| OCS | occipital condyle syndrome; Ondine's curse syndrome; open canalicular system; oral contraceptive ste... |
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| OCT | object classification test; optimal cutting temperature; oral contraceptive therapy; ornithine carba... |
| OES | oral esophageal stethoscope; optical emission spectroscopy |
| OGTT | oral glucose tolerance test |
| OHA | oral hypoglycemic agents |
| Guerin's sinus | A cul-de-sac or diverticulum behind the valve of the navicular fossa. (05 Mar 2000) |
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| petrosal sinus | See: inferior petrosal sinus, superior petrosal sinus. (05 Mar 2000) |
| petrosal sinus sampling | Sampling of blood levels of the adrenocorticotropic hormone (acth) by withdrawal of blood from the inferior petrosal sinus. The inferior petrosal sinus arises from the cavernous sinus and runs to the internal jugular vein. Sampling of blood at this level is a valuable tool in the differential diagnosis of cushing disease, cushing syndrome, and other adrenocortical diseases. (12 Dec 1998) |
| phasic sinus arrhythmia | Sinus arrhythmia in which the irregularity is related to the phases of respiration, the rate being faster in inspiration and slower in expiration. (05 Mar 2000) |
| circular sinus | Dural venous formation which surrounds the hypophysis, composed of right and left cavernous sinuses and the intercavernous sinuses. Synonym: circulus venosus ridleyi, Ridley's circle. A venous sinus at the periphery of the placenta. Synonym: sinus venosus sclerae. (05 Mar 2000) |
| phrenicocostal sinus | The cleftlike extension of the pleural cavity between the diaphragm and the rib cage; pleural effusions collect here when in the upright position, and since the lung only partially enters, this is the site of thoracocentesis. Synonym: recessus costodiaphragmaticus, phrenicocostal sinus. (05 Mar 2000) |
| coccygeal sinus | A fistula opening in the region of the coccyx, being the result of incomplete closure of the caudal end of the neurenteric canal. See: pilonidal sinus. (05 Mar 2000) |
| pilonidal sinus | A dimple in the crease between the buttocks. (12 Dec 1998) |
| piriform sinus | A recess in the anterolateral wall of the nasopharynx on each side of the vestible of the larynx separated from it by the aryepiglottic folds. Synonym: recessus piriformis, piriform recess, piriform sinus. (05 Mar 2000) |
| Morgagni's sinus | The grooves between the anal columns. Synonym: Morgagni's sinus. Pockets or crypts in the columnar zone of the anal canal between the anocutaneous line and the anorectal line; the sinuses give the mucosa a scalloped appearance. Synonym: sinus anales, anal crypts, Morgagni's crypts, rectal sinuses. (05 Mar 2000) |
| congenital sinus tumour | <radiology> Midline depression or tract, lined with stratified squamous epithelium, most common sites: lumbosacral area, occiput, epidermoid or dermoid cyst anywhere along tract (12 Dec 1998) |
| coronary sinus | A short trunk receiving most of the cardiac veins, beginning at the junction of the great cardiac vein and the oblique vein of the left atrium, running in the posterior part of the coronary sulcus and emptying into the right atrium between the inferior vena cava and the atrioventricular orifice. Synonym: sinus coronarius. (05 Mar 2000) |
| coronary sinus rhythm | An ectopic atrial rhythm supposedly originating from a pacemaker at the mouth of the coronary sinus; recognised in the electrocardiogram by P-waves that are inverted in leads II, III, and a VI with a normal or prolonged P-R interval; an ectopic ("lower") atrial rhythm. (05 Mar 2000) |
| costomediastinal sinus | The recess of the pleural cavity between the costal cartilages and the mediastinum. Synonym: recessus costomediastinalis, costomediastinal sinus. (05 Mar 2000) |
| precervical sinus | In young mammalian embryos a depression in the nuchal region caudal to the hyoid arch, with the third and fourth branchial arches and ectodermal grooves in its floor; normally it is obliterated after the second month, but occasionally cervical fistulae persist as vestiges of it. Synonym: precervical sinus. (05 Mar 2000) |