Hydrocephalus

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Hydrocephalus

Hydrocephalus (water-head, term derived from Greek) is an abnormal accumulation of cerebrospinal fluid in the ventricles of the brain, usually due to blockage of CSF outflow in the ventricles or in the subarachoid space at the base of the brain. This increase in intracranial volume results in elevated intracranial pressure and possible compression of the brain.

Clinical presentation

Hydrocephalus is one of the many conditions that causes an increased intracranial pressure. Clinical manifestations of increased intracranial pressure may include headaches, vomiting, nausea, papilledema, altered level of consciousness, or coma. Elevated intracranial pressure may result in uncal and/or cerebellar tonsill herniation, with resulting life threatening brain stem compression. For details on other manifestations of increased intracranial pressure:

The triad of gait instability, urinary incontinence and dementia is a relatively typical manifestation of the distinct entity normal pressure hydrocephalus (NPH). Focal neurologic deficits may also occur, such as abducens nerve palsy and vertical gaze palsy (Parrinaud syndrome due to compression of the quadrigeminal plate, where the neural centers coordinating the conjugated vertical eye movement are located).

Causes

Hydrocephalus can be caused by impaired cerebrospinal fluid (CSF) flow, reabsorption, or excessive CSF production.

The most common cause of hydrocephalus is CSF flow obstruction, hindering the free passage of cerebrospinal fluid through the ventricular system and subarachnoid space (e.g., stenosis of the cerebral aqueduct or obstruction of the interventricular foraminae - foramen of Monro secondary to tumors, hemorrhages, infections or congenital malformations).

Hydrocephalus can also be caused by overproduction of cerebrospinal fluid (relative obstruction) (e.g., papilloma of choroid plexus).

Based on its underlying mechanisms, hydrocephalus can be classified into communicating, and non-communicating (obstructive). Both communicating and non-communicating forms can be either congenital, or acquired.

Communicating hydrocephalus

Communicating hydrocephalus, also known as non-obstructive hydrocephalus, is caused by impaired cerebrospinal fluid resorption in the absence of any CSF-flow obstruction. It has been theorized that this is due to functional impairment of the arachnoid granulations, which are located along the superior sagittal sinus and is the site of cerebrospinal fluid resorption back into the venous system. Various neurologic conditions may result in communicating hydrocephalus, including subarachnoid/intraventricular hemorrhage, meningitis, Chiari malformation, and congenital absence of arachnoidal granulations (Pacchioni's granulations).

Normal pressure hydrocephalus (NPH) is a particular form of communicating hydrocephalus, characterized by enlarged cerebral ventricles, with only intermittently elevated cerebrospinal fluid pressure. The diagnosis of NPH can be established only with the help of continuous intraventricular pressure recordings (over 24 hours or even longer), since more often than not, instant measurements yield normal pressure values. Dynamic compliance studies may be also helpful. Altered compliance (elasticity) of the ventricular walls, as well as increased viscosity of the cerebrospinal fluid, may play a role in the pathogenesis of normal pressure hydrocephalus.

Hydrocephalus ex vacuo also refers to an enlargement of cerebral ventricles and subarachnoid spaces, and is usually due to brain atrophy (as it occurs in dementias), post-traumatic brain injuries and even in some psychiatric disorders, such as schizophrenia. As opposed to hydrocephalus, this is a compensatory enlargement of the CSF-spaces in response to brain parenchyma loss - it is not the result of increased CSF pressure.

Non-communicating hydrocephalus

Non-communicating hydrocephalus, or obstructive hydrocephalus, is caused by a CSF-flow obstruction (either due to external compression or intraventricular mass lesions).

Foramen of Munro obstruction may lead to dilation of one or, if large enough (e.g., in colloid cyst), both lateral ventricles.
Aqueduct of Sylvius, normally narrow to begin with, may be obstructed by a number of genetically or acquired lesions (e.g., atresia, ependymitis, hemorrhage, tumor) and lead to dilatation of both lateral ventricles as well as the third ventricle.
Fourth ventricle obstruction will lead to dilatation of the aqueduct as well as the lateral and third ventricles.
Foramina of Luschka and Magendie may be obstructed due to congenital failure of opening (e.g., Dandy-Walker malformation).
Subarachnoid space surrounding the brainstem may also be obstructed due to inflammatory or hemorrhagic fibrosing meningitis, leading to widespread dilatation, including the fourth ventricle.

Congenital hydrocephalus

The cranial bones fuse by the end of the third year of life. For head enlargement to occur, hydrocephalus must occur before then. The causes are usually genetic but can also be acquire and usually occurs within the first few months of life, which include 1) intraventricular matrix hemorrhages in premature infants, 2) infections, 3) type II Arnold-Chiari malformation, 4) aqueduct atresia and stenosis, and 5) Dandy-Walker malformation.

In newborns and toddlers with hydrocephalus, the head circumference is enlarged rapidly and soon surpases the 97th%. Since the skull bones have not yet firmly joined together, bulging, firm anterior and posterior fontanelles may be present even when the patient is in an upright position.

The infant exhibits fretfulness, poor feeding, and frequent vomiting. As the hydrocephalus progresses, torpor sets in, and the infants shows lack of interest in his surroundings. Later on, the upper eyelids become retracted and the eyes are turned downwards (due to hydrocephalic pressure on the mesencephalic tegmentum and paralysis of upward gaze). Movements become weak and the arms may become tremulous. Papilledema is absent but there may be reduction of vision. The head becomes so enlarged that the child may eventually be bedridden.

About 80-90% of fetuses or newborn infants with spina bifida - often associated with meningocele or myelomeningocele - develop hydrocephalus.

Acquired hydrocephalus

This condition is acquired as a consequence of CNS-infections, meningitis, brain tumors, head trauma, intracranial hemorrhage (subarachnoid or intraparenchymal) and is usually extremely painful for the patient.

Effects

Because of the areas of the brain that are most affected from hydrocephalus, thought and learning may be adversely affected, for example the sufferer may have learning and/or behavioural difficulties, motivation and visual problems. Learning disorders are common among those with hydrocephalus, who tend to score better on verbal IQ than on performance IQ, which is thought to reflect the distribution on nerve damage to the brain. However the effects of hydrocephalus differs considerably between individuals and some are of average or above average intelligence. Someone with hydrocephalus may have problems with co-ordination and be clumsy. They may hit puberty earlier than the average. About 1:3 will develop epilepsy.

Treatment

State-of-the-art hydrocephalus treatment is surgical. It involves the placement of a ventricular catheter (a tube made of silastic), into the cerebral ventricles to bypass the flow obstruction/malfunctioning arachnoidal granulations and drain the excess fluid into other body cavities, from where it can be resorbed. Most shunts drain the fluid into the peritoneal cavity (ventriculo-peritoneal shunt), but alternative sites include the right atrium (ventriculo-atrial shunt), pleural cavity (ventriculo-pleural shunt), and gallbladder. An alternative treatment is the endoscopic third venstriculostomy (ETV), whereby a surgically created opening in the floor of the third ventricle allows the CSF to flow directly to the basal cisterns, thereby shortcutting any obstruction, as in aqueductal stenosis.

Third ventriculostomy (i.e. a surgical connection between the third ventricle and the subarachnoid space) should be considered as an alternative therapeutic option to traditional CSF-shunting procedures (ventriculo-peritoneal shunt, ventriculo-atrial shunt).

Shunt complications

Examples of possible complications include shunt malfunction, shunt failure, and shunt infection.

Although a shunt generally works well, it may stop working if it disconnects, becomes blocked, or it is outgrown. If this happens the cerebrospinal fluid will begin to accumulate again and a number of physical symptoms will develop, some extremely serious, like seizures.

The shunt failure rate is also relatively high and it is not uncommon for patients to have multiple shunt revisions within their lifetime.

The diagnosis of cerebro-spinal buildup is complex and requires expertise.

History

Hydrocephalus was first described by Hippocrates, but it remained an intractable condition until the 20th century, when shunts and other neurosurgical treatment modalities were developed. It is often informally referred to as 'water on the brain'. Most patients with hydrocephalus find this term offensive, however.

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