Brain, Nervous System and Mental Conditions

Arachnoid Cyst

What Is an Arachnoid Cyst?

An arachnoid (pronounced ah-RACK-noid) cyst is a fluid-filled sac located inside the head or spine. Arachnoid cysts develop between the brain or spinal cord and the arachnoid membrane. This is one of three membranes that cover the brain and spinal cord. The fluid in the cyst often is cerebrospinal fluid (CSF), a clear liquid that protects and nourishes the brain and spinal cord.

Arachnoid cyst

Arachnoid cysts that are located around the spinal cord are less common than those that appear inside the head. In a child's head, an arachnoid cyst can be located between the brain and the skull. A cyst can also be located inside the brain. Arachnoid cysts in the brain form in open spaces called ventricles that normally contain and circulate cerebrospinal fluid.

About two-thirds of the arachnoid cysts we find in the head are located in the upper part of the brain. The other third are in the cerebellum, located in the lower part of the brain.

Arachnoid Cyst in Children

Arachnoid cysts are often present when a child is born (congenital). These cysts develop due to abnormalities in the developing baby's brain and spinal cord that happen while a woman is pregnant. Arachnoid cysts that are present at birth are called primary arachnoid cysts.

In small number of young children, the development of an arachnoid cyst may be related to a head injury. They may also form as a result of meningitis, tumors or complications after brain surgery. These are called secondary arachnoid cysts. Secondary arachnoid cysts are less common than arachnoid cysts that are present at birth.

Arachnoid Cyst at Seattle Children's

Our medical team has cared for many children with arachnoid cysts. We have extensive experience diagnosing arachnoid cysts. Our doctors perform the latest procedures that children with arachnoid cysts may need. We use state-of-the-art equipment.