Sinus ostium

A sinus ostium (plural: sinus ostia) is the opening that connects a sinus to the nasal cavity itself. It is a tight area that tends to have a higher percentage of cilia than the surrounding mucosa.

If the sinus ostium is blocked, the entire sinus thus becomes the pathologic cavity or cystlike lesion. As mucus is accumulated and the sinus cavity has filled, the increase in intraantral pressure results in a thinning, displacement and, in some cases, destruction of the sinus walls. If the mucocele becomes infected, it is called a pyocele or a mucopyocele.