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Sinus

In anatomy, a sinus is a cavity, recess, or channel, such as a tube or canal carrying blood or lymph. The term is most commonly used to refer to the paranasal sinuses. The paranasal sinuses are four pairs of air-filled cavities located within the bones of the skull surrounding the nasal cavity, including the frontal, ethmoidal, sphenoidal, and maxillary sinuses.^[1] These spaces are extensions of the nasal cavity, lined with a mucous membrane continuous with that of the nose, and connected to it via small openings known as ostia.^[2] They develop as outgrowths from the nasal mucosa during embryogenesis, with ethmoidal and maxillary sinuses beginning around the 10th to 12th week of gestation, sphenoidal around the third to fourth month, and frontal postnatally.^[2] The functions of the paranasal sinuses are multifaceted but not fully elucidated, with key roles including reducing the overall weight of the skull to facilitate head mobility, humidifying and warming inhaled air to protect the respiratory tract, and producing mucus that traps inhaled particles and pathogens for clearance via mucociliary action.^[3] Additionally, they contribute to vocal resonance by acting as echo chambers that modify sound during speech and may aid in the production of nitric oxide to enhance immune defense within the nasal passages.^[4]^[5] Anatomically, the frontal sinuses occupy the frontal bone above the eyes, the ethmoidal sinuses form a honeycomb-like structure between the eyes within the ethmoid bone, the sphenoidal sinuses sit deep in the sphenoid bone behind the eyes, and the maxillary sinuses are the largest, located in the cheekbones below the eyes.^[6]^[7] These sinuses vary in size and shape among individuals, with full development typically completing by late adolescence or early adulthood.^[1] Their strategic positioning also provides structural support to the facial bones while allowing for drainage into the nasal cavity to maintain airflow and pressure equalization.^[2]

Definition and Etymology

Definition

In anatomy, a sinus is defined as a recess, cavity, or channel within a body structure, such as a bone or organ.^[8] These structures are often lined with specialized epithelium or endothelium and may facilitate the passage of fluids, mucus, or blood.^[9] Unlike a general cavity, which may be a broader hollow space without a defined contour, a sinus typically features a pouch-like or curved form with a narrow opening.^[10] A key distinction exists between a sinus and a fistula: while a fistula is an abnormal passageway connecting two epithelialized surfaces or cavities, a sinus is blind-ended, terminating without linking to another point.^[11] Anatomical sinuses fall into broad categories, including air-filled cavities that lighten skeletal structures and blood-filled channels that aid venous drainage.^[12] A common example of an air-filled anatomical sinus is the paranasal type, located within facial bones.^[1]

Etymology

The word sinus originates from the Latin sinus, meaning "bay," "curve," or "fold." This root evoked images of enclosed or winding spaces, such as a river's bend or a natural inlet, and entered English via Medieval Latin borrowings.^[13]^[14] In non-medical historical contexts, sinus described practical and geographical features in ancient Roman texts. It denoted the fold in a toga draped across the chest, serving as a pouch or sac for holding small objects, as referenced in classical literature like Virgil's works. Geographically, the term applied to coastal inlets or gulfs, such as Sinus Siculus for the strait near Sicily, emphasizing concave formations akin to bodily recesses.^[13]^[14] The term's evolution into medical usage began in the late 1500s, appearing in English anatomy translations around 1598 to designate curved cavities. By the 16th and 17th centuries, it featured prominently in anatomical descriptions of hollow, bent structures, drawing directly from its Latin connotations of folds and bays. This adoption during the Renaissance marked a shift toward precise terminology for internal body spaces.^[15]^[13]^[14]

Anatomical Structures

Paranasal Sinuses

The paranasal sinuses are a group of four paired, air-filled cavities within the bones of the skull surrounding the nasal cavity. These sinuses include the frontal, maxillary, ethmoid, and sphenoid sinuses, each occupying specific positions that contribute to their structural integration with the facial skeleton. They are lined with pseudostratified ciliated columnar epithelium and connected to the nasal cavity via narrow openings called ostia, which allow for drainage and ventilation.^[2] The frontal sinuses are located in the frontal bone, superior to the orbits and within the forehead region. They are irregular, triangular or pyramidal in shape, with an average volume of 4 to 7 mL per side, and are often separated by a thin bony septum. The maxillary sinuses, the largest of the paranasal sinuses, reside within the maxillary bones beneath the orbits and in the cheek area, forming a pyramidal structure with a base facing the nasal cavity and an average volume of approximately 15 mL. The ethmoid sinuses consist of multiple thin-walled air cells (typically 5 to 15 per side) situated between the orbits in the ethmoid bone, with a total volume of about 2 to 3 mL bilaterally. Finally, the sphenoid sinuses are housed within the body of the sphenoid bone, posterior to the nasal cavity and superior to the nasopharynx, exhibiting variable cuboidal or irregular shapes with volumes ranging from 0.5 to 8 mL. Each sinus drains into the nasal cavity through specific ostia: the frontal via the frontonasal duct into the middle meatus, the maxillary through the hiatus semilunaris into the middle meatus, the anterior and middle ethmoid cells into the ethmoidal infundibulum of the middle meatus, the posterior ethmoid cells into the superior meatus, and the sphenoid into the sphenoethmoidal recess.^[2]^[1]^[2] These sinuses maintain close anatomical relations with adjacent structures, enhancing their role in the skull's architecture while posing risks in pathology. The thin bony walls shared with the orbits—such as the floor of the frontal and maxillary sinuses and the medial wall (lamina papyracea) of the ethmoid sinuses—separate them from the orbital contents. The roofs of the ethmoid and sphenoid sinuses form parts of the cranial floor, adjoining the brain and meninges. Inferiorly, the floor of the maxillary sinus is contiguous with the oral cavity, often in proximity to the apices of the upper teeth (mean distance of about 2 mm). Laterally, the sphenoid sinuses relate to critical neurovascular elements like the optic nerves and internal carotid arteries. These relations underscore the sinuses' embedded position within the skull, where the ostia ensure mucociliary clearance into the nasal passages.^[2]^[1] Anatomical variations in the paranasal sinuses are common, including asymmetries in size and shape between sides, as well as congenital absences or hypoplasia. For instance, the frontal sinuses exhibit significant variability, with unilateral aplasia occurring in approximately 15% of individuals and bilateral aplasia in about 5%. The maxillary sinuses show asymmetries in up to 25% of cases, often due to dental influences or septa, while ethmoid and sphenoid variations include extra cells like Haller or Onodi cells. Such differences can affect ostia positioning and drainage pathways but are typically asymptomatic.^[2]^[16]^[1]

Dural Venous Sinuses

The dural venous sinuses are a network of endothelial-lined venous channels located between the periosteal and meningeal layers of the dura mater, serving as the primary pathways for draining venous blood from the brain, meninges, and calvaria. Unlike typical veins, these sinuses lack valves, allowing bidirectional blood flow, and are formed by separations in the dural folds without muscular walls, relying on surrounding dural support for structure. They receive blood primarily from cerebral veins, diploic veins of the skull, and emissary veins connecting extracranial structures, ultimately directing deoxygenated blood toward the internal jugular veins.^[17]^[18] Major dural venous sinuses include the superior sagittal sinus, which runs along the superior attachment of the falx cerebri from the crista galli to the internal occipital protuberance, collecting blood from the superior cerebral hemispheres and arachnoid granulations. The inferior sagittal sinus, positioned along the inferior free edge of the falx cerebri above the corpus callosum, drains the medial and deep cerebral regions and joins the great cerebral vein to form the straight sinus at the junction of the falx cerebri and tentorium cerebelli. The transverse sinuses, paired structures, course horizontally along the posterior attachment of the tentorium cerebelli within the occipital bone's groove, receiving blood from the confluence of sinuses and continuing into the sigmoid sinuses. The sigmoid sinuses, S-shaped continuations of the transverse sinuses, descend through the posterior cranial fossa to the jugular foramen, where they empty into the internal jugular veins via the jugular bulb.^[17]^[18]^[19]^[20] The cavernous sinuses, paired and located lateral to the sella turcica in the sphenoid bone, differ from other sinuses by their trabeculated, plexus-like interior and critical neurovascular contents, including cranial nerves III (oculomotor), IV (trochlear), V (ophthalmic and maxillary divisions), and VI (abducens), as well as the internal carotid artery. These sinuses drain the orbits via ophthalmic veins, the pterygoid plexus, and connect across the midline via intercavernous sinuses, ultimately emptying into the superior and inferior petrosal sinuses en route to the internal jugular vein. In contrast to the air-filled paranasal sinuses, the dural venous sinuses are vascular conduits embedded in the meninges for cerebral venous return.^[17]^[18]^[19]

Coronary Sinus

The coronary sinus is the largest vein of the heart, serving as the principal channel for venous drainage of the myocardium. It is situated in the coronary sulcus, which demarcates the atrioventricular groove on the posterior surface of the heart, running along the inferior aspect of the left atrium between the left atrium and left ventricle. This structure measures approximately 2 to 5 cm in length and has a caliber of about 1 cm, originating from the confluence of the great cardiac vein and the oblique vein of the left atrium (also known as the vein of Marshall). It courses posteriorly and empties into the right atrium via an ostium located posteroinferiorly, between the openings of the inferior vena cava and the tricuspid valve.^[21]^[22]^[23] The coronary sinus receives blood from several major tributaries that collect deoxygenated blood from the heart muscle. Key tributaries include the great cardiac vein, which drains the anterior and lateral aspects of the left ventricle; the middle cardiac vein, which runs along the posterior interventricular sulcus to serve the posterior left ventricle and parts of the right ventricle; and the oblique vein of the left atrium (vein of Marshall), a remnant of the embryonic left superior vena cava that primarily drains the left atrium. Additional tributaries may include the small cardiac vein and posterior veins of the left ventricle, though their connections can vary. At its ostium, the coronary sinus is often guarded by the Thebesian valve, a thin, semicircular flap that partially or completely covers the opening to prevent retrograde flow from the right atrium into the sinus, although this valve may be absent or rudimentary in some individuals.^[21]^[22]^[23] In terms of anatomical relations, the coronary sinus lies medial to the entrance of the inferior vena cava and superior to the septal leaflet of the tricuspid valve, forming the base of the triangle of Koch, an important landmark for the atrioventricular node. It is closely adjacent to the posterior walls of the left atrium and ventricle, facilitating the collection of approximately 55% of the deoxygenated blood from the coronary venous system before directing it into the right atrium for recirculation. This venous pathway ensures efficient drainage of the majority of the myocardial capillary beds, excluding the anterior cardiac veins and the smallest cardiac veins (Thebesian veins), which drain directly into the cardiac chambers.^[21]^[22]^[23]

Physiology and Development

Functions

The paranasal sinuses contribute to respiratory physiology by humidifying and warming inhaled air, thereby conditioning it for optimal gas exchange in the lower airways.^[3] They also produce mucus through goblet cells in their epithelial lining, which traps pathogens and particulates before they reach the lungs.^[24] Additionally, these sinuses enhance voice resonance by acting as air-filled chambers that amplify sound waves during speech.^[3] In the context of trauma, the paranasal sinuses may function as a crumple zone, absorbing and distributing impact forces to protect the brain from facial injuries.^[25] The dural venous sinuses facilitate the drainage of deoxygenated blood from the brain and its meninges into the internal jugular veins, maintaining cerebral circulation.^[26] They play a key role in cerebrospinal fluid (CSF) absorption, particularly through arachnoid granulations protruding into the superior sagittal sinus, which allow CSF to enter the venous bloodstream and regulate intracranial pressure.^[27] This drainage mechanism helps stabilize pressure within the cranial cavity by balancing fluid dynamics and preventing pathological elevations.^[28] The coronary sinus serves as the primary conduit for collecting deoxygenated venous blood from the myocardial capillaries, channeling approximately 55% of the heart's venous return directly into the right atrium.^[21] By directing this blood flow separately from the oxygenated blood entering the left atrium via the pulmonary veins, the coronary sinus ensures minimal mixing of systemic and pulmonary circulations within the cardiac chambers.^[21] The paranasal sinuses integrate structural and physiological roles by lightening the overall weight of the skull, reducing its mass without compromising integrity.^[3] They also support thermoregulation, with their vascular mucosa aiding in warming inspired air and potentially contributing to selective brain cooling through heat exchange.^[29]

Embryological Development

The embryological development of the paranasal sinuses begins with the formation of nasal placodes in the frontonasal prominence around the fourth week of gestation, followed by invagination into nasal pits by weeks 5 to 6, establishing the lateral nasal wall from which outpouchings emerge.^[30] These outpouchings, known as ethmoturbinals, appear as folds on the lateral nasal wall by the eighth week, with the first ethmoturbinal giving rise to the agger nasi cell and uncinate process, the second to the middle turbinate, and the third to the superior turbinate.^[2] The ethmoid sinuses develop first, forming 3 to 4 air cells by the 8th to 10th week through evaginations into the ethmoidal labyrinth; the maxillary sinus initiates around the 10th week as an outpouching from the middle meatus into the maxilla; the sphenoid sinus starts in the third month via invagination of nasal mucosa into the presphenoid cartilage; and the frontal sinus begins in the third or fourth month as an extension from the frontonasal recess, though significant pneumatization occurs postnatally from age 1 to 2 years.^[31] Full pneumatization of all paranasal sinuses is not achieved until adolescence, with the maxillary and frontal sinuses reaching adult size by ages 15 and late teens, respectively.^[2] The dural venous sinuses arise from the primary capillary plexus within the developing dura mater, derived from neural crest and mesodermal tissues, around the 7th to 8th week of gestation.^[17] This plexus reorganizes into venous channels, with the superior sagittal sinus forming from the marginal vein along the midline of the developing brain, while the transverse sinuses derive from the tentorial sinus associated with the tentorium cerebelli.^[17] The cavernous sinuses emerge from the primitive carotid plexus, and the sigmoid sinuses develop as continuations of the transverse sinuses, all integrating with the arachnoid granulations by later fetal stages to facilitate venous drainage.^[32] The coronary sinus originates from the left horn of the sinus venosus during the third to fourth week of embryonic development, as the primitive heart tube differentiates into the bulbus cordis, ventricle, and sinus venosus.^[21] The right horn of the sinus venosus enlarges and incorporates into the right atrium, while the smaller left horn persists as the coronary sinus, receiving tributaries from the left common cardinal vein (future oblique vein of Marshall) and developing cardiac veins by weeks 4 to 5.^[21] This structure ultimately drains venous blood from the coronary circulation into the right atrium near the inferior vena cava orifice.^[33] Developmental anomalies of sinuses can arise from disruptions in these processes, such as agenesis of the frontal sinus, which occurs unilaterally in approximately 5% and bilaterally in 4% of adults due to failed outpouching from the frontonasal recess.^[31] Defects in the uncinate process, which forms from the first ethmoturbinal by the eighth week, often lead to variations like maxillary sinus hypoplasia, classified into types based on the degree of pneumatization failure and associated with altered ethmoidal infundibulum development.^[2]

Clinical Significance

Common Disorders

Sinusitis, also known as rhinosinusitis, is the inflammation of the paranasal sinuses and nasal cavity mucosa, commonly affecting the maxillary, frontal, ethmoid, and sphenoid sinuses.^[34] It manifests in acute form, lasting up to 12 weeks, or chronic form, persisting beyond 12 weeks, with symptoms including nasal congestion, facial pain, and purulent discharge.^[35] Primary causes encompass viral infections, which account for most acute cases, bacterial superinfections in about 0.5% to 2% of viral episodes, and allergic triggers that exacerbate mucosal inflammation.^[36] Allergies contribute significantly, with sensitization to antigens linked to increased incidence of both acute and chronic variants.^[37] Prevalence is high, impacting approximately 10-15% of adults annually in the United States, with chronic forms diagnosed in about 11.6% of adults.^[38]^[34] Cerebral venous sinus thrombosis (CVST), involving clot formation in the dural venous sinuses such as the superior sagittal or transverse sinuses, is a rarer disorder that impedes venous drainage from the brain.^[39] It presents with symptoms like severe headache in up to 90% of cases, seizures, focal neurological deficits, and papilledema due to increased intracranial pressure.^[40] Risk factors include dehydration, which promotes blood stasis, and coagulopathies such as thrombophilia or antiphospholipid syndrome, alongside prothrombotic conditions like pregnancy and oral contraceptive use.^[41]^[39] CVST is uncommon, with an estimated annual incidence of 3-4 cases per million population, predominantly affecting young adults and showing a female predominance due to hormonal factors.^[39] Issues involving the coronary sinus, such as ostial atresia or fistulas, are rare congenital anomalies where the coronary sinus fails to connect properly to the right atrium or develops abnormal communications with coronary arteries.^[42]^[43] Atresia leads to unroofing or diversion of venous drainage, often associated with other cardiac defects like persistent left superior vena cava, while fistulas cause left-to-right shunting and potential ischemia. These defects are rare congenital anomalies with a prevalence of approximately 0.3-0.4% in patients with congenital heart disease, typically presenting in infancy with heart failure or arrhythmias.^[44] Among sinus-related disorders, those affecting the paranasal sinuses, particularly sinusitis, are the most prevalent, far outnumbering vascular or cardiac variants.^[34] Epidemiological patterns show paranasal sinusitis is more common in females, with nearly double the rate of chronic forms compared to males, and peaks in adulthood between ages 45 and 54.^[45] Age and gender disparities in venous and coronary sinus conditions are less pronounced, though CVST shows a slight female bias.^[39] These vulnerabilities often stem from the paranasal sinuses' proximity to nasal passages, facilitating infectious spread.^[34]

Diagnosis and Treatment

Diagnosis of sinus-related conditions varies by the specific anatomical structure involved, with imaging and endoscopic techniques playing central roles. For paranasal sinus disorders such as sinusitis, computed tomography (CT) scans are considered the gold standard, providing detailed visualization of mucosal thickening, air-fluid levels, and bony structures to confirm inflammation or obstruction. Magnetic resonance imaging (MRI) is preferred for evaluating dural venous sinuses, particularly in detecting thrombosis, as it excels at identifying flow voids and parenchymal involvement without radiation exposure. For coronary sinus anomalies, electrocardiography (ECG) and echocardiography are initial diagnostic tools, assessing electrical conduction and structural defects like atrial septal communications. Additional diagnostic methods enhance precision across sinus types. Nasal endoscopy is commonly used for paranasal sinuses, allowing direct visualization of the nasal cavity and ostiomeatal complex to identify polyps, tumors, or purulent discharge in conditions like chronic sinusitis. For dural venous sinuses, magnetic resonance venography (MRV) or computed tomography venography (CTV) provides detailed mapping of venous flow and clot location, often following initial MRI findings. In coronary sinus evaluation, advanced imaging such as cardiac MRI or transesophageal echocardiography may be employed to delineate persistent left superior vena cava drainage or fistulas. Treatment strategies are tailored to the underlying pathology and sinus type, emphasizing conservative measures before invasive options. Acute paranasal sinusitis is typically managed with antibiotics like amoxicillin-clavulanate for bacterial infections and decongestants such as pseudoephedrine to reduce swelling, alongside saline irrigation for symptom relief. Dural venous sinus thrombosis requires immediate anticoagulation with heparin or low-molecular-weight heparin to prevent clot propagation, followed by oral anticoagulants such as warfarin or direct oral anticoagulants (DOACs) for 3-12 months, depending on underlying risk factors, with surgical intervention reserved for refractory cases involving abscesses.^[46] Coronary sinus defects, such as those associated with arrhythmias, may be treated via catheter ablation to isolate arrhythmogenic foci, particularly in persistent left superior vena cava connections. Advancements in minimally invasive techniques have improved outcomes for chronic paranasal sinus conditions. Functional endoscopic sinus surgery (FESS) involves the use of endoscopes to widen sinus ostia and remove diseased tissue, reducing recurrence rates in chronic rhinosinusitis while preserving normal mucosa; studies report success rates exceeding 80% in symptom improvement. For dural venous issues, endovascular thrombolysis with tissue plasminogen activator has emerged as an adjunct to anticoagulation in severe thrombosis, though its use is guided by multidisciplinary protocols to balance bleeding risks. In coronary sinus management, image-guided percutaneous closure devices offer alternatives to open surgery for associated septal defects, minimizing procedural morbidity.

Historical Context

Early Descriptions

The term "sinus," derived from the Latin word for "bay" or "curve" and rooted in the Greek kolpos meaning "bosom" or "gulf," originally evoked natural hollows or folds, influencing its early application to anatomical cavities.^[13]^[15] In ancient medicine, Hippocrates (c. 400 BCE) provided some of the earliest references to structures resembling the paranasal sinuses, describing "empty cavities" within the head through which air passes to produce voice with an echoing quality, and emphasizing the importance of keeping nasal cavities clear to prevent abnormalities causing disease.^[14] These observations, found in the Hippocratic Corpus, treated the nasal region holistically but lacked precise anatomical delineation, viewing such spaces primarily as pathways for air and secretions.^[47] Galen (2nd century CE), building on this through extensive animal dissections, noted cranial sinuses as part of the head's vascular and bony architecture, including the confluence of dural venous sinuses at the torcular Herophili, though his human inferences were indirect due to dissection restrictions.^[48]^[14] Galen's works, such as On Anatomical Procedures, portrayed these as supportive hollows for blood distribution and cranial stability, without distinguishing specific paranasal types.^[49] Medieval scholars advanced these ideas amid humoral theory. Avicenna (Ibn Sina, 11th century) in his Canon of Medicine linked sinus-related nasal congestion and catarrh to headaches, classifying head pains as arising from imbalances like excess phlegm accumulating in cranial hollows, and recommending nasal irrigations for relief.^[50]^[51] This text integrated Greek knowledge with clinical observations, associating sinus inflammation with chronic cephalalgia but without detailed imaging or isolation of individual sinuses. Early European anatomists, such as Andreas Vesalius in his 1543 De humani corporis fabrica, offered the first systematic illustrations of paranasal structures, showing frontal sinuses in cross-section and sphenoid sinuses divided by a septum, proposing they lighten the skull and resonate sound.^[14] Vesalius's copperplate engravings marked a shift toward empirical visualization, yet coverage remained sparse, omitting the maxillary sinus entirely.^[52] These pre-modern accounts were constrained by technological limits, perceiving sinuses broadly as "hollows" or bays in bone without insight into their mucosal lining, epithelial functions, or microbial roles, often attributing them to vague purposes like spirit drainage or weight reduction.^[14] Dissections were rudimentary, relying on surface probes and animal proxies, which obscured interconnections with the nasal cavity and vascular systems.^[53]

Modern Advancements

In the 19th century, microscopic techniques advanced the understanding of sinus histology, particularly the endothelial lining of venous structures. By the early 20th century, electrocardiographic and polygraphic methods illuminated cardiac sinus function. Sir James Mackenzie, using his ink polygraph invented around 1885, recorded venous and arterial pulses to demonstrate the benign nature of sinus arrhythmia—a normal variation in heart rate tied to respiration—thus distinguishing it from pathological rhythms and advancing recognition of normal sinus rhythm in clinical practice.^[54] The mid-20th century brought transformative treatments for sinus-related infections via the antibiotic era. Penicillin's mass production and clinical deployment in the 1940s revolutionized management of bacterial sinusitis, often caused by streptococcal or staphylococcal pathogens, by dramatically reducing infection severity and mortality rates; U.S. output escalated from 21 billion units in 1943 to 6.8 trillion by 1945, enabling widespread use against such conditions.^[55] Imaging innovations in the 1970s further enhanced sinus visualization. The first computed tomography (CT) scan, performed in 1971 by Godfrey Hounsfield and James Ambrose, introduced cross-sectional imaging that soon enabled precise, non-invasive assessment of paranasal sinus anatomy and pathology, supplanting plain radiography and improving diagnostic accuracy for conditions like sinusitis.^[56] Building on endoscopic advancements, functional endoscopic sinus surgery (FESS), pioneered by Walter Messerklinger and Heinz Stammberger in the 1970s and 1980s, revolutionized paranasal sinus treatment by emphasizing minimally invasive restoration of sinus drainage and ventilation, significantly reducing complications compared to traditional open procedures.^[57] Advancements extended to non-paranasal sinuses, with magnetic resonance venography (MRV) emerging in the late 20th and early 21st centuries to map dural venous sinus variations noninvasively; studies using contrast-enhanced MRV have quantified anatomical diversity, such as asymmetries in the confluence of sinuses, aiding in surgical planning and thrombosis diagnosis.^[58] Similarly, for the coronary sinus, the 21st-century development of the coronary sinus reducer (CSR)—an implantable device narrowing the sinus to improve myocardial perfusion—has shown symptom relief in refractory angina patients, with trials demonstrating reduced angina frequency over 6 months post-implantation.^[59] In the 21st century, genetic research has uncovered links between mutations and sinus disorders, expanding beyond paranasal focus to developmental and inflammatory pathways. Mutations in the CFTR gene, such as ΔF508, are strongly associated with chronic rhinosinusitis (CRS), particularly in European-ancestry populations, increasing susceptibility through impaired mucociliary clearance; replicated studies confirm elevated CRS risk (P<0.05) in carriers, influencing both with- and without-nasal-polyps phenotypes.^[60] Complementing genetic insights, biologics have emerged as targeted therapies for severe CRS with nasal polyps (CRSwNP); dupilumab, approved by the FDA in 2019, inhibits IL-4 and IL-13 signaling to reduce inflammation and polyp burden, with subsequent approvals for agents like omalizumab and mepolizumab as of 2025.^[61] Surgical technologies have also progressed, with minimally invasive robotics enhancing precision in sinus procedures post-2010. The da Vinci system, adapted for transoral robotic surgery (TORS), facilitated initial nasopharyngectomies for recurrent tumors in 2012–2015, achieving up to 86% 2-year local control with reduced complications compared to open approaches; emerging flexible robots, such as concentric tube prototypes developed at Vanderbilt University (post-2010), target transnasal access to paranasal sinuses, overcoming rigidity limitations for skull base interventions.^[62]^[63]

Other Contexts

Botanical Sinuses

In botany, a sinus is defined as the space, indentation, or recess between two lobes or teeth on a leaf margin, maintaining the continuity of the leaf blade without dividing it into separate leaflets. This feature is particularly prominent in lobed leaves, where sinuses form the valleys separating the projecting lobes. For instance, in palmate leaves of species like the sugar maple (Acer saccharum), the sinuses create distinct separations between the five rounded lobes, contributing to the overall dissected appearance of the blade.^[64]^[65]^[66] Sinuses also appear in serrated or dentate leaf margins, where smaller marginal sinuses occur between the tooth-like projections, as seen in leaves of oaks (Quercus spp.) or elms (Ulmus spp.). These structures play a key role in leaf morphology by influencing surface area and venation patterns, which optimize photosynthesis. Specifically, the lobing facilitated by sinuses allows for compensatory increases in vein length, maintaining hydraulic efficiency and carbon assimilation despite reduced laminar area in the sinus regions. This adaptation supports effective light capture and gas exchange in diverse light regimes.^[67]^[68] From an evolutionary perspective, sinuses in lobed leaves represent adaptations to environmental pressures, such as enhancing wind resistance by reducing drag through leaf reconfiguration during high winds, as observed in broad-leaved species with lobed bases. These traits have evolved multiple times across angiosperms, reflecting selective advantages in temperate and variable habitats.^[69]^[70]

Geographical Features

In geography, the term "sinus" derives from Latin for "bay" or "gulf" and has been used historically to denote elongated inlets or bodies of water. Ancient geographers applied it to significant maritime features, such as Sinus Arabicus, the classical name for the Red Sea, reflecting its position adjacent to the Arabian Peninsula in texts from the Hellenistic and Roman periods.^[71] This nomenclature emphasized the sea's role as a vital trade route, with descriptions appearing in works by Ptolemy and Strabo that detailed its extent from the Gulf of Suez to the Bab el-Mandeb Strait.^[72] In astronomy, particularly selenography, "sinus" designates small lunar plains or bay-like formations, often basaltic maria extensions, as defined by the International Astronomical Union (IAU) nomenclature conventions. These features are capitalized in official usage (e.g., Sinus Medii) and represent lava-flooded depressions resembling terrestrial bays. The IAU's Working Group for Planetary System Nomenclature oversees approvals, drawing from a historical name bank while adhering to rules that prioritize classical, mythological, or scientific themes for new designations.^[73] Prominent examples include Sinus Medii, a central lunar mare approximately 300 km wide at the intersection of the Moon's equator and prime meridian, named in 1651 by Giovanni Battista Riccioli in his influential Almagestum Novum map, which laid the foundation for modern lunar naming.^[74] Another is Sinus Successus, a 100 km-wide bay along the eastern edge of Mare Fecunditatis, characterized by its outward bulge and proximity to the flooded crater Condon.^[75] IAU conventions have remained stable since their formalization in the 20th century, with incremental additions like the 2023 naming of Sinus Viscositatis but no substantive revisions to the "sinus" descriptor post-2020. In 2025, Firefly Aerospace's Blue Ghost Mission 3 successfully landed near Sinus Viscositatis on March 2, carrying NASA payloads to study the region's geology and support future lunar exploration.^[76]^[77]

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Frontal sinus aplasia is present unilaterally in 15% and bilaterally in 5% of normal adults. Maxillary sinus aplasia is extremely rare, whereas maxillary sinus ...
[17]
Neuroanatomy, Dural Venous Sinuses - StatPearls - NCBI Bookshelf
Dural venous sinuses are a group of sinuses or blood channels that drains venous blood circulating from the cranial cavity.Introduction · Structure and Function · Physiologic Variants · Clinical Significance
[18]
Dural Venous Sinuses - Superior Sagittal - TeachMeAnatomy
### Summary of Dural Venous Sinuses Anatomy
[19]
Dural venous sinuses: Anatomy, location and function - Kenhub
Generally, the walls of these drainage pathways are formed by visceral periosteum and dural reflection, both lined with endothelium. The inferior sagittal and ...
[20]
[PDF] MBB Lab 2, Part B Dural Folds, Dural Sinuses, and Arterial Supply to ...
FUNCTIONAL ANATOMY: Dural venous sinuses are venous channels that lack valves, which means venous blood may flow through them in either direction. Page 10 ...
[21]
Anatomy, Thorax, Coronary Sinus - StatPearls - NCBI Bookshelf
The coronary sinus is the major venous tributary of the greater cardiac venous system; it is responsible for draining most of the deoxygenated blood leaving ...
[22]
Coronary sinus: Anatomy, tributaries, drainage - Kenhub
The coronary sinus is a large venous structure located on the inferior aspect of the left atrium, coursing within the left atrioventricular groove.
[23]
Coronary sinus | Radiology Reference Article - Radiopaedia.org
Oct 27, 2024 · The coronary sinus is the largest cardiac venous structure. It returns the majority of the blood supply for the left ventricle to the right atrium.
[24]
Mucus production in the nasal sinuses - PubMed
Goblet cells showed the highest density in the maxillary sinuses. 9700 per mm2, while in the other sinuses their density was approximately the same, from 5 900 ...
[25]
Association of frontal sinus volume and cerebral injury ... - PubMed
One hypothesis theorizes that the sinuses, in the event of a traumatic injury, function as a crumple zone to distribute and absorb energy to protect the brain ...
[26]
Neuroanatomy, Superior Sagittal Sinus - StatPearls - NCBI Bookshelf
Jan 23, 2023 · In addition to draining blood from the cerebral cortex, the superior sagittal sinus plays a significant role in cerebrospinal fluid (CSF) ...Missing: absorption | Show results with:absorption
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Physiology, Cerebral Spinal Fluid - StatPearls - NCBI Bookshelf
Aug 9, 2025 · ... venous sinuses drives CSF into the venous system through these structures, facilitating absorption. However, contemporary models no longer ...
[28]
Mechanical and structural characterisation of the dural venous sinuses
Dec 10, 2020 · The dural venous sinuses are large venous conduits within the dura mater layer of the meninges that are responsible for draining virtually all ...
[29]
Human paranasal sinuses and selective brain cooling - PubMed
For one, the paranasal sinuses have been regarded as warmers of respiratory air, when in actuality these structures appear to function in cooling the blood.
[30]
Pediatric paranasal sinuses—Development, growth, pathology ... - NIH
They begin as an outpouching of the lateral nasal wall, at the level of the anterosuperior portion of the middle nasal meatus.
[31]
Embryology of the Cavernous Sinus and Relevant Veins - PMC - NIH
In the early embryonic stages, the neural tube is surrounded by the primitive capillary plexus and undifferentiated mesenchymal tissue, the primary meninx, and ...
[32]
Congenital Defects Tutorial - Normal Cardiac Development
The left sinus horn receiving venous blood becomes the coronary sinus. The umbilical system. The unpaired umbilical vein provides the embryo with nutrient ...
[33]
Acute Sinusitis - StatPearls - NCBI Bookshelf - NIH
Aug 2, 2025 · Rhinosinusitis is the inflammation of the nasal cavity and paranasal sinuses, typically resulting from infection, allergy, or other causes.
[34]
Chronic Sinusitis - StatPearls - NCBI Bookshelf
Chronic sinusitis is an inflammation of the sinus or nasal passages occurring for more than 12 weeks at a time. It may present as chronic sinusitis without ...
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The prevalence of bacterial infection in acute rhinosinusitis - NIH
Other review articles, and clinical guidelines suggest that acute bacterial sinusitis complicates 0.5% to 2% of acute viral sinus infections in adults. The ...Missing: paranasal | Show results with:paranasal
[36]
The association between allergy and sinusitis - PubMed Central - NIH
Dec 25, 2021 · Allergy is related to sinusitis incidence. It is likely that sensitization status could reduce the incidence of sinusitis, albeit in an antigen-specific manner.Missing: paranasal | Show results with:paranasal
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FastStats - Sinus Conditions - CDC
Chronic Sinusitis · Number of adults with diagnosed sinusitis: 28.9 million · Percent of adults with diagnosed sinusitis: 11.6%.
[38]
Cerebral Venous Sinus Thrombosis - StatPearls - NCBI Bookshelf
May 4, 2025 · Risk factors include prothrombotic states such as pregnancy, the postpartum period, oral contraceptive use, and thrombophilia. The superior ...
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An Integrated Approach on the Diagnosis of Cerebral Veins and ...
Headache is the most common symptom of CVT (about 90% of cases in the ISCVT cohort). It is usually the initial one, and can develop isolated, or can precede ...
[40]
Cerebral venous sinus thrombosis risk factors - PubMed
It is more often related to neoplasm, pregnancy, puerperium, systemic diseases, dehydration, intracranial tumors, oral contraceptives, and coagulopathies are ...
[41]
New Developments in the Pathophysiology, Workup, and Diagnosis ...
Dural venous sinus thrombosis (DVST) is a rare cause of stroke, which typically affects young women. The importance of identifying pre-disposing factors ...
[42]
An unusual pair: coronary artery fistula and coronary sinus ostium ...
Coronary fistula are rare and often present in early adulthood with symptoms of right heart overload from left to right shunting or ischaemia in the distal ...
[43]
Coronary Fistulas: A Case Series - PMC - NIH
Congenital coronary fistula is a rare malformation and accounts for only 14% of all coronary anomalies. The incidence is 0.002% among the general population, ...
[44]
Ostial atresia of the coronary sinus in patients with supraventricular ...
They found 15 cases with ostial CS atresia among 13,842 patients (0.11%). These data suggest that the incidence of OACS is around 0.1%. Shum's study involved ...Missing: defects | Show results with:defects
[45]
Commentary on gender differences in prevalence, treatment, and ...
Epidemiology studies reported that women have nearly double the rate of chronic rhinosinusitis (CRS) when compared with men,1,2 whereas other studies found no ...
[46]
https://emedicine.medscape.com/article/1162804-treatment
[47]
Galen on the Brain: Anatomical Knowledge and Physiological ...
For Galen, the torcular is the anatomical conﬂuence of the four cranial venous sinuses, from which blood is distributed to the brain.103 Von Staden points ...
[48]
[PDF] Galen on anatomical procedures [electronic resource]
anatomy. The dissection scene on the front of this jacket illustrates Galen ... sinuses in man. Fig. 26. Diagram of fourth ventricle and neighbouring parts ...
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Types of Nasal Delivery Drugs and Medications in Iranian ...
Nasal route is one of the ancient and topical prescriptions used in headache. In Iranian traditional medicine, physicians such as Avicenna were prescribing ...Missing: sinuses | Show results with:sinuses
[50]
Relationship Between Cerebrospinal Fluid and Catarrh According to ...
A postnasal drip (PND) or catarrh refers to the drainage of secretions from the paranasal sinuses or nose into the posterior nasal space and the oropharynx.
[51]
(PDF) Evolution of the paranasal sinuses' anatomy through the ages
Aug 10, 2025 · Vesalius' images of the skull and the sphenoid bone. The images constitute anatomical drawings from Vesalius' work 'De Humani Corporis Fabrica.
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https://www.researchgate.net/publication/259568082_Evolution_of_the_paranasal_sinuses%27_anatomy_through_the_ages
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Rudolf albert von koelliker - PMC - NIH
Full Text. The Full Text of this article is available as a PDF (289.1 KB). References. 1. Cameron GR: Rudolf Albert v. Koelliker (1817–1905).Missing: venous sinus endothelium 1850s
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James Mackenzie • LITFL • Medical Eponym Library
Aug 29, 2025 · Mackenzie showed that many irregularities, such as extrasystoles and sinus arrhythmia, were benign, and clarified the natural history of ...
[55]
Alexander Fleming Discovery and Development of Penicillin
The introduction of penicillin in the 1940s, which began the era of antibiotics, has been recognized as one of the greatest advances in therapeutic medicine.
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Milestones in CT: Past, Present, and Future - PMC - NIH
In 1971, the first patient CT exam by Ambrose and Hounsfield paved the way for not only volumetric imaging of the brain but of the entire body.
[57]
Dural Venous Sinus Variations Observed in Magnetic Resonance ...
This study aims to evaluate the anatomical variations of the dural venous sinuses using Magnetic Resonance Venography.
[58]
Coronary Sinus Reducer Eases Symptoms in Refractory Angina
Apr 8, 2024 · An implantable coronary sinus reducer (CSR) in patients with refractory angina significantly reduces symptoms over 6 months of follow-up compared with a ...Missing: modern 21st
[59]
Genetics of Chronic Rhinosinusitis: State of the Field and Directions ...
Apr 1, 2014 · Genetic approaches have provided insight into the etiology of many chronic relapsing and remitting diseases. Study of the genetic susceptibility ...
[60]
Current Advances in Robotics for Head and Neck Surgery ... - MDPI
The purpose of this review is to outline the current status of robotics in head and neck surgery in the context of the present literature.3. Results · 3.1. Pharynx · 3.3. Paranasal Sinuses And...
[61]
Robotic surgery for the sinuses and skull base - NIH
Advances in the design of robotic arms, materials, and shape will potentially give surgeons significant advantage over traditional endoscopic techniques.
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UIPlants: Botanic Terminology
Heart-shaped; can be overall leaf shape, or leaf base with the notched section connecting to the petiole. ... On a lobed leaf a sinus is the valley between the ...
[63]
Lake Forestry Glossary
Sinus: A leaf sinus is the space or division (indentation) between two lobes orteeth that does not break the continuity of the structure Sinus only at the base ...
[64]
Ecophysiological Analysis of Leaf Shape - Plant Physiology
The area between the lobes of a leaf is called a sinus. A leaf with very deep and fine lobes that make the leaf almost appear to be compound is called dissected ...Missing: definition | Show results with:definition
[65]
Increases in vein length compensate for leaf area lost to lobing in ...
Jul 19, 2022 · ... leaf sinus, or “lobiness” (Welter et al., 2007; Demmings et al ... The evolution and functional significance of leaf shape in the angiosperms.Missing: adaptation | Show results with:adaptation
[66]
The Role of Leaf Lobation in Elongation Responses to Shade in the ...
The results show that extensive leaf lobation can enable greater leaf elongation in response to shade from surrounding herbaceous vegetation.
[67]
Drag and Reconfiguration of Broad Leaves in High Winds
Leaves with lobed bases and long petioles had lower drag, fluttered little and reconfigured into increasingly acute cones. Pinnately compound leaves had the ...
[68]
Leaf form diversity and evolution: a never-ending story in plant biology
Apr 9, 2024 · Leaf form varies at different levels, reflecting adaptations to environmental factors like temperature, light, and water, and can occur within ...
[69]
Dictionary of Greek and Roman Geography/Arabicus Sinus
Sep 13, 2025 · These passages show that Herodotus knew the Red Sea ... The ancient geographers first became well acquainted with the Red Sea under the Ptolemies.
[70]
Red Sea - Digital Collections
Historically the Red Sea was called Sinus Arabicus (Arabian Gulf), because Arabs occupied both sides of it. Holy Scripture refers to it as the Reed Sea , or ...
[71]
IAU Rules and Conventions - Planetary Names
All official IAU nomenclature should be capitalized, including the unique name and the descriptor term. The single exception is the term crater; the unique name ...Missing: sinuses | Show results with:sinuses
[72]
05. Riccioli, Giovanni Battista - Linda Hall Library
The Riccioli moon map is historically of great importance, since it provided the basis for the system of lunar nomenclature still in use.Missing: Sinus Medii
[73]
Sinus Successus - Gazetteer of Planetary Nomenclature
MOON – Sinus Successus. East. West. centric. graphic. 180°. 360°. Latitude ... – MOON – Sinus Successus. – Planetographic east 180. +−. Draw a polylineDraw a ...
[74]
Sinus Viscositatis: Bay of Stickiness -- the firstly-named lunar feature ...
Jan 12, 2023 · Yes, we have the first named lunar feature of 2023, and it's a bay called Sinus Viscositatis -- the 'Bay of Stickiness'.