The ventricular system is a set of four interconnected cavities located within the brain parenchyma. These spaces are continuous with the central canal of the spinal cord and are lined with specialized ciliated cells called ependymal cells. Their primary contents are cerebrospinal fluid, which provides mechanical protection and chemical stability to the central nervous system.
The third ventricle is a narrow, slit-like cavity positioned along the midline between the two halves of the thalamus. Below it, the fourth ventricle sits anterior to the cerebellum and posterior to the pons and upper medulla oblongata. Both structures act as vital transit chambers for fluid movement through the lower brain regions.
Passageways connect the individual ventricles to maintain continuous fluid flow. The interventricular foramina, also known as the foramina of Monro, link each lateral ventricle to the third ventricle. Further down, the narrow cerebral aqueduct of Sylvius carries fluid from the third ventricle directly into the fourth ventricle. Blockage in these narrow channels quickly leads to fluid buildup above the obstruction.
Cerebrospinal fluid is manufactured primarily by the choroid plexus, a network of capillaries covered by ependymal cells found within all major ventricles. These specialized tissues actively secrete fluid from blood plasma at a steady rate, producing roughly 500 milliliters daily in an adult human. A common misconception is that fluid is static, whereas it continually forms, circulates, and reabsorbs into the venous bloodstream.
Fluid flows in a strict, predictable direction starting from the lateral ventricles, passing through the foramen of Monro into the third ventricle, and moving down the cerebral aqueduct into the fourth ventricle. From the fourth ventricle, openings called the median and lateral apertures release the fluid into the subarachnoid space surrounding the brain and spinal cord. Ultimately, arachnoid granulations absorb the fluid back into the dural venous sinuses.
Obstruction anywhere along the narrow ventricular pathways prevents normal fluid drainage, leading to an abnormal accumulation known as hydrocephalus. As fluid builds up, intracranial pressure rises, compressing surrounding brain tissue and causing symptoms like severe headache, vomiting, and papilledema. Nurses monitoring clients with suspected ventricular issues must track changes in the level of consciousness and measure head circumference in infants.