Sphenoid sinus

The sphenoid sinus is one of the four paired paranasal sinuses that is contained within the body of the sphenoid bone. The sphenoid sinuses vary in size and shape, and owing to the lateral displacement of the intervening septum, which may insert on the carotid canal, they are rarely symmetrical. They cannot be palpated during an extraoral examination.
The following are their average measurements: vertical height, 2.2 cm; transverse breadth, 2 cm; antero-posterior depth, 2.2 cm.
Structure.
When exceptionally large the sphenoid sinuses may extend into the roots of the pterygoid processes or great wings, and may invade the basilar part of the occipital bone.
Each sinus opens into the roof of the nasal cavity via apertures on the posterior wall of the sphenoethmoidal recess directly above the choana. The apertures are located high on the anterior walls of the sinuses themselves.
Development.
They are not present at birth, they slowly develop with the growth of the skull. Just after puberty the sinuses finish development.
Nerve supply.
The mucous membrane receives sensory innervation by the posterior ethmoidal nerves (branch of the ophthalmic nerve), and postganglionic parasympathetic fibers of the facial nerve that synapsed at the pterygopalatine ganglion which controls secretion of mucus.
Clinical significance.
If the tumor spreads laterally, the cavernous sinus and all its constituent nerves could be in danger.
An endonasal surgical procedure called a sphenoidotomy may be carried out to enlarge the sphenoid sinus, usually in order to drain it. 
Use in neurosurgery.
Because only thin shelves of bone separate the sphenoidal sinuses from the nasal cavities below and hypophyseal fossa above, the pituitary gland can be surgically approached through the roof of the nasal cavities by first passing 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.