The sphenoid sinuses (also sphenoidal sinuses) are the most posteriorly located paranasal sinuses. They are positioned centrally within the body of the sphenoid bone. Sometimes, they extend also into the wings of the sphenoid.

The anterior surface of the sphenoidal sinuses forms the posterosuperior wall of the nasal cavity. The openings that lead into the sphenoidal sinuses are found on the anterior wall of the body of the sphenoid.

Both sphenoid sinuses are divided into two parts by a bony septum. Usually, the septum is not located in the midline but is bent to one or the other side. Therefore, the sphenoidal sinuses are not symmetrical.

The sphenoidal sinuses are drained into the superior nasal meatus via the sphenoethmoidal recess. Both sinuses are related to several important neurovascular structures, such as the optic nerve (CN II) and the internal carotid artery.

The sphenoidal sinus can be identified during imaging studies from the age of two. It continues developing throughout life and matures in size at around 12 to 14 years of age. However, its development may also continue into the third decade of life. The typical volume of the sphenoidal sinus is 0.017 to 0.27 oz (0.5 to 8 ml).

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Sphenoid sinus