The arachnoid cyst is a small and benign sac that develops between the brain or spinal cord and the arachnoid membranes. This is one of the three membranes which cover the brain and the spinal cord. Most often, it happens in the brain, where it is also called an intracranial cyst, but also it is known as arachnoid cyst which can develop in the spinal cord as well.
You should know that arachnoid cyst is not a brain tumor. This is a benign cyst that is usually filled with clear CSF (cerebrospinal fluid). It is most often present at birth but it may not be detected for years. In many cases, the arachnoid cyst causes no symptoms at all. If the arachnoid cyst is going to create symptoms, then it usually does in early life. [1,2]
Most often, this is happening in the first twelve months of a child’s life and sometimes not until adolescence as the cyst grows and it is almost always before the age of twenty. The arachnoid cyst which is causing symptoms needs to be evaluated for possible treatment because it can continue to grow and it can cause neurological damage because it puts pressure on the surrounding brain tissue.
The symptoms of the arachnoid cyst depend on where in the central nervous system it happens. You should know that intracranial cysts cause different symptoms than spinal cysts do. It is noticed that the arachnoid cyst happens more commonly in boys than in girls . When the arachnoid cyst is present at birth, then it is known as a primary cyst. Those arachnoid cysts which develop later in the lifer are known as secondary cysts.
Symptoms of Arachnoid Cyst:
There are some cases when the arachnoid cyst is causing no symptoms at all. When the arachnoid cyst cause symptoms, then these symptoms depend on where the cyst is located. When the arachnoid cyst is located around the brain, then these symptoms include :
- Ataxia (this is a lack of muscle control)
- Hemiparesis (this is weakness or paralysis on one side of the body)
- Decreased cognitive performance
- Difficulties with balance and walking
- Hearing and visual disturbances
- Behavioral changes
- Developmental delay
- Hydrocephalus (this is an accumulation of fluid in the brain which can change the shape of an infant’s head)
- Nausea and vomiting
The arachnoid cyst around the spinal cord compresses the spinal cord or nerve roots and it causes symptoms, such as
- Tingling or numbness in the legs or arms
- Back and leg pain
The arachnoid cysts which cause any of the mentioned symptoms need to be evaluated for possible treatment because as it continues to grow, it can cause neurological damage because it puts pressure on the surrounding brain tissue.
Many of the mentioned symptoms can be caused by other health problems, so this is a reason why you should see your doctor as soon as you notice any of the mentioned symptoms so he or she will give you the right diagnosis and treatment. Usually, doctors diagnose the arachnoid cyst with sureness so they can give their patients much needed treatment.
Also, there is an option for surgery to drain or to remove the arachnoid cyst which is also safe and effective. There are some cases when doctors can discover the arachnoid cyst by accident which means that the scan is done for another reason. There are some arachnoid cysts that can be detected on a prenatal ultrasound.
If the arachnoid cyst is not causing any symptoms, then no treatment will be necessary. But the arachnoid cyst which causes symptoms needs to be evaluated for the treatment. Your doctor will give you the right diagnosis because many of the symptoms of the arachnoid cyst are the same as with other health conditions.
Usually, doctors drain the arachnoid cyst and if you have decided to make surgery, then it needs to be done by a professional doctor.
Causes of Arachnoid Cyst:
The exact cause for the primary arachnoid cyst is not known. It develops in a fetus during pregnancy but no one knows which the cause is for it [1,2]. The secondary arachnoid cyst can be caused by a complication of brain surgery, illness (brain tumor or meningitis), or trauma (a fall, accident, or another injury). 
 National Institute of Neurological Disorders and Stroke. Arachnoid cysts information page. 2019. Retrieved from www.ninds.nih.gov/Disorders/All-Disorders/Arachnoid-Cysts-Information-Page
 Oberbauer RW, Haase J, Pucher R. Arachnoid cysts in children: a European co-operative study. Child’s Nervous System. 1992;8:281–6.
 Jafrani R, Raskin JS, Kaufman A, Lam S. Intracranial arachnoid cysts: Pediatric neurosurgery update. Surgical Neurology International. 2019;10:15. doi:10.4103/sni.sni_320_18
 Mustansir F, Bashir S, Darbar A. Management of arachnoid cysts: A comprehensive review. Cureus. 2018;10(4):e2458. doi:10.7759/cureus.2458
 Zuckerman SL, Prather CT, Yengo-Kahn AM, et al. Sport-related structural brain injury associated with arachnoid cysts: a systematic review and quantitative analysis. Neurosurgical Focus. 2016;40(4):E9. doi:10.3171/2016.1.FOCUS15608.