Hydrocephalus classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun M.D., PhD.,Kalsang Dolma, M.B.B.S.[2]

Overview

Hydrocephalus is classified based upon the underlying cause such as impaired cerebrospinal fluid (CSF) flow, impaired CSF reabsorption, or excessive CSF production.

Classification Scheme

Based on its underlying mechanisms, hydrocephalus can be classified into

• Communicating (non-obstructive)
• Non-communicating (obstructive).

Both communicating and non-communicating forms can be either

• Congenital
• Acquired.

Communicating hydrocephalus

Communicating hydrocephalus, also known as non-obstructive hydrocephalus,

• It 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,
• Arachnoid granulations 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

1. subarachnoid/intraventricular hemorrhage
2. meningitis
3. Chiari malformation
4. 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.

Main article: 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 enlargementof 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 Monro obstruction may lead to dilation of one or, if large enough (e.g., in colloid cyst), both lateral ventricles.
• The 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.
• The foramina of Luschka and foramen of Magendie may be obstructed due to congenital failure of opening (e.g., Dandy-Walker malformation).
• The 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 acquired and usually occur within the first few months of life, which include

• intraventricular matrix hemorrhages in premature infants
• infections
• type II Arnold-Chiari malformation
• aqueduct atresia and stenosis
• Dandy-Walker malformation.

Main articles: Arnold-Chiari malformation and Dandy-Walker malformation

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.