Arachnoid cysts are seen in up to 1.1% of the population with a gender distribution of 2:1 male:female Only 20% of these have symptoms, usually from secondary hydrocephalus.

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.

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) 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.

Some scientists debate whether arachnoid cysts are a true congenite condition or if this should be separated from secondary cysts. A recent study shows differences in communication between the arachnoid cyst and the subarachnoid space by CT cisternography

. A comparison of arachnoid cyst fluid and CSF in a series of patients show differences in chemical composition.

Arachnoid cysts can also occur secondary to other disorders such as Marfan syndrome, arachnoiditis, or agenesis of the corpus callosum.

Cysts derived from CNS tissues are very common in America. They are a subtype of cerebrovascular diseases, which are the third leading cause of death in America. Generally, CNS cysts are present in all geographic regions, races, ages, and sexes. However, certain types of CNS cysts are more prevalent in certain types of individuals than others. Some examples of incidence rates in specific types of cysts include:

- Arachnoid cysts are more prevalent in males than females

- Colloid cysts are more prevalent in adults

- Dermoid cysts are more prevalent in children under 10 years of age

- Epidermoid cysts are more prevalent in middle-aged adults

Many CNS cysts form in the womb during the first few weeks of development as a result of congenital defects. In adults cysts may also form due to a head injury or trauma, resulting in necrotic tissues (dead tissue), and can sometimes be associated with cancerous tumors or infection in the brain. However, the underlying reasons for cyst formation are still unknown.

When Tarlov cysts are ruptured or drained they cause leakage of cerebrospinal fluid (CSF). Ruptures of Tarlov cysts have been reported associated with communicating aneurysms and from fracture in the proximity of the cysts. An undetected rupture can cause intracranial hypotension, including orthostatic neurological symptoms along with headache, nausea, and vomiting that improve when supine. The ruptured cysts can be patched either with a biosynthetic dural patch or using a blood patch to stem the flow of CSF.

Patients with third ventricular colloid cysts become symptomatic when the tumor enlarges rapidly, causing CSF obstruction, ventriculomegaly, and increased intracranial pressure. Some cysts enlarge more gradually, however, allowing the patient to accommodate the enlarging mass without disruption of CSF flow, and the patient remains asymptomatic. In these cases, if the cyst stops growing, the patient can maintain a steady state between CSF production and absorption and may not require neurosurgical intervention.

Because of the unclear pathogenesis and pathophysiology of Tarlov cysts, there is no consensus on the optimal treatment of symptomatic sacral perineural cysts. Patients often choose to pursue treatment when the progression of neurological deficits seriously impacts their quality of life.

Since cysts are innervated, microfenestration and surgical sleeving of the cysts to diminish the amount of accumulated cerebrospinal fluid and decrease compression of the spine and spinal nerves has been successful in a number of patients. The cysts are carefully separated enough from surrounding tissue to be wrapped with fatty tissue or pericardial biomaterial to excise the fluid from the cyst. If the cyst does not drain spontaneously, then it is drained and patched using a biosynthetic dural patch.

The use of this technique is done in the U.S. and is spreading in Europe but recovery is generally extensive. Microfenestration alone has been done with some success in Asia.

A biopolymer plate is also being used experimentally to strengthen a sacrum thinned by cystic erosion by Dr. Frank Feigenbaum.

The risks of CSF leakage are higher on patients that have bilateral cysts on the same spinal level or clusters of cysts along multiple vertebrae, but immediate recognition of the leakage and repair can mitigate that risk.

Various treatment methods have been tried in the past, including the extraction of cerebrospinal fluids from the cyst, fibrin glue injection and the complete or partial removal of cyst. Epidurals can provide temporary relief but are not generally recommended as they can cause cysts to enlarge. Extraction of fluid can provide limited or no relief depending on rate the cysts refill and the need to repeat the procedure. Removal of the cyst results in irreversible damage to the intersecting spinal nerve.

Although fibrin-glue therapy initially had been thought to be a promising therapy in the treatment of these cysts, there have been multiple problems associated with the fibrin glue therapy including seepage of fibrin. It is no longer recommended for use at present by the Health Department in some countries and neurosurgeons previously performing the procedures.

Nevertheless, all types of surgical treatment pose common risks, including neurological deficits, infection and inflammation, spinal headache, urinary disturbances, and leakage of cerebrospinal fluids.

Here is an article for treatment of meningeal diverticulum. Feigenbaum F1, Henderson FC. Giant sacral meningeal diverticula: surgical implications of the "thecal tip" sign. Report of two cases. J Neurosurg Spine. 2006 Nov;5(5):443-6.

A colloid cyst is a tumor containing gelatinous material in the brain. It is almost always found just posterior to the foramen of Monro in the anterior aspect of the third ventricle, originating from the roof of the ventricle. Because of its location, it can cause obstructive hydrocephalus and increased intracranial pressure. Colloid cysts represent 0.5–1% of intracranial tumors.

Symptoms can include headache, vertigo, memory deficits, diplopia, behavioral disturbances and in extreme cases, sudden death. Intermittency of symptoms is characteristic of this lesion. Untreated pressure caused by these cysts can result in brain herniation. Colloid cyst symptoms have been associated with 4 variables: cyst size, cyst imaging characteristics, ventricular size, and patient age. The developmental origin is unclear, though they may be of endodermal origin, which would explain the mucin-producing, ciliated cell type. These cysts can be surgically resected, and opinion is divided about the advisability of this.

Treatment ranges from simple enucleation of the cyst to curettage to resection. There are cysts—e.g., buccal bifurcation cyst—that resolve on their own, in which just close observation may be employed, unless it is infected and symptomatic.

Recurrence rate is higher in aspirated cysts than in excised ones. Ganglion cysts have been found to recur following surgery in 12% to 41% of patients.

A six-year outcome study of the treatment of ganglion cysts on the dorsum (back) of the wrist compared excision, aspiration, and no treatment. Neither excision nor aspiration provided long-term benefit better than no treatment. Of the untreated ganglion cysts, 58% resolved spontaneously; the post-surgery recurrence rate in this study was 39%. A similar study in 2003 of ganglion cysts occurring on the palmar surface of the wrist states: "At 2 and 5 year follow-up, regardless of treatment, no difference in symptoms was found, regardless of whether the palmar wrist ganglion was excised, aspirated or left alone."

The most commonly accepted probable cause of ganglion cysts is the "herniation hypothesis", by which they are thought to occur as "an out-pouching or distention of a weakened portion of a joint capsule or tendon sheath." This description is based on the observations that the cysts occur close to tendons and joints, the microscopic anatomy of the cyst resembles that of the tenosynovial tissue, the fluid is similar in composition to synovial fluid, and dye injected into the joint capsule frequently ends up in the cyst, which may become enlarged after activity. Dye injected into the cyst rarely enters the joint, however, which has been attributed to the apparent formation of an effective and one-way "check valve", allowing fluid out of the joint, but not back in.

In synovials, posttraumatic degeneration of connective tissue and inflammation have been considered as causes. Other possible mechanisms for the development of ganglion cysts include repeated mechanical stress, facet arthrosis, myxoid degeneration of periarticular fibrous tissues and liquefaction with chronic damage, increased production of hyaluronic acid by fibroblasts, and a proliferation of mesenchymal cells. Ganglion cysts also may develop independently from a joint.

A cyst is a closed sac, having a distinct membrane and division compared with the nearby tissue. Hence, it is a cluster of cells that has grouped together to form a sac (not unlike the manner in which water molecules group together, forming a bubble); however, the distinguishing aspect of a cyst is that the cells forming the "shell" of such a sac are distinctly abnormal (in both appearance and behaviour) when compared with all surrounding cells for that given location. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, sometimes a cyst may resolve on its own. When a cyst fails to resolve, it may need to be removed surgically, but that would depend upon its type and location.

Cancer-related cysts are formed as a defense mechanism for the body, following the development of mutations that lead to an uncontrolled cellular division. Once that mutation has occurred, the affected cells divide incessantly (and become known as cancerous), forming a tumour. The body encapsulates those cells to try to prevent them from continuing their division and to try to contain the tumour, which becomes known as a cyst. That said, the cancerous cells still may mutate further and gain the ability to form their own blood vessels, from which they received nourishment before being contained. Once that happens, the capsule becomes useless and the tumour may advance from benign to a cancer.

Some cysts are neoplastic and thus, are called cystic tumors; many types are not neoplastic. Some are dysplastic or metaplastic. Pseudocysts are similar to cysts (having a sac filled with fluid), but lack an epithelial lining.

Factors increasing the risk of a subdural hematoma include very young or very old age. As the brain shrinks with age, the subdural space enlarges and the veins that traverse the space must travel over a wider distance, making them more vulnerable to tears. This and the fact that the elderly have more brittle veins make chronic subdural bleeds more common in older patients. Infants, too, have larger subdural spaces and are more predisposed to subdural bleeds than are young adults. For this reason, subdural hematoma is a common finding in shaken baby syndrome. In juveniles, an arachnoid cyst is a risk factor for a subdural hematoma.

Other risk factors for subdural bleeds include taking blood thinners (anticoagulants), long-term alcohol abuse, dementia, and the presence of a cerebrospinal fluid leak.

Treatment for dermoid cyst is complete surgical removal, preferably in one piece and without any spillage of cyst contents. Marsupialization, a surgical technique often used to treat pilonidal cyst, is inappropriate for dermoid cyst due to the risk of malignancy.

The association of dermoid cysts with pregnancy has been increasingly reported. They usually present the dilemma of weighing the risks of surgery and anesthesia versus the risks of untreated adnexal mass. Most references state that it is more feasible to treat bilateral dermoid cysts of the ovaries discovered during pregnancy if they grow beyond 6 cm in diameter.

The thyroglossal tract arises from the foramen cecum at the junction of the anterior two-thirds and posterior one-third of the tongue. Any part of the tract can persist, causing a sinus, fistula or cyst. Most fistulae are acquired following rupture or incision of the infected thyroglossal cyst. A thyroglossal cyst is lined by pseudostratified, ciliated columnar epithelium while a thyroglossal fistula is lined by columnar epithelium.

Blocked sebaceous glands, swollen hair follicles, high levels of testosterone and the use of androgenic anabolic steroids will cause such cysts.

A case has been reported of a sebaceous cyst being caused by the human botfly.

Hereditary causes of sebaceous cysts include Gardner's syndrome and basal cell nevus syndrome.

The clinical management of a cyst of Montgomery depends upon the symptoms of the patient.

If there are no signs of infection, a cyst of Montgomery can be observed, because more than 80% resolve spontaneously, over only a few months. However, in some cases, spontaneous resolution may take up two years. In such cases, a repeat ultrasonography may become necessary. If, however, the patient has signs of an infection, for example reddening (erythema), warmth, pain and tenderness, a treatment for mastitis can be initiated, which may include antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs). With treatment, inflammatory changes usually disappear quickly. In rare cases, drainage may become necessary. A surgical treatment of a cyst of Montgomery, i.e. a resection, may become necessary only if a cyst of Montgomery persists, or the diagnosis is questioned clinically.

The prognosis seems to be excellent. In one series, all adolescent patients with a cyst of Montgomery had a favourable outcome.

A pineal gland cyst is a usually benign (non-malignant) cyst in the pineal gland, a small endocrine gland in the brain. Historically, these fluid-filled bodies appeared on of magnetic resonance imaging (MRI) brain scans, but were more frequent at death, seen in of autopsies. A 2007 study by Pu "et al". found a frequency of 23% in brain scans (with a mean diameter of 4.3 mm).

It was once believed that smaller cysts (less than 5.0 mm) were usually asymptomatic, but for larger cysts (greater than 5.0 mm), symptoms could include headache, unexpected seizures, visual disturbances, memory loss, cognitive decline, muscle fasciculations, nausea, weakness, fatigue, light sensitivity, tinnitus, circadian rhythm dysfunction, or hydrocephalus if the cyst impinged on the superior colliculi or caused obstruction of the cerebral aqueduct. Newer research shows that the size of the cyst does not necessarily correlate to the presence of symptoms. In some cases, it will need to be removed before life-threatening situations occur.

Despite the pineal gland being in the center of the brain, due to recent advancements in endoscopic medicine, endoscopic brain surgery to drain and/or remove the cyst can be done with the patient spending 1-3 nights in the hospital, and being fully recovered in weeks, rather than a year, as is the case with open-skull brain surgery.

The National Organization for Rare Disorders states that pineal cysts larger than 5.0 mm are "rare findings" and are possibly symptomatic. If narrowing of the cerebral aqueduct occurs, many neurological symptoms may exist, including headaches, vertigo, nausea, muscle fasciculations, eye sensitivity, and ataxia. Continued monitoring of the cyst might be recommended to monitor its growth, and surgery may be necessary.

In a small population of people with larger, symptomatic cysts, the following comorbid conditions have been noted: Pseudotumor cerebri (elevated intracranial pressure), empy sella, hormonal disturbances, flattened optic discs, chiari malformation, sjogren's, POTS, dysautonomia, PCOS.

Thyroglossal Duct Cysts are a birth defect. During embryonic development, the thyroid gland is being formed, beginning at the base of the tongue and moving towards the neck canal, known as the thyroglossal duct. Once the thyroid reaches its final position in the neck, the duct normally disappears. In some individuals, portions of the duct remain behind, leaving small pockets, known as cysts. During a person's life, these cyst pockets can fill with fluids and mucus, enlarging when infected, presenting the thyroglossal cyst.

There is not a specific theory behind the etiology of the unicameral bone cyst, however, according to many researchers and doctors, there is a commonly known theory hypothesized by Jonathan Cohen in 1970. Cohen studied interstitial fluid in six children undergoing treatment for unicameral bone cysts. He believed that the chemical composition of the fluid found in the bone cyst was similar to the chemical make-up in serum. Cohen theorized that the unicameral bone cyst occurs when interstitial fluids in cancellous bones quickly accumulate in one region from blockage.

One of the other theories is that the cysts result from a disorder of the growth plate. Another is that the cysts result from problems with circulation that are caused by a developmental anomaly in the veins of the affected bone. The role trauma plays in the development of these cysts is unknown. Some speculate that repeated trauma puts the bone at risk for developing a bone cyst. This, however, has not been proven.

Spinal dermoid cysts are benign ectopic growths thought to be a consequence of embryology errors during neural tube closure. Their reported incidence is extremely rare, accounting for less than 1% of intramedullary spinal cord tumours. It has been proposed that a possible 180 cases of spinal dermoid tumours have been identified over the past century in the literature.

Dermoid cysts more often involve the lumbosacral region than the thoracic vertebrae and are extramedullary presenting in the first decade of life.

Various hypotheses have been advanced to explain the pathogenesis of spinal dermoids, the origin of which may be acquired or congenital.

- Acquired or iatrogenic dermoids may arise from the implantation of epidermal tissue into the subdural space i.e. spinal cutaneous inclusion, during needle puncture (e.g. lumbar puncture) or during surgical procedures on closure of a dysraphic malformation.

- Congenital dermoids, however, are thought to arise from cells whose position is correct but which fail to differentiate into the correct cell-type. The long-time held belief was that the inclusion of cutaneous ectodermal cells occurred early in embryonic life, and the displaced pluripotent cells developed into a dermoid lesion.

Spinal abnormalities, e.g. intramedullary dermoid cysts may arise more frequently in the lumbosacral region (quite often at the level of the conus medullaris) and may be seen with other congenital anomalies of the spine including posterior spina bifida occulta as identified by the neuroradiological analysis.

Subdural hematomas are most often caused by head injury, when rapidly changing velocities within the skull may stretch and tear small bridging veins. Subdural hematomas due to head injury are described as traumatic. Much more common than epidural hemorrhages, subdural hemorrhages generally result from shearing injuries due to various rotational or linear forces. Subdural hemorrhage is a classic finding in shaken baby syndrome, in which similar shearing forces classically cause intra- and pre-retinal hemorrhages. Subdural hematoma is also commonly seen in the elderly and in alcoholics, who have evidence of cerebral atrophy. Cerebral atrophy increases the length the bridging veins have to traverse between the two meningeal layers, hence increasing the likelihood of shearing forces causing a tear. It is also more common in patients on anticoagulants or antiplatelet drugs, such as warfarin and aspirin. Patients on these medications can have a subdural hematoma after a relatively minor traumatic event.

A further cause can be a reduction in cerebral spinal fluid pressure which can create a low pressure in the subarachnoid space, pulling the arachnoid away from the dura mater and leading to a rupture of the blood vessels.

About 90% of pilar cysts occur on the scalp, with the remaining sometimes occurring on the face, trunk and extremities. Pilar cysts are significantly more common in females, and a tendency to develop these cysts is often inherited in an autosomal dominant pattern. In most cases, multiple pilar cysts appear at once.

Epidermoid cysts commonly result from implantation of epidermis into the dermis, as in trauma or surgery. They can also be caused by a blocked pore adjacent to a body piercing. They are also seen in Gardner's syndrome and Nevoid Basal Cell Carcinoma Syndrome on the head and neck. They can be infected by bacteria and form a pimple-like shape.

Bronchogenic cysts are small, solitary cysts or sinuses, most typically located in the region of the suprasternal notch or over the manubrium.