An arachnoid cyst is a collection of cerebrospinal fluid (CSF) in the arachnoid membranes of the brain or spinal cord that may be asymptomatic but can also cause headaches, back pain, weakness, paralysis, or seizures.
An arachnoid cyst can be congenital (present since birth), caused by a defect in the formation of the arachnoid membrane during fetal development, or acquired, caused by trauma or infection and developing over time.
Treatment of an arachnoid cyst is managed by a pediatrician, pediatric neurologist, and/or neurologist and may require placement of a permanent shunt in the brain to drain the fluid and prevent it from building back up again or an open craniotomy.
Main symptoms
Symptoms of an arachnoid cyst vary based on the location of the cyst:
1. Cerebral arachnoid cyst
The main symptoms of a cerebral arachnoid cyst are:
- Headache;
- Nausea and vomiting;
- Dizziness or vertigo;
- Ringing in the ears;
- Hearing or vision problems;
- Loss of balance or coordination;
- Seizures.
A cerebral arachnoid cyst may also cause developmental delays or regression in children, hydrocephalus, or increased intracranial pressure.
A cerebral arachnoid cyst, also known as an intracranial arachnoid cyst, does not typically cause symptoms, however symptoms may arise when the cyst increases in size and starts compromising other structures in the brain or when the cyst bursts.
2. Spinal arachnoid cyst
The main symptoms of a spinal arachnoid cyst are:
- Back pain;
- Muscles weakness in the legs;
- Mild paralysis in one arm or leg;
- Numbness or tingling in the hands, arms, or legs;
- Muscle spasms.
Other complications may include neurogenic bladder, urinary incontinence, or scoliosis.
A spinal arachnoid cyst is rarer than a cerebral arachnoid cyst and typically affects the thoracic spine.
These cysts are usually asymptomatic and are only discovered on a routine exam or diagnostic testing for another condition.
Confirming a diagnosis
The diagnosis of an arachnoid cyst is made by a pediatrician, pediatric neurologist, or neurologist and is usually discovered through diagnostic testing for other conditions.
When a child presents with symptoms, an arachnoid cyst can be diagnosed using imaging tests like a CT scan (computed tomography) or MRI (magnetic resonance imaging), which allows for visualization of the location and size of the cyst as well as the surrounding structures.
Different types
The main types of arachnoid cysts are:
- Type I arachnoid cysts: Small cysts that do not cause symptoms and are located in the anterior and middle cranial fossa;
- Type II arachnoid cysts: Medium-sized cysts located along the Sylvian fissure that cause displacement of the temporal lobe;
- Type III arachnoid cysts: Large cysts located in the middle cranial fossa that cause displacement of the temporal, frontal, and parietal lobes.
The type of arachnoid cyst can be identified by a doctor based on diagnostic exams and presenting symptoms.
Possible causes
Causes of arachnoid cysts can be divided into two categories, which are:
1. Primary arachnoid cysts
Primary arachnoid cysts are caused by an abnormal growth in the brain or the spinal cord during fetal development.
This type of cyst, also known as a congenital arachnoid cyst, is present at birth and causes symptoms when the cyst compresses the brain or spinal nerves.
2. Secondary arachnoid cysts
Secondary arachnoid cysts have several potential causes, including brain or spinal cord injuries, infections like meningitis, or tumors.
These cysts are also known as acquired arachnoid cysts.
Treatment options
Treatment of an arachnoid cyst is managed by a pediatrician, pediatric neurologist, and/or neurologist and varies based on the size and location of the cyst in addition to any symptoms.
The main treatments for an arachnoid cyst are:
1. Regular follow up
Arachnoid cysts that are not causing symptoms do not require treatment, however regular medical follow up is recommended to monitor the condition.
In these cases, the cyst is periodically monitored on CT scan or MRI to check if it has grown in size or changed in shape or appearance.
2. Permanent drainage system
A permanent drainage system, also known as a shunt, involves permanent placement of a tube in the brain with a valve that drains liquid from the cyst into the abdomen or thorax to be reabsorbed by the body.
This treatment of cerebral arachnoid cysts helps reduce pressure in the brain.
3. Microsurgical fenestration
Microsurgical fenestration involves making a hole in the cranium to access the cyst and incisions to drain the cyst so that the fluid can be absorbed by the surrounding tissues, reducing pressure exerted on the brain.
While this procedure is more invasive than the above treatments, it is more effective and definitive.
4. Endoscopic fenestration
Endoscopic fenestration is an advanced technique that offers the same benefits as microsurgical fenestration while being less invasive.
Endoscopic fenestration is a quick procedure that does not require opening the cranium.
This procedure is performed using an endoscope, which is a type of tube with a small camera at the end that drains the fluid from the cyst into the brain.