Arachnoid Cysts: Symptoms, Prognosis, Treatment


Arachnoid cysts are sacs that are filled with cerebrospinal fluid between the brain or spinal cord and the arachnoid membrane. Basically, the brain and spinal cord are protected by a fluid named cerebrospinal fluid. And there are three membranes covering the brain and spinal cord, with the arachnoid membrane, a delicate fibrous layer, being one of them. When the cerebrospinal fluid is trapped inside one of the membranes, arachnoid cysts may occur. Generally, arachnoid cysts are more common inside the brain than around the spinal cord. Arachnoid cysts can be present at birth or acquired in later life. Primary arachnoid cysts are present at birth, which are caused by developmental abnormalities in the brain and spinal cord during the beginning weeks of pregnancy. Congenital defects in the end form arachnoid cysts. As for secondary arachnoid cysts, they are due to trauma, head injury, meningitis, tumors, brain surgery and so on.

In the United States, about 3% of children have an arachnoid cyst. In the general population, about 1% of people have arachnoid cysts but only 0.2% with the disease needs medical treatment. That is to say, arachnoid cysts are benign at about 80% of the time. Overall, men are four times more likely to have arachnoid cysts than women. People with the disease are most likely to be teenage boys, but arachnoid cysts do happen to both gender and the age of the patients range from a few months to nearly 80 years old.



In general, there are two main types of arachnoid cysts.

For arachnoid cysts that arise in the arachnoid membrane surrounding the brain, they are called intracranial arachnoid cysts. Similarly, for those that arise in the arachnoid membrane surrounding the spinal cord, they are called spinal arachnoid cysts. Arachnoid cysts that arise in different places may show different signs and symptoms.



In most cases, people with arachnoid cysts show no symptoms but the disease can be detected with a CT scan or an MRI of the brain. That’s also the reason why the disease is often found accidentally and often misdiagnosed. However, if a child’s cysts show no symptoms, it is possible that it needs no treatment. Depending on the specific size and location of the arachnoid cysts, the doctor may suggest treatment methods accordingly.

When a larger cyst forms, it can pressure the brain or the spinal cord and its surrounding nerves. In that case, a series of symptoms will occur:

  • Headache
  • Nausea and vomiting
  • Fatigue
  • Vertigo
  • Difficulties in vision and hearing
  • Loss of coordination and balance
  • Head bobbing
  • Behavioral and learning disorders
  • Partial paralysis
  • Hallucinations
  • Tingling or numbness in the legs or arms
  • Pain, numbness in the back, arm, and legs
  • Abnormally large head
  • Loss of bladder and/or bowel control



Although researches on the exact causes of arachnoid cysts are still ongoing, there are several reasons for the condition. Most arachnoid cysts happen during infancy, which is caused by development malformations in the brain or the spinal cord. However, some other arachnoid cysts develop later in life. These cysts may have a lot of causes.



Usually, with proper treatment, signs, and symptoms of arachnoid cysts can resolve or improve over time. However, if left untreated, arachnoid cysts may lead to permanent neurological damage.



Whether to treat arachnoid cysts or not depends on the location and size of the cyst. If the cyst is small and does not do damage to its surrounding tissues, there may be no need to receive treatment. However, if the cyst is large, doctors may advise the individual to use some therapies or surgically remove the cysts.

Here are some treatment methods the doctor may use:

  • Drug therapy: certain medications can be prescribed by the doctor to help to reduce the pain, headache and so on.
  • Open craniotomy fenestration: in the operation, cerebrospinal fluid can be drained into the subarachnoid area and gets absorbed.
  • Cerebral shunts: depending on where the cyst is, internal shunt and cystoperitoneal shunt can be used. The shunt is a device that diverts fluids into the abdominal cavity. With cerebral shunts, the pressure in the brain or the spinal cord can be relived.
  • Capsular resection: in rare cases, when the cysts pressure the surrounding tissues too much, microscopic capsular may invade the brain. Under the severe situation, the doctor may recommend to surgically remove the section in a quick manner.


Keywords: arachnoid cysts.


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