Fluid on the brain

As I am currently on my final week of paediatrics and something I have seen being queried a lot of on the neonatal ward is hydrocephalus. But what actually is hydrocephalus….

To know this, we need to look at one of the protective features of the brain, the cerebral spinal fluid (CSF). The CSF is produced in the choroid plexus which is situated in the lateral ventricles within the brain. The ventricles are spaces that exist within our brain, this is where CSF is present as well as around the outside of the brain and spinal cord. The ventricular structure and the choroid plexus anatomy is shown in the diagram (apologise for the drawing, getting to grips with a new stylus). From superior to inferior; there are two lateral ventricles that form almost a backwards C shape. The anterior horns of the lateral ventricles drain into the third ventricle through the intraventricular foramen. The CSF then passes into the fourth ventricle through the cerebral aqueduct which lies medially to the inferior horns of the lateral ventricles. Once in the fourth ventricle the CSF can either flow into the central canal that runs through the spinal cord or can exit the ventricular system into the subarachnoid cisterns. The subarachnoid space is the area that contains CSF around the outside of the brain. It exits via 3 foramina (holes) called the central median aperture and the two lateral apertures. The CSF can then move around to arachnoid space until it reaches the superior sagittal sinus (which is an area of the subarachnoid space that runs between the two hemispheres of the brain). In the superior sagittal sinus there are small projections called arachnoid granulations who’s role is to reabsorb the CSF and drain it into the venous sinuses and then passing it into the jugular vein.

There are many points in this ventricular system that can get blocked such as the cerebral aqueduct and the foramina. A blocked of one of these can led to non-communicating hydrocephalus. Due to the blocked flow of CSF. This results in normal production but lack of reabsorption. The increased level of CSF within the ventricular system causes the ventricles to enlarge which can be seen on a cranial ultrasound scan in a neonate.

The other form of hydrocephalus is called communicating. This is when there is a lack of absorption due to an abnormality in the arachnoid granulations. In an older age group this can be due to fibrosis after a haemorrhage.

The increased amount of CSF in the ventricles causes pressure on the brain and can result in raised intracranial pressure. This is a very serious complication that can be fatal. Symptoms especially in infants are quite vague involving increased sleepiness, seizures and vomiting. If this occurs prior to the fusion of skull bones in a baby then it can result in macrocephaly (enlarged head).

The treatment for this is usually surgical and involves placement of a shunt from the ventricles to either the right atrium or the peritoneum.

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