Hydrocephalus

Hydrocephalus ('water-head', term derived from Greek) is an abnormal accumulation of cerebrospinal fluid in the ventricles of the brain. This increase in intracranial volume results in elevated intracranial pressure and compression of the brain. more...

Clinical presentation

Like various other neurologic conditions (brain tumors, strokes, traumatic brain injury, etc.), hydrocephalus results in elevated intracranial pressure. Possible clinical manifestations include: headaches, vomiting (in some cases not accompanied by nausea), papilledema, somnolence, coma. Elevated intracranial pressure may result in uncal and/or cerebellar tonsill herniation, with resulting life threatening brain stem compression. Normal pressure hydrocephalus (NPH) is distinguished by a relatively typical clinical triad: gait instability, urinary incontinence and dementia. 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 is caused by impaired cerebrospinal fluid (CSF) production, flow or resorption.

The most common cause of hydrocephalus is a flow obstruction, hindering the free passage of cerebrospinal fluid through the ventricular system and subarachnoid space (e.g. stenosis of the cerebral aqueduct, obstruction of the interventricular foraminae - foramen of Monro). This can be secondary to tumors, hemorrhages, infections or congenital malfomations. It can also be caused by overproduction of cerebrospinal fluid (relative obstruction).

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.

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 genesis of normal pressure hydrocephalus. Brain atrophy, as it occurs in dementias, after traumatic brain injuries and even in some psychiatric disorders, such as schizophrenia, may also result in an enlargement of cerebral ventricles and subarachnoid spaces. 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.

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