Types of Hydrocephalus



Hydrocephalus is a defect that causes excess cerebrospinal fluid (CSF) to build up in the brain. The brain is surrounded and cushioned by this fluid, which also fills open structures deep in the brain, called ventricles. With hydrocephalus, the fluid becomes trapped in the brain ventricles, which causes them to enlarge. We explain more about hydrocephalus here.


For most types of hydrocephalus, surgery is the only treatment option. On this page, we discuss the different types of hydrocephalus, which are classified according to the cause and symptoms of hydrocephalus.


Communicating vs Non-Communicating Hydrocephalus

There are two main classifications for hydrocephalus:

  • Communicating hydrocephalus (or non-obstructive) – after the brain fluid becomes blocked, it can still flow between the ventricles.
  • Non-communicating hydrocephalus (or obstructive) – the brain fluid becomes blocked in one or more of the narrow passages that connect the ventricles.


Both communicating and non-communicating hydrocephali can be subdivided into:

  • congenital hydrocephalus (present at birth)
  • acquired hydrocephalus (occurs following birth).


Communicating hydrocephalus can also be subdivided into:

  • normal pressure hydrocephalus (NPH)
  • hydrocephalus ex-vacuo.


The below image illustrates the two main types of hydrocephalus:

  • non-communicating hydrocephalus is shown in the left scan;
  • the right shows communicating, normal pressure hydrocephalus (NPH).


In a brain without hydrocephalus, the blue areas – which is the fluid on the brain – would be less visible.


communicating vs obstructive non hydrocephalus brain


Non-Communicating Hydrocephalus

Non-communicating hydrocephalus — also called obstructive hydrocephalus — occurs when the flow of cerebrospinal fluid (CSF) is blocked along one or more of the narrow passages connecting the ventricles.


Communicating Hydrocephalus

Also known as non-obstructive hydrocephalus, communicating hydrocephalus occurs when the flow of cerebrospinal fluid (CSF) is blocked after it exits the ventricles. This form is called communicating because the CSF can still flow between the ventricles, which remain open.


Normal Pressure Hydrocephalus (NPH)

This type only affects people ages 50 years or older. It may develop after a stroke or injury. As opposed to other types of hydrocephalus, NPH develops slowly due to the gradual blocking of CSF drainage, which subsequently causes slow fluid buildup over time. The enlarged ventricles then press on the brain and cause symptoms. These include dementia-like signs similar to Alzheimer’s disease, and walking difficulties that resemble Parkinson’s disease. That’s why the diagnosis is often problematic. The good news, however, is that unlike those conditions, NPH can be resolved.


In most cases, the cause of NPH is undetermined. However, NPH can occur due to bleeding in the brain following a head injury, stroke, brain tumor, meningitis (an infection of the tissue surrounding the brain), or even following brain surgery.


Since diagnosis is complicated by the fact that many people assume the symptoms of NPH (difficulty walking/gait disturbances, cognitive challenges/mild dementia, urinary urgency or incontinence) are related to aging, it is important to recognize that those symptoms may be part of NPH, which is a treatable condition.


Hydrocephalus Ex-Vacuo

Hydrocephalus ex-vacuo occurs from brain damage caused by stroke or injury. In this condition, there may be an actual shrinkage of brain substance. Although there is more cerebrospinal fluid (CSF) than usual, and the ventricles are enlarged, the CSF pressure may or may not be elevated in hydrocephalus ex-vacuo.


This dilation of the cerebral ventricles, which is due to loss of brain tissue, is a common result of brain diseases such as luekoystrophies (a group of rare genetic disorders that affect the central nervous system), multiple sclerosis, multiple strokes, Alzheimer’s disease, Huntington’s disease and other related diseases.


hydrocephalus causes normal pressure communicating non

Causes of Hydrocephalus

Whether communicating or non-communicating, hydrocephalus can be subdivided into two different causal categories:

  • Congenital
  • Acquired


Speculation is that hydrocephalus may result from inherited genetic abnormalities, such as the genetic defect that causes aqueductal stenosis. One of the most common causes of hydrocephalus is “aqueductal stenosis.” In this case, hydrocephalus results from a narrowing of the aqueduct of Sylvius, a small passage between the third and fourth ventricles in the middle of the brain.


It can also be caused by developmental disorders, such as those associated with neural tube defects including spina bifida and encephalocele (in newborns, a protrusion of some or all of the brain through a defect in the skull).


Other possible causes include complications of premature birth such as intraventricular hemorrhage, and diseases such as meningitis, tumors, traumatic head injury, or subarachnoid hemorrhage, which block the exit of cerebrospinal fluid (CSF) from the ventricles to the cisterns or eliminate the passageway for CSF within the cisterns.


Congenital Hydrocephalus

Affecting one out of every 1,000 newborns, congenital hydrocephalus is the type that is present at birth. Congenital hydrocephalus is a buildup of excess cerebrospinal fluid (CSF). The extra fluid can increase pressure in the baby’s brain, which then causes brain damage and physical as well as mental problems. Discovering the condition early and treating it quickly can help limit any long-term problems. But long-term effects greatly depend on the cause of the fluid buildup, how bad it gets, and how the baby responds to treatment. Early treatment (before age 4 months) is important to help limit or prevent brain damage. However, congenital hydrocephalus is now often diagnosed before birth through a routine ultrasound. Treatment focuses on reducing the amount of fluid in the brain to relieve pressure.


Congenital hydrocephalus is caused by a complex interaction of genetic and environmental factors during fetal development. One of the most common causes of congenital hydrocephalus is “aqueductal stenosis” (a narrowing of the aqueduct of Sylvius, a cerebral aqueduct). Another common cause of hydrocephalus is a neural tube defect (NTD).


Other Causes of Congenital Hydrocephalus

  • Birth defect (such as spina bifida)
  • Genetic defect
  • Mother’s infections during pregnancy (such as rubella, mumps, toxoplasmosis or syphilis)


Symptoms of Congenital Hydrocephalus

Medical problems associated with congenital hydrocephalus may include:

  • Chiari malformations, an abnormality at the base of the brain where the spinal column joins the skull
  • Craniosynostosis, when the bones in the skull fuse together before the brain has stopped growing
  • Dandy-Walker syndrome, when the fourth ventricle is enlarged because of partial or complete closure of its outlets
  • Hydranencephaly, a rare condition in which the brain’s cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal fluid
  • Vein of Galen aneurysmal malformations, a tangled mass of dilated vessels supplied by an enlarged artery


Signs of Congenital Hydrocephalus

  • Abnormal head enlargement
  • Downward deviation of eyes
  • Headache, irritability, nausea, sleepiness, vomiting
  • Prominent scalp veins
  • Skull bones may feel separated
  • Tense, bulging fontanel


hydrocephalus classification acquired congenital

Acquired Hydrocephalus

Acquired hydrocephalus develops at the time of birth or at some point afterward. This type of hydrocephalus can affect individuals of all ages and may be caused by injury or disease. The following conditions may cause CSF obstruction and subsequently acquired hydrocephalus:

  • Bleeding (hemorrhage)
  • Brain trauma (i.e., result of injury)
  • Brain tumor
  • Cyst (i.e., a fluid-filled sac)
  • Infection (e.g., cerebral abscess, bacterial meningitis)


Premature births may be a risk factor for hydrocephalus. Hemorrhaging, traumatic brain injury, and infection are seen in some premature births.


Symptoms of Acquired Hydrocephalus

  • Chronic headaches
  • Cognitive challenges or complaints
  • Difficulty walking/gait disturbances
  • Urinary urgency or incontinence


Pseudotumor Cerebri

Pseudotumor cerebri (PTC) is caused by high pressure in the fluid surrounding the brain. Pseudotumor cerebri means “false brain tumor” because it mimics a tumor or hydrocephalus.


The difference between pseudotumor cerebri and hydrocephalus is that PTC fluid is encased in the extracellular space (located around each brain cell) rather than in the ventricles. In essence, then, the ventricles are compressed with PTC and expanded in the case of hydrocephalus.


PTC is often associated with overweight adolescents or sudden weight gain (such as in pregnancy). It is sometimes treated with shunting.