Development of an In Vivo Model for Eustachian Tube Dysfunction

Abstract

Otitis media is often connected to Eustachian tube dysfunction (ETD). Until now, there was no large animal model available for the examination of new treatment methods such as stents for the Eustachian tube (ET). Thus, the aim of the study was to develop a method to reproducibly induce ETD by injection of fillers and without permanent closure of the ET. Tools for safe injection of hyaluronic acid (HA) in the surrounding of the ET were developed. In ex vivo experiments, HA mixed with Imeron^® was injected close to the nasopharyngeal orifice of the ET of blackface sheep. The established depot was visualized using cone beam computer tomography and magnetic resonance imaging, and stents could be placed into the ET. A reliable position of the HA depot was achieved. This method was transferred to in vivo, and middle ear ventilation was investigated by tympanometry. ETD was achieved with amounts of 2.5 mL HA or higher. None of the animals showed any sign of discomfort or complications. The induced ETD lasted for 3 to 13 (maximum observation period) weeks and was also combined with middle ear effusion. A model of ETD based on injection of HA next to the ET was successfully established and is now available to test novel treatment options for ET functionality.

Keywords: Eustachian tube dysfunction; animal model; cone beam CT; hyaluronic acid; otitis media with effusion; tympanometry.

Figure 3

CBCT scans of cadaver heads after injection of 0.3 mL HA (A; case 13) or 1 mL HA (B; case 19b). The depots (white arrows) were visualized by addition of Imeron^® and were classified as good (A) and good with rostral bulge (B) (compare Table 1).

Figure 1

Injection instrument with the retractable cannula being pushed forward.

Figure 2

Endoscopic view of the pharyngeal orifice of the ET. The cannula is inserted in the target area (marked in red) in front of the crescent-shaped ET orifice (black arrows).

Figure 4

MRI images of a cadaver head (cases 22 and 23). The HA depots are marked by white arrows.

Figure 5

CBCT scan of a head with stent prototypes inserted into the ETs. (A): Both depots (cases 1 (left ET) and 2 (right ET)) are visible and marked by white arrows. Next to the depots, air filled stents can be seen. The green line indicates the course of the left ET. (B): Enlargement of one stented ET with the depot. The yellow lines (A; B; C) mark the position of the respective cross sections depicted on the right side.

Figure 6

Endoscopic view of the ET of in vivo case 12 after injection of HA. A bulge is clearly visible in the ventro-rostral area of the tube (compare Figure 2). The insertion instrument is still in place.

Figure 7

Endoscopic view of the nasopharynx of in vivo case 21/22. (A) Before HA injection; (B) after injecting the left tube (case 21, shown here on the right); (C) after bilateral injection; (D) on day 7. The ET orifices are marked by black arrows.

Figure 8

Success of the induction of ETD 7 days after injection of different amounts of HA.

Figure 9

Endoscopic view of the tympanic membrane, (A) physiologic membrane (case 21, before the injection); (B) bulbed membrane (case 21, week 1); (C) fluid level in front of the membrane (case 10, week 1).

Figure 10

MRI image of case 21 after 13 weeks. The HA depot is marked by a white arrow.