| isocyclic compound | Any compound in which the constituent atoms, or any part of them, form a ring. Used mainly in organic chemistry where: 1) numerous compound's contain rings of carbon atoms (carbocyclic compound's) or carbon atoms plus one or more atoms of other types (heterocyclic compound's), usually nitrogen, oxygen, or sulfur; 2) where the atoms in the ring are all of the same element (homocyclic or isocyclic compound); 3) where the ring is saturated or contains nonconjugated double bonds (alicyclic compound), the compound is similar in properties to the corresponding acyclic compound (e.g., cyclohexane resembles hexane); 4) where the ring contains conjugated double bonds in a closed loop in which there are 4n + 2 (where n is an integer) delocalised π electrons (Huckel's rule) (aromatic compound; e.g., benzene, pyridine), it is more stable than the corresponding saturated ring and exhibits unusual chemical properties characteristic of itself and not of other types of rings or of acyclic compound's. These aromatic compounds have the ability to sustain an induced ring current. Synonym: closed chain compound, ring compound. (05 Mar 2000) |
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| open chain compound | An organic compound in which the chain does not form a ring. Synonym: aliphatic compound, open chain compound. (05 Mar 2000) |
| organic compound | <chemistry> A compound containing carbon. (11 Jan 1998) |
| lens, compound | <microscopy> A lens composed of two or more separate pieces of glass or other optical maternal. These component pieces or elements may or may not be cemented together. A common form of compound lens is a two-element objective, one element being a converging lens of crown glass and the other a diverging lens of flint glass. The combination of suitable glasses or other optical materials (plastics, minerals) properly ground and polished reduces aberrations normally present in a single lens. (05 Aug 1998) |
| adrenal cyst | <radiology> Same characteristics as renal cysts, but less common, thick wall, septations, calcifications suggests pseudocyst (12 Dec 1998) |
| adventitious cyst | 1. An accumulation of fluid in a cystlike loculus, but without an epithelial or other membranous lining. Synonym: adventitious cyst, false cyst. 2. A cyst whose wall is formed by a host cell and not by a parasite. 3. A mass of 50 or more Toxoplasma bradyzoites, found within a host cell, frequently in the brain; formerly called a pseudocyst, but now considered a true cyst enclosed in its own membrane within the host cell that may rupture to release particles that form new cysts, and apparently is infective to another vertebrate host. See: bradyzoite. Origin: pseudo-+ G. Kystis, bladder (05 Mar 2000) |
| allantoic cyst | Cyst occurring in a persistent portion of the urachus, presenting as an extraperitoneal mass in the umbilical region. It is characterised by abdominal pain, and fever if infected. It may rupture, leading to peritonitis, or it may drain through the umbilicus. (12 Dec 1998) |
| alveolar hydatid cyst | A hydatid cyst of a multiloculate type, usually in the liver, caused by Echinococcus multilocularis, adults of which are in foxes; larvae (alveolar hydatid) are found chiefly in microtine rodents, but also among humans such as trappers and others handling pelts of infected foxes and other carnivores; growth is by exogenous budding and is not limited by an outer laminated membrane as in the hydatid cyst from E. Granulosus; necrosis, cavitation, contiguous spread, and death usually ensue. Synonym: multilocular hydatid cyst, multiloculate hydatid cyst. (05 Mar 2000) |
| aneurysmal bone cyst | <radiology> ABC, 10 - 30 yrs, 75% before skeletal maturity, sites: long bones; also, flat bones Findings: metaphyseal if unfused, metaepiphyseal after fusion, lytic, expansile, thin, continuous rim, thin internal bony strands (12 Dec 1998) |
| angioblastic cyst | Mesenchymal tissue capable of forming blood in the embryo. (05 Mar 2000) |
| apical periodontal cyst | An inflammatory odontogenic cyst derived histogenetically from Malassez' epithelial rests surrounding the root apex of a nonvital tooth. Synonym: periapical cyst, radicular cyst, root end cyst. (05 Mar 2000) |
| apoplectic cyst | A pseudocyst formed of extravasated blood as in a stroke. (05 Mar 2000) |
| arachnoid cyst | A fluid-filled cyst lined with arachnoid membrane, frequently situated near the lateral aspect of the fissure of Sylvius; usually congenital in origin. Synonym: leptomeningeal cyst. (05 Mar 2000) |
| baker cyst | <radiology> Bursal fluid collection between: medial head of gastrocnemius muscle and, semimembranosus tendon, associated with knee injury, may contain osteocartilaginous fragments (12 Dec 1998) |
| Baker's cyst | <rheumatology> A synovial cyst or pouch that occurs in the synovial lining of the knee. Presents in the popliteal fossa (are behind the knee). Synovial fluid escapes from the knee joint and into the cyst in individuals who suffer from degenerative and other joint disease. Typically these cysts are not painful unless swelling is extensive. Aspiration of the cyst is therapeutic only temporarily since recurrence is common. most disappear spontaneously after several years. Larger cysts can be removed surgically. Rupture of a Baker's cyst can present with painless and swelling to the calf. (27 Sep 1997) |