General Concepts

Jaime Gasco and Remi Nader

Where is CSF produced?

In the choroid plexus of the lateral ventricles and roof of the third and fourth ventricles

Anywhere else?

Yes. There is an unclear number of extrachoroidal sources of CSF production.

What are those sources?

Parenchymal subarachnoid space and ependymal surface

What is the production rate of CSF?

0.33 cc/min, not influenced significantly by the intracranial pressure (ICP)

What is the primary site of absorption?

Via arachnoid villi into the dural sinuses at the convexities

True or false: Arachnoid villi only exist near the sagittal sinus.

False; there are spinal arachnoid villi as well, near the spinal root ganglia.

Does this process require energy?

No. This is a process that does not require energy (valvular system). It is based both on a hydrostatic pressure difference between the subarachnoid space and venous sinuses as well as on an “osmotic gradient” created due to the fact that protein content in plasma is significantly greater than in CSF.

Is absorption at the sagittal sinus influenced by outflow pressure?

Yes, indeed. It is influenced as well by the gradient between ICP and that of the sagittal sinus (5–7 mm Hg).

Any other proposed mechanisms of absorption of CSF?

Via choroid plexus and “lymphatic type” drainage. It is important to recognize that this drainage contribution, although not as important in magnitude, constitutes an exciting area of research.

Absorption from subarachnoid space → craniospinal perineural spaces → lymphatics

The main point of CSF drainage from the cranial spaces to the lymph runs through what structure?

The cribriform plate, via the subarachnoid space around the olfactory nerves into the submucosal space, located underneath the nasal epithelium