An arachnoid cyst usually develops in the head, but may also develop around the spinal cord. It is named an arachnoid cyst because it occurs in the space between the brain (or spinal column) and the arachnoid membrane. This is one of three membrane layers surrounding the brain and spine. If in the head, the cyst will grow between the brain and skull or in pockets around the brain called ventricles. The cyst is usually filled with cerebrospinal fluid (CSF). CSF is a naturally-occurring protective fluid that surrounds the brain and spinal column. The fluid accumulates in the cyst as the walls of the cyst do not permit drainage into the CSF system.
Arachnoid cysts in children are usually congenital, or present at birth. These cysts are called primary arachnoid cysts. Arachnoid cysts that are not congenital, but develop later in life, are called secondary arachnoid cysts. Primary arachnoid cysts are more common than secondary arachnoid cysts. Men are more likely to develop arachnoid cysts than females.
Primary arachnoid cysts, the congenital version, are usually caused by an abnormal growth of the brain and spinal column while the baby is developing in utero. This can be genetic. However, the exact cause of these growths is not known.
Non-congenital arachnoid cysts in both children and adults can have several causes. These include trauma or injury to the head, meningitis, and tumors. They may also occur as a reaction to brain surgery. Arachnoid cysts are most common in children.
Arachnoid cysts are primarily asymptomatic. Most people don’t realize they have one until being examined for other issues, such as head injuries.
Symptoms may develop if the cyst grows or is pressing on nerves or sensitive areas in the brain or spinal cord. The most common symptoms of cysts in the brain include:
- problems hearing, seeing or walking
- neurological problems
- balance issues
Common symptoms of cysts on the spinal column include:
- back pain
- lack of feeling or tingling in the arms or legs
- muscle weakness or spasms
- problems controlling the bladder and bowels
Diagnosing Arachnoid Cysts | Diagnosis
Imaging is used to diagnose an arachnoid cyst, primarily CT scan and MRI, to look at your brain or spine. Usually a CT scan will find the cyst and it will be examined further with an MRI to exclude other conditions, such as tumors.
An arachnoid cyst with no symptoms or other complications may not be treated. A doctor will monitor the cyst over time to watch for growth or changes in the cyst.
For symptomatic cysts, removal is common. Cysts in the brain may not be taken out with surgery because of the risks. Rather, one of two procedures will be used. The first involves a small incision near the cyst and insertion of an endoscope with a small camera on the end. The endoscope is used to gently open the cyst, allowing the fluid to drain. The fluid will mix in with the cerebrospinal fluid and redistribute through the body. This procedure is called fenestration.
The second possible procedure for an arachnoid cyst includes putting a small tube, or catheter, through an incision into the cyst. The shunt allows the fluid to drain to another part of the body, such as the belly.
For symptomatic cysts on the spinal column, removal might be possible. If not possible, fenestration or shunting are the best solutions.
Generally, treatment of a symptomatic cyst will resolve the symptoms. For asymptomatic cysts, a doctor will continue to monitor the cyst and treat if symptoms appear, but the affected patient should be able to enjoy a normal life with the cyst.
If arachnoid cysts are left untreated but are bleeding or growing rapidly, there could be permanent neurological damage. This is a severe outcome.