Dynamic compliance of the CSF system in iNPH (Part I) - in vitro investigation of the impact of spinal canal stenoses.

Spinal canal stenosis is an age-related degenerative condition observed mainly in the cervical and lumbar regions. Recent research has suggested that such stenoses influence cerebrospinal fluid (CSF) dynamics in idiopathic normal pressure hydrocephalus (iNPH) patients by increasing spinal canal flow resistance thereby directly impacting craniospinal dynamic compliance and intracranial pressure (ICP). This study experimentally investigates the effects of cervical and lumbar spinal stenoses on CSF dynamics using a validated in vitro model. To simulate varying degrees of stenosis, controlled reductions in the spinal canal cross-sectional area were applied, and resulting changes in bidirectional cervical CSF flow, ICP, and compliance were measured. The results indicate that mild to moderate stenoses have minimal impact on CSF dynamics, whereas severe stenoses (cervical < 33% and lumbar < 17% of initial cross sectional area) significantly alter CSF dynamics. These alterations were characterised by reduced dynamic compliance, decreased spinal CSF flow and increased ICP amplitudes up to 7.85 mmHg. These findings suggest that spinal stenoses critically alter key CSF dynamics, potentially contributing to iNPH. Further studies are required, especially on other influencing factors such as age-related changes in viscoelastic properties of the dural sac and the relevance of dynamic compliance of the CSF system, which will be addressed in Part II of this series.