Anatomy of Sphenoid Sinus

Study Notes

Carotid canal protrusion into the sphenoid sinus occurs in 24-36% of subjects, and dehiscence in carotid canal exists in 22-34% of cases
Optic canal bulging into the sphenoid sinus occurs in 5-8% of subjects, and optic canal dehiscence may exist in about 10% of cases
The vidian nerve usually runs in the floor of the sinus, but occasionally may run within the sinus
The ostium of the sphenoid sinus opens into the sphenoethmoidal recess halfway to two-thirds up to the anterior wall of the sinus medial to the posterior end of the superior turbinate

The nasal cavity includes three functional areas: vestibular, respiratory, and olfactory
The limen nasi separates the vestibular and respiratory areas
The vestibule of the nose is lined with stratified squamous epithelium, which is continuous with the skin of the face
The respiratory region is lined with pseudostratified ciliated columnar epithelium with goblet cells
The submucosa contains seromucinous acini

The sphenoid sinus is bordered superiorly by the planum sphenoidale and sella turcica and pituitary gland
The posterior wall of the sinus is formed by the clivus, which separates the sinus from the posterior cranial fossa
The lateral wall of the sphenoid sinus is related to several neurovascular structures, including the optic nerve, carotid artery, maxillary nerve, and vidian nerve

Pneumatization of the sphenoid sinus may be conchal (very small, 0.4%), presellar (25-30%), sellar (commonest type, 70-75%), and occasionally post-sellar, exceeding the posterior limit of the sellar

The agger nasi cell is the most anterior of all ethmoid cells, present in up to 98% of CT scans, and defines the anterior aspect of the frontal recess
The ethmoid bulla is the largest and most prominent ethmoid cell and drains into the middle meatus
Ethmoid cells may pneumatize into the adjacent sinuses and affect their drainage