Nasal Cavity
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Direct answer
Air enters a cavity bounded by a septum medially, conchae-covered lateral walls, a hard-palate floor and the cribriform plate roof, and leaves through the choanae into the nasopharynx. The three meatuses beneath the conchae drain everything nearby: the nasolacrimal duct into the inferior meatus, the posterior ethmoid cells into the superior meatus, and the frontal, maxillary and anterior ethmoid sinuses through the hiatus semilunaris of the middle meatus — the ostiomeatal complex that functional endoscopic sinus surgery targets. The anteroinferior septum carries Kiesselbach's plexus, the source of nine in ten nose bleeds, and the olfactory mucosa under the cribriform plate is the plate's reason for causing anosmia and CSF rhinorrhoea when fractured.
What you must remember
- Roof: cribriform plate of the ethmoid between the frontal's nasal and the sphenoid's body — fracture tears the olfactory nerves (anosmia) and dura (CSF rhinorrhoea).
- Floor: palatine process of maxilla and horizontal plate of palatine bone; a cleft of this floor is the complete cleft palate communicating nose and mouth.
- Septum: septal (quadrangular) cartilage in front, perpendicular plate of ethmoid above and behind, vomer posteroinferiorly; dislocations of the cartilage from the vomerine groove cause deflection.
- Lateral wall: superior, middle and inferior conchae (a supreme concha sometimes); middle meatus bears the ethmoidal bulla and the uncinate process bounding the hiatus semilunaris.
- The sphenopalatine foramen, behind the middle concha, transmits the sphenopalatine artery — the artery of the nasal cavity — and the nasopalatine nerve.
- Kiesselbach's plexus on the anteroinferior septum anastomoses the anterior ethmoidal, septal branches of the sphenopalatine and greater palatine, and septal branches of the superior labial arteries; it accounts for the great majority of bleeds.
- Woodruff's plexus of veins posteroinferiorly underlies posterior epistaxis of the elderly.
- The sphenoethmoidal recess above the superior concha drains the sphenoid sinus.
Working through epistaxis step by step using the walls
A boy arrives with active bleeding after a punch to the nose; an elderly hypertensive man arrives with blood trickling down the throat. The two cases divide along the cavity's geography. The boy's bleed is from Kiesselbach's plexus — visible on the anteroinferior septum on speculum examination. First aid follows the anatomy: sit the patient up, pinch the soft distal nose (not the bony bridge) for ten minutes to compress the septal anastomosis, and apply topical vasoconstrictor; cautery of the visible point with silver nitrate per current ENT practice settles most. The elderly man's is a posterior bleed from the sphenopalatine territory or Woodruff's plexus, not visible anteriorly; it needs an endoscopic examination, a posterior pack or balloon, and targeted sphenopalatine artery cautery or ligation, with blood pressure controlled concurrently.
Now use the same walls for trauma. Clear fluid dripping from the nose after a head injury, worsening on sitting up and bending forward, with a salty or sweet taste, suggests CSF from a cribriform plate fracture; the fluid tests positive for glucose or beta-2 transferrin, and the risk is ascending meningitis — hence per current practice avoidance of nasal packing where possible and consideration of prophylactic measures per local protocol. Anosmia accompanying it localises the injury to the olfactory fibres' passage through the same plate.
Where students slip
The drainage pattern is the question most often fumbled: "frontal, maxillary and anterior ethmoid sinuses drain into the middle meatus" must be delivered as one sentence, with the posterior ethmoid to the superior meatus, the sphenoid to the sphenoethmoidal recess and the nasolacrimal duct to the inferior meatus — the nasolacrimal pairing with the inferior meatus is the discriminating mark. Second, the septum's bones are named the wrong way round; the perpendicular plate of the ethmoid lies posterosuperiorly and the vomer posteroinferiorly, with the septal cartilage anterior — and a deviated septum's commonest site is the junction of cartilage with vomer. Third, remember the nose's blood supply comes from both internal and external carotid systems — ophthalmic (ethmoidal) versus maxillary (sphenopalatine) and facial branches — which is why severe epistaxis can require ligation at more than one station.
Frequently asked questions
Which arteries form Kiesselbach's plexus?
Anterior ethmoidal, sphenopalatine septal branches, greater palatine septal branches and superior labial septal branches, anastomosing on the anteroinferior septum.
Which structure forms the roof of the nasal cavity?
The cribriform plate of the ethmoid bone, pierced by olfactory nerve fibres, flanked in front by the nasal bones and behind by the body of the sphenoid.
Where does the nasolacrimal duct open?
In the inferior meatus of the lateral wall beneath the inferior concha.
Why is the middle meatus the target of endoscopic sinus surgery?
The frontal, maxillary and anterior ethmoid sinuses all drain through the hiatus semilunaris in the middle meatus, so opening this ostiomeatal complex ventilates the sinuses.
What is Woodruff's plexus?
A venous plexus on the posteroinferior lateral wall and septum, the usual source of posterior epistaxis in elderly hypertensive patients.