What is hydrocephalus? Hydrocephalus is a condition in which excess fluid collects in the brain. The fluid, called cerebrospinal fluid, is produced in cavities located deep within the brain known as ventricles. The fluid fills the ventricles and flows into the spinal cord and out into the subarachnoid space where it absorbed. The subarachnoid space is a space between the layers of the membrane that cover the brain and spinal cord. Normally, cerebrospinal fluid is absorbed as quickly as it is produced, so that the amount stays relatively constant. Hydrocephalus occurs when something blocks the flow or absorption of the fluid, or if an excess amount of fluid is produced. As the pressure of the fluid increases, the ventricles enlarge and the brain is pressed against the skull, damaging the brain tissue. Hydrocephalus may be present at birth, and can occur with other abnormalities, genetic conditions, or infections. It can also occur after birth as a result of certain infections, bleeding in the brain, injury, or tumors of the brain or spinal cord. Unlike adult skulls, which are solid bone, infant skulls have fibrous tissue connecting the bony plates, allowing their heads to expand if hydrocephalus is present. With age, the fibrous connections ossify, or become bony, which means that the skull cannot expand if hydrocephalus occurs later in life. Symptoms of hydrocephalus depend upon age, and may range from irritability, sleepiness, and poor feeding to vomiting, personality and memory changes, difficulty walking, and urinary incontinence. Treatment is aimed at fixing the cause of the hydrocephalus and relieving the pressure on the brain. It is not known how many adults are affected by hydrocephalus, but it is estimated that it occurs in about one in every 500 children (Source: NINDS). Hydrocephalus can have serious complications, so it is important that it be evaluated and treated without delay. Seek immediate medical care (call 911) for serious symptoms, such as difficulty breathing, absent pulse or heartbeat, high fever (higher than 101 degrees Fahrenheit), seizures, severe headache, stiff neck, or severe sleepiness or drowsiness. Poor feeding, unusual irritability, high-pitched, shrill cries, and persistent vomiting in infants and children also need emergency evaluation. Seek prompt medical care if you or someone you are with has symptoms suggestive of hydrocephalus, such as progressive memory loss, personality changes, difficulty thinking, increasing sleepiness, headache, coordination and walking problems, urinary incontinence, or vomiting. Additional symptoms in children may include slow growth, changes in facial appearance, increase in head size, and downward gaze.