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In anatomy, the term nasal meatus [1] can refer to any of the three meatuses (passages) through the skull ' s nasal cavity: the superior meatus (meatus nasi superior), middle meatus (meatus nasi medius), and inferior meatus (meatus nasi inferior). The nasal meatuses are the spaces beneath each of the corresponding nasal conchae.
The cells are grouped into anterior, middle, and posterior groups; the groups differ in their drainage modalities, [2] though all ultimately drain into either the superior or the middle nasal meatus [3] of the lateral wall of the nasal cavity.
Sphenoidotomy, a form of endonasal surgery, may be done to enlarge the sphenoid sinus, usually in order to drain it. [ 8 ] The sphenoid sinus should be distinguished from an Onodi cell , an anatomic variant that is the rearmost ethmoidal air cell .
A narrow opening called a sinus ostium from each of the paranasal sinuses allows drainage into the nasal cavity. The maxillary sinus is the largest of the sinuses and drains into the middle meatus. Most of the ostia open into the middle meatus and the anterior ethmoid, that together are termed the ostiomeatal complex. [32]
The frontonasal duct passes inferior-ward [5] to open either [3] into the middle nasal meatus at the anterior end of [3] the ethmoidal infundibulum, [3] [5] [2] or into the anterior ethmoidal air cells (which then in turn drain into the nasal cavity). [3] The duct is lined by mucous membrane. [citation needed]
The superior attachment of the uncinate process determines the drainage pattern of the frontal sinus. In the first case, the infundibulum and the frontal recess are separated from each other, forcing the frontal sinus to drain directly into the middle meatus and not into the ethmoidal infundibulum.
The frontonasal duct may or may not drain into the ethmoidal infundibulum - this is determined by the place of attachment of the uncinate process of the ethmoid bone: if the uncinate process is attached to the lateral nasal wall, the frontonasal duct will open directly into the middle nasal meatus; if otherwise, it will drain into the infundibulum.
Furthermore, the drainage orifice lies near the roof of the sinus, and so the maxillary sinus does not drain well, and infection develops more easily. The maxillary sinus may drain into the mouth via an abnormal opening, an oroantral fistula, a particular risk after tooth extraction.