Cause of hydrocephalus

Why the ventricles become enlarged

This can happen either when there is an obvious obstruction in the channels through which cerebrospinal fluid flows, or for other reasons.

  1. If a blockage occurs anywhere preventing the circulation of cerebrospinal fluid, the ventricles upstream from this point become enlarged. Secondary hydrocephalus may occur as a complex condition caused by a separate brain disorder. (In practical terms, this can happen when a blockage is caused by: blood from a brain hemorrhage flowing into the ventricles and forming a thrombus (blood clot); a brain tumor; or other similar causes.)

    M Matsumae. Understanding the tumor. Clinical study. Vol 29, No. 14, 2008
    Medical Friend Co. Ltd. Illustrator Kitahara Isao

  2. Hydrocephalus may also occur if the circulation of cerebrospinal fluid becomes backed up (or is assumed to be backed up) even in the absence of any condition obstructing the ventricles or channels (when there is no obvious point of blockage), resulting in enlargement of the ventricles. This may have many causes, ranging from cases in which the cause of the condition is poorly understood (including occurrence as a congenital abnormality), to complications of specific brain disorders (including subarachnoid hemorrhage and meningitis).
  3. Hydrocephalus is also known to occur with overproduction of cerebrospinal fluid (by a specific type of tumor within the ventricles) completely independent of its circulation.

Congenital and acquired causes of hydrocephalus

Hydrocephalus that is already present at birth is called "congenital hydrocephalus". It is well known that this can be caused by a congenital disability (deformity), or possibly by infection in the womb, but in rare cases it may also be due to another specific cause or to genetic factors. Congenital hydrocephalus can also be divided into conditions that clearly result from impaired circulation of cerebrospinal fluid (due to obstruction or stenosis), and those in which there is no obvious point of impaired circulation (when the flow of cerebrospinal fluid is assumed to be backed up).

Hydrocephalus occurring after birth is called "acquired hydrocephalus." Causes may include: 1) intracranial hemorrhage (due to blood flowing into the cerebral ventricles, subdural hematoma (blood pooling between the skull and brain) due to injury, or similar causes); 2) inflammation (due to meningitis or other infection); or 3) brain tumor. Acquired hydrocephalus can occur at any age.

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