Sinus of sphenoid bone

At a glance

English

Sinus of sphenoid bone

Latin (TA2)

Sinus ossis sphenoidei

System

Bone

Region

Head

Side

Single, on the midline

About the sinus of sphenoid bone

The sphenoidal sinuses are two air spaces hollowed out of the sphenoid's body, at the very back of the upper nasal cavity. They are the deepest of the paranasal sinuses and cannot be felt or examined from outside the head. A thin bony septum divides them, but it usually lies off the midline, so the two are rarely equal in size or shape. On average each measures a little over 2 cm in height and in depth and about 2 cm across.

The sinuses have important neighbours on every side. Above lie the sella turcica with the pituitary gland and, further forward, the optic chiasm; on each side runs the cavernous sinus with the internal carotid artery and the nerves to the eye muscles, and the optic nerve may bulge into the upper side wall. In front are the posterior ethmoidal cells and the nasal cavity, below is the roof of the nasopharynx, and behind is the clivus. When they are very large the sinuses can spread into the pterygoid processes at their roots, the greater wings or even the occipital bone's basilar part, and the septum may be anchored onto the bony bulge of the carotid artery.

Each sinus drains through an opening high on its front wall into the sphenoethmoidal recess, above and behind the superior concha and just over the choana. Because the opening sits high, the sinus relies on its cilia rather than gravity to clear its mucus. The sinuses are tiny at birth, grow slowly with the skull through childhood and reach their adult size in the late teens.

Clinically, the sinus is the usual corridor for operations on the pituitary gland through the nose. The thin bone between the sinus and the carotid artery and optic nerve makes its side walls a hazard during such surgery. Sphenoidal sinusitis tends to give a deep, poorly localised headache and, though uncommon, can spread to the cavernous sinus or the optic nerve. A fracture of the skull base may fill the sinus with blood, seen as a fluid level on a scan.

Function and supply

Nerve supply

Sensation comes from the posterior ethmoidal nerve, a branch of the nasociliary nerve from the ophthalmic nerve, and from branches of the maxillary nerve through the pterygopalatine ganglion; secretory fibres come from the facial nerve and relay in that ganglion.

Blood supply

The posterior ethmoidal artery from the ophthalmic artery and branches of the sphenopalatine and pharyngeal arteries from the maxillary artery.