NORD is very grateful to Hrayr K. Shahinian, MD, FACS, Director, and Yoon Ra, MSc, Clinical Research, Skull Base Institute, for assistance in the preparation of this report.
Synonyms of Arachnoid Cysts
- cysts, arachnoid
- intracranial arachnoid cysts
- spinal arachnoid cysts
Arachnoid cysts are fluid-filled sacs that occur on the arachnoid membrane that covers the brain (intracranial) and the spinal cord (spinal). There are three membranes covering these parts of the central nervous system: the dura mater, arachnoid, and pia mater. Arachnoid cysts appear on the arachnoid membrane, and they may also expand into the space between the pia mater and arachnoid membranes (subarachnoid space). The most common locations for intracranial arachnoid cysts are the middle fossa (near the temporal lobe), the suprasellar region (near the third ventricle) and the posterior fossa, which contains the cerebellum, pons, and medulla oblongata.
In many cases, arachnoid cysts do not cause symptoms (asymptomatic). In cases in which symptoms occur, headaches, seizures and abnormal accumulation of excessive cerebrospinal fluid in the brain (hydrocephalus) are common. The exact cause of arachnoid cysts is unknown. Arachnoid cysts are classified according to their specific location.
In most cases, arachnoid cysts are present at birth (congenital), but usually do not cause any symptoms (asymptomatic) throughout an individual's life. Less often, arachnoid cysts may develop because of head injury, the presence of a tumor, infection or surgery on the brain
Whether symptoms develop depends upon the size and the specific location of the cyst within the brain. Small cysts usually do not cause symptoms. However, cysts can increase in size causing symptoms to appear, especially if they press against a cranial nerve, the brain, or the spinal cord.
Most cases of arachnoid cysts that are associated with symptoms occur in childhood. The specific symptoms present vary from case to case. It is important to note that affected individuals will not have all of the symptoms listed below.
The most common symptoms associated with arachnoid cysts are usually nonspecific and include headaches, nausea, vomiting, dizziness and the accumulation of excessive cerebrospinal fluid in the brain (hydrocephalus), resulting in increased intracranial pressure In rare cases, in some children, an arachnoid cyst can cause malformation of certain cranial bones, resulting in an abnormally enlarged head (macrocephaly). .
A variety of additional symptoms occur in some individuals with arachnoid cysts depending upon the size and location of the cyst. Most cysts occur near the middle fossa region of the brain. Such symptoms include lethargy, seizures, vision abnormalities and hearing abnormalities. Neurological signs may be present because arachnoid cysts may cause increased pressure on structures of the brain. Such neurological findings may include developmental delays, behavioral changes, an inability to control voluntary movements (ataxia), difficulties with balance and walking and cognitive impairment. Weakness or paralysis on one side of the body (hemiparesis) has also been reported.
In addition to hydrocephalus, cysts located in the suprasellar region may be associated with vision disturbances, continuous bobbing of the head, and abnormalities affecting certain hormone-producing glands that help to regulate the rate of growth, sexual development, and certain metabolic functions (endocrine system).
Although they occur much less often than those found within the skull (intracranial), arachnoid cysts may also arise near the spine (spinal arachnoid cysts). Spinal arachnoid cysts may be associated with progressive weakness of the legs, tingling or numbness in the hands or feet, abnormal side-to-side curvature of the spine (scoliosis), back pain, and involuntary muscle spasms (spasticity) that result in slow, stiff movements of the legs. In rare cases, these cysts may cause paralysis of the legs (paraplegia). Urinary tract infections may also occur in individuals with spinal arachnoid cysts.
Other symptoms and physical findings have been reported to be associated with arachnoid cysts including migraine headaches, attention-deficit disorder and difficulties understanding or expressing language (aphasia). The exact cause and effect relationship between these findings and arachnoid cysts is not clear.
The exact cause of arachnoid cysts is not known. Researchers believe that most cases of arachnoid cysts are developmental malformations that arise from the unexplained splitting or tearing of the arachnoid membrane. According to the medical literature, cases of arachnoid cysts have run in families (familial cases) suggesting that a genetic predisposition may play a role in the development of arachnoid cysts in some individuals.
In some cases, arachnoid cysts occurring in the middle fossa are accompanied by underdevelopment (hypoplasia) or compression of the temporal lobe. The exact role that temporal lobe abnormalities play in the development of middle fossa arachnoid cysts is unknown.
Some complications of arachnoid cysts can occur when a cyst is damaged because of minor head trauma. Trauma can cause the fluid within a cyst to leak into other areas (e.g., subarachnoid space). Blood vessels on the surface of a cyst may tear and bleed into the cyst (intracystic hemorrhage), increasing its size. If a blood vessel bleeds on the outside of a cyst, a collection of blood (hematoma) may result. In the cases of intracystic hemorrhage and hematoma, the individual may have symptoms of increased pressure within the cranium and signs of compression of nearby nerve (neural) tissue.
Arachnoid cysts can also occur secondary to other disorders such as Marfan's syndrome, arachnoiditis, or agenesis of the corpus callosum. (For more information on these disorders, choose the specific disorder name as your search term in the Rare Disease Database).
Arachnoid cysts affect males more often than females. These cysts may occur at any age and have been found in all races and geographic locations. They are the most common type of intracranial cyst. Because many cases of arachnoid cysts have no symptoms, it is difficult to determine the true frequency of this disorder in the general population.
Symptoms of the following disorders can be similar to those of arachnoid cysts. Comparisons may be useful for a differential diagnosis:
Brain tumors are growths in the brain that can be either cancerous (malignant) or noncancerous (benign). The symptoms of malignant and benign brain tumors are similar, and depend on the type of tumor and its location. Symptoms may include recurrent headache, seizures, emotional instability, nausea, and/or facial pain or numbness. There are many different types of brain tumors. (For more information on these disorders, choose "Brain Tumor" as your search term in the Rare Disease Database).
Dandy-Walker malformation is a rare malformation of the brain that is present at birth (congenital). It is characterized by an abnormally enlarged space at the back of the brain (cystic 4th ventricle) that interferes with the normal flow of cerebrospinal fluid through the openings between the ventricle and other parts of the brain (foramina of Magendia and Luschka). Excessive amounts of fluid accumulate around the brain and cause abnormally high pressure within the skull, swelling of the head (congenital hydrocephalus), and neurological impairment. Motor delays and learning problems may also occur. Dandy-Walker malformation is a form of "obstructive" or "internal noncommunicating hydrocephalus", meaning that the normal flow of cerebrospinal fluid is blocked resulting in the widening of the ventricles. (For more information on this disorder, choose "Dandy-Walker" as your search term in the Rare Disease Database).
Empty sella syndrome is a rare disorder characterized by enlargement or malformation of a structure in the head known as the sella turcica. The sella turcica is a saddle-shaped depression located in the bone at the base of skull (sphenoid bone), in which resides the pituitary gland. In empty sella syndrome, the malformed sella turcica is often either partially or completely filled with cerebrospinal fluid. As a result, the pituitary gland is often compressed and flattened so that the sella turcica appears empty. Most individuals with empty sella syndrome do not have any associated symptoms. Occasionally, headaches or pituitary dysfunction may occur. Empty sella syndrome may occur as a primary disorder, for which the cause is unknown (idiopathic), or as a secondary disorder, in which it occurs due to an underlying condition or disorder such as a pituitary tumor or trauma in the pituitary region. (For more information on this disorder, choose "Empty Sella" as your search term in the Rare Disease Database).
Porencephaly is a general term for certain disorders that affect the central nervous system. Porencephaly may be classified as sporadic or familial. Sporadic porencephaly can have many different causes including infection just before or just after birth (perinatal infection), trauma, maternal disease or sickness, maternal diabetes, or maternal use of alcohol or drugs such as cocaine during pregnancy. Autosomal dominant porencephaly type I occurs due to mutations of the COL4A1 gene. In porencephaly, cysts or cavities form on the surface of the brain. These cysts or cavities may become filled with cerebrospinal fluid, a colorless fluid that normally surrounds the brain and spinal cord to provide protection and nourishment. The severity and associated symptoms of porencephaly vary dramatically from one person to another based upon the size and exact locations of the fluid-filled cavities or cysts. Some infants develop serious complications shortly after birth; others individuals may have mild symptoms that may go undetected. The signs and symptoms of porencephaly may include weakness or paralysis of one side of the body (hemiparesis or hemiplegia), seizures, varying degrees of cognitive impairment, and migraines. Individuals with autosomal dominant porencephaly type I are predisposed to damage to small blood vessels, including the small vessels within the brain. (For more information on this disorder, choose "porencephaly" as your search term in the Rare Disease Database).
A diagnosis of arachnoid cysts is often made incidentally, often during examination of an individual with seizures. A diagnosis may be suspected based upon a detailed patient history, a thorough clinical examination, and a variety of specialized tests, especially advanced imaging studies such as computed tomography (CT scan) and magnetic resonance imaging (MRI). CT scans and MRIs can reveal or confirm the presence of arachnoid cysts. During CT scanning, a computer and x-rays are used to create a film showing cross-sectional images of the brain's tissue structure. During MRI, a magnetic field and radio waves are used to create cross-sectional images of the brain.
Most arachnoid cysts are found incidentally and remain constant in size, leading many physicians to recommend conservative treatment. When no symptoms are present, no treatment may be necessary and affected individuals may be periodically monitored. If symptoms arise, a cyst can be reevaluated.
When treatment is necessary the specific therapy used depends upon whether symptoms are present, the size of the cyst and the specific location of the cyst within the skull.
In cases where treatment is recommended, therapy traditionally consists of one of two procedures - an open craniotomy fenestration or ventriculoperitoneal shunting.
During a craniotomy fenestration, a portion of the skull is removed to give a surgeon access to the cyst, where multiple openings are made in the cyst wall, (fenestrations), to allow cerebrospinal fluid to drain into the subarachnoid space where the fluid is reabsorbed into the surrounding tissue. Alternatively, some cases may be treated by surgically inserting a device (shunt) into the cyst to provide drainage either into the ventricular system of the brain or into the abdominal cavity. This will drain the cyst and provide an adequate passageway for cerebrospinal fluid to circulate.
More recently, advancements in minimally invasive brain and skull base surgery have evolved these traditional procedures into fully endoscopic techniques, distinguished by shorter operating times, fewer complications, excellent outcomes with faster recovery and overall decreased patient morbidity. While the approach varies depending on the size and location of the arachnoid cyst, fully endoscopic surgical management has provided the surgeon with superior access for either fenestration, or in other cases, resection of the cyst without the complications and risks associated with brain manipulation or retraction. Few facilities provide minimally invasive, endoscope assisted fenestrations, endoscopic shunt placement and endscope assisted or fully endoscopic resection of arachnoid cysts as treatment when indicated.
Spinal arachnoid cysts may be treated by the complete surgical removal (resection) of the cyst, if possible. Surgery generally leads to a resolution of symptoms. In some cases, complete surgical removal of a spinal cyst is not possible. In such cases, fenestration or shunting of the cyst to drain the fluid may be necessary.
Other treatment is symptomatic and supportive.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
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For information about clinical trials sponsored by private sources, contact:
Contact for additional information about Arachnoid Cysts:
Skull Base Institute
8635 W. 3rd Street; Suite 1170W
Los Angeles, CA 90048
Organizations related to Arachnoid Cysts
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National Institute of Neurological Disorders and Stoke. Arachnoid Cysts Information Page. http://www.ninds.nih.gov/disorders/arachnoid_cysts/arachnoid_cysts.htm.
Updated September 16, 2011. Accessed February 16, 2012.
Khan AN. Arachnoid Cyst Imaging. Emedicine Journal. http://emedicine.medscape.com/article/336489-overview. Updated May 25, 2011. Accessed February 16, 2012.
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