| LASH | left anterior superior hemiblock |
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| LSR | lanthanide shift reagent; lecithin/ sphingomyelin ratio; left superior rectus [muscle]; liver/spleen... |
| LSVC | left superior vena cava |
| MSO | management service organization; medial superior olive; medical staff organization |
| OAISO | overaction of the ipsilateral superior oblique |
| sigmoid sinus | The S-shaped dural venous sinus lying deep to the mastoid process of the temporal bone and immediately posterior to the petrous temporal bone; it is continuous with the transverse sinus and empties into the internal jugular vein as it passes through the jugular foramen. Synonym: sinus sigmoideus. (05 Mar 2000) |
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| sinus | <anatomy> A notch, depression or cavity on the surface of an organ. (09 Oct 1997) |
| sinus alae parvae | A paired dural venous sinus beginning on the parietal bone, running along the sphenoidal ridges and emptying into the cavernous sinus. Synonym: sinus sphenoparietalis, Breschet's sinus, sinus alae parvae. (05 Mar 2000) |
| sinus anales | 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) |
| sinus aortae | The space between the superior aspect of each cusp of the aortic valve and the dilated portion of the wall of the ascending aorta, immediately above each cusp. Synonym: sinus aortae, Petit's sinus, Valsalva's sinus. Arlt's sinus, an inconstant depression on the lower portion of the internal surface of the lacrimal sac. Barber's pilonidal sinus, pilonidal sinus occurring in barbers, usually in the web between the fingers, due to the burying of exogenous hairs by the alternate loosening and tightening of tissues of the hand by the manipulation of scissors. (05 Mar 2000) |
| sinus arrest | <cardiology, physiology> Cessation of sinus activity; the ventricles may continue to beat under ectopic atrial, atrioventricular junctional, or idioventricular control. See: sinus standstill, atrial standstill. (05 Mar 2000) |
| sinus arrhythmia | <cardiology, physiology> An increase in heart rate during inspiration. A normal physiologic response, more pronounced in children. (27 Sep 1997) |
| sinus barotrauma | Sinus troubles, particulaqrly with pain, due to changing atmospheric pressures, as when going up or down in a plane. Also called aerosinusitis or barosinusitis. (12 Dec 1998) |
| sinus bradycardia | <cardiology, physiology> Bradycardia originating in the normal sinus pacemaker. (05 Mar 2000) |
| sinus caroticus | <anatomy> A slight dilation in the carotid artery at its bifurcation into the external and internal carotid arteries, it contains baroreceptors (pressure sensors) that when stimulated, will cause a reflex slowing of the heart, vasodilation and a fall in blood pressure. (27 Sep 1997) |
| sinus cavernosus | <radiology> Contents: III oculomotor n., IV trochlear n., V-1 ophthalmic n. (trigeminal n.), V-2 maxillary n. (trigeminal n.), VI abducens n. Note: mandibular n. (V-3) passes through foramen rotundum (12 Dec 1998) |
| sinus circularis | sinus venosus sclerae |
| sinus coronarius | 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) |
| sinus durae matris | Endothelium-lined venous channels in the dura mater. Synonym: sinus durae matris, cerebral sinuses, cranial sinuses, sinuses of dura mater, venous sinuses. (05 Mar 2000) |
| sinus epididymidis | A narrow space between the body of the epididymis and the testis. Synonym: sinus epididymidis. Ethmoidal sinuses, ethmoidal air-cells; evaginations of the mucous membrane of the middle and superior meatuses of the nasal cavity into the ethmoidal labyrinth forming multiple small paranasal sinuses; they are subdivided into anterior, middle and posterior ethmoidal sinuses. Synonym: antra ethmoidalia. (05 Mar 2000) |