Introduction
The Eustachian tube (ET) is an anatomical structure that extends from the nasopharynx up to the middle ear and is composed of a bony and a cartilaginous part. Its normal function is vital for healthy hearing (1). This epithelial-lined tube has three main functions: (i) equalization of the pressure in the middle ear to the atmospheric pressure. This is important to curb the untoward effects of external pressure fluctuations on the tympanic membrane. (i) clearance of middle ear secretions, (iii) prevention of middle ear from nasopharyngeal secretions containing microorganisms and precluding transmission of one’s own speech sounds back to their ear (2).
Eustachian tube dysfunction might be due to either obstruction of the tube or persistent opening of it (3). ET, under physiologic conditions, remains passively closed and only briefly opens in case of swallowing or Valsalva maneuver. When the ET remains permanently open, this condition is called patulous Eustachian tube (PET). Although its prevalence is much less compared with the obstructive pathologies of the ET, PET is associated with annoying symptoms that lower the quality of life of the affected patients. Patients with PET mainly complaint about hearing their own voice (autophony), their breathing (aerophony) or sound of eating or drinking in a disturbing way. Inflicted patients can also report other more nonspecific symptoms such as aural fullness, vertigo, and tinnitus (4).
Due in part to its inaccessible nature, there is not a single reliable test correctly diagnose ET dysfunction. Constellation of the aforementioned symptoms in a patient suggests the presence of PET; however, these symptoms can also be reported by patients with several other disorders. Thus, more objective and reliable tests are needed. Tympanometry is the commonly used office-based test to evaluate the ET function indirectly. This test measures the one-time middle ear pressure. Normal pressures measured with tympanometry does not exclude obstructive ET dysfunction or PET. Breathing-synchronous tympanic membrane movement is accepted as a specific finding of PET but, to diagnose PET, various objective and subjective findings, such as medical history, physical examination and ET function tests, are combined, because there is no single test available to evaluate ET function accurately. Clinical tympanic membrane movement can be carried out by visual observation, continuous impedance recording, or sonotubometry (5, 6). However, these tests are not well standardized and limited in cases of intermittent PET or patients who had low acoustic impedance.
Radiologic imaging of the ET is also without its own problems. Currently, there is no single radiologic imaging modality that can provide details of all related structures of the ET per se. The collapsed nature of the ET at rest makes it more difficult to image the entire tube. One can think that this cannot be a problem for a PET patient. However, the ET temporarily closes when the patient lies supine, which is the usual position in sectional imaging modalities (7). Thus, several investigators tried to find some ways to overcome these difficulties, such as CT imaging in a seated patient or positioning the patient in 45 degrees in a standard CT scanner (8-10). However, these modifications are not always technically feasible. One other solution to the imaging problem of PET is performing a Valsalva maneuver during CT scanning. Self-administered pressure increases force the ET to open even in a patient who is lying supine.