The Eustachian tube (ET) bridges the realm of the nasal cavity and upper aerodigestive tract with the ear and serves to optimize its special sensory role of hearing. The middle ear and mastoid system behaves as an auxiliary sinus and the ET can be thought of as a long, dynamic ostium with a functional valve located within the cartilaginous portion. Failure of the “valve” to function properly can occur if it dilates insufficiently to adequately aerate the middle ear or if it fails to close following dilation. It is affected by all of the same pathophysiologic processes as the nose and other sinuses.
The net effect of the middle ear gas exchange is to cause a constant absorption of gases from the middle ear air space into the venous blood system, creating an ongoing tendency toward developing negative pressure compared to ambient atmospheric pressure. When appropriate, the ET should dilate, typically with a swallow or yawn for about 400 msec, to restore the middle ear pressure toward ambient, optimizing the function of the tympanic membrane. If the dilatory effort is consistently insufficient to adequately aerate the middle ear, ET dilatory dysfunction results with the possible consequences of negative middle ear pressure, retraction of the tympanic membrane, otitis media with effusion, tympanic membrane perforation, conductive hearing loss, fixation of retraction pockets and ultimately cholesteatoma.
Most of the pathology that is responsible for dilatory dysfunction has been observed within the cartilaginous portion and is most commonly due to inflammatory disease, which can be readily diagnosed with transnasal endoscopy. A careful assessment of the dynamics of the ET by endoscopy can be very effective in determining the etiology, location and severity of dilatory and patulous dysfunction within the functional valve in the cartilaginous portion. Vocalizing “K-K-K” demonstrates isolated excursions of the Levator Veli Palatini (LVP) muscle. Swallows start with elevation of the LVP that acts as a scaffold upon which the additional contraction of the Tensor Veli Palatini muscle should be seen to dilate the valve open under normal circumstances. Yawns or vocalizing “Ahhh” can demonstrate a maximal dilatory effort. Disorders of dilation may be observed and classified. Inflammatory disease can be graded on a recently validated mucosal inflammation score instrument. The etiology of the inflammation can be investigated and treated, with the most common causes being infectious or reflux in younger children and over age 6, allergic disease, reflux, rhinosinusitis, adenoid hypertrophy and other commonly known causes of nasopharyngeal inflammation.
Treatment of the underlying medical conditions can result in improvement of ET function and resolution of middle ear disease. When the medical causes have been optimally treated, but ET dilatory dysfunction persists, possibly due to irreversibly injured mucosa, biofilms or other pathology, tympanostomy tubes are usually recommended. When tubes fail to resolve the problem, treatment of the underlying pathology with surgery can be offered. Surgery may involve turbinate reduction, sinus surgery, adenoidectomy, or balloon dilation of the ET. All of these procedures are designed to remove irreversibly injured tissue and provide a fresh start, assuming the underlying medical conditions are adequately controlled. Failure to control the medical problems can lead to recurrence of inflammatory disease.
Failure of the functional valve to close results in patulous dysfunction. Once thought to be rare, it is now clear that the diagnosis is frequently missed. It can be related to weight loss, chronic illnesses (especially rheumatologic), but it often occurs after long-standing inflammatory dilatory dysfunction with atrophy and decreased mucus production. This may occur particularly with chronic allergic rhinitis. Patients develop frequent sniffing strategies to minimize their symptoms, despite negative middle ear pressure or effusions, raising suspicion that dilatory dysfunction has transitioned to patulous dysfunction. Examination of the tympanic membrane by otoscopy or tympanometry for excursions with ipsilateral nasal breathing can be diagnostic and endoscopy of the ET will reveal a defect in the functional valve, usually within the antero-lateral wall. Conservative management is usually successful, but surgical correction is sometimes indicated.
This presentation will show some practical aspects of ET physiology that are relevant to surgeons, methods for evaluating ET function and a systematic approach for diagnosing pathology. Accurate diagnosis of ET disorders will lead to successful management and when appropriate, surgical indications will be clear.
