Arachnoid cyst
Encyclopedia
Arachnoid cysts are cerebrospinal fluid
covered by arachnoidal cells and collagen
that may develop between the surface of the brain
and the cranial base or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord
. Arachnoid cysts are a congenital disorder
, and most cases begin during infancy; however, onset may be delayed until adolescence.
. Intracranial arachnoid cysts usually occur adjacent to the arachnoidal cistern. Spinal arachnoid cysts may be extradural, intradural, or perineural and tend to present with signs and symptoms indicative of a radiculopathy
.
Arachnoid cysts may also be classified as primary(congenital) or secondary(acquired) and have been reported in humans, cats, and dogs
Arachnoid cysts can be relatively asymptomatic or present with insidious symptoms; for this reason, diagnosis is often delayed.
Symptoms vary by the size and location of the cyst(s), though small cysts usually have no symptoms and are discovered only incidentally. On the other hand, a number of symptoms may result from large cysts:
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.
There are some cases where hereditary disorders have been connected with arachnoid cysts.
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 syndrome
, arachnoiditis
, or agenesis of the corpus callosum
.
. Frequently, arachnoid cysts are incidental findings on MRI scans performed for other clinical reasons. In practice, diagnosis of symptomatic arachnoid cysts requires symptoms to be present, and many with the disorder never develop symptoms.
Additional clinical assessment tools that can be useful in evaluating a patient with arachnoid cysts include the mini-mental state examination
(MMSE), a brief questionnaire-based test used to assess cognition
. Myelograms are contraindicated for people with arachnoid cysts.
A 1994 study found surgery necessary for good outcome in patients >65 years old when the cysts began displaying symptoms.
More specific prognoses are listed below:
.
A study that looked at 2,536 healthy young males found a prevalence of 1.7% (95% CI
1.2 to 2.3%). Only a small percentage of the detected abnormalities require urgent medical attention.
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
covered by arachnoidal cells and collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
that may develop between the surface of the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
and the cranial base or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. Arachnoid cysts are a congenital disorder
Congenital disorder
A congenital disorder, or congenital disease, is a condition existing at birth and often before birth, or that develops during the first month of life , regardless of causation...
, and most cases begin during infancy; however, onset may be delayed until adolescence.
Classification
Arachnoid cysts can be found on the brain, or on the spineVertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
. Intracranial arachnoid cysts usually occur adjacent to the arachnoidal cistern. Spinal arachnoid cysts may be extradural, intradural, or perineural and tend to present with signs and symptoms indicative of a radiculopathy
Radiculopathy
Radiculopathy is not a specific condition, but rather a description of a problem in which one or more nerves are affected and do not work properly . The emphasis is on the nerve root...
.
Arachnoid cysts may also be classified as primary(congenital) or secondary(acquired) and have been reported in humans, cats, and dogs
Arachnoid cysts can be relatively asymptomatic or present with insidious symptoms; for this reason, diagnosis is often delayed.
Signs and symptoms
Patients with arachnoid cysts may never show symptoms, even in some cases where the cyst is large. Therefore, while the presence of symptoms may provoke further clinical investigation, symptoms independent of further data cannot -- and should not -- be interpreted as evidence of a cyst's existence, size or location.Symptoms vary by the size and location of the cyst(s), though small cysts usually have no symptoms and are discovered only incidentally. On the other hand, a number of symptoms may result from large cysts:
- Cranial deformation or macrocephalyMacrocephalyMacrocephaly , occurs when the head is abnormally large; this includes the scalp, the cranial bone, and the contents of the cranium.-Causes:...
(enlargement of the head), particularly in children - Cysts in the suprasellar region in children have presented as bobbing and nodding of the head called bobble-head doll syndromeBobble-Head Doll SyndromeBobble-head doll syndrome is a rare neurological movement disorder in which patients, usually children around age 3, begin to bob their head and shoulders forward and back, or sometimes side-to-side, involuntarily, in a manner reminiscent of a bobblehead doll. The syndrome is related to cystic...
. - Cysts in the left middle cranial fossa have been associated with ADHD in a study on affected children.
- HeadacheHeadacheA headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
s. A patient experiencing a headache does not necessarily have an arachnoid cyst.- In a 2002 study involving 78 patients with a migraine or tension-type headache, CT scans showed abnormalities in over a third of the patients, though arachnoid cysts only accounted for 2.6% of patients in this study.
- A study found 18% of patients with intracranial arachnoid cysts had non-specific headaches. The cyst was in the temporal location in 75% of these cases.
- SeizureSeizureAn epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
s - HydrocephalusHydrocephalusHydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...
(excessive accumulation of cerebrospinal fluid) - Increased intracranial pressureIntracranial pressureIntracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
- Developmental delay
- Behavioral changes
- Nausea
- HemiparesisHemiparesisHemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....
(weakness or paralysis on one side of the body) - AtaxiaAtaxiaAtaxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
(lack of muscle control) - Musical hallucinationHallucinationA hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid,...
- Pre-senile dementiaDementiaDementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
, a condition often associated with Alzheimer's diseaseAlzheimer's diseaseAlzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death... - In elderly patients (>65 years old) symptoms were similar to chronic subdural hematomaSubdural hematomaA subdural hematoma or subdural haematoma , also known as a subdural haemorrhage , is a type of haematoma, a form of traumatic brain injury. Blood gathers within the outermost meningeal layer, between the dura mater, which adheres to the skull, and the arachnoid mater, which envelops the brain...
or normal pressure hydrocephalusHydrocephalusHydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...
:- Dementia
- Urinary incontinenceUrinary incontinenceUrinary incontinence is any involuntary leakage of urine. It is a common and distressing problem, which may have a profound impact on quality of life. Urinary incontinence almost always results from an underlying treatable medical condition but is under-reported to medical practitioners...
- Hemiparesis
- Headache
- Seizures
Location-specific symptoms
- A supratentorialSupratentorialIn anatomy, the supratentorial region of the brain is the area located above the tentorium cerebelli. The area of the brain below the tentorium cerebelli is the infratentorial region. The supratentorial region contains the cerebrum, while the infratentorial region contains the cerebellum....
arachnoid cyst can mimic a Ménière's diseaseMénière's diseaseMénière's disease is a disorder of the inner ear that can affect hearing and balance to a varying degree. It is characterized by episodes of vertigo and tinnitus and progressive hearing loss, usually in one ear. It is named after the French physician Prosper Ménière, who, in an article published...
attack. - Frontal arachnoid cysts have been associated with depression.
- Cysts on the left temporal lobe have been associated with psychosisPsychosisPsychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...
. However this remains controversial and subjective to the individual clinician. A left fronto-temporal cyst more specifically showed symptoms of alexithymiaAlexithymiaAlexithymia from the Ancient Greek words λέξις and θυμός modified by an alpha-privative—literally "without words for emotions"—is a term coined by psychotherapist Peter Sifneos in 1973 to describe a state of deficiency in understanding, processing, or describing...
. - Cyst on the right sylvian fissure resulted in new onset of schizophreniaSchizophreniaSchizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
-like symptoms at age 61. - A patient with a cyst on the left middle cranial fossaMiddle cranial fossaThe middle fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest....
had auditoryAuditory systemThe auditory system is the sensory system for the sense of hearing.- Outer ear :The folds of cartilage surrounding the ear canal are called the pinna...
hallucinations, migraineMigraineMigraine is a chronic neurological disorder characterized by moderate to severe headaches, and nausea...
-like headaches, and periodic paranoiaParanoiaParanoia [] is a thought process believed to be heavily influenced by anxiety or fear, often to the point of irrationality and delusion. Paranoid thinking typically includes persecutory beliefs, or beliefs of conspiracy concerning a perceived threat towards oneself... - Patients with left temporal lobe cysts had mood disturbances similar to manic depression (bipolar disorder) and were known show outward aggression
- Most neurosurgeons remain skeptical on the correlation between arachnoid cyst and mental illness and consider the two partially related.
Causes
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.In some cases, arachnoid cysts occurring in the middle fossa are accompanied by underdevelopment (hypoplasia
Hypoplasia
Hypoplasia is underdevelopment or incomplete development of a tissue or organ. Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells. Hypoplasia is similar to aplasia, but less severe. It is technically not the opposite of hyperplasia...
) or compression of the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
. The exact role that temporal lobe abnormalities play in the development of middle fossa arachnoid cysts is unknown.
There are some cases where hereditary disorders have been connected with arachnoid cysts.
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
Subarachnoid space
In the central nervous system, the subarachnoid cavity is the interval between the arachnoid membrane and pia mater....
). 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
Hematoma
A hematoma, or haematoma, is a localized collection of blood outside the blood vessels, usually in liquid form within the tissue. This distinguishes it from an ecchymosis, which is the spread of blood under the skin in a thin layer, commonly called a bruise...
) 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 syndrome
Marfan syndrome
Marfan syndrome is a genetic disorder of the connective tissue. People with Marfan's tend to be unusually tall, with long limbs and long, thin fingers....
, arachnoiditis
Arachnoiditis
Arachnoiditis is a neuropathic disease caused by the inflammation of the arachnoid, one of the membranes that surround and protect the nerves of the central nervous system, including the brain and spinal cord...
, or agenesis of the corpus callosum
Agenesis of the corpus callosum
Agenesis of the corpus callosum is a rare birth defect in which there is a complete or partial absence of the corpus callosum. Agenesis of the corpus callosum occurs when the corpus callosum, the band of white matter connecting the two hemispheres in the brain, fails to develop normally,...
.
Diagnosis
Diagnosis is principally by MRIMagnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
. Frequently, arachnoid cysts are incidental findings on MRI scans performed for other clinical reasons. In practice, diagnosis of symptomatic arachnoid cysts requires symptoms to be present, and many with the disorder never develop symptoms.
Additional clinical assessment tools that can be useful in evaluating a patient with arachnoid cysts include the mini-mental state examination
Mini-mental state examination
The mini–mental state examination or Folstein test is a brief 30-point questionnaire test that is used to screen for cognitive impairment. It is commonly used in medicine to screen for dementia...
(MMSE), a brief questionnaire-based test used to assess cognition
Cognition
In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...
. Myelograms are contraindicated for people with arachnoid cysts.
Treatment/Management
Treatment for arachnoid cysts occurs when symptoms present themselves. A variety of procedures may be used to decompress (remove pressure from) the cyst.- Surgical placement of a cerebral shuntCerebral shuntCerebral shunts are commonly used to treat hydrocephalus, the swelling of the brain due to excess buildup of cerebrospinal fluid . If left unchecked, the cerebral spinal fluid can build up leading to an increase in intracranial pressure which can lead to intracranial hematoma, cerebral edema,...
:- An internal shunt drains into the subdural compartment.
- A cystoperitoneal shunt drains to the peritoneal cavityPeritoneal cavityThe peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall...
.
- Fenestration:
- CraniotomyCraniotomyA craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often a critical operation performed on patients recording, brain imaging, and for neurological manipulations such as electrical stimulation and chemical...
with excisionSurgerySurgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical... - Various endoscopic techniques are proving effective, including laser-assisted techniques.
- Craniotomy
- Drainage by needle aspiration or burr hole.
- Capsular resection
- Pharmacological treatments may address specific symptoms such as seizures or pain.
A 1994 study found surgery necessary for good outcome in patients >65 years old when the cysts began displaying symptoms.
Prognosis
Most arachnoid cysts are asymptomatic, and do not require treatment. Where complications are present, leaving arachnoid cysts untreated, may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding). However, with treatment most individuals with symptomatic arachnoid cysts do well.More specific prognoses are listed below:
- Patients with impaired preoperative cognitionCognitionIn science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...
had postoperative improvement after surgical decompression of the cyst. - Surgery can resolve psychiatric manifestations in selected cases.
Epidemiology
Arachnoid cysts are seen in 4% of the population. Only 20% of these have symptoms, usually from secondary hydrocephalusHydrocephalus
Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...
.
A study that looked at 2,536 healthy young males found a prevalence of 1.7% (95% CI
Confidence interval
In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...
1.2 to 2.3%). Only a small percentage of the detected abnormalities require urgent medical attention.
See also
- Wikipedia's Medical disclaimer and this useful pageCyberchondriaCyberchondria refers to the unfounded escalation of concerns about common symptomology based on review of search results and literature online. Articles in popular media position cyberchondria anywhere from temporary neurotic excess to adjunct hypochondria...
. - Acoustic NeuromaAcoustic neuromaA vestibular schwannoma, often called an acoustic neuroma, is a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve . The term "vestibular schwannoma" involves the vestibular portion of the 8th cranial nerve and arises from Schwann cells, which are...
- ArachnoiditisArachnoiditisArachnoiditis is a neuropathic disease caused by the inflammation of the arachnoid, one of the membranes that surround and protect the nerves of the central nervous system, including the brain and spinal cord...
- Brain Tumors, GeneralBrain tumorA brain tumor is an intracranial solid neoplasm, a tumor within the brain or the central spinal canal.Brain tumors include all tumors inside the cranium or in the central spinal canal...
- Dandy-Walker syndromeDandy-Walker syndromeDandy–Walker syndrome , or Dandy–Walker complex, is a congenital brain malformation involving the cerebellum and the fluid filled spaces around it. A key feature of this syndrome is the partial or even complete absence of the part of the brain located between the two cerebellar hemispheres...
- Empty Sella SyndromeEmpty sella syndromeEmpty sella syndrome is a disorder that involves the sella turcica, a bony structure at the base of the brain that surrounds and protects the pituitary gland...
- PorencephalyPorencephalyPorencephaly is a type of cephalic disorder involving encephalomalacia. This is an extremely rare disorder of the central nervous system involving a cyst or cavity in a cerebral hemisphere. The cysts or cavities are usually the remnants of destructive lesions, but are sometimes the result of...
- SyringomyeliaSyringomyeliaSyringomyelia is a generic term referring to a disorder in which a cyst or cavity forms within the spinal cord. This cyst, called a syrinx, can expand and elongate over time, destroying the spinal cord. The damage may result in pain, paralysis, weakness, and stiffness in the back, shoulders, and...
- Hyperprolactinemia
- Panhypopituitarism
- Arnold-Chiari MalformationArnold-Chiari malformationArnold–Chiari malformation, or often simply Chiari malformation, is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum , sometimes causing non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid outflow...
- HydrocephalusHydrocephalusHydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...