What is congenital hydrocephalus?

Congenital hydrocephalus is a buildup of excess cerebrospinal fluid (CSF) within the brain that is present at birth. The excess fluid can increase pressure in the baby's brain, possibly resulting in brain damage and loss of mental and physical abilities. Prompt diagnosis and treatment is important to help limit serious long-term problems. But long-term effects of congenital hydrocephalus mostly depend on what causes it, how bad it gets, and how a baby responds to treatment.

See a picture of congenital hydrocephalus.

Research shows that about 1 baby out of every 1,000 is born with the condition.¹ This means about 999 babies out of every 1,000 are not born with hydrocephalus. The condition also occurs in most children who are born with open neural tube defects.¹

Another form of hydrocephalus, called acquired hydrocephalus, may occur at any time after birth. This topic covers only congenital hydrocephalus.

What causes congenital hydrocephalus?

Congenital hydrocephalus is caused by an imbalance between the brain's production of cerebrospinal fluid (CSF) and the body's ability to distribute or absorb it properly.

Normally, CSF flows through and out of chambers in the brain called ventricles, and then around the brain and spinal cord, providing nutrition and a protective cushion. The fluid is then reabsorbed by the thin tissue that surrounds the brain and spinal cord. With hydrocephalus, the fluid can't move where it needs to or is not absorbed as it should be. And in rare cases, the brain makes too much CSF.

Congenital hydrocephalus may result from either genetic or other causes, such as prenatal hemorrhage (bleeding in the fetus before birth) or infections, such as toxoplasmosis, syphilis, cytomegalovirus (CMV), rubella, or mumps. The condition is often associated with other birth defects, especially spina bifida.

What are the symptoms?

The most obvious symptom of hydrocephalus is an unusually large head that is noticed at birth or within the first 9 months of life. But keep in mind that babies' heads grow a lot during the first year. It is only when the head size grows faster than the normal rate for a baby's height and weight that doctors may become concerned. Also, the soft spot (fontanelle) may feel firm or bulge outward. Other symptoms in an infant may include irritability, excessive sleeping, vomiting, poor feeding, and eyes that gaze downward much of the time.

How is congenital hydrocephalus diagnosed?

Most cases of congenital hydrocephalus are diagnosed during a physical exam soon after birth based on the larger-than-normal size of the baby's head. In rare cases, a diagnosis is made later in childhood. There may be reasons other than congenital hydrocephalus for why a baby has a larger-than-normal head. Imaging tests are usually done to see whether congenital hydrocephalus is a possibility. A computed tomography (CT) scan, magnetic resonance imaging (MRI), or ultrasound may be done to help confirm the diagnosis or to provide a more detailed picture of the brain and its structures.