Arachnoid Cysts

Arachnoid cysts are benign fluid-filled sacs in the brain or spine. The three most common surgical treatments for arachnoid cysts in the brain are craniotomy fenestration, endoscopic cyst fenestration, or shunt placement. The nonsurgical treatment is close observation of the cyst.

Usually, arachnoid cysts develop between the surface of the brain and the skull base, or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord. Less often, they arise in the spine.

Arachnoid cysts are the most common type of intracranial cyst and are typically found in the temporal fossa, the posterior fossa and the suprasellar region.

Untreated arachnoid cysts may cause permanent, severe neurological damage due to expansion of the cyst, hydrocephalus, or hemorrhage. With treatment, most individuals with arachnoid cysts have a good prognosis.


Symptoms of an arachnoid cyst depend on the cyst’s size and location. Small cysts are usually asymptomatic and are discovered only incidentally. Large cysts may cause cranial deformation or macrocephaly as a result of hydrocephalus, particularly among infants and young children whose skulls still have fontanels. Symptoms may include:

  • Headache, which is often worse in the morning upon waking
  • Nausea and vomiting
  • Seizures
  • Increased intracranial pressure
  • Developmental delay
  • Behavioral changes
  • Hemiparesis
  • Ataxia
  • Vision disturbances


A neurological examination is typically conducted to evaluate symptoms and identify any problems. This exam consists of assessing ability to swallow, sense of smell, hearing, eye movements, sensation, motor function, balance, and coordination.

Imaging studies are the main component of diagnosis. Computed tomography (CT) scans or magnetic resonance imaging (MRI) scans may be used to visualize the mass. These studies can be performed with or without contrast enhancement.

For infants, ultrasonography is typically used instead of CT or MRI scans to image the cyst.

Risk Factors

The cause of arachnoid cysts is currently unknown.

Most instances are sporadic. Research suggests that these cysts develop when the arachnoid membrane splits, allowing cerebrospinal fluid to flow in and become trapped.

Arachnoid cysts occur more often among males than females and can arise at any age. Most cases are congenital, but may not be noticed until later in life.


At Columbia, our neurosurgeons use the latest surgical techniques to treat arachnoid cysts, providing the best possible outcomes.

No surgical treatment is typically needed for cysts that are asymptomatic. Instead, the cyst is closely monitored with imaging tests for any changes, and treatment may be recommended later if the cyst produces problems.

For symptomatic cysts, the first step of treatment is often surgery. Surgical options include shunt placement, craniotomy fenestration and a more recent method called endoscopic cyst fenestration.

The neurosurgeon can surgically place a permanent drainage system, called a shunt, to remove pressure from the cyst. Shunt placement is a minimally invasive procedure and may be appealing due to the simplicity of the operation.

Alternatively, craniotomy fenestration can be done to fenestrate the walls of the cyst, allowing the fluid to drain out. Craniotomy fenestration begins with temporary removal of a piece of skull bone so that surgeons can access the brain. Because of its high success rate, this procedure is typically favored over shunt placement.

Microsurgical advances have made possible another technique, endoscopic cyst fenestration. Endoscopic cyst fenestration is a minimally invasive technique in which a burr hole is made and an endoscope is guided through the opening. Upon reaching the cyst, the neurosurgeon fenestrates the walls of the cyst, draining the fluid. It is the procedure of choice for most instances of arachnoid cysts.