The Eustachian tube, also termed the pharyngotympanic or auditory tube, is vital in regulating middle ear homeostasis, with complex anatomy designed to achieve this function. It travels medially from the middle ear, directing down and forwards to open just posterior to the end of the inferior turbinate—the bony lateral third travels past both squamous and petrous portions of the temporal bone. The medial two-thirds is fibrocartilaginous, opening out into the nasopharynx as a mucosal elevation known as the torus tubarius. The tube opens on positive pressure, e.g., yawning, sneezing, swallowing, and the Valsalva maneuver, by contraction of the levator veli palatini and tensor veli palatini muscles.
Through the Eustachian tube's complex structure, it can carry out its three main functions:
Firstly, by having a patent and open Eustachian tube, the pressure of the middle ear is equalized to that of the nasopharynx (i.e., towards atmospheric pressure). This has assistance from active mucosal gas exchange within the middle ear. With the maintenance of middle ear pressure, tympanic membrane compliance is optimized for hearing.
Secondly, it contains tube mucociliary transport. This consists of ciliated cells that clear inflammatory products and secretions from the middle ear and Eustachian tube, transporting them towards the direction of the nasopharynx for elimination.
Lastly, a functioning Eustachian tube protects the middle ear from loud sounds and potential hazards, including pathogens and secretions from the nasopharynx.
Eustachian tube dysfunction (ETD) is the failure of the Eustachian tube in maintaining any of the three roles mentioned above. This categorizes as either acute (less than three months presentation) or chronic ETD (more than three months). ETD affects 1% of the population, with symptoms including aural fullness or 'popping sounds,' reduced hearing, tinnitus, autophony, otalgia, and imbalance. It can be broadly categorized into baro-challenged induced, patulous, and dilatory ETD.