Brain 101: The Ventricles and CSF Flow

by Karima Roumila

This blog submission brings us to the close of Brain Awareness Week. As a follow up to the previous article on the anatomy and physiology of the brain, we would like to continue our learning and explore the terms we so often hear when dealing with hydrocephalus. These definitions are taken from our various educational publications, which are all found primarily under the Education and Support  section of our website.

Ventricles

The Ventricles are four cavities in the brain. To the rights is a drawing of the ventricles. As you look at the drawing, imagine the ventricles as chambers filled with fluid. There are four in all: the two lateral ventricles, the third ventricle and the fourth ventricle. As you can see, the ventricles are interconnected by narrow passageways. Your neurosurgeon can learn valuable information about the patient’s condition by closely monitoring the size and shape of these ventricles.

Illustration of Ventricles

Illustration by Lynne Larson

Endoscopic Third Ventriculostomy (ETV) is a surgical treatment option for hydrocephalus and an alternative to a shunt device. A neurosurgeon makes a small hole in the floor of the third ventricle, allowing CSF to flow from the blocked lateral ventricles.

Cerebrospinal Fluid Circulation and Absorption

CSF is formed within the ventricles by small, delicate tufts of spe­cialized tissue called the choroid plexus. The solid arrows in the draw­ing below, Cerebrospinal fluid (CSF) Circulatory Pathway, show the major pathway of CSF flow. Beginning in the lateral ventricles, CSF flows through two passageways into the third ventricle. From the third ventricle it flows down a long, narrow passageway (the aqueduct of Sylvius) into the fourth ventricle. From the fourth ventricle it passes through three small openings (foramina) into the subarachnoid space surrounding the brain and spinal cord. CSF is absorbed through blood vessels over the surface of the brain back into the bloodstream. Some absorption also occurs through the lymphatic system. Once in the bloodstream, it is carried away and filtered by our kidneys and liver in the same way as are our other body fluids.

Illustration of circulation of CSF

Illustration by Lynne Larson

The ventricular system is the major pathway for the flow of CSF. CSF also flows directly from the ventricles into the brain tissue sur­rounding them. This is shown by the broken arrows. Here the CSF passes through the spaces between the cells to where it eventually enters the subarachnoid space. It is believed that the brain tissue does not absorb any CSF, but simply provides another pathway for the fluid moving to the subarachnoid space. Some small amounts of CSF are also absorbed into lymphatic channels along the membranes covering the nerves (nerve sheaths) as they leave the brain stem and spinal cord .

Our bodies produce approximately a pint (500 ml) of CSF daily, continuously replacing CSF as it is absorbed. Under normal conditions there is a delicate balance between the amount of CSF that is pro­duced and the rate at which it is absorbed. Hydrocephalus occurs when this balance is disrupted. Although there are many factors that can disrupt this balance, the most common is a blockage, or obstruc­tion, somewhere along the circulatory pathway of CSF. The obstruction may develop from a variety of causes, such as brain tumors, cysts, scarring and infection.

Normal pressure hydrocephalus (NPH) is an abnormal accumulation of cerebrospinal fluid (CSF) that causes the ventricles in the brain to become enlarged, sometimes with little or no increase in intracranial pressure (ICP). With continuous pressure-recording techniques now available, we know that the phrase “normal pressure” is misleading, because many patients have fluctuations in CSF pressure ranging from high to normal to low. However, normal pressure hydrocephalus, or NPH, continues to be the common name for the condition, as originally coined by Dr. Salomon Hakim in 1964.

 

To learn more about hydrocephalus, visit these areas of our website:

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