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Cyst
Micrograph of a mediastinal bronchogenic cyst, H&E stain
Classification and external resources
Specialty	Pathology, general surgery
MedlinePlus	003240
MeSH	D003560
[edit on Wikidata]

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 receive 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.

Terminology

A small cyst that requires magnification to be seen, may be called a microcyst. Similarly, a cyst that is larger than usual or compared to others, may be called a macrocyst.

Types

• 
  Acne cyst – Pseudocysts associated with cystic acne - an inflammatory nodule with or without an associated epidermoid inclusion cyst


• 
  Arachnoid cyst (between the surface of the brain and the cranial base or on the arachnoid membrane)


• 
  Baker's cyst or popliteal cyst (behind the knee joint)


• 
  Bartholin's cyst (near the vagina)


• Breast cyst


• 
  Buccal bifurcation cyst^[1]
  


• Calcifying odontogenic cyst


• 
  Ceruminous cyst (ear)


• 
  Chalazion cyst (eyelid)


• 
  Chocolate cyst of ovary


• 
  Choroid plexus cyst (in the brain)


• 
  Colloid cyst (in the brain)


• 
  Cysticercal cyst – an infection due to the larval stage of Taenia sp. (Crain's backs)


• 
  Dentigerous cyst (associated with the crowns of non-erupted teeth)


• 
  Dermoid cyst (ovaries, testes, many other locations from head to tailbone)


• 
  Epidermoid cyst (skin)


• 
  Epididymal cyst (found in the vessels attached to the testes)


• 
  Fibrous cyst (breast)


• 
  Ganglion cyst (hand and foot joints and tendons)


• Glandular odontogenic cyst


• 
  Glial cyst (in the brain)


• 
  Gartner's duct cyst (vaginal or vulvar cyst of embryological origin)


• 
  Hydatid cyst (an infection in the liver or other parts of the body due to the larval stage of Echinococcus granulosus (tapeworm))


• 
  Hydrocele (testicle)


• 
  Keratocyst (in the jaws, these may appear solitarily or associated with the Gorlin-Goltz or Nevoid basal cell carcinoma syndrome; the latest World Health Organization classification considers Keratocysts as tumors rather than cysts)


• Polycystic liver disease


• 
  Meibomian cyst (eyelid)


• 
  Mucoid cyst (ganglion cysts of the digits)


• Mucous cyst of the oral mucosa


• 
  Myxoid cyst (cutaneous condition often characterized by nail plate depression and grooves)


• 
  Nabothian cyst (cervix)


• Nasolabial duct cyst


• 
  Odontogenic cyst (teeth)


• 
  Ovarian cyst (ovaries, functional and pathological)


• Pancreatic cyst


• Paradental cyst


• 
  Parapelvic cyst (kidney)^[2]
  


• 
  Paratubal cyst (fallopian tube)


• 
  Periapical cyst – this cyst, also known as radicular cyst, is the most common odontogenic cyst
  


• 
  Pericardial cyst^[3]
  


• 
  Peritoneal cyst (lining of the abdominal cavity)


• 
  Pilar cyst (cyst of the scalp)


• 
  Pilonidal cyst (skin infection near tailbone)


• 
  Renal cyst (kidneys)


• Polycystic ovary syndrome


• 
  Pineal gland cyst (in the pineal gland in the brain)


• 
  Radicular cyst – associated with the roots of non-vital teeth, also known as periapical cyst
  


• Residual cyst


• 
  Sebaceous cyst – sac below skin


• 
  Skene's duct cyst, a paraurethral cyst


• 
  Spermatocele (testicle)


• 
  Stafne static bone cyst (an anatomic variant with radiographic cystic appearance in the posterior mandible)


• 
  Tarlov cyst (spine)


• Thyroglossal cyst


• 
  Trichilemmal cyst – same as a pilar cyst, a familial cyst of the scalp


• Vaginal cyst


• Vocal fold cyst

The aneurysmal bone cyst is a neoplastic cyst, more specifically, an aggressive lesion with radiographic cystic appearance.^[4]

Cystic fibrosis

Despite being described in 1938 as the microscopic appearance of cysts in the pancreas,^[5]cystic fibrosis is an example of a genetic disorder whose name is related to fibrosis of the cystic duct (which serves the gallbladder) and does not involve cysts.^[6]

This is just one example of how the Greek root cyst-, which simply means a fluid-filled sac, also is found in medical terms that relate to the urinary bladder and the gallbladder, neither of which involve cysts.

Cystic neoplasm

Examples of neoplastic cysts include:

• Dermoid cyst


• Keratocystic odontogenic tumor


• Calcifying odontogenic cyst

Treatment

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.^[1]

Related structures

A pseudocyst is similar collection without a distinct membrane.

A syrinx in the spinal cord or brainstem is sometimes inaccurately referred to as a cyst.

See also

• List of cutaneous conditions

References

External links

• 
  "Cyst Symptoms and Causes" by Melissa Conrad Stöppler, MD and William C. Shiel, Jr., MD, FACP, FACR.