What Are Normal Patterns of Cerebrospinal Fluid Flow?

Cerebrospinal fluid, commonly known in the medical community by the acronym CSF, normally flows around the brain and through the spinal cord following a standard physiological pattern of circulation. The brain is usually the point of origin. Brain tissues extract the fluid from the bloodstream and certain membranes, and from there it proceeds along an established pathway through the various parts and sections of the brain and cranial space. These are connected to the spine, which shuttles the fluid through the hollow nerve passageways where it is ultimately reintroduced to the bloodstream. This flow is influenced by gravitational fields as well as by the pressure of the circulating bloodstream. In healthy people the system works by itself, but problems or blocks can lead to serious problems. Medical professionals typically monitor the flow paths of cerebrospinal fluid by using magnetic resonance imaging (MRI) studies of patients' brains.

Technically speaking, cerebrospinal fluid flow begins in the high midbrain area from within an area known as the lateral ventricles. The fluid is pulled from the bloodstream and membranes of the brain by areas in the cerebral ventricles and brainstem called the choroid plexus. CSF then flows down into the third ventricle, where more of the fluid is produced, adding to the flow volume. The fluid then drains down into the fourth ventricle through a space called the Aqueduct of Sylvius. Some CSF is also produced in the fourth ventricle, but this fluid takes another path away from the main flow and goes directly down to the cisterna magna, a large basin-shaped area at the bottom of the skull.

The main volume of the cerebrospinal fluid flow then goes down into the subarachnoid space and out through openings called cisterna into other parts of the brain and into the spinal column. The largest opening is called the cisterna magna. This is where the main volume meets up with the fluid that was produced in the fourth ventricle.

Cerebrospinal fluid goes from the cisterna magna almost directly down into the spine. It returns to the brain in the area of the superior sagittal sinus, a groove along the top of the skull that runs from the front of the head to the back. Here, the CSF is then reabsorbed into the bloodstream by the arachnoid villi, which are spongy tissues found in this region.

In most cases, the flow of cerebrospinal fluid can only be seen by an MRI or other specialized imaging technology. It is all but invisible externally, and the flow is usually necessarily interrupted when cavities are opened during surgery. As such, most of what is known about actual flow patterns comes from scans and real-time testing. These have generally shown that if CSF pressure is higher than that of the veins into which it is being absorbed — basically, the blood pressure — then it will be absorbed back into the bloodstream. The rate at which CSF is absorbed depends upon the venous pressure.

CSF flow can be altered by changes in gravitational fields. For example, being suspended head-down above the earth at any distance would be a gravitational influence upon fluid flow. It’s important to note here that the fields produced by standard MRIs are magnetic fields, which differ from the gravitational field influences of a large planetary mass and don’t usually affect the cerebrospinal fluid flow in the same way.

When all is going properly, the fluid should be able to seamlessly flow from one region to the next. If the pressure of the CSF is much lower than the venous pressure, however, it cannot be reabsorbed back into the bloodstream. This can lead to blockages, which may have serious health consequences. Medical professionals can sometimes install CSF shunts to alleviate this condition, and to help regulate CSF flow again within the body. People with this problem usually need to submit to regular monitoring, as well as examination to figure out what caused the problem in the first place — and how to fix it or avoid it in the future.