Cranial Sinuses: Large endothelium-lined venous channels situated between the two layers of DURA MATER, the endosteal and the meningeal layers. They are devoid of valves and are parts of the venous system of dura mater. Major cranial sinuses include a postero-superior group (such as superior sagittal, inferior sagittal, straight, transverse, and occipital) and an antero-inferior group (such as cavernous, petrosal, and basilar plexus).Maxillary Sinus: The air space located in the body of the MAXILLARY BONE near each cheek. Each maxillary sinus communicates with the middle passage (meatus) of the NASAL CAVITY on the same side.Paranasal Sinuses: Air-filled spaces located within the bones around the NASAL CAVITY. They are extensions of the nasal cavity and lined by the ciliated NASAL MUCOSA. Each sinus is named for the cranial bone in which it is located, such as the ETHMOID SINUS; the FRONTAL SINUS; the MAXILLARY SINUS; and the SPHENOID SINUS.Cavernous Sinus: An irregularly shaped venous space in the dura mater at either side of the sphenoid bone.Sinus of Valsalva: The dilatation of the aortic wall behind each of the cusps of the aortic valve.Carotid Sinus: The dilated portion of the common carotid artery at its bifurcation into external and internal carotids. It contains baroreceptors which, when stimulated, cause slowing of the heart, vasodilatation, and a fall in blood pressure.Frontal Sinus: One of the paired, but seldom symmetrical, air spaces located between the inner and outer compact layers of the FRONTAL BONE in the forehead.Paranasal Sinus Diseases: Diseases affecting or involving the PARANASAL SINUSES and generally manifesting as inflammation, abscesses, cysts, or tumors.Sphenoid Sinus: One of the paired air spaces located in the body of the SPHENOID BONE behind the ETHMOID BONE in the middle of the skull. Sphenoid sinus communicates with the posterosuperior part of NASAL CAVITY on the same side.Coronary Sinus: A short vein that collects about two thirds of the venous blood from the MYOCARDIUM and drains into the RIGHT ATRIUM. Coronary sinus, normally located between the LEFT ATRIUM and LEFT VENTRICLE on the posterior surface of the heart, can serve as an anatomical reference for cardiac procedures.Sinus Thrombosis, Intracranial: Formation or presence of a blood clot (THROMBUS) in the CRANIAL SINUSES, large endothelium-lined venous channels situated within the SKULL. Intracranial sinuses, also called cranial venous sinuses, include the superior sagittal, cavernous, lateral, petrous sinuses, and many others. Cranial sinus thrombosis can lead to severe HEADACHE; SEIZURE; and other neurological defects.Sick Sinus Syndrome: A condition caused by dysfunctions related to the SINOATRIAL NODE including impulse generation (CARDIAC SINUS ARREST) and impulse conduction (SINOATRIAL EXIT BLOCK). It is characterized by persistent BRADYCARDIA, chronic ATRIAL FIBRILLATION, and failure to resume sinus rhythm following CARDIOVERSION. This syndrome can be congenital or acquired, particularly after surgical correction for heart defects.Ethmoid Sinus: The numerous (6-12) small thin-walled spaces or air cells in the ETHMOID BONE located between the eyes. These air cells form an ethmoidal labyrinth.Paranasal Sinus Neoplasms: Tumors or cancer of the PARANASAL SINUSES.Tachycardia, Sinus: Simple rapid heartbeats caused by rapid discharge of impulses from the SINOATRIAL NODE, usually between 100 and 180 beats/min in adults. It is characterized by a gradual onset and termination. Sinus tachycardia is common in infants, young children, and adults during strenuous physical activities.Maxillary Sinus Neoplasms: Tumors or cancer of the MAXILLARY SINUS. They represent the majority of paranasal neoplasms.Pilonidal Sinus: A hair-containing cyst or sinus, occurring chiefly in the coccygeal region.Transverse Sinuses: The two large endothelium-lined venous channels that begin at the internal occipital protuberance at the back and lower part of the CRANIUM and travels laterally and forward ending in the internal jugular vein (JUGULAR VEINS). One of the transverse sinuses, usually the right one, is the continuation of the SUPERIOR SAGITTAL SINUS. The other transverse sinus is the continuation of the straight sinus.Superior Sagittal Sinus: The long large endothelium-lined venous channel on the top outer surface of the brain. It receives blood from a vein in the nasal cavity, runs backwards, and gradually increases in size as blood drains from veins of the brain and the DURA MATER. Near the lower back of the CRANIUM, the superior sagittal sinus deviates to one side (usually the right) and continues on as one of the TRANSVERSE SINUSES.Sinoatrial Node: The small mass of modified cardiac muscle fibers located at the junction of the superior vena cava (VENA CAVA, SUPERIOR) and right atrium. Contraction impulses probably start in this node, spread over the atrium (HEART ATRIUM) and are then transmitted by the atrioventricular bundle (BUNDLE OF HIS) to the ventricle (HEART VENTRICLE).