A brain cyst or cystic brain lesion is a fluid-filled sac in the brain. It can be noncancer (benign) or cancer (malignant). Benign means that the growth doesn't spread to other parts of the body. A cyst may contain blood, pus, or other material. In the brain, cysts sometimes contain cerebrospinal fluid (CSF). CSF is a clear liquid that bathes and cushions the brain and spinal cord. Some brain cysts begin before birth.

Even if a brain cyst isn't cancer, it can still cause problems. The cyst may press against brain tissue and cause symptoms. These include headache, vision problems, or nausea. You may need surgery to remove the cyst if this happens. If the cyst is small and not growing and isn't likely to cause symptoms, your doctor may advise watching it instead of surgery.

There are different types of brain cysts:

• Arachnoid cyst. This is a cyst between the brain and the arachnoid membrane. This membrane is one of the protective coverings around the brain. An arachnoid cyst contains CSF. These appear most often in children. They can form from problems in the way the brain or spinal cord develops before birth. They may also happen in adults. This type of cyst happens more often among males than females.
• Leptomeningeal cyst. This is linked with a fracture of the skull. It often happens in children younger than 3 years. It is also known as a growing skull fracture. It's called a cyst even though it often contains solid material instead of fluid.
• Colloid cyst. This is a gel-filled cyst. It often forms in one of the four ventricles of the brain. The ventricles are the CSF reservoirs in the brain. Colloid cysts often happen in the third ventricle. This is in a central spot in the brain. The cysts can lead to blockage of CSF flow off and on and cause positional headaches. These are headaches that happen when a person is in a certain position. These tend to appear during adulthood.
• Dermoid cyst. This is a rare type of cyst. It forms when a few skin cells get trapped when the brain and spinal cord form before birth. These cysts may even contain sweat gland cells or hair follicle cells. These often appear in children.
• Epidermoid cyst. This is also called an epidermoid tumor. Like a dermoid cyst, it forms from a bit of tissue that gets trapped when the brain and spinal cord form. Epidermoid cysts don't contain sweat glands or hair follicle cells. They grow very slowly. These cysts often first appear when a person is an adult.
• Pineal cyst. This happens on the pineal gland in the middle of the brain. This type of cyst often only shows up during imaging scans done for another reason. Pineal cysts seldom cause problems. They can sometimes affect vision if they do grow large. They can appear in people of any age.
• Brain abscess. This happens anywhere in the brain as a single cyst or multiple cysts. Abscesses and pockets of infection are often caused by a bacterial infection. They are sometimes caused by a parasite or a fungus.
• Neoplastic cyst. This is due to a benign or malignant tumor. It's called metastatic when a brain tumor starts outside the brain.

Brain cysts are caused by the buildup of fluid in an area of the brain. The cysts can form during the first few weeks when a fetus is growing in the uterus. Some cysts might form because of a head injury. Or other trauma to the brain. In other cases, there may be links between a brain cyst and a noncancer tumor or a cancer tumor.

The symptoms generally depend on which part of the brain the cyst is growing in. In some cases, a small cyst may not cause any symptoms. Some cysts are “silent” (cause no symptoms) until they grow large. In other cases, the symptoms may be due to blockage of the normal flow of CSF. This can cause increased pressure on the brain (intracranial pressure).

Symptoms may be different for each person, but can include:

• Headache (common).
• Nausea and vomiting.
• Vertigo or dizziness.
• Hearing or vision problems.
• Trouble with balance and walking.
• Facial pain.
• Seizures (not common).

Your doctor may discover a brain cyst when it shows up on an imaging scan done for another reason. In other cases, you may be having symptoms related to the cyst. Your doctor may refer you to a neurologist. This is a doctor who specializes in diagnosing and treating diseases of the central nervous system. Or you may be referred to a neurosurgeon. This is a surgeon who does brain or spinal cord surgery.

The process to diagnose a cyst starts with a health history and a physical exam. Your doctor will ask about your symptoms and past health conditions. They may also ask about your family's health history. The physical exam may include a nervous system exam. Imaging tests may be done to look at the brain. Contrast dye may be used to help show more detail in the images. The tests may include:

• CT scan. This is an imaging test that uses X-rays and a computer to make detailed images of the body. Scans may be done of your brain and spinal cord.
• MRI. This test uses large magnets and a computer to create images of the body. MRI scans of your brain and spinal cord may be done to get more information about the cyst and nearby tissues.

Scans may be repeated over time to learn if the cyst is growing.

If a brain cyst is causing problems, your doctor may advise removing it with surgery. If the cyst is not causing symptoms and it isn't growing, your doctor may suggest watching it closely with repeated brain scans. Treatment can vary by the type of cyst. For example:

• If you have an arachnoid cyst, your doctor may puncture the cyst sac and drain the fluid. The fluid drains into the CSF or it's pulled out with a needle. The sac may fill with fluid again if your doctor drains the cyst without removing part of the sac or placing a permanent draining tube.
• If you have a dermoid or epidermoid cyst, your doctor will likely remove it. The complete cyst with its sac will likely be removed. It may regrow and cause symptoms again after a few years if the cyst isn't fully removed.
• Colloid cysts often cause a buildup of excess CSF. This is known as hydrocephalus. This can create a dangerous increase in pressure within the brain. A shunt or drainage tube can relieve some of this pressure. Colloid cysts can be hard to remove because they are often located deep within the brain. Your doctor may use special surgical methods with tiny endoscopic tools sent through a thin tube into the brain to remove these.
• Pineal cysts often cause no problems. It's often possible to manage these by watching for any changes.
• Tumor cysts can be treated with surgery, radiotherapy, or chemotherapy. These may be done alone or in combination.
• Abscesses are treated with antibiotics, antifungals, or antiparasite medicines. You may also need surgery.

• Brain cysts are fluid-filled sacs that may form in the brain. They can be noncancer (benign) or cancer (malignant).
• Brain cysts may appear in children or adults. In some cases, brain cysts begin before birth but don't cause any symptoms until much later.
• A brain cyst that doesn't cause symptoms will sometimes show up during an imaging scan done for another reason.
• There are different types of brain cysts. These include arachnoid, colloid, dermoid, epidermoid, pineal, infectious, and tumor cysts.
• Brain cysts may press against brain tissue and cause symptoms even when they aren't cancer. Sometimes a cyst may block the normal flow of CSF. This can cause problems.
• Your neurologist or neurosurgeon may advise surgically removing the cyst. If the cyst is small and not likely to cause symptoms, your doctor may instead advise watching it to see if it remains stable.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your provider tells you.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions, especially after office hours or on weekends and holidays.