# Sphenoid sinus

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{{short description|One of the four paired paranasal sinuses}}
{{Infobox bone
| Name        = Sphenoid sinus
| Latin       = sinus sphenoidalis
| Image       = File:Gray856.png
| Caption     = Lateral wall of nasal cavity; the three nasal conchæ have been removed. (Sphenoidal sinus visible at upper right, in dark circle.)
| Image2      = File:Illu_nose_nasal_cavities.jpg
| Caption2    = Nose and nasal cavities. (Sphenoid sinus labeled at upper right.)
| Nerve       = [Posterior ethmoidal nerve](/source/Posterior_ethmoidal_nerve)s, and orbital branches of the [pterygopalatine ganglion](/source/pterygopalatine_ganglion)
}}
The '''sphenoid sinus''' is a paired [paranasal sinus](/source/paranasal_sinus) in the [body](/source/Body_of_sphenoid_bone) of the [sphenoid bone](/source/sphenoid_bone). It is one pair of the four paired paranasal sinuses.<ref name=":1">Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 64</ref> The two sphenoid sinuses are separated from each other by a septum. Each sphenoid sinus communicates with the [nasal cavity](/source/nasal_cavity) via the opening of sphenoidal sinus.<ref name=":2">{{Cite book |title=Sobotta anatomy textbook |date=2018 |others=Friedrich Paulsen, Tobias M. Böckers, J. Waschke, Stephan Winkler, Katja Dalkowski, Jörg Mair |isbn=978-0-7206-7617-4 |location=Amsterdam |oclc=1082911887}}</ref>{{Rp|page=500}} The two sphenoid sinuses vary in size and shape, and are usually asymmetrical.<ref name=":3">{{Cite book |last=Gray |first=Henry |url=https://archive.org/details/anatomyofhumanbo1918gray/page/998/mode/2up?view=theater |title=Gray's Anatomy |year=1918 |edition=20th |pages=998–999}}</ref>

==Structure==
thumb|left|Paranasal sinuses
On average, a sphenoid sinus measures 2.2&nbsp;cm vertical height, 2&nbsp;cm in transverse breadth; and 2.2&nbsp;cm antero-posterior depth.<ref name=":3" />

Each spehoid sinus is in the [body of sphenoid bone](/source/body_of_sphenoid_bone), just under the [sella turcica](/source/sella_turcica). The sphenoid sinuses are separated from each other medially by the septum of sphenoidal sinuses, which is usually asymmetrical.<ref name=":2" />{{Rp|page=500}}

An opening of sphenoidal sinus forms a passage between each sphenoidal sinus<ref name=":2" />{{Rp|page=500}} and the nasal cavity. Posteriorly, an opening of sphenoidal sinus opens into the sphenoidal sinus by an aperture high on the anterior wall the sinus; anteriorly, an opening of sphenoidal sinus opens into the roof of the nasal cavity via an aperture on the posterior wall of the [sphenoethmoidal recess](/source/sphenoethmoidal_recess), just over the [choana](/source/choana).<ref name=":0">Human Anatomy, Jacob, Elsevier, 2008, page 211</ref>

===Innervation===
The mucous membrane receives sensory{{Citation needed|date=January 2023}} innervation from the [posterior ethmoidal nerve](/source/posterior_ethmoidal_nerve) (branch of the [ophthalmic nerve (CN V<sub>1</sub>)](/source/ophthalmic_nerve)) and from branches of the [maxillary nerve (CN V<sub>2</sub>)](/source/Maxillary_nerve).<ref name=":13">{{Cite book |last=Morton |first=David A. |title=The Big Picture: Gross Anatomy |date=2019 |others=K. Bo Foreman, Kurt H. Albertine |isbn=978-1-259-86264-9 |edition=2nd |location=New York |pages=246 |oclc=1044772257}}</ref>

[Postganglionic](/source/Postganglionic) [parasympathetic](/source/parasympathetic) fibers of the [facial nerve](/source/facial_nerve) that [synapse](/source/synapse)d at the [pterygopalatine ganglion](/source/pterygopalatine_ganglion) control [mucus](/source/mucus) [secretion](/source/secretion).{{Citation needed|date=November 2022}}

=== Anatomical relations ===
Nearby structures include the [optic canal](/source/optic_canal), the [optic nerve](/source/optic_nerve), the [internal carotid artery](/source/internal_carotid_artery), the [cavernous sinus](/source/cavernous_sinus), the [trigeminal nerve](/source/trigeminal_nerve), the [pituitary gland](/source/pituitary_gland), and the [anterior ethmoidal cells](/source/anterior_ethmoidal_cells).<ref name=":2" />{{Rp|page=500}} One study found that [carotid canal](/source/carotid_canal) protrudation into the sphenoid sinus wall was present in 23.9–32.1% of males and 35.5–36.2% of females, dehiscence in carotid canal was detected more in females (34%) than in males (22%), [optic canal](/source/optic_canal) protrudation was 33.3 and 30.5% in males and females, and optic canal dehiscence was detected in 11.3% of males and 9.9% of females.<ref name="Asal 519–529">{{Cite journal |last1=Asal |first1=Neşe |last2=Bayar Muluk |first2=Nuray |last3=Inal |first3=Mikail |last4=Şahan |first4=Mehmet Hamdi |last5=Doğan |first5=Adil |last6=Arıkan |first6=Osman Kürşat |date=June 2019 |title=Carotid canal and optic canal at sphenoid sinus |journal=Neurosurgical Review |volume=42 |issue=2 |pages=519–529 |doi=10.1007/s10143-018-0995-4 |issn=1437-2320 |pmid=29926302|s2cid=49331277 }}</ref>

=== Anatomical variation ===
The sphenoid sinuses vary in size and shape; because of the lateral displacement of the intervening [septum](/source/septum) of sphenoid sinuses, the pair rarely is symmetrical.<ref name=":3" />

When exceptionally large, the sphenoid sinuses may extend into the roots of the [pterygoid processes](/source/pterygoid_processes) or [greater wings of sphenoid bone](/source/Greater_wing_of_sphenoid_bone), and may invade the [basilar part](/source/basilar_part_of_occipital_bone) of the [occipital bone](/source/occipital_bone).<ref name=":3" />

The septum of the sphenoidal sinuses may be partly or completely absent. Other septa also may be incomplete.<ref name=":2" />{{Rp|page=500}}

===Development===
The sphenoidal sinuses are minute at birth;<ref name=":3" /><ref name=":0" /> their main development takes place after puberty.<ref name=":0" />

==Clinical significance==
The sphenoid sinuses cannot be palpated on physical examination.<ref name=":1" /> However, patients with isolated [sphenoid sinusitis](/source/sphenoid_sinusitis) may complain of [occipital](/source/Occipital_bone) or vertex headache, retro-orbital pain, [otalgia](/source/otalgia), drowsiness, or [meningitis](/source/meningitis)-like symptoms.<ref name="Ishak 29–30">{{Cite journal |last1=Ishak |first1=NL |last2=Subha |first2=ST |last3=Abu Bakar |first3=S |date=2019-04-30 |title=Isolated sphenoid sinusitis: A big headache |journal=Malaysian Family Physician |volume=14 |issue=1 |pages=29–30 |issn=1985-207X |pmc=6612268 |pmid=31289629}}</ref>

A potential complication of sphenoidal [sinusitis](/source/sinusitis) is [cavernous sinus thrombosis](/source/cavernous_sinus_thrombosis).<ref name="Ishak 29–30"/>

If a fast-growing tumor erodes the floor of the sphenoidal sinus, the [vidian nerve](/source/vidian_nerve) may be in danger.{{Citation needed|date=November 2022}} If the tumor spreads laterally, the [cavernous sinus](/source/cavernous_sinus) and all its constituent nerves may be in danger.<ref name="Kozlowski" />

Sphenoidotomy, a form of endonasal surgery, may be done to enlarge the sphenoid sinus, usually in order to drain it.<ref name="Kozlowski">{{cite journal |last1=Kozłowski |first1=Z |last2=Mazerant |first2=M |last3=Skóra |first3=W |last4=Dabrowska |first4=K |title=[Sphenoidotomy--the treatment of patients with isolated sphenoid sinus diseases]. |journal=Otolaryngologia Polska = The Polish Otolaryngology |date=2008 |volume=62 |issue=5 |pages=582–6 |doi=10.1016/S0030-6657(08)70319-6 |pmid=19004262}}</ref>

The sphenoid sinus should be distinguished from an [Onodi cell](/source/Onodi_cell), an anatomic variant that is the rearmost [ethmoidal air cell](/source/Ethmoid_sinus). Onodi cells typically extend back to lie superolateral to the sphenoid sinus and thus near the [optic nerve](/source/optic_nerve) and [internal carotid artery](/source/internal_carotid_artery).<ref>{{Cite web |last=Gaillard |first=Frank |title=Sphenoethmoidal air cell {{!}} Radiology Reference Article {{!}} Radiopaedia.org |url=https://radiopaedia.org/articles/sphenoethmoidal-air-cell-1?lang=us |access-date=2023-11-12 |website=Radiopaedia |language=en-US}}</ref> Failure to recognize an Onodi cell on [CT scan](/source/CT_scan) before surgery may put these structures at risk. One study found that an Onodi cell was present in 26.6% of males and 19.1% of females.<ref name="Asal 519–529"/>

===Transsphenoidal surgery===
{{Main|Transsphenoidal surgery}}
Because only thin shelves of bone separate the sphenoidal sinuses from the nasal cavities, below, and from the [hypophyseal fossa](/source/hypophyseal_fossa), above, the [pituitary gland](/source/pituitary_gland) can be reached surgically through the roof of the nasal cavities by passage through the anterioinferior aspect of the sphenoid bone and into the sinuses, followed by entry through the top of the sphenoid bone into the hypophyseal fossa.{{Citation needed|date=November 2022}}

==References==
{{Gray's}}
{{Reflist}}

==External links==
* {{SUNYAnatomyLabs|33|st|07|12}}
* {{NormanAnatomy|lesson9}} ({{NormanAnatomyFig|latnasalwall3}})

{{Skull}}
{{Nose anatomy}}
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Category:Bones of the head and neck
Category:Rhinology
Category:Otorhinolaryngology
Category:Sinus surgery

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Adapted from the Wikipedia article [Sphenoid sinus](https://en.wikipedia.org/wiki/Sphenoid_sinus) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Sphenoid_sinus?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.