| bronchopulmonary sequestration | A developmental anomaly in which a mass of nonfunctioning lung tissue lacks normal connection with the tracheobroncheal tree and receives an anomalous blood supply originating from the descending thoracic or abdominal aorta. The mass may be extralobar, i.e., completely separated from normally connected lung, or intralobar, i.e., partly surrounded by normal lung. (12 Dec 1998) |
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| sequestration | 1. Formation of a sequestrum. 2. Loss of blood or of its fluid content into spaces within the body so that it is withdrawn from the circulating volume, resulting in haemodynamic impairment, hypovolaemia, hypotension, and reduced venous return to the heart. Origin: L. Sequestratio, fr. Sequestro, pp. -atus, to lay aside (05 Mar 2000) |
| sequestration cyst | A collection of cancerous cells which form cysts that contain one or more of the three primary embryonic germ layers: skin, hair or teeth. (27 Sep 1997) |
| sequestration dermoid | An obsolete term for epidermal cyst. (05 Mar 2000) |
| disc sequestration | <radiology> Complete separation of disc material with rupture through posterior longitudinal ligament into the epidural space; free fragment herniation findings: migration superiorly/inferiorly with compression of nerve roots above/below the level of herniation, disc material noted more than 9mm from disc space Differential diagnosis: postoperative scarring (retraction of thecal sac to the site of surgery), epidural abscess/tumour, conjoined nerve root: 2 nerve roots arising simultaneously from the thecal sac; normal variant in 1-3% see: degenerative disc disease (12 Dec 1998) |
| intralobar sequestration | <radiology> Nonfunctioning portion of lung <indent>WITHIN visceral pleura of a pulmonary lobe, left lower lobe (67%); rarely in upper lobes, arterial supply: SYSTEMIC, usually aorta, venous drainage: usually via pulmonary. Vv. (occasionally systemic), usually does not communicate with bronchial tree, cystic, may become infected, not associated with other abnormalities see: sequestration Cf: extralobar sequestration (12 Dec 1998) |
| extralobar sequestration | <radiology> Accessory lung: lung tissue in its own pleura, left lower lobe (90%), systemic arterial AND venous connection (unlike intralobar) results in L to R shunt, associated with congenital anomalies of diaphragm: eventration, paralysis, ipsilateral hernia, XR: homogeneous ST mass, rarely infected see also: sequestration Cf: intralobar sequestration (12 Dec 1998) |
| acromioclavicular disk | The articular disk of fibrocartilage usually found between the acromial end of the clavicle and the medial border of the acromion. Synonym: discus articularis acromioclavicularis, acromioclavicular disk, Weitbrecht's cartilage. (05 Mar 2000) |
| Airy disk | <microscopy> The image of a bright point object as focused by a lens system. With monochromatic light, it consists of a central point of maximum intensity surrounded by alternate circles of light and darkness caused by the reinforcement and interference of diffracted rays. The light areas are called maxima and the dark areas minima. The distribution of light from the centre to the outer areas of the figure was investigated mathematically by Sir George Airy. The diffraction disk forms a basis for determining the resolving power of an ideal lens system. The diameter of the disk depends largely on the aperture of the lens. The diffraction of light causing the Airy disk is a factor limiting the resolution of a well corrected optical system. The bright disk of light (surrounded by alternating dark and bright diffraction rings)that is formed by a perfect diffraction-limited lens, focusing an image of an infinitely small source of light. For a minute absorbing spot, the diffraction pattern is a dark Airy disk surrounded by brighter and darker diffraction rings. Since the Airy disk is the smallest unit that makes up the image of a luminous or absorbing object (formed by a properly corrected microscope lens in focus), the radius of the disk determines the limit of resolution of the microscope. (05 Aug 1998) |
| articular disk | A plate or ring of fibrocartilage attached to the joint capsule and separating the articular surfaces of the bones for a varying distance, sometimes completely; it serves to adapt two articular surfaces that are not entirely congruent. Synonym: discus articularis, articular disk, fibrocartilago interarticularis, fibroplate, interarticular fibrocartilage, intra-articular cartilage. (05 Mar 2000) |
| blastodermic disk | The aggregation of blastomeres of a telolecithal ovum after cleavage has occurred. (05 Mar 2000) |
| blood disk | <haematology> A discoid cell (3m diameter) found in large numbers in blood, important for blood coagulation and for haemostasis by repairing breaches (small breaks) in the walls of blood vessels. Platelet _ granules contain lysosomal enzymes, dense granules contain ADP (a potent platelet aggregating factor) and serotonin (a vasoactive amine). They also release platelet-derived growth factor which presumably contributes to later repair processes by stimulating fibroblast proliferation. Synonym: thrombocytes. (09 Oct 1997) |
| bulging disk | A condition that results in the abnormal protrusion (bulging), herniation or prolapse of a vertebral disc from its normal position in the vertebral column. The displaced disc may exert force on a nearby nerve root causing the typical neurologic symptoms of radiating pain (to an extremity), numbness, tingling and weakness. Recurrent episodes of severe back pain are common. Treatment includes non-steroidal anti-inflammatories, corticosteroids and rest. More advanced cases may require surgical intervention (for example laminectomy, micro-disc surgery). (27 Sep 1997) |
| Burlew disk | An abrasive-impregnated rubber wheel used in dentistry for polishing. Synonym: Burlew wheel. (05 Mar 2000) |
| vacuum disk phenomenon | The appearance of a radiolucent stripe in an intervertebral disk, a manifestation of disk degeneration; a misnomer since there is gas present. (05 Mar 2000) |