The chances of intracranial epidermoids is about 1% of all brain tumors. This benign tumor of the brain is made up of normal skin cells (stratified epithelial lining) on the outside, and fatty acids and keratin are on the inside of the tumor or sac. Only the sticky outer membrane is alive thus sticking to brain tissues and nerves.

Epidermoid tumors strongly adhere to the brain stem or cranial nerves. Often the lining of the tumor connected to the brain stem or parts difficult to "peel" away are left behind leaving residual tumor after surgery, this can contribute to the risk of regrowth.

These tumors arise when epidermal cells become trapped during neural tube closure. This occurs between the 3rd to 5th week of fetal development.

In most cases, the cause of acoustic neuromas is unknown. The only statistically significant risk factor for developing an acoustic neuroma is having a rare genetic condition called neurofibromatosis type 2 (NF2). There are no confirmed environmental risk factors for acoustic neuroma. There are conflicting studies on the association between acoustic neuromas and cellular phone use and repeated exposure to loud noise. In 2011, an arm of the World Health Organization released a statement listing cell phone use as a low grade cancer risk. The Acoustic Neuroma Association recommends that cell phone users use a hands-free device.

Meningiomas are significantly more common in women than in men; they are most common in middle-aged women. Two predisposing factors associated with meningiomas for which at least some evidence exists are exposure to ionizing radiation (cancer treatment of brain tumors) and hormone replacement therapy.

According to a Dutch source juvenile pilocytic astrocytoma occurs at a rate of 2 in 100,000 people. Most affected are children ages 5–14 years. According to the National Cancer Institute more than 80% of astrocytomas located in the cerebellum are low grade (pilocytic grade I) and often cystic; most of the remainder are diffuse grade II astrocytomas.

Tumors of the optic pathway account for 3.6-6% of pediatric brain tumors, 60% of which are juvenile pilocytic astrocytomas. Astrocytomas account for 50% of pediatric primary central nervous system tumors. About 80-85% of cerebellar astrocytomas are juvenile pilocytic astrocytomas.

Recent genetic studies of pilocytic astrocytomas show that some sporadic cases have gain in chromosome 7q34 involving the BRAF locus.

The overall complication rate following surgery is around 20%; cerebrospinal fluid leak is the most common.

Grade I pilocytic astrocytoma and cerebellar gliomas are not associated with recurrence after complete resection. Grade II astrocytomas and cerebellar gliomas are more likely to recur after surgical removal. Pilomyxoid astrocytomas may behave more aggressively than classic pilocytic astrocytoma.

After complete surgical removal, in cases of progressive/recurrent disease or when maximal surgical removal has been achieved, chemotherapy and/or radiation therapy will be considered by the medical team.

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.

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.

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.

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 cognition had postoperative improvement after surgical decompression of the cyst.

- Surgery can resolve psychiatric manifestations in selected cases.

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.

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.

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

The standard treatment of COC is enucleation and curettage (E&C). Recurrence following E&C is rare.

Recurrence rate of solid form of tumour is lower than classic form.

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

The calcifying odotogenic cyst or the Gorlin cyst, now known in the WHO Classification of Tumours as the calcifying cystic odontogenic tumor, is a benign odontogenic tumor of cystic type most likely to affect the anterior areas of the jaws. It is most common in people in their second to third decades but can be seen at almost any age. On radiographs, the calcifying odontogenic cyst appears as a unilocular radiolucency (dark area). In one-third of cases, an impacted tooth is involved. Microscopically, there are many cells that are described as "ghost cells", enlarged eosinophilic epithelial cells without nuclei.

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."

A Rathke's cleft cyst is a benign growth found on the pituitary gland in the brain, specifically a fluid-filled cyst in the posterior portion of the anterior pituitary gland. It occurs when the Rathke's pouch does not develop properly and ranges in size from 2 to 40mm in diameter.

Asymptomatic cysts are commonly detected during autopsies in 2 to 26 percent of individuals who have died of unrelated causes. Females are twice as likely as males to develop a cyst. If a cyst adds pressure to the optic chiasm, it may cause visual disturbances, pituitary dysfunction, and headaches. The majority of pituitary patients with chronic headaches have Rathke's Cleft Cysts. This is believed to be caused by the constant change in volume and the drastic changes in vasopressure from fluctuations in gonadotrophs and ADH.

The treatment of choice for symptomatic cysts is drainage and taking a biopsy. Radical excision is more dangerous because of the potential of damaging the patient's pituitary function e.g. ADH storage and lowering growth hormone production.

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.

It is estimated that 7% of women in the western world develop palpable breast cysts.

There is preliminary evidence that women with breast cysts may be at an increased risk of breast cancer, especially at younger ages.

In males, the occurrence of breast cysts is rare and may (but need not) be an indication of malignancy.

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.

There are two types of ESS: "primary" and "secondary".

- Primary ESS happens when a small anatomical defect above the pituitary gland increases pressure in the sella turcica and causes the gland to flatten out along the interior walls of the sella turcica cavity. Primary ESS is associated with obesity and increase in intracranial pressure in women.

- Secondary ESS is the result of the pituitary gland regressing within the cavity after an injury, surgery, or radiation therapy. Individuals with secondary ESS due to destruction of the pituitary gland have symptoms that reflect the loss of pituitary functions, such as intolerance to stress and infection.

Gardner syndrome consists of adenomatous polyps of the gastrointestinal tract, desmoid tumours, osteomas, epidermoid cysts, lipomas, dental abnormalities and periampullary carcinomas. The incidence of the syndrome is 1:14,025 with an equal sex distribution. It is determined by the autosomal dominant familial polyposis coli gene (APC) on chromosome

5.

Gardner syndrome can be identified based on oral findings, including multiple impacted and supernumerary teeth, multiple jaw osteomas which give a "cotton-wool" appearance to the jaws, as well as multiple odontomas, congenital

hypertrophy of the retinal pigment epithelium (CHRPE), in addition to multiple adenomatous polyps of the colon. Gardner syndrome is also associated with familial adenomatous polyposis and may manifest as aggressive fibromatosis (desmoid tumors) of the retroperitoneum.

Desmoid tumors arise most frequently from the aponeurosis of the rectus abdominal muscle of multiparous women. The extra-abdominal form is rare and desmoids of the breast may arise in the mammary gland or may occur as an extension of a lesion arising from the muscles of the chest wall. The incidence of mammary desmoid tumours is less than 0.2% of primary breast neoplasms.

In Gardner’s syndrome the incidence ranges from 4% to 17%. Desmoid tumours associated with Gardner’s syndrome have been shown to have an alteration of the β-catenin pathway and over express β-catenin.

It is common in age group of 10–30 years. It is second most common tumor of spine and commonest benign tumor of pelvis in pediatric population. Incidence is slightly more in males than females (1.3:1).