Intracranial pressure accommodation is impaired by blocking pathways leading to extracranial lymphatics

Tracer studies indicate that cerebrospinal fluid (CSF) transport can occur through the cribriform plate into the nasal submucosa, where it is absorbed by cervical lymphatics. We tested the hypothesis that sealing the cribrifo rm plate extracranially would impair the ability of the CSF pressure-regula ting systems to compensate for volume infusions. Sheep were challenged with constant flow or constant pressure infusions of artificial CSF into the CS F compartment before and after the nasal mucosal side of the cribriform pla te was sealed. With both infusion protocols, the intracranial pressure (ICP ) vs. flow rate relationships were shifted significantly to the left when t he cribriform plate was blocked. This indicated that obstruction of the cri briform plate reduced CSF clearance. Sham surgical procedures had no signif icant effects. Estimates of the proportional flow through cribriform and no ncribriform routes suggested that cranial CSF absorption occurred primarily through the cribriform plate at low ICPs. Additional drainage sites (arach noid villi or other lymphatic pathways) appeared to be recruited only when intracranial pressures were elevated. These data challenge the conventional view that CSF is absorbed principally via arachnoid villi and provide furt her support for the existence of several anatomically distinct cranial CSF transport pathways.