Expansion
Middle for most, superior for posterior ethmoid, sphenoid drains above all
Mnemonic
Almost everything drains into the middle meatus, which is why it is the target of functional endoscopic sinus surgery:
| Sinus | Drains to |
|---|---|
| Frontal | Middle meatus, via the frontonasal duct |
| Maxillary | Middle meatus, via the hiatus semilunaris |
| Anterior and middle ethmoid | Middle meatus |
| Posterior ethmoid | Superior meatus |
| Sphenoid | Sphenoethmoidal recess |
| Nasolacrimal duct | Inferior meatus |
“Only the posterior ethmoid, the sphenoid and the tear duct go elsewhere.”
The maxillary sinus ostium sits high on its medial wall, so it drains against gravity when upright, which is why the maxillary sinus is the one that becomes infected and why a fluid level appears on an occipitomental (Waters) view.
The roots of the upper molars project into the maxillary sinus floor, which is why dental infection causes sinusitis and why extraction can create an oroantral fistula.
Expansion
- Middle meatus - maxillary, frontal, anterior ethmoid sinuses
- Superior meatus - posterior ethmoid sinus
- Sphenoethmoidal recess - sphenoid sinus