In total, twelve patients were included between February 24th and August 15th, 2021, details are listed in Table 1. Patients, who were scheduled to undergo tympanoplasty or tympanomastoidectomy with symptoms and signs of OETD were asked to participate in the study.

Inclusion criteria were as follows: ≥ 18 years old (of both sexes); diagnosed with unilateral or bilateral persistent obstructive eustachian tube dysfunction (OETD). Exclusion criteria were the following: preoperative nasal endoscopy with evidence of anatomic conditions that would prevent transnasal access to the eustachian tube; CT temporal bone scan with evidence of carotid artery dehiscence, superior semicircular canal dehiscence, or extrinsic eustachian tube compression; patient unable to follow protocol for any reason; cleft palate or craniofacial syndrome; prior eustachian tube intervention; and prior radiation to the head and neck. The median age of patients was 37 years (range 24–77 years). All patients underwent unilateral BDET. There were 10 females and 2 males. Patient details are depicted in Table 1.

All procedures were performed under general anesthesia. BDET was carried out with an endovascular balloon (EVB: Advance® 35LP, COOK Medical, Bloomington, Indiana), see Fig. 1A. The balloon is 2 cm long and 6 mm wide, dimensions [14] similar to devices approved for this specific use. Balloons were dilated to 12 atm for 2 min.

Endovascular balloon dilation system. A Endovascular balloon and pressure gauge. B Suction tips used for eustachian tube dilation. From left to right—suction tip with a 45° angled tip, suction tip with a 70° angled tip, “s” shaped malleable suction tip. C Balloon length marking along the distal end of endovascular balloon catheter. The EVB catheter was marked at its distal end (beyond the suction tip) to gauge the balloon length distance at which the entire balloon would be inserted into the eustachian tube

To guide the EVB to the opening of the ET, a curved metal sinus suction catheter was used (Fig. 1B). The balloon was inserted through the lumen of the suction catheter. Three different suction catheters were used. Two suction catheters were both 147 mm in length with an external diameter of 4 mm at the tip (37–14,239 Von Eicken Sinus Cannula Suction, Curved Short, Integra, Princeton, New Jersey, U.S.A.) The curved tip of said suction has an angle of about 70° (Fig. 1B); one of the suctions was altered to a 45° (Fig. 1B) angle by the manufacturer. The third suction used during the study was a malleable suction cannula (Fig. 1B), “S” shaped, 110 mm long and with a 3 mm diameter (MicroFrance®, Integra, Princeton, New Jersey, U.S.A.).

First the nasal cavity and the nasopharynx were inspected and the eustachian tube orifice identified. Once the tip of the catheter was manipulated to the ET opening, the balloon was introduced into its proximal lumen until the tip was visible at the distal end of the catheter. The EVB was inserted into the ET by slowly advancing it along the suction catheter using Seldinger technique. The suction catheter guide was then pulled back slightly to visualize the introduced balloon. The EVB was never advanced against pressure or resistance. Once the proximal silver marker of the 2 cm balloon was visible, it was not introduced further. The EVB was dilated with a pressure gauge to 12 atm. The dilated balloon was left in place for 2 min, deflated and retracted. Steps of BDET are depicted in Fig. 2. As an additional safety precaution, before inserting EVB into the ET orifice the balloon length was marked at the distal end of the suction catheter, see Fig. 1C, to avoid over-insertion of the device.

Intraoperative dilation of eustachian tube using an endovascular balloon. A–C Left orifice of the eustachian tube A the suction tip was brought to the orifice of the eustachian tube, the distal tip of the balloon could be visualized as white marker (solid arrow). B the suction tip was advanced slightly into the eustachian tube to facilitate insertion of the balloon. C the suction tip was retracted to visualize the distal end of the balloon—silver metal marker (dash arrow). D–F Right orifice of the eustachian tube during different steps of eustachian tube dilation. D the balloon was inflated to 12 atm after full insertion. E the balloon was deflated after 2 min. F the orifice is inspected after retraction of the entire system. The tip of the balloon (white) is visible

The orifice and the ET were inspected with a 0° and 30° endoscope to assess for any mucosal damage, adhesion, hematoma, bleeding, infection after each dilation. Photo documentation was carried out in order to review the mucosal tissue after the procedures. Further, a CT temporal bone was carried out after each surgery before the patient was discharged home. CT scan was analyzed by at least two surgeons as well as a radiologist to evaluate any potential damages. Special attention was paid to the following structures: integrity/fracture of the carotid canal, any obvious tissue changes around the ET.

Preoperatively, all patients underwent audiometry, tympanogram, nasal endoscopy, ETDQ-7 (Eustachian Tube Dysfunction Questionnaire 7) and computed tomography (CT) scan. All assessments except for ETDQ-7 are part of the standard work-up for individual patients with otologic conditions prior to surgery in the form of tympanoplasty/tympanomastoidectomy.

Patients were seen in follow-up at two weeks and at two months after the procedure. At the two week follow up appointment, the orifice of the eustachian tube was assessed and photo-documented (Fig. 3). At two months, the ETDQ-7 was repeated as well as an audiogram, tympanogram and tympanic membrane inspection.

Eustachian tube orifice at the two week follow-up