Cysts located in the brain are not truly “brain tumors” because they do not arise from the brain tissue itself. Although they tend to be (benign noncancerous), they are sometimes found in parts of the brain that control vital functions.
There are four main types of cysts found in the brain:
- Arachnoid Cyst (also called Leptomeningeal Cyst): An enlarged, fluid-filled area of the subarachnoid space that occurs in both adults and children.
- Colloid Cyst: Although scientists are not sure of the definitive cause of colloid cysts, most agree that these cysts begin during embryonic development of the central nervous system. Malignant forms are unknown.
- Dermoid Cyst: These cysts most likely form during the early weeks of fetal development even though symptoms may not be noticed until years later. They are usually benign.
- Epidermoid Cyst (also called Epidermoid Tumor): Often referred to as epidermoid tumors. Likely form during the early weeks of fetal development even though the symptoms may not be noticed until decades later.
Cysts can appear in a variety of locations within the brain.
- Arachnoid Cysts appear in the subarachnoid space (between the arachnoid and pia mater layers of the meninges).
- Colloid Cysts are typically attached to the roof of the third ventricle and the choroid plexus.
- Dermoid Cysts, though rarely found in the brain, are usually located at the lower back portion of the brain (the posterior fossa) in older adults and in the lower end of the spine in older children and young adults.
- Epidermoid Cysts tend to be located in the area where the top part of the brain meets the brain stem.
Just like a cyst anywhere else in your body, a cyst in the brain is a tumor-like sphere filled with fluid—much like a balloon filled with water. They may contain fluid, blood, tissue, or tumor cells.
- Arachnoid Cysts are enlarged, fluid-filled areas between layers of the covering of the brain.
- Colloid Cysts tend to contain a thick, gel-like substance called colloid.
- Dermoid and Epidermoid Cysts are tumor-like spheres.
Symptoms depend on the size and location of the cyst.
- Arachnoid Cysts can be found in both adults and children.
- Colloid Cysts almost always occur in adults.
- Dermoid Cysts in the brain tend to occur in children under 10 years old.
- Epidermoid Cysts are most commonly found in middle-aged adults.
The exact cause of cysts is unknown, but it is suspected that certain types form in the early weeks of fetal growth. Nothing specific can be done to prevent the development of cysts.
The type, size, and location of the cyst determine how it will be addressed. Treatment methods for the various types of cysts are briefly explained below:
- Arachnoid Cyst: Treatment may be “watchful waiting,” or the cyst may require surgery.
- Colloid Cyst: Surgery is typically recommended. However, removal can be challenging because of its location.
- Dermoid and Epidermoid Cysts: Surgery is typically recommended. If complete removal is not possible, the remaining portion of the cyst may regrow. Fortunately, this growth may be very slow and it could be years before symptoms return.
Learn more about different treatment options for cysts on our Treatment page.