Transcranial Ultrasound Assessment of Cerebral Pulsatility in Shunt Decision-making for Suspected Idiopathic Normal Pressure Hydrocephalus: a Prospective Cohort Study

Contribution of Cerebral Pulsatility Assessment by Transcranial Ultrasound to the Decision-making for Cerebrospinal Fluid Shunting in Patients With Suspected Idiopathic Normal Pressure Hydrocephalus: a Prospective Cohort Study

This will be a single-center, prospective, analytical cohort study. All included patients will undergo transcranial ultrasound (TPI) with measurement of cerebral pulsatility parameters prior to subtractive lumbar puncture during hospitalization in the neurosurgery department, followed by a second ultrasound assessment either at one year after surgery for operated patients, or at one year after the initial ultrasound assessment for non-operated patients. This ultrasound evaluation will be integrated into the routine work-up, which is already systematically performed in cases of suspected idiopathic normal pressure hydrocephalus (iNPH).

The neurosurgical team's decision to perform cerebrospinal fluid (CSF) shunting will be made blinded to the ultrasound measurements and based solely on the standard clinical protocol.

The primary objective of the study is to demonstrate that the mean amplitude of cerebral pulsatility (MeanBTP) prior to subtractive lumbar puncture is significantly higher in patients who show clinical improvement 12 months after CSF shunting compared with those who do not, with a type I error risk (alpha) of 0.05."

This will be a prospective, single-center cohort study including patients with suspected idiopathic normal pressure hydrocephalus (iNPH). Eligibility will require fulfillment of inclusion criteria and confirmation of non-opposition after written informed consent procedures.

All patients will undergo transcranial pulse imaging (TPI) with measurement of cerebral pulsatility parameters prior to subtractive lumbar puncture during hospitalization. Operated patients will have a second TPI assessment at 12 months post-surgery, while non-operated patients will undergo repeat TPI 12 months after baseline. Ultrasound assessments will be integrated into the standard hydrocephalus work-up.

The decision to perform cerebrospinal fluid (CSF) shunting will be made by the neurosurgical team blinded to ultrasound findings and based solely on standard clinical and radiological criteria. Baseline clinical (demographics, vascular risk factors, cognitive/gait/urinary symptoms, neurological history) and radiological variables (ventricular volume, Evans index, callosal angle, DESH, Radscale) will be collected.

During hospitalization, gait and cognitive function will be evaluated before and 48 hours after lumbar puncture. TPI will provide two indices of cerebral pulsatility: mean brain tissue pulsatility (MeanBTP) and maximal brain tissue pulsatility (MaxBTP), expressed as peak amplitude, peak amplitude mean, and root mean square.

Follow-up will include standardized clinical and radiological assessments. Non-operated patients will be evaluated at 12 months. Operated patients will be seen at 2 months and 12 months postoperatively, with documentation of complications, shunt valve settings, ventricular volume changes, and subdural collections.

Statistical analyses will be performed using STATA v11 (StataCorp, USA). Continuous variables will be expressed as means ± SD or medians; categorical variables as percentages. Normality will be assessed with the Kolmogorov-Smirnov test, and variance equality with F-test. Comparisons will use Student's t-test, chi-square, or Fisher's exact test as appropriate. Cox proportional hazards regression will be applied for multivariable analysis. P < 0.05 will be considered significant.

The primary objective will be to demonstrate that the mean amplitude of cerebral pulsatility (MeanBTP) measured prior to subtractive lumbar puncture will be significantly higher in patients who show clinical improvement 12 months after cerebrospinal fluid (CSF) shunting compared with those who do not, with a type I error risk (alpha) of 0.05.

The secondary objectives will be to correlate cerebral pulsatility (measured by transcranial pulse imaging, TPI) with functional indices of iNPH and CSF shunting outcomes, including: speech therapy evaluation, physiotherapy-based gait assessment, global neurological disability, ventricular volume, and shunt valve opening pressure.

Inclusion Criteria:

• Adult
• Suspected iNPH (= at least 1/3 of the triad symptoms + ventriculomegaly on brain imaging)
• Hospitalised at Tours University Hospital for 'hydrocephalus assessment'
• Patient who has provided written and signed consent

Non-inclusion criteria

• Individuals who objected to data processing
• Walking assessment by the physiotherapy team impossible AND cognitive assessment by the speech therapy team impossible

Exclusion criteria

• Patients already fitted with a CSF shunting system (VPS)
• Suspicion of obstructive hydrocephalus (aqueduct stenosis, tumour, etc.)
• Patients under legal protection (guardianship, curatorship, judicial protection).