Arachnoid Cyst - Causes, Symptoms, Diagnosis, and Treatment

What Is an Arachnoid Cyst?

An arachnoid cyst refers to a sac filled with cerebrospinal fluid (the clear fluid that protects the brain and spinal cord). These cysts form along the arachnoid membrane (one of the protective layers around the brain) or the spinal cord.

An arachnoid cyst is not a tumor, and it is not cancerous either. In many people, it causes no issues and is often found by accident during a brain scan performed for another reason. But sometimes, if the cyst becomes larger, it may put pressure on nearby nerves or brain tissue, leading to symptoms.

Most arachnoid cysts are present from birth. Some can also develop later due to head injury, infection, surgery, or bleeding inside the brain. These cysts are seen more commonly in males than in females.

What Are the Types of Arachnoid Cysts?

Arachnoid cysts are mainly divided into two types:

Primary Arachnoid Cysts:

These are congenital cysts, meaning they are present at birth. They usually develop when the arachnoid membrane does not form properly while the baby is growing in the womb.

Secondary Arachnoid Cysts:

These cysts develop later in life because of another medical condition or injury, such as:

• Head trauma.

• Brain surgery.

• Brain infections.

• Bleeding inside the skull.

• Arachnoiditis (inflammation of the arachnoid membrane).

Doctors also classify arachnoid cysts based on their location. Common locations include:

• Middle cranial fossa (side part of the brain near the temporal lobe).

• Suprasellar region (area near the pituitary gland).

• Posterior fossa (back portion of the brain).

• The thoracic spine (the middle part of the spine), this is the most common spinal location.

What Causes an Arachnoid Cyst?

The exact cause of arachnoid cysts is still not fully understood. Researchers believe most primary cysts happen because the arachnoid membrane splits or develops abnormally before birth.

In some families, more than one person may have an arachnoid cyst. This suggests genetics could play a role in certain cases.

Some medical conditions linked with arachnoid cysts include:

• Marfan syndrome (a disorder that affects connective tissues).

• Corpus callosum agenesis (a condition where part of the brain does not fully develop).

• Arachnoiditis.

Secondary arachnoid cysts may happen after:

• Head injury.

• Brain surgery.

• Brain infections.

• Bleeding inside the brain.

Sometimes, even a mild injury can cause bleeding inside or around the cyst. This may increase intracranial pressure and cause serious symptoms.

What Are the Risk Factors for an Arachnoid Cyst?

Certain factors may increase the chances of developing an arachnoid cyst or related complications. These include:

• Male gender.

• Family history of arachnoid cysts.

• Head injuries.

• Brain infections.

• Marfan syndrome.

• Arachnoiditis.

• Congenital brain abnormalities.

What Are the Symptoms of an Arachnoid Cyst?

Many arachnoid cysts do not cause symptoms. Symptoms usually appear when the cyst grows larger and begins to press on nearby structures. In many cases, symptoms begin before the age of 20.

Symptoms of Brain Arachnoid Cysts:

• Headache.

• Nausea and vomiting.

• Dizziness.

• Seizures (abnormal electrical activities in the brain).

• Vision or hearing problems.

• Extreme tiredness.

• Balance problems.

• Ataxia (loss of muscle coordination).

• Cognitive dysfunction (difficulty with memory and thinking).

• Weakness on one side of the body.

• Hormonal problems or early puberty in children.

• Hydrocephalus (buildup of fluid inside the brain).

• Developmental delay in children.

Symptoms of Spinal Arachnoid Cysts:

• Back pain.

• Leg weakness.

• Tingling or numbness.

• Difficulty walking.

• Scoliosis (curving of the spine).

• Problems controlling the bladder or bowel.

• Frequent urinary tract infections.

• Paralysis in severe cases.

What Are the Complications of an Arachnoid Cyst?

Most arachnoid cysts remain harmless throughout life. Still, larger cysts can sometimes put pressure on the spinal cord or brain and lead to complications such as:

• Hydrocephalus.

• Vision loss.

• Hearing loss.

• Facial pain.

• Seizures.

• Spinal cord compression.

• Balance problems.

• Nerve damage.

• Paralysis of eye muscles.

• Developmental problems in children.

• Bleeding or rupture of the cyst.

In rare situations, untreated pressure on the brain or spinal cord may lead to permanent nerve damage.

How to Diagnose an Arachnoid Cyst?

Many arachnoid cysts are discovered accidentally when someone undergoes a scan for headaches, seizures, or another health issue.

Doctors usually first ask for your detailed medical history and then perform a neurological examination. During the examination, the doctor may check:

• Vision and hearing.

• Eye movements.

• Muscle strength and motor function.

• Sense of smell.

• Reflexes.

• Balance and coordination.

• Sensation.

• Swallowing ability.

Imaging tests help confirm the diagnosis and also show the exact size and location of the cyst.

CT Scan:

A computed tomography (CT) scan creates detailed images of your brain and spine.

MRI Scan:

Magnetic resonance imaging (MRI) uses magnetic fields and radio waves to generate clear-cut images of soft tissues. MRI is commonly used because it provides a clearer view of the cyst and surrounding structures.

Ultrasonography:

In infants, ultrasonography (a scan that uses sound waves) may be used because the skull bones are not yet fully joined.

How to Treat an Arachnoid Cyst?

If the arachnoid cyst is small and does not cause symptoms, doctors may simply monitor it with regular follow-up scans.

Treatment is usually needed when the cyst grows, causes symptoms, or puts pressure on nearby tissues. The main goal is to reduce pressure and improve symptoms.

• Endoscopic Fenestration: Endoscopic fenestration is often the preferred treatment because it is less invasive. The operator uses a thin tube that is attached with a camera and small instruments to create an opening in the cyst wall, so the fluid can drain naturally.

• Craniotomy: Craniotomy is used for difficult cases. In a craniotomy, the surgeon creates an opening in the skull to directly reach the cyst. This procedure is more invasive, but it gives better access to the cyst in certain situations.

• Shunting: A shunt is a thin tube placed inside the cyst to drain fluid into another part of the body where it can be absorbed. This procedure is done if the fluid keeps collecting again.

• Resection: Some spinal arachnoid cysts can be removed completely through surgery. If full removal is not possible, partial removal or drainage may still reduce symptoms.

When Should You See a Doctor?

You should contact a doctor if you develop:

• Persistent headaches.

• Repeated vomiting.

• Seizures.

• Vision or hearing changes.

• Difficulty walking.

• Weakness or numbness.

• Behavioral changes.

• Delayed development in children.

Emergency medical care is needed if you suddenly develop:

• Severe headache.

• Loss of consciousness.

• Sudden paralysis.

• Severe confusion.

• Sudden vision loss.

• Symptoms after a head injury.

What Is the Long-Term Outlook for Arachnoid Cysts?

Most people with arachnoid cysts live healthy and normal lives. Many cysts remain stable and do not require treatment.

If symptoms develop, surgery often helps relieve pressure and improve quality of life. However, in some cases, the cyst may refill with fluid after treatment, so regular follow-up scans may still be needed.

Children who receive early treatment for symptomatic cysts usually have better long-term outcomes.

Conclusion

Arachnoid cysts are noncancerous fluid-filled sacs that can develop in the brain or spinal cord. Many cysts never cause symptoms and are often found accidentally during imaging tests.

However, larger cysts may press on nearby tissues, leading to headaches, seizures, balance problems, vision changes, or spinal symptoms. It is diagnosed through neurological examination, CT, and MRI scans.

Doctors usually advise monitoring for small cysts, while surgery is recommended for larger symptomatic cysts. Consult a brain, spinal cord, and nerve health specialist if you notice the sudden occurrence of any of these symptoms or if they appear after a head injury.

Key Takeaways

• An arachnoid cyst is a noncancerous, fluid-filled sac that develops in the brain or spinal cord.

• Many cysts do not cause symptoms and are often found accidentally during MRI or CT scans.

• Larger cysts can cause headaches, seizures, balance problems, vision changes, back pain, or leg weakness by pressing on nearby tissues.

• Doctors will usually suggest only monitoring for small cysts. For larger cysts with symptoms, doctors may suggest surgery to relieve pressure and improve the symptoms.

• You immediately consult your doctor if you notice a sudden, severe headache, confusion, paralysis, or vision loss. You should also get yourself checked if you suffer from these symptoms after a head injury.