[Gr. kystis, bladder, sac]

1. A closed sac or pouch with a definite wall, containing fluid, semifluid, or solid material. It is usually an abnormal structure resulting from developmental anomalies, obstruction of ducts, or parasitic infection.
2. In biology, a structure formed by and enclosing certain organisms in which they become inactive, such as the cyst of certain protozoans or of the metacercariae of flukes.

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CYST Frontal lobe of the brain

adventitious cyst

A cyst formed around a foreign body.

alveolar cyst

An abnormal membranous cyst containing a gas, liquid, or semisolid substance due to the dilation and subsequent rupture of pulmonary alveoli.

apical cyst

A cyst near the apex of the root of a nonvital tooth.

arachnoid cyst

An abnormal cyst containing cerebrospinal fluid within the arachnoid membrane. The cyst may compress nearby structures within the brain. In infants, the cyst may cause headaches, altered mental status, learning disabilities, or enlargement of the head. In adults, it is an occasional cause of epilepsy.

Baker cyst

SEE: Baker cyst.

Bartholin cyst

SEE: Bartholin, Caspar (the younger)

blood cyst

SEE: Hematoma.

blue dome cyst

1. A mammary cyst containing light, straw-colored fluid, which appears blue when seen through the surrounding tissue.
2. A small dark-blue cyst in the vagina caused by retained menstrual blood seen in endometriosis.

bone cyst

A cyst in bone, usually a normal variant or a benign tumor.

branchial cyst

SEE: Cervical cyst.

cervical cyst

A closed epithelial cyst derived from a pharyngeal groove of its corresponding pharyngeal pouch.
SYN: SEE: branchial cyst; SEE: pharyngeal cyst

chocolate cyst

An ovarian cyst with darkly pigmented gelatinous contents.

colloid cyst

A cyst with gelatinous contents.

complex cyst

A cyst consisting of solid material and fluid-filled cavities. It may have walls of tissue inside it or internal echoes. When a complex cyst is identified on ultrasound, surgical removal is generally indicated to exclude malignancy.

congenital cyst

A cyst present at birth and resulting from abnormal development, such as a dermoid cyst, imperfect closure of a structure as in spina bifida cystica, or nonclosure of embryonic clefts, ducts, or tubules, such as cervical cysts.

daughter cyst

A cyst growing out of the walls of another cyst.

dental cyst

A cyst that forms from any of the odontogenic tissues.

dentigerous cyst

A fluid-filled, epithelial-lined cyst usually surrounding the crown of a tooth that is erupting or has not yet erupted. The tooth normally erupts through the cyst without treatment.
SYN: SEE: eruption cyst; SEE: follicular cyst; SEE: follicular odontoma

dermoid cyst

1. An ovarian teratoma.
2. A nonmalignant cystic tumor containing elements derived from the ectoderm, such as hair, teeth, or skin. These tumors occur frequently in the ovary but may develop in other organs such as the lungs.

distention cyst

A cyst formed in a natural enclosed cavity, such as a follicular cyst of the ovary.

echinococcus cyst

SEE: Hydatid cyst.

endometrial cyst

An ovarian cyst or tumor lined with endometrial tissue, usually seen in ovarian endometriosis.

epidermoid cyst

A benign cyst filled with keratin, sebum, and skin debris that may form on the scalp, the back of the neck, or the axilla. It can be removed surgically.
SYN: SEE: follicular tumor; SEE: sebaceous cyst

eruption cyst

SEE: Dentigerous cyst.

extravasation cyst

A cyst arising from hemorrhage of other body fluids into tissues.

exudation cyst

A cyst caused by trapping of an exudate in a closed area.

follicular cyst

A cyst arising from a follicle, such as a follicular cyst of the thyroid gland, the ovary, or a forming tooth.
SYN: SEE: dentigerous cyst

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FOLLICULAR CYST Follicular cysts seen on ultrasonography of the thyroid gland

ganglion cyst

SEE: Ganglion (2).

Gartner cyst

SEE: Gartner cyst

Gorlin cyst

SEE: Gorlin cyst

hydatid cyst

A cyst formed by the growth of the larval form of Echinococcus granulosus, usually in the liver.
SYN: SEE: echinococcus cyst

implantation cyst

A cyst resulting from displacement of portions of the epidermis, as may occur in injuries.

intraligamentary cyst

A cyst found between the layers of the broad ligament.

involutional cyst

A cyst occurring in the normal involution of an organ or structure, as in the mammary gland.

keratin cyst

A cyst containing keratin.

cyst of liver

A simple cyst, usually small and single; or a hydatid cyst; or a cyst associated with cystic disease of the liver, a rare condition usually associated with congenital cystic kidneys.
SEE: Echinococcus granulosus; SEE: hydatid

meibomian cyst

SEE: Chalazion.

meniscus cyst

A fluid-filled cyst often associated with a degenerative horizontal meniscal tear, more frequently seen in the lateral meniscus of the knee. This ganglion-like cyst may present with a palpable mass at the joint line of the knee and can be visualized by magnetic resonance imaging.

Morgagni cyst

SEE: Morgagni, Giovanni B

morgagnian cyst

SEE: Morgagni, Giovanni B

mother cyst

A hydatid cyst enveloping smaller ones.

mucous cyst

A retention cyst composed of mucus.

nabothian cyst

A cyst caused by closure of the ducts of the nabothian glands in the uterine cervix as a result of chronic cervicitis.

odontogenic cyst

A cyst associated with the teeth, such as a dentigerous or radicular cyst.

ovarian cyst

A fluid-filled cyst that develops in the ovary and consists of one or more chambers. The main types of cysts are follicular cysts, the corpus luteum, teratoma, and endometrioma. The patient's primary complaint is generally pelvic pain or pain during intercourse. The cysts may be palpated during bimanual examination but are diagnosed by ultrasound. Many cysts resolve spontaneously. Although nonmalignant, the cyst may have to be removed surgically because of twisting of the pedicle, which causes gangrene, or because of pressure.
SEE: polycystic ovary syndrome

parasitic cyst

A cyst enclosing the larval form of certain parasites, such as the cysticercus or hydatid of tapeworms or the larva of certain nematodes, i.e., Trichinella.

parovarian cyst

A cyst of the parovarium (epoophoron).
SEE: epoophoron

periapical cyst

SEE: Radicular cyst.

pharyngeal cyst

SEE: Cervical cyst

pilar cyst

An epithelial cyst with a wall that resembles the follicular epithelium. It is filled with a homogeneous mixture of keratin and lipid.
SYN: SEE: trichilemma cyst

pilonidal cyst

A cyst most often found in the sacrococcygeal region, usually at the upper end of the intergluteal cleft. It is due to a developmental defect that permits epithelial tissue to be trapped below the skin, or it may be acquired. This type of cyst may become symptomatic in early adulthood when an infected draining sinus forms.
SYN: SEE: pilonidal fistula

popliteal cyst

SEE: Baker cyst.

porencephalic cyst

An anomalous cavity of the brain that communicates with the ventricular system.

proliferative cyst

A cyst lined with epithelium that proliferates, forming projections that extend into the cavity of the cyst.

radicular cyst

A necrotic, inflammatory cyst that develops at the root of a nonvital tooth. The cyst is attached to the root of the tooth and may be lateral to it if the cyst is associated with a lateral pulp canal.
SYN: SEE: periapical cyst; SEE: root-end cyst

retention cyst

A cyst retaining the secretion of a gland, as in a mucous or sebaceous cyst.

root-end cyst

SEE: Radicular cyst.

sebaceous cyst

SEE: Epidermoid cyst.

seminal cyst

A cyst of the epididymis, ductus deferens, or other sperm-carrying ducts that contain semen.

suprasellar cyst

A cyst of the hypophyseal stalk just above the floor of the sella turcica. Its wall is frequently calcified or ossified.

synovial cyst

An accumulation of synovia in a bursa, synovial crypt, or sac of a synovial hernia, causing a tumor.

theca-lutein cyst

A benign enlargement of the graafian follicle, typically occurring in pregnancies (particularly in multiple pregnancies) or in other conditions that cause markedly elevated levels of serum human chorionic gonadotropin (HCG) levels, e.g., molar pregnancies or choriocarcinomas.
SYN: SEE: hyperreactio luteinalis

trichilemma cyst

SEE: Pilar cyst.

tubo-ovarian cyst

An ovarian cyst that ruptures into the lumen of an adherent uterine tube.

unilocular cyst

A cyst containing only one cavity.

vaginal cyst

A cyst in the vagina.

vitelline cyst

A congenital cyst of the gastrointestinal canal. Lined with ciliated epithelium, it is the remains of the omphalomesenteric duct.

wolffian cyst

A cyst lying in one of the broad ligaments of the uterus.