Information on the following diseases can be found in the Related Disorders section of this report:

• Acoustic Neuroma
• Arachnoiditis
• Brain Tumors, General
• Dandy-Walker Syndrome
• Empty Sella Syndrome
• Epidermoids
• Midline Caves of the Brain
• Porencephaly
• Syringomyelia
• Bobble-Head Doll Syndrome
• Hyperprolactinemia
• Panhypopituitarism

Arachnoid cysts are present at birth (congenital), but, in most cases, may not cause any symptoms (asymptomatic) throughout an individual's life. Whether symptoms occur depends upon the size and location of the cyst. 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.

Suprasellar cysts usually present with headaches, vomiting, and hydrocephalus. Hydrocephalus in children presents with enlarged head due to the pressure of the fluids that fill the empty spaces in the head. In adults, hydrocephalus is noticeable, in extreme cases, in the form of incontinence, imbalance and dementia. Rarely, suprasellar cysts will be accompanied by endocrinological disorders as well.

Temporal fossa cysts frequently go unnoticed (asymptomatic) except for headaches. Since the walls of this form of cyst contain blood vessels, even minor injury may lead to bleeding in the membrane and/or the cyst.

Convexity cysts are usually accompanied by seizures.

Posterior fossa cysts are accompanied by headaches, vomiting, and disorders of the cerebellum (in the lower back of the brain). Hydro-cephalus, due to obstruction of the flow or drainage of the cerebral spinal fluid, is frequently found in these patients.

Pineal arachnoid cysts usually present with obstructive hydrocephalus and "failure of upward gaze."

Headaches, seizures, and the accumulation of excessive cerebrospinal fluid in the brain (hydrocephalus), resulting in increased intracranial pressure, are the most common findings. In children, malformation of certain cranial bones and an abnormally enlarged head (macrocephaly) may also occur.

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, nausea, vomiting, 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) and mental retardation.

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). Endocrine system abnormalities may result in a variety of symptoms such as premature sexual development (precocious puberty).

Spinal arachnoid cysts may be associated with progressive weakness of the legs, 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.
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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.

In a few rare cases, intracranial arachnoid cysts may be inherited as an autosomal recessive trait. In recessive disorders, the condition does not appear unless a person inherits the same defective gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is 25 percent. Fifty percent of their children risk being carriers of the disease, but generally will not show symptoms of the disorder. Twenty-five percent of their children may receive both normal genes, one from each parent, and will be genetically normal (for that particular trait). The risk is the same for each pregnancy.

In a few rare cases, spinal intradural arachnoid cysts may be inherited as an autosomal dominant trait.

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.)
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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. Because many cases of arachnoid cysts have no symptoms, it is difficult to determine the true frequency of this disorder in the general population.
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Symptoms of the following disorders can be similar to those of arachnoid cysts. Comparisons may be useful for a differential diagnosis:

Acoustic neuroma (cerebellopontine angle syndrome) is a benign (noncancerous) tumor of the 8th cranial nerve. The early symptoms of an acoustic neuroma include a ringing sound in the ear (tinnitus) and/or a hearing loss. These symptoms occur due to pressure from the tumor on the 8th cranial nerve. Some cases of arachnoid cysts may initially present with tinnitus and hearing loss and be confused with an acoustic neuroma. The exact cause of acoustic neuromas is unknown. (For more information on this disorder, choose "Acoustic Neuroma" as your search term in the Rare Disease Database.)

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 brain disorder in which the depression across the bone that contains the pituitary gland (sella turcica) appears as an extension of the subarachnoid space and is filled with cerebrospinal fluid. The syndrome may be primary or may be secondary to a pituitary tumor, irradiation, or surgery on the pituitary gland. Symptoms may include headaches, impaired vision, and obesity. Sex-specific differences may be seen, such as excessive hair growth (hirsutism) in women and reduced sex drive (libido) in men. The primary form of Empty Sella syndrome is inherited as an autosomal dominant trait. (For more information on this disorder, choose "Empty Sella" as your search term in the Rare Disease Database.)

Porencephaly is a major congenital malformation of the brain that is characterized by cysts or the formation of cavities (cavitations) within the brain. The symptoms of porencephaly usually include mental retardation, spastic paralysis, mild paralysis of cranial nerves (ophthalmoplegia), and/or epilepsy. Hydrocephalus, low muscle tone (hypotonia), and macrocephaly may also be present in some cases.

The following disorders may be associated with arachnoid cysts as secondary characteristics. They are not necessary for a differential diagnosis:

Hyperprolactinemia occurs when there is an abnormally high amount of prolactin in the blood. Hyperprolactinemia has been associated with the extension of arachnoid cysts into the suprasellar cistern. Symptoms in women may include absence or abnormal cessation of menstruation (amenorrhea) and/or spontaneous milk flow from the breasts (galactorrhea). Symptoms in men have been reported to include impotence and/or abnormally decreased function of the testes.

Panhypopituitarism is a rare disorder characterized by a generalized reduction or cessation of pituitary gland function. This can result when an expanding intrasellar arachnoid cyst causes the pituitary gland to become flattened. Such a cyst can be mistaken for a pituitary tumor.
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Diagnosis
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.

Treatment
No treatment is necessary for asymptomatic arachnoid cysts. In cases where treatment is necessary, therapy usually consists of drainage of the cyst by surgically inserting a device (shunt) to provide a passageway for fluid from the cyst to one of the reservoirs for bodily fluids. This reduces pressure on the cysts and may prevent a recurrence of fluid build-up. In some cases, a more invasive surgical procedure may be necessary to remove an arachnoid cyst.

If the subarachnoid space has become blocked by an arachnoid cyst, it may also be necessary to place a shunt between a ventricle and the space between the layers of the membrane that lines the cavities of the body (the peritoneal cavity). This will bypass the blockage and provide an adequate passageway for cerebrospinal fluid to circulate.

Other treatment is symptomatic and supportive.
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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
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

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