In medicine, a cyst is a closed pocket with a distinct membrane and developing abnormally in a cavity or body structure. They may contain air, liquids or other materials, including parasitic organisms "encapsulated" form active slow reproduction or inactive form of "Spore" (Sporozoite).
The vast majority of cysts are completely benign. This is the case of simple biliary cysts (liver), renal cysts (except in cases of hereditary polycystic kidney), breast cysts. Their content is purely fluid, and their size varies from a few millimeters to several centimeters.
Other cysts may be related to tumor development or malignant Benin, in the case of those that affect the ovaries or pancreas for example. Sometimes it is by compression on adjacent organs they are harmful.
Many bodies are likely to develop cysts:
* Ovarian cyst
* Conjunctival cyst at eye level
* Pilonidal cyst at the sacro-coccigienne
* Coccygeal cyst
* Baker's cyst or popliteal cyst
* Amebic cyst: caused by Entamoeba histolytica
* Hydatid cyst: caused by Echinococcus granulosus (hydatid disease)
* Renal cyst and [[polycystic kidney]]
* Biliary cyst (cyst or hepatic)
* Salivary cyst, salivary glands
* Mucoid cyst of the lip
* Mucoid cysts of fingers
* Dental cyst (periapical cyst)
* Arachnoid cyst
* Dermoid cyst
* Sebaceous cyst
* Fibro-cystic disease of breast
* Chalazion: a cyst Meibomian gland
* Ganglion cyst
* Epididymal cyst
Appearance of cysts on imaging
In ultrasound, a cyst is in the form of a fully anechoic cavity (do not return echoes, and therefore appear black on the screen), rounded usually surrounded by a very thin wall, even invisible. A special feature is the visualization of a "posterior enhancement of echoes" the accumulation of ultrasonic rear of the cyst (which went through without being reflected) is responsible for the formation of a broad band appear whiter the surrounding tissue. This typical aspect allows, when the chance discovery of a cyst on one kidney for example, have a certain diagnostic and Benin say the character of this anomaly.
On a computed tomography (CT), cysts appear as a "ball" homogeneous, often invisible wall, where the average density (in Hounsfield units, HU) is that of a liquid, so close to 0 HU (between 0 and 10 in most cases).
On MRI, the cyst appears well demarcated, hypointense T1 and hyperintense T2 high.
See also Liver