Intraoperative effects of ETV and CPC on intraventricular pressure and pulsation amplitude: A preliminary investigation of the hydrodynamic model of infant hydrocephalus.

Background: The hydrodynamic model of hydrocephalus proposes that ventriculomegaly is driven by exaggerated intraventricular pulsations rather than impaired cerebrospinal fluid (CSF) circulation alone. Under this model, endoscopic third ventriculostomy with choroid plexus cauterization (ETV/CPC) treats hydrocephalus by creating a pulsation absorber and by reducing a primary source of intraventricular pulsation. However, direct intraoperative human evidence supporting this two-step mechanism is lacking. This study aimed to test the hypothesis that ETV followed by CPC would produce measurable, stepwise decreases in mean intraventricular pressure (ICP) and pulsation amplitude in infants with hydrocephalus. Methods: This single-institution proof-of-concept study included infants with symptomatic hydrocephalus undergoing ETV/CPC as the first definitive treatment. A fiber-optic ICP sensor was attached to the operative ventriculoscope and passively recorded mean and pulsatile ICP (pulsation amplitude) throughout the procedure. Longitudinal brain parenchymal volume (BPV) and cerebrospinal fluid volume (CSFV) were obtained through segmentation of clinically acquired T2-weighted MRI and converted to age- and sex-matched z-scores. All patients were followed for a minimum of 6 months postoperatively. Results: Five infants (median corrected age at ETV/CPC 8 months) were included. No surgical complications occurred, and no ETV/CPC failures were observed during follow-up. Overall, mean ICP decreased by 56-97% after the combined procedure in four patients. In three patients (Patients 1, 3, and 5), both mean ICP and pulsation amplitude decreased stepwise following ETV and then CPC, consistent with the hypothesized therapeutic mechanism. Patient 4 demonstrated a large reduction in mean ICP after ETV with minimal additional effect from CPC and no significant change in pulsation amplitude. Patient 2 demonstrated neither a reduction in mean ICP nor a meaningful change in pulsation amplitude after either procedure; this patient also had a delayed and atypical clinical response. Intracranial segmentation demonstrated BPV z-score stabilization within normal range and CSFV plateau in all patients after surgery. Conclusions: This proof-of-concept study provides the first direct intraoperative human evidence supporting the hydrodynamic mechanism of ETV/CPC in a subset of infant with hydrocephalus. Our findings suggest that determination of intraoperative ICP parameters is feasible, safe and might ultimately prove helpful in improving patient selection for ETV/CPC, warranting further investigation in larger cohorts.