Arachnoid Cyst - Brain & Spinal Cord 

Introduction
Arachnoid cysts develop in the brain and only rarely in the spinal cord.  The cysts develop when a layer of tissue separates and fills with fluid, forming a cyst.  The arachnoid membrane is a layer of the protective covering of the brain and spinal cord.  Some arachnoid cysts do not cause symptoms and may not need treatment.  Cysts that cause symptoms are removed with surgery.

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Anatomy
Your brain is located inside of your skull.  It is the control center of your body.  Your brain controls the way you think, behave, feel, and move your body.  Your brain communicates with the nerves in your body for functions you can control, such as talking or moving your arms and legs.  Your brain also controls the life-sustaining functions that happen automatically, including your heartbeat, body temperature, blood pressure, and body metabolism.
 
The spinal cord is an extension of the brain.  The spinal cord is a column of nerves located inside of your spine.  The spinal cord and the brain exchange nerve messages about muscle movements and sensation.
 
Three layers of connective tissue cover the brain and spinal cord.  The pia mater is attached to the brain and spinal cord.  The middle layer is the arachnoid.  The outer layer is the dura mater.  Cerebral spinal fluid flows between the pia mater and arachnoid layer in the subarachnoid space.  Cerebral spinal fluid acts as a shock absorber to protect the delicate nerve structures during movement.

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Causes
An arachnoid cyst forms when the two layers of the arachnoid membrane separate.  Cerebrospinal fluid fills the space, forming a cyst.  People may be born with arachnoid cysts in the brain or spinal cord.  These cysts occur during the early weeks of growth in a developing baby in the womb.  Secondary arachnoid cysts develop after traumatic brain injury, tumors, infection, meningitis, or complications from brain surgery.  The exact reason why arachnoid cysts develop is unclear.
 
Primary arachnoid cysts are more common than secondary arachnoid cysts.  Arachnoid cysts in the spinal cord are rare.  Symptoms of arachnoid cysts occur most frequently before age one and before the age of 20.  Males are four times more likely to experience an arachnoid cyst than females.

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Symptoms
Some people with arachnoid cysts do not experience symptoms.  Symptoms most frequently occur before the age of one and by the age of twenty.  Symptoms depend on the size and location of the cyst.  Cysts grow larger as they fill with more cerebrospinal fluid.  In infants, the size of the head may increase.  Infants may experience developmental delays.
 
Headaches, nausea, vomiting, seizures, or behavioral changes are symptoms of arachnoid cysts.  You may experience changes in hearing, vision, or balance.  Cysts in the spinal cord can cause movement problems, weakness, paralysis, tingling, pain, or numbness.

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Diagnosis
A doctor can diagnose an arachnoid cyst by reviewing your medical history and conducting a thorough neurological examination, physical examination, and some tests.  Your vision and hearing may be tested.  Infants’ developmental levels may be assessed.
 
Imaging tests are used to identify the location and size of the cyst.  Magnetic resonance imaging (MRI) scans and computerized tomography (CT) scans create images of the structures in the brain.  Ultrasound is frequently used in infants.  Cranial pressure may be measured and carefully monitored.

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Treatment
Small cysts that do not cause symptoms may not be treated but will be carefully monitored.  Traditionally, shunts (surgically placed tubes) were used to drain the cerebral spinal fluid from the cysts.  Newer advanced surgical methods, including microneurosurgery and endoscopic surgery, use noninvasive methods to remove or open the covering on the cyst to allow the cerebral spinal fluid to drain and be absorbed naturally.  Symptoms and neurological impairments usually resolve quickly following surgery.  Infants may wear a protective helmet while they recover.

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Prevention
Permanent nerve damage may be avoided with prompt treatment.

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Am I at Risk
Arachnoid cysts are associated with several syndromes, although the exact links are not clear.  You may be at risk for a secondary arachnoid cyst if you have experienced traumatic brain injury, tumors, infection, meningitis, or complications from brain surgery.  Children with kyphoscoliosis (curvature of the spine) appear to have an increased risk for spinal arachnoid cysts.  Developmental disorders of the spinal cord (myelodysplasia) are also associated with arachnoid cyst development.

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Complications
Untreated arachnoid cysts may become larger and cause permanent damage as they compress brain tissues or the spinal cord.  Bleeding or increased intracranial pressure in the brain can cause similar damage.

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This information is intended for educational and informational purposes only. It should not be used in place of an individual consultation or examination or replace the advice of your health care professional and should not be relied upon to determine diagnosis or course of treatment.

The iHealthSpot patient education library was written collaboratively by the iHealthSpot editorial team which includes Senior Medical Authors Dr. Mary Car-Blanchard, OTD/OTR/L and Valerie K. Clark, and the following editorial advisors: Steve Meadows, MD, Ernie F. Soto, DDS, Ronald J. Glatzer, MD, Jonathan Rosenberg, MD, Christopher M. Nolte, MD, David Applebaum, MD, Jonathan M. Tarrash, MD, and Paula Soto, RN/BSN. This content complies with the HONcode standard for trustworthy health information. The library commenced development on September 1, 2005 with the latest update/addition on April 13th, 2016. For information on iHealthSpot’s other services including medical website design, visit www.iHealthSpot.com.