The Microscopic Transcanal Approach in Stapes Surgery Revisited

Summary

This article describes the microscopic transcanal technique for stapes surgery, providing step-by-step surgical instructions for familiarizing surgeons with this approach.

Abstract

The microscopic transcanal (aka transmeatal) surgical approach was first described in the 60s, offering a minimally invasive means of reaching the external auditory canal, the middle ear, and epitympanon. Such an approach avoids a retroauricular or endaural skin incision; however, working through a narrow space needs angled microsurgical instruments and specific training in otologic surgery. The transcanal approach restricts the working space; however, it offers a binocular microscopic vision into the middle ear without extended skin incisions and thus, reducing post-operative pain and bleeding. In addition, this minimally invasive approach avoids scar tissue complications, hypoesthesia of the auricle, and potential protrusion of the pinna. Despite its numerous advantages, this method is still not routinely performed by otologic surgeons. Since this minimally invasive technique is more challenging, there is a need for extensive training in order for it to be widely adopted by otologic surgeons. This article provides step-by-step surgical instructions for stapes surgery and reports possible indications, pitfalls, and limitations using this microscopic transcanal technique.

Introduction

The advent of a binocular operating microscope in otologic surgery in 1951¹ paved the way for a less invasive microscopic transcanal approach. Alternatives were endaural incisions or retroauricular approaches, which are more invasive. The first transcanal stapes surgery was described by Rosen already in 1952^2,3, but at that time, the stapes was mobilized and not removed. In 1956, Shea revolutionized stapes surgery with the use of the first Teflon prosthesis⁴. The transcanal approach proved suitably adapted to this technique since it provided good 3D visualization of the posterior part of the ear canal, tympanic membrane, and middle ear. The indication for a transcanal microscopic method has widened over time, covering a large number of surgical otologic interventions: Tympanotomy⁵, tympanoplasty^6,7,8, ossiculoplasty⁹, antrotomy¹⁰, cholesteatoma^11,12,13, glomus tympanicum¹⁴, labyrinthectomy¹⁵, neurectomy^16,17, intrameatal acoustic neuroma by transpromontory approach^18,19,20 or even cochlea implantation²¹.

This challenging approach requires the use of specialized instrumentation for transcanal surgery (initially described in the 60s)²² and specific surgical training. It restricts working space but does, however, offer a binocular microscopic vision into the middle ear without the need for an extended skin incision and thus, reduces post-operative pain and bleeding. In addition, this minimally invasive approach avoids scar tissue complications, hypoesthesia of the auricle, and protrusion of the pinna. In this article, we provide step-by-step surgical instructions for stapes surgery and report possible indications, pitfalls, and limitations using this microscopic transcanal technique.

Protocol

The local review board of the Bern University (Kantonale Ethikkomission Bern) approved the present study, a formal informed consent was not required for this type of retrospective study.

1. Indications

1. Use the transcanal approach if the diameter of the ear canal is ≥5.5 mm.
   NOTE: The anatomy and shape of the outer ear canal might further limit the working space.
2. Assess the canal's diameter by placing a 5 mm diameter ear speculum. Ensure that the speculum sits comfortably in the canal.
3. Do not use the transcanal approach in anterior perforations with a non-visible anterior rim.
4. Use the inside-out-technique¹¹ for middle ear pathologies such as cholesteatomas, which reach the epitympanon beyond the semicircular canal.

2. Preparation

1. Positioning of the patient: Place the operating table at the lowest position, tilted in a reverse Trendelenburg position (Figure 1A) with the angle (α) of the headrest at its maximal reclination (without head hanging).
   NOTE: This position is contraindicated in patients with atlantoaxial instability. Finally, rotate the head towards the contralateral side (β, Figure 1B).
2. Instruments: Use bent instruments to keep the working field open. Hold the instruments correctly with the fingers, thus preventing any blocked vision (Figure 2 and Figure 3).
   NOTE: Black-colored instruments reduce light reflections.
3. Disinfection and cleaning of the ear canal: Clean the ear canal thoroughly to avoid any intraoperative infection. Disinfect the canal with diluted Povidone Iodine (2.5%-5% due to toxicity).

3. Local anesthesia

1. Perform local anesthesia in two steps:
   1. Inject all four quadrants (23 G needle) with Carbostesin 0.25% (50 mg/20 mL) mixed with Adrenalin 1 mg/mL (final concentration 1:200,000 epinephrine).
   2. Inject within the ear canal using a small bent 27 G needle. Be careful when injecting in the anterior-inferior area to avoid facial paresis.

4. Tympanomeatal flap and speculum holder

1. Perform a tympanomeatal flap using a u-shape incision with a sickle or a round knife starting at 6' o clock position (inferio-anterior). Detach the ear canal skin with a Rosen knife until the inferior annulus rim is reached.
2. Install the speculum holder (Figure 4).
3. Insert the largest possible ear speculum. Make sure that the orientation is correct.
   NOTE: Letters indicating the size of the speculum should be placed superiorly.
4. Complete the tympanomeatal u-shaped flap by cutting the superior-posterior part with the Belucci scissor. Detach the ear canal skin with a Rosen knife until the superior annulus rim is reached.
5. This step might cause bleeding.
6. Use an absorbable gelatin sponge soaked with adrenaline to stop bleeding.
7. Detach the whole flap until the edge of the annulus.

5. Middle ear dissection

1. Make sure that facial nerve monitoring is working before entering the middle ear.
   NOTE: The patient should have recovered from any neuromuscular block, which can be assessed by neuromuscular monitoring (4 TOF, train of four).
2. Enter the middle ear at the posterior-superior part of the annulus since it is easier to detach at this position.
   ​NOTE: Large cholesteatomas or granulation tissue around the middle ear ossicles might hide any anatomical landmark. In this case, inferio-posterior entering of the middle ear might be advised to find other landmarks (CAVE: jugular bulb).
3. Dissect and visualize the anatomical middle ear structures. Visualize the chorda tympani, promontory, incudostapedial joint, stapedial tendon, and the facial nerve (tympanic segment).
4. Widen the posterior-superior part of the ear canal with a bone curette or a 2 mm rough diamond drill (low speed) if any of the above structures are not sufficiently exposed. Put an absorbable gelatin sponge in the middle ear to prevent the entrance of bone dust into the middle ear.

6. Stapes suprastructure removal

1. Disconnect the incudostapedial joint with a small 0.3-0.6 mm hook or a sickle knife and make an anterior movement to prevent breaking of the footplate.
2. Test the mobility of all the three ossicles by touching each ossicle with a needle to confirm isolated ankylosis of the stapes.
3. Use protection glasses or filters integrated into the microscope.
4. Dissect the stapedial tendon with the laser (e.g., diode laser, CO2-Laser). Test the strength of the laser during this procedure. Use a FOX laser with 2.5-3 W energy in pulse mode (30-50 ms); however, this value depends on the device and its probe.
5. Dissect the posterior crus of stapes near the attachment of the footplate ± anterior crus if the footplate is too mobile.
6. Remove the stapes suprastructure. Brake the stapes away from the facial nerve towards the promontory if the anterior crus is still intact. Keep the footplate intact.
   ​NOTE: The footplate should not move while breaking the suprastructure. There is a risk of a longitudinal fracture of the footplate during this procedure.

7. Footplate perforation

1. Use the FOX laser to carbonize/weaken the footplate (2 W, 30 ms pulse mode) by making a rosette pattern.
2. Use a perforator microdrill (skeeter 0.6 mm) to perforate the last shell of the footplate in the posterior third section.
3. If the footplate is too thick, use a diamond microdrill to thin out the footplate until a blue shimmering structure is visible (also known as blue lining).
4. Do not use the suction in the area of the footplate once the footplate is open.

8. Stapes prosthesis insertion

1. Measure the distance between the long process of the incus and the footplate using a measurement instrument with a 4 mm measuring mark. Use a 0.25 mm longer prosthesis than measured.
2. Hold the prosthesis hook with a small alligator ear forceps using a predefined angle of orientation (~20°) prior to insertion.
3. Crimp the stapes hook on the long process of the incus.
   NOTE: The front tine of the crimping instrument moves while the back tine remains stable on the incus.
4. Check the movement of the prosthesis by moving the malleus handle.
5. Avoid the prosthesis from touching the promontory or the facial nerve.
6. Consider using otologic cement if there is an interplay between prosthesis and incus process.
7. Avoid over-crimping since there is a risk for incus necrosis in the long term.
8. Seal the perforated footplate with small water-soaked absorbable gelatin sponge.

9. Wound closure/dressing

1. Reposition the tympanomeatal flap, adapt with silk dressing, and pack with absorbable gelatin sponge soaked with a solution of hydrocortisone 10 mg (1%)/neomycin 3.5 mg/polymyxin B sulfates 10,000 Units.
2. Use a 10 cm ribbon gauze soaked with the same solution for ear canal packing.

Discussion

The current article provides detailed insider information about the transcanal microscopic approach for stapes surgery. We could demonstrate that microsurgery is feasible using a key-hole technique avoiding a retroauricular or endaural incision in the majority of cases.

Some prerequisites, however, have to be met for achieving a successful surgery. The dissectors should be curved. The knives, hooks, and the needle are angled (Figure 1) to improve the visualization and light conditions in such a narrow space²². In addition, instruments should be black-colored, avoiding any microscopic light reflections. Patient positioning is crucial for the transcanal approach since the ear canal is curved, and the light beam of the microscope must be fully aligned with the longitudinal axis of the canal (Figure 2). In addition, it is crucial to hold the instruments correctly (Figure 3) and to keep a suitable ergonomic posture of the hands (Figure 5) for a successful transcanal surgery.

A speculum holder, as shown in Figure 3, allows a two-handed technique and a straight access route to the tympanic membrane/middle ear. The speculum might additionally serve as an instrument guide. Finally, the angle of the fingers/instruments and the angle of the microscope light should be adjusted and optimized. In view of all these parameters, extensive training of transcanal otologic surgery is needed to improve surgical performance.

Alternative approaches include the endaural and retroauricular incision or the endoscopic transcanal approach. The retroauricular incision is advised for inaccessible anterior perforations of the tympanic membrane or subtotal perforations. Such cases, however, might still be accessible through endoscopic approach²³, provided that the ear canal diameter is large enough (>5 mm). The retroauricular approach remains the gold standard if there is a need to open the mastoid cavity. For combined cholesteatoma surgeries (transmeatal and retroauricular transmastoidal approach), we recommend the inside-out technique, which was first described by Roth and Häusler¹¹. This technique suggests as a first step a transcanal access to the middle ear identifying all anatomical structures following the extension of the disease (cholesteatoma) by epitympanectomy. As a second step, a retroauricular incision might follow in cases where transmastoidal access is indicated based on the extension of the cholesteatoma. There is a considerable advantage of this two-step approach since there is a non-negligible proportion of patients who will not need a retroauricular incision (second step) based on a limited extension of the disease.

The transcanal endoscopic approach uses the same route of access and is also limited to an ear canal diameter of >5 mm. Similarly, this approach is minimal-invasive and offers a closer wide-angle view of anatomical structures. In addition, an endoscopic approach offers an angled view of 45° or 70°, which is valuable for the removal of cholesteatomas in the retrotympanum²⁴, the attic region²⁵ or for anterior perforations²³. In cholesteatoma surgery, similarly to the above-mentioned inside-out technique, a transcanal endoscopic cholesteatoma removal is performed, followed by clearance of the disease from the mastoid as necessary. In this context, novel exclusive endoscopic techniques were recently described using a constant suction bone-drilling technique²⁶. Endoscopic surgery, however, is a one-handed technique and challenging in inflamed conditions with associated bleeding. Therefore, the management of bleeding plays a key role in the endoscopic approach to the middle ear²⁷. In addition, endoscopy provides a limited depth of field since it does not offer a binocular view. New 3D endoscopes might improve the depth of field²⁸; however, such endoscopes have a larger diameter of 4 mm.

Compared to the retroauricular approach, the microscopic transcanal approach is minimal-invasive and has several advantages such as avoidance of retroauricular pain, scar tissue complications, hypoesthesia of the auricle, and protrusion of the ear.

The transcanal approach also has limitations. The main limitation is the diameter of the ear canal, which should be at least 5 mm. Any disease without direct or with limited access through the meatus is not suitable for a transcanal approach alone. The approach can be extended by using an endoscope or a combined transmastoidal access.

The transcanal/transmeatal microscopic approach has been a proven technique for more than 70 years; however, this method is still not routinely performed by otologists despite the advantages of this minimally invasive approach. Since the performance of this minimally invasive technique is more difficult and challenging, there is a need for extensive training in order to promote its use by otologic surgeons. This illustrative teaching video offers one additional tool to familiarize otologists with this surgical technique.

Materials

Name	Company	Catalog Number	Comments
Adrenalin	Sintetica
Belucci microscissors	Olympus (former Richards)	8178100FX
Betadine solution (Povidon iodine)	Mundipharma Medical Company
Carbostesin	Sintetica		Bupivacain 2.5 mg/mL
Cup forceps	Olympus (former Richards)
Curette	Olympus (former Richards)	13-0147
Curved suction tubes	Spiggle & Theis	302007NV und6066500100
Drill	Bienair		2 mm rough diamond drill
FOX laser	A.R.C. Laser GmbH
Gelfoam (absorbable gelatine compressed sponge)	Pfizer Injectables	GS-010DP	absorbable gelatin sponge
Gloves	Sempermed		Appropriate size
Hooks	Olympus (former Richards)	13-0201, 13-0202, 13-0204, 13-0206	0.3–0.6 mm
Hydrocortison/neomycin/polymyxin otic /Cortisporin Otic Solution	Pfizer
Needle	Olympus (former Richards)	13-0207	27 G
Operating Microscope	Leica	E 114637
Otologic dissectors	Olympus (former Richards)
Ribbon gauze
Round knifes	Olympus (former Richards)	13-0211 13-0212
Silk dressing	Otosilk
Speculum	Olympus (former Richards)	OK 082R
Surgical Mask	Halyard	48247
Water to rinse	Ringer