Hydrocephalus is a condition arising from an excessive accumulation of cerebrospinal fluid (CSF) within the ventricles, the fluid-filled cavities of the brain.
Overview
The term hydrocephalus derives from the Greek hydro, meaning water, and cephalus, meaning head. Although it translates as “water on the brain”, it in fact denotes an accumulation of cerebrospinal fluid, the clear organic fluid that surrounds the brain and the spinal cord.
Cerebrospinal fluid circulates continuously within the ventricles of the brain and performs a number of important functions. Besides protecting the brain and spinal cord against injury, it serves to carry nutrients to the brain and to remove waste from it.
A rise in cerebrospinal fluid, and with it a rise in intracranial pressure, is damaging to brain tissue. The accumulation results either from increased production and reduced absorption of cerebrospinal fluid, or from an obstruction to its normal flow within the ventricular system.
Although hydrocephalus may arise at any age, it is most common in infants and in adults aged 60 and over.
Causes and Types
Only a small part of the causes of hydrocephalus has been elucidated. Some cases are present at birth, while others develop in childhood or in adult life. Hydrocephalus may be inherited. It is also known to be associated with developmental disorders such as spina bifida and encephalocele, and to arise as a consequence of conditions such as brain tumors, head injury, hemorrhage or meningitis.
Hydrocephalus may be classified according to the manner of its onset, the presence of structural defects, and cerebrospinal fluid pressure.
- Acquired Hydrocephalus
- Develops at birth or in adult life, typically as a result of injury and/or illness.
- Congenital Hydrocephalus
- Present at birth, arising from events during fetal development or as a consequence of genetic abnormalities.
- Communicating Hydrocephalus
- Arises although there is no obstruction to the flow of cerebrospinal fluid within the ventricular system. It results either from inadequate absorption or from an abnormal increase in the quantity of fluid produced.
- Non-communicating (Obstructive) Hydrocephalus
- Arises when the flow of cerebrospinal fluid is blocked along one of the passages connecting the ventricles, so that the pathways above the obstruction dilate and the intracranial pressure rises.
- Normal Pressure Hydrocephalus
- A form of communicating hydrocephalus that may arise at any age but is encountered chiefly in the elderly. It is typically characterized by disturbance of gait, urinary incontinence and forgetfulness.
- Hydrocephalus Ex Vacuo
- Affects adults in particular, and arises from brain injury — following a degenerative condition such as Alzheimer disease, a stroke or trauma — that causes the brain tissue to shrink.
Symptoms
The symptoms of hydrocephalus vary considerably from one person to another and between age groups. In infants and small children, symptoms arising from raised intracranial pressure, such as vomiting, are more common; in adults, disturbance of gait, impairment of cognitive function and loss of balance and coordination come to the fore.
Infants
- unusually large head;
- rapidly enlarging head circumference;
- bulging, tense fontanelle;
- prominent scalp veins;
- downward deviation of the eyes;
- vomiting;
- drowsiness;
- irritability;
- seizures.
Children and Adolescents
- nausea and vomiting;
- papilledema;
- blurred or double vision;
- disturbance of balance and gait;
- slowing of developmental progress;
- change of personality;
- difficulty concentrating;
- seizures;
- loss of appetite;
- urinary incontinence.
Adults
- headache;
- nausea and vomiting;
- difficulty walking or disturbance of gait;
- loss of balance or coordination;
- drowsiness;
- urinary incontinence;
- disturbance of vision;
- impairment of cognitive function;
- memory loss.
Diagnosis
A detailed history must be taken from any patient assessed for possible hydrocephalus, and a thorough neurological examination performed. One or more of the following investigations are usually required in order to confirm the diagnosis and to assess the treatment options.
- computed tomography (CT);
- magnetic resonance imaging (MRI);
- lumbar puncture;
- measurement of intracranial pressure;
- isotope cisternography.
Fundoscopy and gait analysis may also be used to support the diagnosis.
Treatment
Several methods are available for the treatment of hydrocephalus. Depending upon the underlying cause, treatment may consist either in removing the obstruction to the flow of cerebrospinal fluid or in diverting the fluid that has accumulated.
The commonest treatment is the insertion of a device known as a shunt to carry the excess cerebrospinal fluid away from the brain. The shunt is a system placed beneath the skin, comprising a catheter and a valve, which drains the excess fluid from the ventricle into the peritoneal cavity (the abdomen). It removes the excess fluid from the brain continuously and so keeps the intracranial pressure within normal limits.
In certain cases a procedure known as endoscopic third ventriculostomy may be used instead of a shunt. A fiber-optic endoscope is employed to create a new channel along which the cerebrospinal fluid may flow.