Paranasal sinuses

The paranasal sinuses comprise four paired cavities: the frontal, maxillary, ethmoid, and sphenoid sinuses. Each is lined with ciliated pseudostratified columnar epithelium and has a narrow ostium that opens into the nasal cavity. The ostia of the frontal, maxillary, and anterior ethmoid sinuses open into the ostiomeatal 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 respectively. The anatomy is variable and has been extensively reviewed.5

A protective mucous blanket, which envelops bacteria and other irritants, covers the respiratory cilia and is moved constantly along predetermined pathways to the sinus ostia. In the frontal sinus mucus passes up along the intersinus septum, then across the roof of the sinus before returning across the sinus floor to the frontal recess and the middle meatus.6 In the maxillary sinus mucus is moved from the floor of the sinus radially and up the walls of the sinus to the superiorly placed ostium (fig 1).