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Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The
maxillary sinus The pyramid-shaped maxillary sinus (or antrum of Highmore) is the largest of the paranasal sinuses, and drains into the middle meatus of the nose through the osteomeatal complex.Human Anatomy, Jacobs, Elsevier, 2008, page 209-210 Structure It i ...
es are located under the eyes; the
frontal sinus The frontal sinuses are one of the four pairs of paranasal sinuses that are situated behind the brow ridges. Sinuses are mucosa-lined airspaces within the bones of the face and skull. Each opens into the anterior part of the corresponding middle n ...
es are above the eyes; the ethmoidal sinuses are between the eyes and the
sphenoidal sinus The sphenoid sinus is a paired paranasal sinus occurring within the within the body of the sphenoid bone. It represents one pair of the four paired paranasal sinuses.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012 ...
es are behind the eyes. The sinuses are named for the
facial bones The facial skeleton comprises the ''facial bones'' that may attach to build a portion of the skull. The remainder of the skull is the braincase. In human anatomy and development, the facial skeleton is sometimes called the ''membranous visceroc ...
in which they are located.


Structure

Humans possess four pairs of paranasal sinuses, divided into subgroups that are named according to the bones within which the sinuses lie. They are all innervated by branches of the trigeminal nerve (CN V). * The
maxillary sinus The pyramid-shaped maxillary sinus (or antrum of Highmore) is the largest of the paranasal sinuses, and drains into the middle meatus of the nose through the osteomeatal complex.Human Anatomy, Jacobs, Elsevier, 2008, page 209-210 Structure It i ...
es, the largest of the paranasal sinuses, are under the eyes, in the maxillary bones (open in the back of the
semilunar hiatus The semilunar hiatus or hiatus semilunaris, is a crescent-shaped groove in the lateral wall of the nasal cavity just inferior to the ethmoid bulla. It is the location of the openings of the maxillary sinuses. It is bounded inferiorly and anterior ...
of the nose). They are innervated by the
maxillary nerve In neuroanatomy, the maxillary nerve (V) is one of the three branches or divisions of the trigeminal nerve, the fifth (CN V) cranial nerve. It comprises the principal functions of sensation from the maxilla, nasal cavity, sinuses, the palate ...
(CN V2). * The
frontal sinus The frontal sinuses are one of the four pairs of paranasal sinuses that are situated behind the brow ridges. Sinuses are mucosa-lined airspaces within the bones of the face and skull. Each opens into the anterior part of the corresponding middle n ...
es, superior to the eyes, in the
frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, part ...
, which forms the hard part of the forehead. They are innervated by the
ophthalmic nerve The ophthalmic nerve (V1) is a sensory nerve of the face. It is one of three divisions of the trigeminal nerve (CN V). It has three branches that provide sensory innervation to the eye, the skin of the upper face, and the skin of the anterior scal ...
(CN V1). * The
ethmoidal sinus The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. The cells are variable in both size and number in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral e ...
es, which are formed from several discrete air cells within the ethmoid bone between the
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passe ...
and the eyes. They are innervated by the
ethmoidal nerves The ethmoidal nerves, which arise from the nasociliary nerve, supply the ethmoidal cells; the posterior branch leaves the orbital cavity through the posterior ethmoidal foramen and gives some filaments to the sphenoidal sinus. There are two ethmoid ...
, which branch from the
nasociliary nerve The nasociliary nerve is a branch of the ophthalmic nerve, itself a branch of the trigeminal nerve (CN V). It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve. Structure The naso ...
of the ophthalmic nerve (CN V1). * The
sphenoidal sinus The sphenoid sinus is a paired paranasal sinus occurring within the within the body of the sphenoid bone. It represents one pair of the four paired paranasal sinuses.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012 ...
es, in the sphenoid bone. They are innervated by the ophthalmic and maxillary nerve (CN V1 and V2). The paranasal sinuses are lined with respiratory epithelium (ciliated pseudostratified columnar epithelium).


Functions

One known function of the paranasal sinuses is the production of
nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ch ...
, which also functions as a facilitator of oxygen uptake. There is no consensus regarding the physiological functions of the paranasal sinuses. The most likely are: * Decrease in the relative mass of the anterior sections of the skull, especially the bones of the facial skull, against the background of their large volume. The shape of the bones of the facial skull is important because the bones are the attachment points for the facial muscles. * Providing a shock-resistant "buffer" in case of injuries * Isolation of sensitive structures (roots of teeth, eyeballs) from rapid temperature fluctuations in the nasal cavity during inhalation and exhalation. * Humidification and warming of inhaled air, as a result of slow airflow in the sinuses. * Perform the function of a sensory system of air signals (a
baroreceptor Baroreceptors (or archaically, pressoreceptors) are sensors located in the carotid sinus (at the bifurcation of external and internal carotids) and in the aortic arch. They sense the blood pressure and relay the information to the brain, so that ...
organ that responds to changes in environmental pressure).


Development

Paranasal sinuses form developmentally through excavation of bone by air-filled sacs ( pneumatic diverticula) from the nasal cavity. This process begins prenatally (intrauterine life), and it continues through the course of an organism's lifetime. The results of experimental studies suggest that the natural ventilation rate of a sinus with a single sinus ostium (opening) is extremely slow. Such limited ventilation may be protective for the sinus, as it would help prevent drying of its mucosal surface and maintain a near-sterile environment with high carbon dioxide concentrations and minimal pathogen access. Thus composition of gas content in the maxillary sinus is similar to venous blood, with high carbon dioxide and lower oxygen levels compared to breathing air. At birth, only the
maxillary sinus The pyramid-shaped maxillary sinus (or antrum of Highmore) is the largest of the paranasal sinuses, and drains into the middle meatus of the nose through the osteomeatal complex.Human Anatomy, Jacobs, Elsevier, 2008, page 209-210 Structure It i ...
and the ethmoid sinus are developed but not yet pneumatized; only by the age of seven they are fully aerated. The
sphenoid sinus The sphenoid sinus is a paired paranasal sinus occurring within the within the body of the sphenoid bone. It represents one pair of the four paired paranasal sinuses.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, ...
appears at the age of three, and the
frontal sinus The frontal sinuses are one of the four pairs of paranasal sinuses that are situated behind the brow ridges. Sinuses are mucosa-lined airspaces within the bones of the face and skull. Each opens into the anterior part of the corresponding middle n ...
es first appear at the age of six, and fully develop during adulthood.


CT scans, radiographs (x-ray) and other illustrations

File:CT Paranasal Sinuses Coronal MPR Soft Tissue Window.ogg, Coronal CT scan of the paranasal sinuses (Soft Tissue) File:CT Paranasal Sinuses Coronal MPR Bone Window.ogg, Coronal CT scan of the paranasal sinuses (Bone) File:Paranasal sinuses radiograph occipitofrontal.jpg, Paranasal sinuses radiograph (occipitofrontal) File:Paranasal sinuses radiograph occipitomental.jpg, Paranasal sinuses radiograph (occipitomental) File:Paranasal sinuses radiograph lateral.jpg, Paranasal sinuses radiograph (lateral) File:3DPX-002305 Upper respiratory cast 3DFile Nevit Dilmen.stl, 3D cast of maxillary, frontal, ethmoid and sphenoid sinuses, nasal cavity and hypopharynx.


Clinical significance


Inflammation

The paranasal sinuses are joined to the nasal cavity via small orifices called ostia. These become blocked easily by allergic inflammation, or by swelling in the nasal lining that occurs with a
cold Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute thermodynamic ...
. If this happens, normal drainage of mucus within the sinuses is disrupted, and
sinusitis Sinusitis, also known as rhinosinusitis, is inflammation of the mucous membranes that line the sinuses resulting in symptoms that may include thick nasal mucus, a plugged nose, and facial pain. Other signs and symptoms may include fever, hea ...
may occur. Because the maxillary posterior teeth are close to the maxillary sinus, this can also cause clinical problems if any disease processes are present, such as an infection in any of these teeth. These clinical problems can include secondary sinusitis, the inflammation of the sinuses from another source such as an infection of the adjacent teeth.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, p. 68 These conditions may be treated with drugs such as
decongestant A decongestant, or nasal decongestant, is a type of pharmaceutical drug that is used to relieve nasal congestion in the upper respiratory tract. The active ingredient in most decongestants is either pseudoephedrine or phenylephrine (the latter of ...
s, which cause
vasoconstriction Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vesse ...
in the sinuses; reducing inflammation; by traditional techniques of nasal irrigation; or by
corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involve ...
.


Cancer

Malignancies of the paranasal sinuses comprise approximately 0.2% of all malignancies. About 80% of these malignancies arise in the maxillary sinus. Men are much more often affected than women. They most often occur in the age group between 40 and 70 years.
Carcinoma Carcinoma is a malignancy that develops from epithelial cells. Specifically, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that arises from cells originating in the endodermal, mesodermal ...
s are more frequent than
sarcoma A sarcoma is a malignant tumor, a type of cancer that arises from transformed cells of mesenchymal ( connective tissue) origin. Connective tissue is a broad term that includes bone, cartilage, fat, vascular, or hematopoietic tissues, and sar ...
s. Metastases are rare.
Tumours A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
of the sphenoid and frontal sinuses are extremely rare.


Etymology

Sinus is a Latin word meaning a "fold", "curve", or "bay". Compare '' sine''.


Other animals

Paranasal sinuses occur in many other animals, including most mammals, birds, non-avian dinosaurs, and
crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest living ...
ns. The bones occupied by sinuses are quite variable in these other species.


Illustrations

File:Paranasal sinuses numbers.svg, Paranasal sinuses File:Blausen 0800 Sinusitis.png, Illustration depicting sinusitis


See also


References


External links

{{Authority control Human head and neck Bones of the head and neck