Lab: Upper Airways

This laboratory session consolidates the anatomy of the upper airway with clinical applications including the sites of epistaxis, the drainage pathways of the paranasal sinuses, and the endoscopic approach to the maxillary sinus.

The nasal septum is formed by three structures: the vomer posteroinferiorly, the perpendicular plate of the ethmoid posterosuperiorly, and the septal (quadrangular) cartilage anteriorly. The anteroinferior part of the septum is the most common site of epistaxis and is called Little's area or Kiesselbach's plexus. This region receives a rich anastomosis of arterial branches: the anterior ethmoidal artery (from the ophthalmic artery, a branch of the internal carotid), the superior labial artery and greater palatine artery (both from the external carotid system), and the septal branch of the sphenopalatine artery. Posterior epistaxis is less common but more dangerous and typically involves the sphenopalatine artery.

The paranasal sinuses drain via specific ostia. The frontal, anterior ethmoidal, and maxillary sinuses all drain into the middle meatus via the hiatus semilunaris, a crescent-shaped groove in the lateral nasal wall. The posterior ethmoidal sinuses drain into the superior meatus. The sphenoidal sinus drains into the sphenoethmoidal recess above the superior concha. The maxillary sinus ostium is located high on its medial wall, making it vulnerable to obstruction and explaining why maxillary sinusitis is the most common form of sinusitis.

Endoscopic examination of the nose allows direct inspection of the middle meatus. The maxillary sinus can be entered endoscopically through a middle meatal antrostomy — enlarging its natural ostium to improve drainage. The path passes through the middle meatus, inferior to the middle turbinate.

The piriform recess (sinus) is a pear-shaped space lateral to the aryepiglottic fold in the laryngopharynx. It is a common site where foreign bodies, fish bones, and bolus of food lodge. The internal laryngeal nerve runs beneath the mucosa of the piriform recess, which is why trauma or injection in this region can cause laryngeal anaesthesia.

The cricoid cartilage is the only complete ring of the airway and lies at the C6 vertebral level. Clinically, the cricothyroid membrane between the thyroid and cricoid cartilages is the landmark for emergency surgical airway. The membrane is identified by palpating the laryngeal notch (thyroid cartilage) and moving inferiorly to the first horizontal soft depression, which overlies the cricothyroid membrane.