The paranasal sinuses are four sets of cavities situated around and connected to the nose. Lined by ciliated columnar epithelium, they help produce mucous (when stimulated by parasympathetic innervation) for the nasal cavity with which they are connected. They also likely function to lighten the skull and act as resonance chambers for speech. Each sinus is innervated by CN V and named by the bone it is housed in.

CLINICAL CORNER

Sinusitis is inflammation of the paranasal sinuses, which can cause pain (including headache) or pressure in the eyes, nose, cheeks, on one side of the head. Patients may also present with a cough, fever, halitosis, and nasal congestion with thick secretions. The opening of the maxillary sinus is high on its medial wall, making drainage difficult and infection especially likely. axillary sinusitis can cause pain or pressure in the maxillary area. Patients may present with toothache.

Frontal Sinus

The frontal sinus lies above the orbit and can be quite extensive. Developing after birth, it opens into the anterior end of the middle meatus.

Maxillary Sinus

Occupying most of the maxilla, the maxillary sinus lies on both sides of the nasal cavity, above the molars. Its floor is lower than the base of the nasal cavity and therefore also its opening into the middle meatus.

Ethmoidal Sinuses

The ethmoidal sinuses are small, interconnected air cells between the orbit and nose, divided into the anterior, middle and posterior groups. A prominent bulge on the lateral wall, the bulla of the ethmoid, contains the middle ethmoidal air cells. A curved groove beneath the bulla, the hiatus semilunaris, contains the openings of the frontal sinus, anterior ethmoidal air cells and maxillary sinus. The posterior ethmoidal air cells open into the superior meatus.

Sphenoidal Sinus

The sphenoidal sinus is situated beneath the pituitary gland and medial to the cavernous sinuses. It opens into the nasal cavity above the superior concha in a small triangular space known as the sphenoethmoidal recess.

CLINICAL CORNER

Removal of certain pituitary gland tumours is possiblr through transphenoidal hypophysectomy, where an endoscope is inserted through the nose and sphenoidal sinus.