics provides information on hydrodynamic properties of the cerebrospinal compartment: the system which is being modified by a shunt. Our experience of nearly 30 years of studying CSF dynamics in patients requiring shunting and/or shunt revision, combined with all the recent progress made in producing evidence on the clinical utility of CSF dynamics, has led to reconsidering the relationship between CSF circulation testing and clinical improvement. CONCLUSIONS: Despite many open questions and limitations, testing of CSF dynamics provides unique perspectives for the clinician. We have found value in understanding shunt function and potentially shunt response through shunt testing in vivo. In the absence of infusion tests, further methods that provide a clear description of the pre and post-shunting CSF circulation, and potentially cerebral blood flow, should be developed and adapted to the bed-space.

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

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.

Shunt infusion studies: impact on patient outcome, including health economics.

OBJECTIVES: The diagnosis of shunt malfunction is often not straightforward. We have explored, in symptomatic shunted patients with hydrocephalus or pseudotumour cerebri syndrome (PTCS), the accuracy of CSF infusion tests in differentiating a functioning shunt from one with possible problems, and the health economic consequences. METHODS: Participants: hydrocephalus/PTCS patients with infusion tests performed from January 2013 until December 2015. We followed patients up after 6 and 12 months from the test to determine whether they had improved, had persisting symptoms or had required urgent revision. We calculated the total cost savings of revision versus infusion tests and standard protocol of revision and ICP monitoring versus infusion tests. RESULTS: Three hundred sixty-five shunt infusion tests had been performed where a shunt prechamber/reservoir was present. For hydrocephalus patients, more than half of the tests (~ 55%, 155 out of 280) showed no shunt malfunction versus 125 with possible malfunction (ages 4 months to 90 years old). For PTCS patients aged 10 to 77 years old, 47 had possible problems and 38 no indication for shunt malfunction. Overall, > 290 unnecessary revisions were avoided over 3 years' time. Two hundred fifty-eight (> 85%) of those non-surgically managed, remained well, did not deteriorate and did not require surgery. No infections were associated with infusion studies. For Cambridge, the overall savings from avoiding revisions was £945,415 annually. CONCLUSIONS: Our results provide evidence of the importance of shunt testing in vivo to confirm shunt malfunction. Avoiding unnecessary shunt revisions carries a strong health benefit for patients that also translates to a significant financial benefit for the National Health Service and potentially for other healthcare systems worldwide.

Cerebrospinal fluid dynamics in pediatric pseudotumor cerebri syndrome.

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.

Value of computerized shunt infusion study in assessment of pediatric hydrocephalus shunt function-a two center cross-sectional study.

BACKGROUND: Hydrocephalus shunt malfunction can-also in children-occur insidiously without clear symptoms of raised intracranial pressure (ICP) or changes in ventricular size, imposing a diagnostic challenge. Computerized shunt infusion studies enable quantitative shunt function assessment. We report on feasibility and results of this technique in children in a two center cross-sectional study. MATERIAL AND METHODS: Shunt infusion study (SIS) is performed with two needles inserted into a pre-chamber for ICP recording and CSF infusion. After baseline ICP recording, constant rate infusion is started until a new ICP plateau (ICPpl) is reached. Dedicated software containing the shunt's resistance characteristics calculates ICP and its amplitude outflow resistance and critical shunt pressure (CSP). Overall, 203 SIS were performed in 166 children. Shunts were defined as functional if ICPpl was 5 mmHg above CSP and borderline in between. RESULTS: Forty-one shunts (20.2%) were found obstructed, 26 (12.8%) had borderline characteristics, and 136 (67%) were functional. Baseline ICP in obstructed shunts was significantly above shunt operating pressure. CSF outflow resistance (Rout) and ∆ICP plateau were significantly elevated in obstructed shunts, with cut-off thresholds of 8.07 mmHg min/ml and 11.74 mmHg respectively. Subgroup analysis showed smaller ventricles in 69% of revised cases. CONCLUSION: SIS is a feasible, reliable, and radiation-free technique for quantitative shunt assessment to rule out or prove shunt malfunction. Dedicated software containing shunt hydrodynamic characteristics is necessary and small children may need short-term sedation. Due to the clinical and inherent economic advantages, SIS should be more frequently used in pediatric neurosurgery.

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

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.

Use of CSF infusion studies to unblock occluded hydrocephalus ventricular shunt catheters: a preliminary report of two patients.

Two patients with ventriculoperitoneal shunts presented with symptoms of raised intracranial pressure indicative of possible shunt malfunction. During investigation, to eliminate this possibility, cerebral spinal fluid infusion studies were performed, which indicated proximal occlusion of the shunts in both cases. Retrograde flush of the ventricular catheter was performed during temporary compression of the siphon-control device, a manoeuvre which blocks distal flow. After the use of this technique, both patients' symptoms improved and they have remained symptom-free for over 2 years. This case report validates the role that infusion studies can play in clearing a blocked ventricular catheter shunt.

Validation of Davson's equation in patients suffering from idiopathic normal pressure hydrocephalus.

INTRODUCTION: The so-called Davson's equation relates baseline intracranial pressure (ICP) to resistance to cerebrospinal fluid outflow (Rout), formation of cerebrospinal fluid (If) and sagittal sinus pressure (PSS) There is a controversy over whether this fundamental equation is applicable in patients with normal pressure hydrocephalus (NPH). We investigated the relationship between Rout and ICP and also other compensatory, clinical and demographic parameters in NPH patients. METHOD: We carried out a retrospective study of 229 patients with primary NPH who had undergone constant-rate infusion studies in our hospital. Data was recorded and processed using ICM+ software. Relationships between variables were sought by calculating Pearson product correlation coefficients and p values. RESULTS: We found a significant, albeit weak, relationship between ICP and Rout (R = 0.17, p = 0.0049), Rout and peak-to-peak amplitude of ICP (AMP) (R = 0.27, p = 3.577e-05) and Rout and age (R = 0.16, p = 0.01306). CONCLUSIONS: The relationship found between ICP and Rout provides indirect evidence to support disturbed Cerebrospinal fluid circulation as a key factor in disturbed CSF dynamics in NPH. Weak correlation may indicate that other factors-variable PSS and formation of CSF outflow-contribute heavily to linear model expressed by Davson's equation.

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

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.