The lateral ventricles are a pair of fluid-filled cavities situated deep within the brain, forming the largest components of the overall ventricular system. These internal spaces are entirely contained within the two large cerebral hemispheres, one ventricle residing in the left and the other in the right. The ventricles are lined by a specialized tissue called ependyma and are filled with cerebrospinal fluid (CSF), which serves protective and functional roles for the central nervous system. This network of four interconnected ventricles is responsible for the production and circulation of this fluid.
General Location and Overall Shape
The lateral ventricles adopt a characteristic large, curved C-shape, sometimes described as a horseshoe shape, as they follow the path of the brain’s main structures. This distinctive curve wraps around the basal ganglia and the central thalamus, two masses of gray matter situated in the core of the brain. The two lateral ventricles are separated from each other by a thin, vertical membrane known as the septum pellucidum. The C-shape extends from the frontal lobe, curves backward into the parietal and occipital regions, and then sweeps forward into the temporal lobe. The ventricle connects to the third ventricle through a small opening called the interventricular foramen (Foramen of Monro), which serves as the passageway for CSF flow.
Specific Anatomical Components
The extensive C-shaped structure of the lateral ventricle is divided into five distinct segments, each projecting into a different region of the surrounding cerebral tissue. The most anterior part is the anterior horn, which extends into the frontal lobe. Posterior to the interventricular foramen is the body of the lateral ventricle, which travels through the parietal lobe beneath the corpus callosum. As the body sweeps backward, it widens into a triangular area called the atrium, or trigone, where three of the ventricular projections meet. From this central meeting point, the posterior horn projects backward into the occipital lobe, and the inferior horn extends downward and forward into the temporal lobe, running along the structure of the hippocampus.
Function in Cerebrospinal Fluid Production
The primary function of the lateral ventricles is to produce cerebrospinal fluid. This production is carried out by the choroid plexus, a specialized network of capillaries and modified epithelial cells located along the floor of the lateral ventricle’s body and atrium. These choroid epithelial cells are joined by tight junctions, forming a blood-cerebrospinal fluid barrier that strictly regulates which substances pass from the blood into the ventricular space. The choroid plexus cells actively secrete sodium ions into the ventricle, creating an osmotic gradient that draws water across the epithelial layer. This secretory action produces approximately 500 milliliters of CSF every day in an adult human. Once formed, the cerebrospinal fluid exits the lateral ventricles through the interventricular foramen, moving toward the third ventricle to continue its circulation.
Clinical Implications of Ventricular Changes
Because the lateral ventricles are confined spaces within the rigid skull, any alteration to their size or shape can have significant clinical consequences. The most common condition involving these spaces is hydrocephalus, which refers to the excessive accumulation of cerebrospinal fluid. This buildup causes the ventricles to enlarge, placing undue pressure on the surrounding brain tissue and potentially causing neurological damage. Hydrocephalus can result from a blockage in the narrow passages between the ventricles, preventing the normal flow of CSF, or from an issue with the reabsorption of the fluid back into the bloodstream. Conditions such as tumors, infections, or head injuries can also directly impact the ventricles, either by obstructing the flow of CSF or by physically distorting the shape and volume of the ventricular space. Radiologists frequently use measurements like the Evans index, which compares the width of the anterior horns to the internal skull diameter, to assess for abnormal ventricular enlargement.