The middle ear is an air-filled chamber within the skull that is periodically vented when the eustachian tube opens. Middle ear disease may be due, at least in part, to failure or inadequacy of eustachian tube function.
There is no well-accepted definition of eustachian tube dysfunction, but it is commonly understood to mean that the eustachian tube has failed to provide adequate ventilation to the middle ear. However, this imprecise definition excludes the common condition of a patulous (chronically patent) eustachian tube. Eustachian tube dysfunction is more accurately defined as failure of the functional valve of the eustachian tube to open and/or close properly.
This topic will discuss the pathophysiology, evaluation, and treatment of eustachian tube dysfunction. Specific diseases associated with eustachian tube dysfunction are discussed elsewhere. (See "Acute otitis media in children: Epidemiology, microbiology, clinical manifestations, and complications" and "Otitis media with effusion (serous otitis media) in children: Clinical features and diagnosis" and "Acute otitis media in adults (suppurative and serous)" and "Chronic otitis media, cholesteatoma, and mastoiditis in adults" and "Ear barotrauma" and "Etiology of hearing loss in adults" and "Management of otitis media with effusion (serous otitis media) in children".)
Knowledge of the anatomy and function of the eustachian tube is important to understanding its pathophysiology. The eustachian tube runs from the anterior wall of the middle ear cavity to open into the nasopharynx (figure 1). The nasopharyngeal and tympanic ends are wider than the middle of the tube, with the bony isthmus being the narrowest portion. The eustachian tube passes superiorly, posteriorly, and laterally from the nasopharynx . Its total length in adults ranges 36 to 38 mm. Children have shorter, more horizontal tubes, immature floppy elastic cartilage, and larger adenoids compared to adults, which place them at a higher risk for obstruction and reflux of nasopharyngeal secretions and pathogens (figure 2) [2,3]. The eustachian tube in children usually reaches adult length by age six.
The eustachian tube is not just a static pipe; it is a dynamic organ having a lumen, skeleton, mucosal lining, and surrounding soft tissue and muscles (figure 3) [4,5]. The skeleton of the tube is formed of cartilage in its inferior and medial two-thirds, and bone in the superior and lateral one-third. The bony portion lies within the petrous part of the temporal bone, while the cartilaginous portion is firmly attached superiorly to the sphenoid bone . The bony portion is normally patent and does not open and close dynamically as does the cartilaginous portion . Within the bone and cartilage are the four muscles related to eustachian tube function: tensor veli palatini (TVP), levator veli palatini (LVP), tensor tympani, and salpingopharyngeus. The most important muscles for dilation are the TVP, the principal active tubal dilator, and the LVP, which sets the cartilaginous skeleton into position against which the TVP can complete the dilation . The anterolateral wall is membranous and consists of the luminal mucosa, submucosa, and the TVP muscle . The lining of the eustachian tube is continuous with the rest of the respiratory tract.