What Is Hydrocephalus?

The brain produces fluid called cerebral spinal fluid (CSF). Excessive amounts of CSF can cause damage to the brain and even death. The condition of excess CSF in the brain is known as hydrocephalus. Understanding the ventricular system which makes most of the CSF will help you to understand the different types of hydrocephalus discussed in this website.

Understanding The Ventricular System In The Brain Which Makes Most Of The Brain (CSF) Fluid

Cerebral Spinal Fluid (CSF) is mostly made in the ventricular system of the brain. This fluid then circulates throughout the brain as well as down the spine. This is the same fluid obtained with a spinal tap (lumbar puncture). Notice how the fluid filled structure (the ventricular system drawn in purple) occupies space in all the lobes of the brain.

Anatomy (Nomenclature) of the Ventricular System

ventricular system parts labeled

The ventricular system sections are mostly named by which lobe of the brain they occupy. Therefore, the occipital horn is located in the occipital lobe. The temporal horn is in the temporal lobe. The body of the ventricle crosses the parietal lobe. The frontal horn is in the frontal lobe. The III (3rd) ventricle is at the level of the thalamus or top of the brainstem. The IV (4th) ventricle is in the posterior fossa under the cerebellum at the posterior aspect of the brainstem at the level of the pons. The aqueduct (of Sylvius) connects the III ventricle with the IV ventricle. Sometimes people will refer to the right or left lateral ventricle. This usually refers to the frontal horn, body, occipital and temporal horns on that particular side of the brain. To review the flow animation, the Cerebral Spinal Fluid will flow from the lateral ventricle down through the foramen of monro into the III ventricle. From there it proceeds down the aqueduct into the IV ventricle. There are three openings in the IV ventricle: two openings laterally (to the sides) are the foramen of Lushka and medially or in the middle is the foramen of Magendie.

This picture shows how the csf flows within the ventricular system. When it reaches the bottom of the ventricular system (IVth ventricle) it circulates down into the spinal cord and out into the brain. When there is too much fluid in the ventricular system, the ventricles dilate and squeeze the surrounding brain tissue. This is hydrocephalus.

Ventricular System and CAT Scan or MRI Scan Radiographic Correlation

One can correlate the labeled anatomic parts of the ventricle above with the radiologic studies below, to better understand how to read the CT or MRI scan.

body of the lateral ventricles CT with Frontal Horn and IIIrd Ventricle labeled hemorrhage in the frontal horn going into the IIIrd Ventricle via the Foramen of Monro IVth ventricle labeled

Enlarged Ventricular System Compared To Normal Size Ventricular System

Ventricles showing Hydrocephalus Normal size Ventricles

Hydrocephalus is developing in the first ventricular system image. Notice how the ventricular system is becoming larger and rounded, especially frontally compared to the second image. As the ventricles are becoming round, details of the shape are gone due to the expansion (roundness). Since the skull is a closed space containing the brain, increasing the size of the fluid compartment (the ventricles) begins to displace (and compress) the adjacent parts of the brain resulting in neurological symptoms.