Arachnoid cysts are fluid-filled sacs that occur on the arachnoid membrane that covers the brain (intracranial) and the spinal cord (spinal). There are three membranes covering these parts of the central nervous system: the dura mater, arachnoid, and pia mater. Arachnoid cysts appear on the arachnoid membrane, and they may also expand into the space between the pia mater and arachnoid membranes (subarachnoid space). The most common locations for intracranial arachnoid cysts are the middle fossa (near the temporal lobe), the suprasellar region (near the third ventricle) and the posterior fossa, which contains the cerebellum, pons, and medulla oblongata.
Arachnoid cysts are usually asymptomatic. That means they don’t tend to produce symptoms. As a result, most people who have an arachnoid cyst don’t realize it until they’re examined for other issues, such as head injuries.
In some cases, arachnoid cysts do cause symptoms. Symptoms depend on the location and size of the cyst. For example, symptoms may develop if you have a cyst that presses on nerves or sensitive areas of your brain or spinal cord. If it’s located in your brain, the cyst may produce one or more of the following symptoms:
- problems hearing, seeing, or walking
- Developmental delay
- balance issues
If it’s located in your spinal column, it may cause symptoms such as:
- back pain
- muscle weakness or spasms
- lack of feeling or tingling in your arms or legs
- problems controlling your bladder or bowels
If you develop these symptoms, contact your doctor.
A diagnosis of arachnoid cysts is often made incidentally, often during the examination of an individual with seizures. A diagnosis may be suspected based upon a detailed patient history, a thorough clinical examination, and a variety of specialized tests, especially advanced imaging studies such as computed tomography (CT scan) and magnetic resonance imaging (MRI). CT scans and MRIs can reveal or confirm the presence of arachnoid cysts. During CT scanning, a computer and x-rays are used to create a film showing cross-sectional images of the brain’s tissue structure. During MRI, a magnetic field and radio waves are used to create cross-sectional images of the brain.
- Burr hole drainage; A very simple, fast and minimally-invasive treatment is burr hole drainage of the cyst. There is a high rate of recurrence and return of symptoms with this procedure, however.
- Craniotomy; A craniotomy can also be performed to remove the cyst wall and ensure normal communication with the cerebrospinal fluid pathways. This is a more invasive procedure but allows for direct inspection of the cyst.
- Endoscopic fenestration; Another option is the minimally invasive endoscopic fenestration of the cyst, where the physician drains the cyst with a needle.
- Shunting; Shunting of the cyst is the simplest surgical procedure. A patient becomes dependent on the shunt, however, which can cause complications.