The sphenoid sinus is a paired paranasal sinus in the body of the sphenoid bone. It is one pair of the four paired paranasal sinuses.[1] The two sphenoid sinuses are separated from each other by a septum. Each sphenoid sinus communicates with the nasal cavity via the opening of sphenoidal sinus.[2]: 500 The two sphenoid sinuses vary in size and shape, and are usually asymmetrical.[3]
Structure
On average, a sphenoid sinus measures 2.2 cm vertical height, 2 cm in transverse breadth; and 2.2 cm antero-posterior depth.[3]
Each spehoid sinus is in the body of sphenoid bone, just under the sella turcica. The sphenoid sinuses are separated from each other medially by the septum of sphenoidal sinuses, which is usually asymmetrical.[2]: 500
An opening of sphenoidal sinus forms a passage between each sphenoidal sinus[2]: 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, just over the choana.[4]
The sphenoid sinuses vary in size and shape; because of the lateral displacement of the intervening septum of sphenoid sinuses, the pair rarely is symmetrical.[3]
The septum of the sphenoidal sinuses may be partly or completely absent. Other septa also may be incomplete.[2]: 500
Development
The sphenoidal sinuses are minute at birth;[3][4] their main development takes place after puberty.[4]
Clinical significance
The sphenoid sinuses cannot be palpated on physical examination.[1] However, patients with isolated sphenoid sinusitis may complain of occipital or vertex headache, retro-orbital pain, otalgia, drowsiness, or meningitis-like symptoms.[7]
If a fast-growing tumor erodes the floor of the sphenoidal sinus, the vidian nerve may be in danger.[citation needed] If the tumor spreads laterally, the cavernous sinus and all its constituent nerves may be in danger.[8]
Sphenoidotomy, a form of endonasal surgery, may be done to enlarge the sphenoid sinus, usually in order to drain it.[8]
The sphenoid sinus should be distinguished from an Onodi cell, an anatomic variant that is the rearmost ethmoidal air cell. Onodi cells typically extend back to lie superolateral to the sphenoid sinus and thus near the optic nerve and internal carotid artery.[9] Failure to recognize an Onodi cell on 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.[6]
Because only thin shelves of bone separate the sphenoidal sinuses from the nasal cavities, below, and from the hypophyseal fossa, above, the 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]
^ abKozłowski, Z; Mazerant, M; Skóra, W; Dabrowska, K (2008). "[Sphenoidotomy--the treatment of patients with isolated sphenoid sinus diseases]". Otolaryngologia Polska = the Polish Otolaryngology. 62 (5): 582–6. doi:10.1016/S0030-6657(08)70319-6. PMID19004262.