What is normal pressure hydrocephalus, the brain disorder affecting Billy Joel?

Singer Billy Joel said Friday he was recently diagnosed with normal pressure hydrocephalus, a brain disorder. He said it's affected his hearing, vision and balance.

The brain disorder can cause problems with walking, bladder control and thinking.

In a statement, Joel said he's undergoing specific physical therapy and has been advised to pause performances while he recovers. 

Here are some facts about the condition.

What is hydrocephalus?

Hydrocephalus is an abnormal buildup of fluid within the brain. 

Cerebrospinal fluid (CSF), which is produced in the brain's four hollow ventricles or chambers, protects and cushions the brain and spine and normally gets reabsorbed into the bloodstream.

But when the flow of CSF to the outside of the brain is interrupted or blocked, too much builds up.  

What happens in normal pressure hydrocephaly?

Normal pressure hydrocephaly can result from a blow to the head, infection, tumour, a complication of surgery or other reasons.

But many people develop it without any of these factors, according to the U.S. National Institute of Neurological Disorders and Stroke. 

The increase in CSF happens slowly enough that pressure does not increase in the skull. 

Normal pressure hydrocephaly is more likely to be diagnosed in people over the age of 55. Joel is 76.

Another type of hydrocephaly is congenital hydrocephalus, which is present at birth. It can be caused by health conditions, such as spina bifida.

How is it diagnosed?

When normal pressure hydrocephalus is suspected, a family physician may refer you to a neurologist. The specialist evaluates how the person walks, processes information and speaks and may order tests and imaging, such as a CT scan. 

The symptoms of normal pressure hydrocephalus are similar to Alzheimer's and Parkinson's diseases, the advocacy group Hydrocephalus Canada said.

"The combination of dementia-like symptoms, altered walking (shuffling feet, short steps, a feeling like one's feet are stuck to the floor) and urinary incontinence should alert your health care provider to consider [hydrocephalus]," the group said. 

Bladder function may also be affected. 

What are the treatment options?

In the most common treatment, surgeons place a shunt that drains the excess CSF from the brain to elsewhere in the body, such as the chest cavity. 

A shunt is a flexible piece of tubing that is attached to a valve that controls the flow of CSF.