Neurosurgery - Patient Care and Treatment
Aqueductal obstruction (Stenosis)
The most common cause of congenital hydrocephalus (fluid on the brain that’s present at birth) is a blocked or narrowed cerebral aqueduct - the long, narrow passageway between the third and fourth ventricles in the brain. This may be caused by infection, hemorrhage or a tumor. Fluid collects upstream from the obstruction, producing hydrocephalus.
Neural tube defects, or myelomeningocele
"Spina bifida" is a common term, but "neural tube defect" (or NTD) is a better term. A myelomeningocele is an open NTD where the spinal cord is exposed at birth. It often lacks cerebrospinal fluid (CSF). This form of NTD is associated with widespread abnormalities of the central nervous system.
The Chiari II malformation and hydrocephalus occur in 90% of NTDs. In the Chiari II malformation, part of the cerebellum and the fourth ventricle extend downward through the opening at the base of the skull, blocking the flow out of the fourth ventricle and therefore producing hydrocephalus.
Intraventricular hemorrhage is an acquired form of hydrocephalus that most frequently affects premature newborns. It happens when small blood vessels lying alongside the ventricular lining rupture. Blood may block or scar the ventricles, or may plug the arachnoid villi, the areas where CSF is absorbed along the sagittal sinus.
Meningitis is an inflammation of the membranes of the brain and spinal cord. It may be caused by bacterial infections or, less often, viral infections. These can scar the delicate membranes that line the cerebral spinal fluid (CSF) pathway. Hydrocephalus may develop after meningitis if scarring restricts or blocks the flow of CSF as it passes through the narrow passageways of the ventricles, or as it passes over the surfaces of the brain in the subarachnoid space.
A head injury can damage the brain's tissues, nerves or blood vessels. Blood from these ruptured vessels may enter the CSF pathways. Blood causes inflammation, which may scar the meninges. Blood cells may also block the CSF absorptive sites. This restricts the flow of CSF and hydrocephalus develops.
In children, brain tumors are usually located in the back of the brain (posterior fossa). As a tumor grows, it may fill or compress the fourth ventricle, blocking the flow of spinal fluid. In other areas of the brain, a tumor may similarly block or compress the ventricular system, causing hydrocephalus.
Arachnoid cysts are congenital (present at birth) and may occur anywhere in the brain. In children, they are often located in the back of the brain near the third ventricle. The cysts are filled with cerebral spinal fluid (CSF) and are lined with the arachnoid membrane (one of the three meningeal coverings). Some arachnoid cysts are self-contained, while others may be connected by a passageway with the ventricles or subarachnoid space. The entrapped fluid may block the CSF pathways, producing hydrocephalus.
In Dandy-Walker Syndrome, the fourth ventricle is enlarged because its outlets are partly or completely closed. In addition, part of the cerebellum fails to develop. Dandy-Walker Syndrome can be associated with abnormal development - or lack of development - in other parts of the brain as well. Obstruction at the aqueduct may also occur.