Hydrocephalus Awareness Month Post 1: What Is Hydrocephalus?

The first in a month long educational series for Hydrocephalus Awareness Month.

I have answered this question a few times on this blog, but probably the biggest thing I get asked is "What is hydrocephalus?" The word hydrocephalus comes from the Greek hydro (water) and cephalus (head), thus water on the brain. In a person not affected with hydrocephalus, the brain fluid (cerebral spinal fluid) is produced within the ventricles in the brain and in the choroid plexus. It circulates through the ventricular system within the brain, and then is absorbed into the bloodstream. The fluid is constantly in motion and has several purposes, including to cushion the brain to act as a protector against injury, to provide nutrients and proteins to the brain and to carry waste away from the brain. In most brains this system works well and the ventricles remain within a normal range which keeps the pressure inside the brain at the appropriate levels.

In a brain affected with hydrocephalus, for some reason (and there are several), the cerebral spinal fluid is not circulated out of the brain into the bloodstream, or CSF is developed at too quickly a rate for the brain to effectively remove it. This causes the ventricles to enlarge and increase pressure inside the head. In worst case scenarios, the result of the increased pressure is brain damage.

Hydrocephalus does not differentiate between race, sex, or age. It affects infants, children, young adults, and the elderly. Over 1,000,000 people in the United States currently live with hydrocephalus and for every 1,000 babies born in the US, 1 to 2 will be born with hydrocephalus. Hydrocephalus is the most common reason for brain surgery in children.

Normal brain CT scan - dark areas are the fluid in the ventricles

Brain with hydrocephalus - notice the enlarged ventricles in the shape of a butterfly.

There are several different classifications of hydrocephalus:

Congenital Hydrocephalus: This is the type that Nicholas is affected with - it is present at birth and is typically caused by a combination of genetic and environmental factors during fetal development. It is typically diagnosed before birth with ultrasound and fetal MRI (Nicholas was officially diagnosed at 21 weeks gestation but our attention was brought to the possibility at around 13 weeks gestation when he had ventricles on the high end of normal during the NT scan).

Compensated Hydrocephalus: This is diagnosed in adulthood but may have been congenital.

Acquired Hydrocephalus: This develops after birth as a result of head trauma, a brain tumor, cysts, brain bleed, etc.

Normal Pressure Hydrocephalus: This occurs in older adults when the ventricles increase but the pressure does not increase within the brain. The cause of this is typically unknown and it is often - upwards of 20% of the time - misdiagnosed as Alzheimer's. You may have seen a recent Grey's Anatomy about this type of hydrocephalus.

There are several causes of congenital hydrocephalus and the cause of Nicholas's is the most frequently occurring cause: Aqueductal stenosis. There is a passageway between the third and fourth ventricles in the brain (in the back of your head) called the aqueduct of Sylvius. Aqueductal stenosis occurs when this is either narrowed to the point where CSF cannot be effectively removed or there is a complete blockage. We believe Nicholas has a complete blockage based on the CT scans of his brain. I've frequently been asked if we could just have surgery to go in and remove the blockage and at this time, that technology does not exist.

When Nicholas was officially diagnosed with hydrocephalus (he didn't even have a name yet at that time!), his ventricles measured 13 mm. Ventricles that are within normal ranges are expected to be  below 10 mm. For comparison, in the same MRI that officially diagnosed Nicholas, Emily's ventricles were 4.5 mm. At the last ultrasound that I remember his ventricles being measured (I had one ultrasound per month due to my "high risk" pregnancy with twins and ahem advanced maternal age), his ventricles were measuring at around 55 mm. He was born with a head circumference of a typical 18 month old.

Stay tuned tomorrow for more about hydrocephalus. What is a shunt and is it really brain surgery?