"Pseudo" intracranial compliances in hydrocephalus patients
Résumé
Introduction: A “Pseudo” Intracranial compliance (C_infus) as compensatory mechanism can be simply calculated by combining the increase in intracranial pressure (ICP) with the large volume of liquid slowly injected during infusion test. As Contrary to Marmarou’s doctrine, during cardiac cycle, cerebral blood and cerebrospinal fluid (CSF) flows lead to small intracranial volume change that acts as rapid physiological infusion test, resulting in ICP increase related to physiological brain compliance (C_physio). PC-MRI can measure CSF and blood flows during cardiac cycle. Aim of this work, is to observe whether C_physio could be complementary to C_infus.
Methods: 15 patients (71 ± 9 years) with suspected normal pressure hydrocephalus underwent PC-MRI and infusion test within few days. C_infus was calculated by dividing the volume injected by the ICP change during infusion. Amplitude of ICP change during cardiac cycle (PICM+) was calculated before the start of injection. Intracranial arteries and veins flows and cervical CSF oscillations were measured by PC-MRI to calculate intracranial liquid volume change during cardiac cycle (VPCMRI), origin of physiological ICP pulsatility. Then we calculated C_physio = VPCMRI /PICM+.
Results: C_infus (0.720 ± 0.39 mL/mmHg) was significantly higher than C_physio (0.115 ± 0.09 mL/mmHg) with poor correlation (R2 = 0.15, p > 0.05).
Conclusions: These preliminary results show that the two compliances are different, uncorrelated and complementary. C_infus reflects the brain capacity to respond to continuous volume injection over prolonged time, it could be associated mainly with resistance to CSF outflow and venous compliance. C_physio reflects instantaneous physiological compliance of intracranial volume directly related to brain biomechanics.