Sinus Anatomy and Function

The function of the paranasal sinuses is not clear, but theories include humidification and warming of inspired air, lightening of the skull, improvement of vocal resonance, absorption of shock to the face or skull, and secretion of mucus to assist with air filtration.

The four paranasal sinuses (maxillary, frontal, ethmoid and sphenoid) develop as outpouchings of the nasal mucosa. They remain connected to the nasal cavity via narrow ostia with a lumen diameter of 1 to 3 mm. The sinuses are lined with mucoperiosteum, which is thinner and less richly supplied with blood vessels and glands than the mucosa of the nasal cavity. Cilia sweep mucus toward the ostia. The ostia of the frontal, maxillary and anterior ethmoid sinuses open into the osteomeatal complex, which lies in the middle meatus lateral to the middle turbinate. The posterior ethmoid and sphenoid sinuses open into the superior meatus and sphenoethmoid recess. The osteomeatal complex is important because the frontal, ethmoid and maxillary sinuses drain through this area.