Stenting the Eustachian tube to treat chronic otitis media - a feasibility study in sheep

Abstract

Background: Untreated chronic otitis media severely impairs quality of life in affected individuals. Local destruction of the middle ear and subsequent loss of hearing are common sequelae, and currently available treatments provide limited relief. Therefore, the objectives of this study were to evaluate the feasibility of the insertion of a coronary stent from the nasopharynx into the Eustachian tube in-vivo in sheep and to make an initial assessment of its positional stability, tolerance by the animal, and possible tissue reactions.

Methods: Bilateral implantation of bare metal cobalt-chrome coronary stents of two sizes was performed endoscopically in three healthy blackface sheep using a nasopharyngeal approach. The postoperative observation period was three months.

Results: Stent implantation into the Eustachian tube was feasible with no intra- or post-operative complications. Health status of the sheep was unaffected. All stents preserved their cylindrical shape. All shorter stents remained in position and ventilated the middle ear even when partially filled with secretion or tissue. One of the long stents became dislocated toward the nasopharynx. Both of the others remained fixed at the isthmus but appeared to be blocked by tissue or secretion. Tissue overgrowth on top of the struts of all stents resulted in closure of the tissue-lumen interface.

Conclusion: Stenting of the Eustachian tube was successfully transferred from cadaver studies to an in-vivo application without complications. The stent was well tolerated, the middle ears were ventilated, and clearance of the auditory tube appeared possible. For fixation, it seems to be sufficient to place it only in the cartilaginous part of the Eustachian tube.

Keywords: Auditory tube; Middle ear ventilation; Otitis media; Sheep as animal model; Stent; Tissue reaction.

Fig. 1

Study design in weeks. The arrows indicate time points of general anesthesia with endoscopic control (white), instillation of inflammatory mediators, or stent implantation

Fig. 2

Endoscopic view of the ET for the evaluation of stent position and inflammation. Examples of (a) no [endoscopic score 1–3], (b) mild [score 4–6] and (c) moderate [score 7–9] inflammation in the nasopharyngeal orifice region are shown

Fig. 3

Coronal CT sections of both stents (*) in-situ for each sheep. Tympanic cavity (ME), nasopharynx (NP) and spinal canal were used for orientation and evaluation. The lines indicate the regions of histologic evaluation

Fig. 4

Slice of the ET with plotted ellipse illustrating the region of analysis of stent expansion. Depicted are Rüdinger’s safety canal (RC), auxiliary gap (AG), the tubal cartilage (C) and free lumen (L_F) of the ET. An ellipse is depicted on the struts (*) indicating the position of the stent

Fig. 5

Recorded endoscopic score values. a Left (long stent) and (b) right (short stent) ET of each sheep under general anesthesia in the course of the experiment. In the first GA (week − 1) a score of zero was observed

Fig. 6

Areas of tissue occurrence (T), lumen (L), secretion (S) and free lumen (L_F). Depicted are parts 1 (a) and 4 (b) of the ET for both stents (compare Fig. 3). The total area of the ET (ROI) was set as 100%

Fig. 7

Mean stent area. Parts 1 and 4 (compare Fig. 3) of the implanted 2.75 mm × 26 mm (a) and 2.0 mm × 20 mm (b) stents with the calculated reference for each stent size. The data are shown as mean + SD

Fig. 8

Percentage of struts not covered by tissue. Depicted from the nasopharynx (part 1) to the middle ear (part 4) for both types of stents

Fig. 9

Interface between mucosa and lumen. Illustrated are the Eustachian tube (ET) and the nasal cavity (NC) of sheep 3 (right ET, part 4) showing prismatic epithelium (Prism. epith.) topped with cilia at 2× magnification