A ferritin tracer study of compensatory spinal CSF outflow pathways in kaolin-induced hydrocephalus

Spinal drainage of cerebrospinal fluid (CSF) into the lymphatic system is important in physiological and pathological conditions in both humans and rodents. However, in hydrocephalus and syringomyelia the exact CSF pathway from the central canal into the lymphatic tissue around the spinal nerves remains obscure. We therefore induced syringomyelia and hydrocephalus in 36 Lewis rats by injection of 0.1 ml kaolin into the cisterna magna. At 2, 4 and 6 weeks later cationized ferritin was stereotactically infused into the cisterna magna of controls and into the lateral ventricles of hydrocephalic animals followed by dissection of brain, spinal cord and spinal nerves. CSF pathway and tracer flow were studied by light and electron microscopy. We found that in rats with kaolin-induced CSF outflow obstruction, CSF passes from central canal syringes through ruptured ependyma and dorsal columns into the spinal subarachnoid space, from where it is absorbed along spinal nerves into extradural lymphatic vessels. Taken into account that spinal hydrostatic pressure in humans differs significantly from pressure in animals due to the upright gait, we conclude that spinal compensatory CSF outflow pathways might be of even greater importance in human hydrocephalus.