Hydrocephalus is a neurological disorder in which there is excessive accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain. In hypertensive hydrocephalus, the CSF accumulates resulting in increased pressure inside the brain. The ventricles swell and the brain tissue is stretched and squashed.
In normal cases, the CSF circulates through the brain's ventricles and the spinal cord, and continuously drains away into the circulatory system. Hydrocephalus occurs when the normal CSF flow pathway becomes obstructed or when there is over-secretion of fluid. An over-secretion occurs when there is an imbalance between the amount of CSF that is produced and the amount which is reabsorbed into the blood stream. Obstructions can come about due to a variety of causes such as tumours, cysts, scarring, blood clots, and developmental abnormalities.
Hydrocephalus in infants is often more severe than in adults because the developing brain is particularly vulnerable to injury and because the immature skull enlarges via the open sutures. Infants and young children with hydrocephalus have abnormally large heads because the pressure of the fluid has caused the individual skull bones to bulge outward at their juncture points. Compression of the brain by the accumulating fluid eventually causes convulsions and intellectual difficulties.
Broadly speaking, there are two types of hydrocephalus: high pressure (hypertensive) and normal pressure. Of these, the former is far more common than the latter, which is why high pressure hydrocephalus is usually simply referred to as 'hydrocephalus'.
High pressure hydrocephalus (from here on referred to only as 'hydrocephalus') can be categorised in three different ways:
1.Congenital or Acquired
2.Non-communicating (Obstructive) or Communicating
3.Internal or External
Since these describe different aspects of the condition, each case will fall into all three categories.
Congenital Hydrocephalus refers to the condition being present at birth. This can be due to either environmental or genetic reasons, though the latter (i.e. hereditary hydrocephalus) is very rare. Often the cause of congenital hydrocephalus cannot be determined.
Acquired hydrocephalus will develop after birth and can occur at any age. The most common causes of acquired hydrocephalus are trauma to the head, infection, tumour, cyst, haemorrhage, or infection of the central nervous system.
Non-communicating hydrocephalus refers to obstruction of the CSF pathways within the interior of the brain or at the tentorial notch. Communicating hydrocephalus refers to an inability of the CSF to pass through the arachnoidal villi to get back into the blood stream. This can occur when the arachnoidal villi become inflamed by infection, where the inflammatory process blocks the microscopic pores through which the CSF must pass when moving from the subarachoidal space into the blood.
Internal hydrocephalus refers to an accumulation of CSF within the ventricles of the brain. External hydrocephalus refers to accumulation of fluid outside the ventricles.
Normal pressure hydrocephalus (NPH) is the enlargement of the ventricles of the brain without increased CSF pressure, which in turn leads to compression of the brain tissue. NPH is caused by the same factors as other forms of hydrocephalus. It most commonly occurs in adults over 60. NPH develops slowly due to the gradual build up of blockage and CSF pressure.
A neurological examination with a Computer Tomography (CT) Scan or with a Magnetic Resonance Imaging (MRI) will provide anatomic pictures of the ventricles and will determine if the CSF flow is blocked by a mass.