Weill Medical College of Cornell University

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Arachnoid Cysts

Developmental cysts of the brain, or arachnoid cysts, cause symptoms based on the location and size of the cyst. Arachnoid cysts develop between the surface of the brain and the normal fluid space surrounding the brain, the subarachnoid space. This fluid is contained within the arachnoid membrane, one of three membranes that covers the brain and the spinal cord. Most cases begin during infancy but onset may be delayed until adolescence. The majority of arachnoid cysts do not cause symptoms and never require treatment.

However, symptomatic arachnoid cysts may cause permanent neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding). With treatment, most individuals with arachnoid cysts do well.

Symptoms

Symptoms of an arachnoid cyst depend on cyst size and location. Small cysts are usually asymptomatic and are discovered only incidentally. Large cysts may cause cranial deformation or macrocephaly (enlargement of the head), producing such symptoms as:

• Headaches
• Seizures
• Hydrocephalus (excessive accumulation of cerebrospinal fluid)
• Increased intracranial pressure
• Developmental delay
• Behavioral changes
• Hemorrhages
• Decreased cognitive performance
• Hemiparesis (weakness or paralysis on one side of the body)
• Ataxia (lack of muscle control)

Treatment

Treatment for arachnoid cysts is recommended only in the presence of symptoms.

• When symptoms warrant, the surgical placement of a permanent drainage system, a type of shunt, to remove pressure from the cyst may be required. Shunt placement is appealing due to the simplicity of the operation.
• Alternatively, an open surgical procedure to create an aperture in the walls of the cyst may be performed, called fenestration. Cyst fenestration is typically favored due to the high success rate of this procedure.
• Endoscopic cyst fenestration is a technique that couples the minimally invasive benefits of shunting with the advantage of open fenestration by avoiding shunt implantation. This is the preferred first-line therapeutic approach since indwelling hardware and all shunt-related complications can be avoided.