The sphenoidal sinus is the most posterior of the paranasal sinuses.
Structure
Location and Boundaries
The sphenoidal sinuses are located within the body of the sphenoid bone, behind the nasal cavity and above the nasopharynx. They communicate with the nasal cavity at the sphenoethmoidal recess from their anterior end.
Relations
Anteriorly with the posterior part of the nasal cavity
Inferiorly with the nasopharynx.
Laterally with the cavernous sinus, carotid artery, mandibular nerve (V3) and temporal lobe of the brain.
Posteriorly with the midbrain.
Superiorly with the pituitary fossa, pituitary gland, optic chiasm and hypothalamus
Medially with the contralateral sphenoid sinus.
Macroscopic Appearance
The sinuses are lined with pale pink mucosa. They are frequently assymetrical.
Microscopic Appearance
The mucosa is lined with pseudostratified columnar epithelium of respiratory type.
Physiological Variations
The sphenoidal sinuses are particularly small in children. They enlarge at puberty.
Neurovascular Supply
Arterial Supply
The sphenoidal sinuses are supplied by the posterior ethmoidal artery and nasal branches of the sphenopalatine arteries.
Venous Drainage
Veins drain via the posterior ethmoidal vein to the superior ophthalmic vein.
Lymphatics
Theses sinuses drain to retropharyngeal nodes only.
Innervation
The posterior ethmoidal nerve (branch of the nasopalatine nerve (V1)) provides general sensory supply. Secretomotor fibres are derived from the pterygopalatine ganglion (VII)
Routes of Cancer Spread
Cancer of the sphenoidal sinus is relatively rare. They may be invaded locally by pituitary adenoma.
Local Invasion
This may be extensive and catastrophic. Invasion superiorly may occur in the pituitary gland or optic chiasm. Lateral invasion quickly involves the cavernous sinus and internal carotid artery. Invasion posteriorly may damage the brainstem. Inferior invasion into the nasopharynx is probably the least likely to cause problems.
Lymphatic Spread
Generally occurs to retropharyngeal nodes.
Neurological Spread
Tumours may invade along nerves, leading back to divisions of the ophthalmic nerve (V1).
