Arachnoid Cysts – Primary Steps for Primary Care
A frequent reason for urgent calls to our neurosurgery clinic is the incidental finding of an arachnoid cyst on a CT or MRI scan of the brain. Often these imaging studies are ordered for headaches, possible seizures, post-concussion symptoms or other neurologic concerns. As the ordering physician, the primary care doctor must determine what role, if any, the cyst is playing in the child’s condition. Fortunately, arachnoid cysts rarely, if ever, cause symptoms or need surgical intervention.
The first description of arachnoid cysts can be traced back to the early to mid-1800s. Even back then, they were noted to be chronic, associated with brain and bone remodeling, and with little likelihood of change over time. They can be diagnosed at any age, with some prenatal studies showing formation as early as the first trimester.
There is a slight predisposition for cyst occurrence in males, on the left and in the middle fossa, but they can be found in all areas of the brain. Many theories have been proposed as to the cause of arachnoid cysts, but none have been conclusive.
How common are they?
1-3% – incidence of arachnoid cysts in the population
50% – in the middle fossa
40% – in the posterior fossa
What is the natural history of arachnoid cysts?
Multiple studies have shown the likelihood of arachnoid cyst growth during childhood to be very small. Cysts found after the age of 4 years are highly unlikely to ever grow or change (1).
Most cysts are found incidentally on imaging obtained for unrelated reasons. Cysts rarely are found in locations of the brain that result in hydrocephalus or endocrine disturbances.
There is little conclusive evidence to suggest that arachnoid cysts cause or are related to headaches unless they are causing overt hydrocephalus. Or that they are causative of seizures, developmental delays or cognitive deficits (3, 4).
There appears to be minimal risk of hemorrhage or rupture of cysts less than 5cm in diameter (2). There exists some debate as to sports involvement after diagnosis and this is a topic best addressed in a clinic visit.
What should you do with an arachnoid cyst?
- Do NOT tell the family this will need surgery or is the source of all the child’s complaints (it likely does not and is not).
- Do NOT send the family to the emergency room unless they are exhibiting life-threatening symptoms. The acute recognition of a chronic problem, does not create an emergency.
- DO call our clinic or place a referral to our physicians. We will be happy to discuss the diagnosis with the family and help them determine what, if any, follow-up or additional imaging will be needed.
What can you tell the family while they wait for an appointment?
- Treat their underlying complaint. Standard treatments for headaches, concussions, seizure work-up, etc., are all appropriate and safe.
- Advise the child to refrain from contact sports until you can discuss the cyst and associated risks with the patient and family.
- Reassure the family that these cysts are common, usually asymptomatic, and most frequently do NOT require surgery.