(sī'nŭs)

Plural: sinuses

sinus

[L., sinus, curve, hollow]

1. A recess.
2. A cavity with a narrow opening.
3. An endothelium-lined, air-filled cavity within a bone. When lay people speak of sinuses, they usually mean the paranasal sinuses.
4. An endothelium-lined channel for venous blood.
5. A channel leading to an abscess.

accessory nasal s.Paranasal sinus.

air s.Paranasal sinus.

anal s.Any of the sinuses lining the anal canal between the anal columns. Inferiorly the anal sinuses end as anal valves.

aortic s.Within the aorta, the sinus behind each of the three leaflets of the aortic valve. The right and left coronary arteries each originate from an orifice in an aortic sinus, leaving one aortic sinus (the noncoronary sinus) as a blind pouch.SYN: sinus of Valsalva.

basilar s.Transverse sinus (2).

carotid s.The small sinus at the base of the internal carotid artery with baroreceptors in its wall. These receptors respond to changes in arterial blood pressure, and their signals are carried to the hindbrain by the glossopharyngeal nerve (CN IX).

s. cavernosus Cavernous sinus.

cavernous s.A dural sinus found along the sides of the sella turcica in the middle cranial fossa. It is drained by the inferior and the superior petrosal sinuses. The right and left cavernous sinuses are connected by the anterior and the posterior intercavernous sinuses. Tributaries of the cavernous sinus include the superior ophthalmic, superficial middle cerebral, and inferior cerebral veins and the sphenoparietal sinuses. SYN: sinus cavernosus.

cerebral s.Dural sinus.

circular s.Any of a set of four connected dural sinuses encircling the sella turcica and pituitary gland at the base of the brain. The four sinuses are the right and left cavernous sinuses and the anterior and posterior intercavernous sinuses.

coccygeal s.A sinus in the midline of the gluteal cleft just over the coccyx.

coronary s.The short, fat vein on the posterior aspect of the heart that runs in the atrioventricular groove that receives the cardiac veins from the heart and opens into the right atrium.

SEE: coronary artery for illus.

cranial s.Any of the large veins between the two layers of the cranial dura mater.

cranial venous s.Sinus (3).

dermal s.A congenital sinus tract connecting the surface of the body with the spinal canal.

draining s.An abnormal sinus leading from inside the body to the outside, usually due to an infection.

dural s.Any of several large endothelium-lined sinuses into which veins of the brain and inner skull empty and which then empty into the internal jugular vein. These venous sinuses are found between the two layers (periosteal and meningeal) of the dura mater. Their walls have no muscle, and they have no valves to give direction to the blood flow. The venous sinuses in the skull include the superior sagittal, inferior sagittal, straight, transverse, and cavernous sinuses. SYN: cerebral sinus; dural venous sinus.

dural venous s.Dural sinus.

ethmoid s.Any of the 3 to 18 paranasal sinuses on each side of the skull in and adjacent to the ethmoid bone. The ethmoid sinuses can be categorized as anterior, middle, or posterior. The anterior group drains into the semilunar hiatus; the middle drain on the surface of the ethmoid bulla, which itself is an expand ed ethmoid air cell; and the posterior drain into the superior meatus. Ethmoid sinuses have very thin walls and are connected via openings in the septa between the sinuses. SYN: ethmoid air cell; ethmoid cell.

frontal s.Either of a pair of paranasal sinuses in the frontal bones just above the orbits. These sinuses lie adjacent to each other in the midline but are usually completely separated by a bony septum. Each frontal sinus drains into the ipsilateral nasal cavity through an opening (the frontonasal canal) into the semilunar hiatus of the middle meatus.

genitourinary s.Urogenital sinus

hair s.The sinus formed when hair is embedded in the skin and acts as a foreign body.

inferior longitudinal s.Inferior sagittal sinus.

inferior petrosal s.A dural sinus that drains the cavernous sinus posteriorly into the superior jugular bulb of the internal jugular vein.

inferior sagittal s.An unpaired midline dural sinus running along the inferior, free margin of the falx cerebri. It drains blood from veins in the falx and from the medial surfaces of the hemispheres, and it empties, posteriorly, into the straight sinus. SYN: inferior longitudinal sinus.

intercavernous s.Either of two sinuses (anterior sinus, posterior sinus) that connect the right and left cavernous sinuses at the base of the brain. All sinuses being valveless, the cavernous and intercavernous sinuses form a circle (the circular sinus) that envelops the sella turcica.

lactiferous s.The dilated end of any of the 15 to 20 lactiferous ducts immediately inside the tip of the nipple, which convey milk from the mammary gland s during lactation.

lateral s.Either of two large venous sinuses in the inner side of the skull passing near the mastoid antrum and emptying into the jugular vein.

lymph s.Any of the endothelium-lined channels through which lymph flows inside lymph nodes. The walls of lymph sinuses are coated with T and B lymphocytes and phagocytic cells, which filter the passing lymph. Lymphocytes and macrophages move in and out of the lymph through the sinus walls. SYN: lymph channel.

marginal s.1Considered together, the many dilated veins or venous lakes that collect blood in the intervillous space of the placenta and drain into the uterine veins.2A dural sinus that is located along the inside of the rim of the foramen magnum and drains into the vertebral venous plexus.3A blood-filled sinus in the marginal zone of the spleen. In the passage from the red pulp to the white pulp, some arterial blood flows along and percolates through the endothelium-lined walls of the marginal sinus before entering the arterial capillary beds of the white pulp.

mastoid s.The mastoid antrum and the mastoid air cells.

SEE: mastoid air cell; mastoid antrum.

maxillary s.Either of a pair of paranasal sinuses filling the bodies of the maxillary bones. The maxillary sinuses are large and pyramidal, with average dimensions of 3.5 cm × 2.5 cm × 3.2 cm. The medial floor of the maxillary sinus is immediately above the roots of the first and second upper molars. Each maxillary sinus drains into the ipsilateral nasal cavity through an opening in the lateral wall of the hiatus semilunaris, under the middle nasal concha.SYN: antrum of Highmore; maxillary antrum.

occipital s.A slender dural sinus running in the posterior (attached) margin of the falx cerebelli. It begins near the foramen magnum, ascends along the midline of the occipital bon, and empties into the confluence of the sinuses.

paranasal s.An air sinus in the frontal, maxillary, sphenoid, or ethmoidal facial bone. Most paranasal sinuses occur in pairs. The paranasal sinuses are lined with ciliated epithelium that secretes mucus. The sinuses open into the lateral walls of the nasal cavities via small holes. Healthy paranasal sinuses are radiolucent.SYN: accessory nasal sinus; air sinus.

SEE: illus.

TabersPlus.

pericardial s.Either of two sinuses (oblique sinus, transverse sinus) between the visceral and parietal layers of the serous pericardium. The oblique sinus runs along the posterior surface of the left atrium between the orifices of the right and the left pulmonary veins. The transverse sinus runs along the posterior surface of the base of the heart between the outflow vessels (the aorta and the pulmonary trunk) in front and the inflow vessels (the pulmonary veins) behind.

pilonidal s.Pilonidal fistula.

pleural s.Any of the sinuses in the pleural sac along the anterior and inferior portions of the lung that the lung does not occupy. SYN: pleural recess.

s. pocularis A sinus in the prostatic part of the urethra. SYN: sinus prostaticus.

s. prostaticus Sinus pocularis.

pulmonary s.Either of the sinuses within the pulmonary trunk behind each of the three leaflets of the pulmonary valve.

s. rectus Straight sinus.

renal s.The indentation on the medial side of each kidney into which the hilum leads. The renal sinus contains the renal pelvis, fat, and neurovascular elements.

rhomboid s.The fourth cranial ventricle.

sigmoid s.The continuation of the transverse sinus. It begins when the superior petrosal sinus joins the transverse sinus, it ends at the jugular canal, where is is continuous with the internal jugular vein.

sphenoid s.Either of a pair of paranasal sinuses in the sphenoid bone just above and behind the nasal cavity. The sphenoid sinuses are located next to the optic chiasm, the pituitary gland , and the internal carotid arteries. Each sphenoid sinus drains through an opening in the sphenoethmoidal recess at the very top of the ipsilateral nasal cavity.

sphenoparietal s.A venous sinus uniting the cavernous sinus and a meningeal vein.

s. of spleen A large-capacity venous sinus in the spleen.

straight s.An unpaired midline dural sinus where the falx cerebri and the tentorium cerebelli meet. The straight sinus is the posterior continuation of the inferior sagittal sinus, where it is joined by the great cerebral vein. The straight sinus empties into the transverse sinus contralateral to the one joined by the superior sagittal sinus. The straight sinus often communicates with the confluence of the sinuses. SYN: sinus rectus.

superior petrosal s.A slender dural sinus that drains the cavernous sinus posteriorly into the transverse sinus.

superior sagittal s.A long unpaired midline channel along the attached edge of the falx cerebri. It begins in the front near the crista galli of the ethmoid bone; it extends along the entire inner roof of the skull to the internal occipital protuberance posteriorly. Its posterior end (the confluence of the sinuses) is dilated and usually joins the right transverse sinus. The other transverse sinus and the occipital sinus also communicate with the confluence of the sinuses. Tributaries of the superior sagittal sinus include the ascending frontal cerebral veins, superior cerebral veins, diploic veins draining the skull bones, and a number of irregularly shaped venous lacunae. Numerous arachnoid granulations (sites of the return of water and filtrate from the cerebrospinal fluid) protrude into the superior sagittal sinus.

tarsal s.Sinus tarsi.

s. tarsi A space between the top of the calcaneus bone and the bottom of the tarsal bone. SYN: tarsal sinus.

tentorial s.

SEE: sinus rectus.

terminal s.A vein encircling the vascular area of the blastoderm.

transverse s.Either of two dural sinuses in the lateral edge of the tentorium cerebelli along each lateral superior border of the posterior cranial fossa. One transverse sinus (usually the right) is a continuation of the superior sagittal sinus; the other transverse sinus (typically the smaller of the two) is the continuation of the inferior sagittal sinus. Both transverse sinuses usually have a connection near their origin, in the region of the confluence of sinuses. The transverse sinuses run anteriorly and turn downward to become the sigmoid sinuses at the front edges of the tentorium cerebelli, where they are joined by the superior petrosal sinuses. Tributaries of the transverse sinuses include inferior cerebral, inferior cerebellar, and diploic veins.

s. tympani A sinus in the medial wall of the tympanic cavity beside the promontory and adjacent to the round window. The sinus tympani can be more than 3 mm deep.

urogenital s.In the embryo, a sinus behind the urogenital membrane and separated from the future rectum by the urorectal septum. The urachus and the mesonephric ducts, i.e., the wolffian ducts, open into the urogenital sinus. The sinus will later give rise to major parts of the urinary bladder, urethra, vagina, and genitourinary tract gland s. SYN: genitourinary sinus.

uterine s.Any of the venous sinuses in the walls of the uterus during pregnancy.

uteroplacental s.Any of the slanting venous sinuses from the placenta that convey the maternal blood from the intervillous lacunae back into the uterine veins.

s. of Valsalva Aortic sinus.

s. of venal canal The portion of the right atrium of the heart posterior, and to the left of, the crista terminalis. The inferior and superior vena caval veins empty into it.

venous s.A large-capacity sinus that carries venous blood. Important venous sinuses are those of the dura mater draining the brain and those of the spleen.

s. venosus In the embryo, the portion of the developing heart tube that leads into the cavities destined to form the atria and ventricles. The major embryonic veins (umbilical vein, vitelline vein, common cardinal vein) all lead into the sinus venosus. The sinus venosus will eventually become the posterior smooth wall of the right atrium, including the openings from the coronary sinus and the venae cava.

venous s.A valveless irregularly shaped venous sinus lined by endothelial cells. Large venous sinuses include the coronary sinus of the heart and the dural sinuses inside the skull; small venous sinuses are found inside certain tissues, such as the spleen.