Evaluation of Eustachian tube function by contrast roentgenography

CT imaging of the eustachian tube using focal contrast medium administration: a feasibility study

OBJECTIVES

We aim to develop an imaging technique for visualization of the Eustachian tube (ET) lumen.

STUDY DESIGN

A prospective, experimental study in an animal model and in human cadaver specimens.

METHODS

Applying iodixanol to the middle ear in two human temporal bone specimens, followed by computed tomography (CT) examinations, we optimized contrast dilution, CT algorithm, and head positioning for visualization of contrast passage through the ET. Myringotomy was performed on eight rabbits. Based on the cadaver study, a 20% iodixanol solution was applied to the middle ear, and subsequent CT scans were performed to observe iodixanol in the epipharynx. For some animals, the procedure was repeated on the contralateral ear. We performed the procedure twice on four subjects. Twenty examinations were included. Iodixanol appearance in the ET and the epipharyngeal orifice was assessed qualitatively on CT scans. The tympanic membrane was inspected after 1 or 2 weeks, and histopathological examination of six contrast-exposed temporal bones was performed.

RESULTS

The cadaver study provided information on imaging technique and contrast dosage. In rabbits, iodixanol passed through the ET in 19 of the 20 ears. Qualitatively, optimal visualization was seen after 9 to 12 minutes. Clinical inspection after 1 or 2 weeks revealed normal middle ear status. Histopathological samples showed no sign of inflammatory reaction in the tympanic membrane, middle ear, or ET.

CONCLUSION

Iodixanol application to the middle ear is feasible, safe, and demonstrates patency of the ET.

LEVEL OF EVIDENCE

N/A.

Imaging of the Eustachian tube and its function: a systematic review

Introduction

The Eustachian tube is a complex and inaccessible structure, which maintains middle ear ventilation to facilitate transmission of sound from the tympanic membrane to the cochlea. A renewed interest in treatments for eustachian tube dysfunction has led to a demand for methods of imaging the Eustachian tube, and assessing tube opening non-invasively. This review aims to summarise the use of imaging in the anatomical assessment of the Eustachian tube, and to explore how radiological techniques can be used to assess tube function.

Methods

A systematic review of the literature was performed with narrative data analysis.

Results

With high-resolution images, the soft and bony anatomy of the Eustachian tube can be assessed in detail. CT and MRI are best suited to identifying features associated with obstructive or patulous Eustachian tube dysfunction, though true assessments of function have only been achieved with contrast enhanced radiographs and scintigraphy. A single modality has yet to provide a complete assessment. No test has entered routine clinical use, but further development and research is underway.

Conclusion

Significant information can be gained from imaging the Eustachian tube, and as faster acquisition techniques are developed, it is possible that dynamic imaging of tubal opening could play an important role in the assessment of patients with ET dysfunction.

CONTRAST-ENHANCED COMPUTED TOMOGRAPHIC IMAGING OF THE AUDITORY TUBE IN MESATICEPHALIC DOGS

Computed tomography after contrast medium injection was performed in three mesaticephalic canine cadavers to image the auditory tube. Cadavers were positioned in lateral recumbency for imaging. A myringotomy incision was made in the left tympanic membrane of each dog, and contrast medium was infused into the ear canal and middle ear through a balloon-tip catheter. With this method, contrast medium filled the left bulla and auditory tube in all three cadavers. Computed tomography following contrast medium injection was effective for evaluation of the canine auditory tube. Future studies are required to determine the usefulness, as well as the safety, of this procedure in the evaluation of the auditory tube in other breeds of dogs as well as dogs with otitis

Mechanism and Rate of Middle Ear Fluid Absorption

Several mechanisms have been suggested to explain the clearance of fluids from the middle ear. These include a pumping action through the eustachian tube, mucociliary beating through the tube, outflow of water to the blood due to osmotic gradients and an active Na(+) transport driving water absorption. In order to assess these mechanisms, the middle ear cavity of paralyzed, ventilated (eustachian tube occluded) guinea pigs was filled with fluids varying in osmotic pressure (hypotonic, isotonic, hypertonic) to which a vertical tube was attached. The change in height of fluid in the tube was taken as a measure of changes in middle ear fluid volume. A greater fluid volume reduction was seen with the hypotonic (1/5 saline) solution. A small volume increase was observed with the hypertonic solution. These results provide evidence that in these experimental conditions, water absorption due to osmotic gradients can contribute to middle ear fluid clearance.

Passive and dynamic properties of the eustachian tube: quantitative studies in a model

OBJECTIVE

To question the conception of Eustachian tube (ET) dysfunction by investigating some of its passive and active properties.

BACKGROUND

Middle ear (ME) fluid accumulation accompanied by a negative pressure is generally accepted to be induced by ET dysfunction, implying that the origin of pathology is within the tube.

METHODS

Pressure changes were continuously and directly measured in a ME model having human dimensions, constructed with a patent ET, and employing different mastoid sizes. Various liquids were introduced into the ME chamber while maintaining atmospheric pressure. The model was tilted to a 45 degrees angle below the horizon, causing the liquid to block the tympanic inlet of the ET. Then either the ME was opened to the atmosphere (simulating an insertion of a ventilating tube) and the ET was inspected for liquid passage through it, or the cartilaginous ET was compressed and opened, imitating the "pumping" action of the ET at the process of deglutition.

RESULTS

ET blockage produced a ME negative pressure in the range of -8 to -10 mm H2O. ET pumping caused a ME pressure change of 2 to 60 mm H2O, a greater change when a smaller mastoid was used.

CONCLUSIONS

ET obstruction by intratympanic fluid may cause a negative pressure in an ME having a normal, patent ET. Clearance of such fluid would be facilitated according to its viscosity. The ET pumping mechanism may play a major role in fluid transport and pressure regulation of the ME.

Effect of exogenous surfactant on ventilatory and clearance function of the rat's eustachian tube

HYPOTHESIS AND BACKGROUND

The Eustachian tube has three important functions with respect to the middle ear: ventilation, clearance, and protection. Surfactants are assumed to be important to maintain these functions. The administration of exogenous surfactant may therefore be effective to improve the function of the Eustachian tube. This randomized, double-blind, placebo-controlled study was designed to investigate the effect of exogenous surfactant on the function of the Eustachian tube in rats.

MATERIALS AND METHODS

Exogenous surfactant was administered into the middle ear of 10 otologically healthy rats, and 10 other rats received placebo. The effect on the opening and closing pressure (passive ventilatory function) and the dye clearance time (clearance function) of the rat's Eustachian tube was measured.

RESULTS

A significant decrease in the opening pressure was seen after the administration of surfactant. Both surfactant and placebo caused an increase in the closing pressure. A serious disturbance of the dye clearance time was induced in 13 rats, and the test failed in 1 rat. In the remaining 6 rats, no significant differences in the dye clearance time were observed between the two groups.

CONCLUSIONS

Exogenous surfactant decreased the closing forces of the Eustachian tube even in otologically healthy rats. No significant effect on the mucociliary clearance was observed, but this may have resulted from the small number of rats. Additional randomized, double-blind, placebo-controlled trials should be conducted to determine the clinical relevance of these changes and to further assess the effect of surfactant on the function of the Eustachian tube.

Analysis of the dysfunctional eustachian tube by video endoscopy

OBJECTIVE

Human eustachian tubes with known pathologic conditions of the ear were inspected endoscopically, and video recordings were made for slow-motion analysis of the pathophysiologic changes.

SETTING

Ambulatory office in a tertiary referral center.

SUBJECTS

Forty-four adults with 64 ears having pathologic conditions.

INTERVENTIONS

Transnasal endoscopic examination of the nasopharyngeal opening of the eustachian tube during rest, swallowing, and yawning to study the dilatory movements of the eustachian tube.

MAIN OUTCOME MEASURES

Slow-motion video analysis of the dilatory movements of the eustachian tube.

RESULTS

Sixty-four ears and eustachian tubes with pathologic changes were studied. Tubal function was graded on (1) the extent of lateral excursion and progression of dilatory wave as estimates of tensor veli palatini and dilator tube muscle function, reduced function being observed in 43 tubes; (2) the degree of mucosal disease, which was significant in 48 tubes; (3) obstructive mucosal changes, which were present in 15 tubes; (4) ease and frequency of tubal dilation with maneuvers-26 tubes opened moderately, 21 opened minimally, and 11 were unable to open; and (5) patulous tubes-all 6 clinically patulous tubes showed concavities in the superior third of the tube, which is convex in normal subjects. All tubes with active pathologic conditions of the ear (otitis media with effusion, tympanic membrane retraction, draining ear, cholesteatoma) had significant abnormalities. A correlation could not be made between the severity of middle ear disease and the severity of observed eustachian tube dysfunction.

CONCLUSIONS

Slow-motion endoscopic video analysis is a potentially useful technique in classifying types of pathologic changes in the eustachian tube. Additional studies of dysfunctional tubes are needed to predict outcomes in operative ear cases and to design intratubal therapy for chronically dysfunctional tubes.

Serial anatomy of the auditory tube: correlation to CT and MR imaging

Serial anatomy of the auditory tube (AT), was studied in nine anatomical specimens, according to transverse, coronal and specific oblique planes and was correlated to computed tomography and magnetic resonance imaging. In order to assess the orientation of the oblique plane, parallel to the AT, 30 AT specimens were catheterized: the mean angle between the AT and the Virchow plane or the bony palate was 34 degrees. The bony portion is better explored with CT, whereas the cartilaginous portion is better studied with MR. The cartilage, posterior and medial, is closed anteriorly and inferiorly by a fibrous membrane (lamina membranacea), which is not seen on CT or MR images. The AT is closely related to the tensor veli palatini muscle (TVPM) anterolaterally, and the levator veli palatini muscle inferiorly (LVPM); both are well imaged on the oblique plane. They are bounded by fascias: the submucosal fascia (tela submucosa) is medial, the pharyngobasilar fascia runs between the TVPM and the LVPM and the auditory tube; the fascia of Weber-Liel is lateral to the TVPM. Fascias are difficult to distinguish from the surrounding fatty tissue and the adjacent muscles. The auditory tube and its muscles, forming the lateral wall of the nasopharynx, are well studied by CT and MR imaging, using the transverse or, preferably oblique plane, together with coronal plane.

Evaluation of clearance function of the Eustachian tube by sequential contrast CT

Comparisons of Eustachian tube (ET) functions studied by sequential contrast computerized tomography (CT) and by tubotympanic aerodynamics (TTAG) were made. ET clearance function was assessed by the shape of the cartilaginous portion before, during and at the end of swallowing; ventilatory function was studied by TTAG. ET clarity, real-time dynamics and resolution were all better when observed with sequential CT. Contrast medium was instilled into the middle ear via a drumhead perforation and 1 scan/sec taken during swallowing. We classified ET function based on the presence or absence of a) movement of the cartilaginous portion, and b) contrast medium in the ET as i) movement present, contrast medium seen in ET: ii) movement absent, contrast medium present in ET; and iii) movement present, no contrast medium in the ET. Ventilatory and clearance functions did not parallel one another, attributable to some mechanical, differences between the two functions.