Raised intracranial pressure increases CSF drainage through arachnoid villi and extracranial lymphatics

We demonstrated previously that about one-half of cerebrospinal fluid (CSF) removed from the cranial vault was cleared by extracranial lymphatic vessels. In this report we test the hypothesis that lymphatic drainage of CSF increases as intracranial pressure (ICP) is elevated in anesthetized sheep. Catheters were inserted into both lateral ventricles, cisterna magna, cervical lymphatics, and jugular vein. A ventriculocisternal perfusion system was employed to regulate CSF pressures and to deliver a protein tracer (I-125-labeled human serum albumin) into the CSF compartment. I-131-labeled human serum albumin was injected intravenously to permit calculation of plasma tracer loss and tracer recirculation into lymphatics. ICP was controlled by adjusting the height of the inflow reservoir and the cisterna magna outflow catheter appropriately. The experimental design consisted of a 3-h period of lower pressure followed by a 3-h period of higher pressure in the same animal (10-20 or 20-30 cmH(2)O). We determined that incremental changes in ICP were associated with higher CSF transport through lymphatic and arachnoid villi routes in all eight animals tested (P = 0.004).