Robot-Assisted Transcanal Endoscopic Ear Surgery for Congenital Cholesteatoma

Summary

This protocol describes the removal of congenital cholesteatoma using minimally invasive transcanal endoscopic ear surgery with a two-handed approach and a robotic endoscope holder.

Abstract

Congenital cholesteatoma accounts for 25% of cholesteatoma cases in children. Transcanal Endoscopic Ear Surgery (TEES) is ideal for these patients because it offers a wide endoscopic view of the middle ear and a minimally invasive approach. The two main limitations are the loss of one operative hand and a narrow external auditory canal in younger children. Here, we present the case of a 3-year-old patient with a Potsic stage III congenital cholesteatoma adherent to the incus and branches of the stapes. A robotic-assisted TEES procedure was performed, during which a robotic arm with 6 degrees of freedom held a 0°, 2.9 mm wide endoscope, enabling the surgeon to work in a narrow environment with both hands. The procedure's duration was 2 h and 9 min, including 16 min for the installation and draping of the robotic arm. After a trans-canal approach, the cholesteatoma was dissected from the ossicles using both a needle (or sickle knife) and suction to stabilize the ossicles and limit the risk of hearing trauma. The cholesteatoma was debulked to reduce its size, allowing it to be pushed under the malleus anteriorly and then separated from other adherences before removal. A tragal cartilage graft was used to reinforce the tympanic membrane.

Introduction

Congenital cholesteatoma (CC) accounts for 25% of cholesteatoma cases in children, and its proportion within cholesteatoma cases has increased in recent years due to improved public health measures and earlier detection worldwide^1,2. The size and ossicular involvement of CC significantly impact the prognosis and surgical strategy. As a result, CC can be classified according to the Potsic classification³. When diagnosed early, these lesions are typically confined to the tympanic cavity or may extend to the epitympanum with an intact matrix, involving the ossicles (Potsic stage III) or not (Potsic stage I or II). In more advanced cases, distinguishing CC from acquired cholesteatomas can be challenging, with diffluent lesions in the epitympanum or mastoid regions and altered tympanic membranes (Potsic stage IV).

Patients with CC without mastoid involvement (Potsic stage I to III) make excellent candidates for total endoscopic ear surgery (TEES), which involves a minimal trans-canal incision and offers an excellent view of the entire tympanic cavity and epitympanic region. Numerous studies have demonstrated that TEES yields similar residual rates compared to the traditional microscopic approach^4,5,6,7,8,9. TEES has been adopted by many pediatric otology centers worldwide, providing a safe and efficient technique that also enhances ergonomics for surgeons, allowing them to sit upright while facing the screen^5,7,8,10. However, during TEES, safely dissecting the ossicles can be challenging in stage III lesions due to the lack of counter-stabilization when using an instrument in the second hand, increasing the risk of ossicular subluxation and inner ear trauma from excessive ossicle mobilization. Additionally, the lack of suction during dissection can lead to poor visibility due to bleeding or endoscope fogging. A robotic arm designed for middle ear surgery and cochlear implantation has been employed as a robotic dynamic endoscope holder, providing six degrees of freedom, including three translational and three rotational axes throughout the procedure. Its safety during robot-assisted TEES has already been reported in the adult population¹¹.

This article reports the robotic setup and surgical procedure for a stage III congenital cholesteatoma in a 3-year-old child, using robotic-assisted TEES. This approach allows for the dissection of the cholesteatoma with two hands while benefiting from an endoscopic view and a trans-canal approach.

Protocol

This study was conducted in compliance with the European GDPR and registered at AP-HP, Hôpital Necker - Enfants Malades (number 20200727144143). The study adhered to the CARE guidelines¹², and both parents provided written consent to record the surgical video of the procedure and to publish a case report^13,14. The surgical strategy mirrored the one typically used in our tertiary referral center with a microscope, involving the use of both hands. The primary difference was the surgical approach, which was trans-canal, eliminating the need for atticotomy or canalplasty.

1. Pre-operative procedures

1. Diagnose congenital cholesteatoma during otoscopy in the clinic, where a white mass is visible behind a normal tympanic membrane. Discuss the tympanoplasty procedure and approach with the parents (and the patient, considering their age), explaining the benefits and risks.
2. Check the pre-operative auditory work-up to assess ossicular involvement in cases of conductive hearing loss and to verify the absence of associated sensorineural hearing loss.
3. Prepare for the tympanoplasty procedure with a pre-operative CT scan to assess the feasibility of total endoscopic ear surgery (TEES) and to check for mastoid involvement.
   NOTE: Ossicular involvement can also be assessed to determine the Potsic stage³. Stage I and II patients are ideal candidates for TEES, while stage III cases may be more challenging due to the difficulty of safely dissecting the ossicular chain with one hand. Potsic stage IV lesions require mastoidectomy, and a traditional endaural or postauricular approach is usually preferred.
4. Assess the size of the external ear canal using a speculum (see Table of Materials), which is particularly important in infants.
   ​NOTE: If a size 4 speculum can be inserted, TEES can be easily performed. It is more challenging but still possible to perform TEES if a size 3 speculum can be inserted (the canal is between 3 and 4 mm wide at its narrowest).

2. Preparation for the surgery

1. Perform a checklist to confirm the side of the lesion and ensure that a CT scan and audiometry results are available before commencing the procedure.
2. Install the robotic arm (endoscope holder) (see Table of Materials) on the robot and ensure it is in a neutral position.
3. After patient intubation^13,14, tilt the patient's head and secure it in a 30° rotation away from the surgeon. Tilt the patient's headrest backward and incline the surgical bed in an anti-Trendelenburg position to position the patient's head horizontally.
4. Secure the patient's head to the table using an adhesive elastic band placed on the forehead.
5. Set up facial nerve monitoring (see Table of Materials).
6. Drape the surgical microscope, at least for the initial procedures, to facilitate a transition to the microscope during the procedure if difficulties arise with the robot.
   NOTE: This is essential to ensure the highest quality of patient care while still advancing along the learning curve.
7. Drape the robotic arm and the robot.
8. Install and drape the space mouse after attaching it to the surgical bed next to the surgeon (see Figure 1), which controls the robotic arm's multi-directional movement.
   NOTE: The space mouse can be fixed on either side of the surgeon, but in this studt, it's positioned toward the patient's feet, allowing the surgeon to sit directly next to the scrub nurse (who is positioned at the head of the patient, as shown in Figure 2).
9. Disinfect the surgical site and cover it with surgical drapes, exposing only the external ear.
10. Position the robot opposite the surgeon (on the other side of the bed) so that the robotic arm (endoscope holder) can extend over the patient's head toward the surgeon, aligning with the external auditory canal (as illustrated in Figure 1).
11. Place the video tower opposite the surgeon, preferably on either side of the robot (ideally toward the patient's feet), ensuring a comfortable view of the screen. For a left tympanoplasty, position the video tower to the right of the robot (as shown in Figure 1 and Figure 2).

3. Onset of the surgery

1. Position the endoscope holder over the auditory canal meatus and insert the endoscope into the endoscope holder. Use a 25 cm long telescope with the robotic arm to reduce the risk of conflicts with the surgeon's hands during the procedure.
   NOTE: The telescope has a width of 2.9 mm, and a 0° scope is typically used, although 30° or 45° scopes may be useful for certain steps.
2. Clean and disinfect the ear canal, and carefully examine the tympanic membrane.
3. Administer local anesthesia (using a solution containing 10 mg/mL xylocaine and 0.005 mg/mL adrenaline) to the upper portion of the bony auditory canal (vascular strip).
4. Harvest tragal cartilage (conchal cartilage can be used as an alternative). Place a small gauze in the ear canal during this stage to prevent the accumulation of coagulated blood.

4. Congenital cholesteatoma (CC) procedure

1. Make an incision from 12 o'clock to 8 o'clock for the trans-canal approach using an angled cautery needle with low power (4 Watts) (see Table of Materials) to prevent retraction. Use suction to clear any smoke or blood that may obstruct the view.
   1. Open the tympanic cavity inferiorly, posteriorly, and superiorly along the chorda tympani until the malleus neck is identified.
      NOTE: Extend the skin incision if there is tension in the flap to prevent tearing.
2. Identify and debulk the lesion: ensure that the posterior portion of the congenital cholesteatoma (CC) is clearly visible, and its involvement with the incus and stapes can be accurately assessed.
   1. Elevate the tympanum from the manubrium to push the tympano-meatal flap anteriorly. Open the CC matrix in the controllable posterior-inferior portion and debulk it using a large suction.
      NOTE: A stage III CC is typically too large to be removed without inducing ossicular trauma or the risk of dislocation.
3. Separate the CC from the incus and stapes using a hook or needle and push it anteriorly under the malleus with a Fisch microdissector (see Table of Materials).
   NOTE: Exercise great care to avoid ossicular trauma, and use suction as a counterforce to stabilize the ossicles during dissection.
4. Dissect the CC from the promontory and cochleariform process and remove the CC.
   NOTE: Be especially cautious when dissecting the medial-anterior side of the malleus, using a hook or Fisch microdissector.
5. Inspect the tympanic cavity using an angled endoscope.
   NOTE: With an intact ossicular chain, the endoscope must be manipulated very cautiously, especially with an angled view. Robotic control of the endoscope is highly useful for rotating it 360° while maintaining the shaft in the same position and at the exact same depth. To inspect the ossicles, use a soap-soaked cotton ball to wipe the medial side of the malleus and incus and between the crus of the stapes to detect any residual squamous cells¹⁵.
6. Reinforce the tympanic membrane and insert cartilage in an underlay position to prevent subsequent retraction pockets. Replace the tympano-meatal flap on the bony canal and pack it with absorbable foam, starting with the anterior part of the tympanum to avoid any subsequent lateralisation.
7. Discharge the patient according to an outpatient protocol. Administer auricular antibiotic drops for three weeks and schedule a post-operative check-up at one month.
   NOTE: No external dressing is necessary.

Representative Results

The case study reports a robotic-assisted total endoscopic ear surgery (TEES) for a Potsic stage III left congenital cholesteatoma in a 3-year-old child. The robotic arm was equipped with a 0° and 30°, 25 cm long, and 2.9 mm wide scope, connected to a 1080p full-HD camera and screen.

The pre-operative work-up revealed a typical congenital cholesteatoma with a CT scan showing a round anterior mass medial to the malleus, extending posteriorly between the stapedial crus and anteriorly into the supratubal recess (Figure 3). The ossicular chain remained intact. Audiometric testing indicated a slight 10 dB conductive hearing loss on the side of the lesion (Figure 4). The 3-year-old patient had a narrow external auditory canal, allowing only a size 3 speculum to be inserted. Therefore, the microscope was prepared as a backup, and the family was informed that an endaural approach might be necessary.

The installation of the robotic arm took 16 min, and the overall installation time (from intubation to incision, including all draping and instrument preparation) was 27 min. The total surgery duration (from intubation to closure) was 2 h and 9 min. The entire TEES was conducted with a 0° endoscope, except for a 10 min interval when a 30° scope was used to examine between the stapedial crus and the epitympanum. The microscope was not utilized.

A tragal graft was harvested through a direct incision and sutured before the endoscopic stage. The tympano-meatal flap was elevated from the malleus after a trans-canal approach, following which the congenital cholesteatoma (CC) was debulked, dissected from the incus and stapedial crus, and pushed forward under the malleus (Figure 5). It was then removed with an intact anterior and superior matrix. Due to the large size of the CC, a tragal graft was placed in an underlay fashion to prevent any future tympanic retraction before repositioning the tympano-meatal flap.

The procedure proceeded without surgical difficulties, particularly concerning the use of the robot. Passive movement of the endoscope could occur if it was pushed aside by an instrument, but this was gradual and did not obstruct the vision. Conversely, the instruments remained secure and stable throughout the procedure.

At the 6-week follow-up, the tympanic membrane and external auditory canal were healed without any epidermal inclusion cyst or myringitis. The 6-week post-operative audiometry indicated a slight conductive hearing loss, likely due to the use of underlay cartilage to reinforce the tympanic membrane. Importantly, there was no sensorineural hearing loss, which was the primary concern after extensive ossicular manipulation and dissection. The patient will undergo non-EPI diffusion-weighted MRI scans at 18 and 36 months after surgery, along with clinical and audiological follow-up for 8 to 10 years¹.

Figure 1: Operating theatre setup for left tympanoplasty. In this proposed setup, the robot is positioned opposite the surgeon, aligned with the patient's external auditory canal axis. For a left tympanoplasty, the video tower is placed slightly to the left, towards the patient's feet. In the case of a right tympanoplasty, where the external auditory canal axis differs, the robot would be positioned towards the patient's feet. Please note that the surgical microscope should be draped and located in a corner of the room, though it's not depicted in the figure. Please click here to view a larger version of this figure.

Figure 2: Peri-operative installation for left tympanoplasty. (A) The robot arm holder centralizes the endoscope to evenly distribute weight and minimize tube tension. (B) Observe the positioning of the video tower on the side opposite to the surgical field. The surgeon has a multi-directional control device, the space mouse, on the left for controlling the robotic endoscope holder. (C) The surgeon performs surgery on the left ear, facing the video tower, which is placed on the opposite side of the patient. (D) A close-up view from the surgeon's perspective shows the robotic arm holding the endoscope in line with the external auditory canal. Both surgical hands remain free for instrument manipulation and suction, akin to the conventional microscopic technique. The endoscope is capable of tilting, rotating, and translating at varying speeds using the space mouse. Please click here to view a larger version of this figure.

Figure 3: Pre-operative CT-scan. The lesion is marked with an asterisk (*). (A) The transverse plane reveals an extensive congenital cholesteatoma involving the malleus and extending anteriorly into the supratubal recess. (B) In the transverse plane, the supratubal recess (§) is clearly visible, along with the extension between the crus of the stapes, which appears intact (stage III congenital cholesteatoma). The retrotympanum (marked with ¤) is devoid of any lesions. (C) The coronal plane displays a typical round mass medial to the malleus. (D) In the coronal plane, the extension of the lesion into the supratubal recess (§) is shown anteriorly. Please click here to view a larger version of this figure.

Figure 4: Audiometry (pre and post-operative). Left: Pre-operative audiometry reveals a slight 10 dB conductive hearing loss in the left ear, causing a minor asymmetry with the normal hearing in the right ear. Right: Six weeks post-operation, a 10 dB conductive hearing loss is observed in the left ear (likely due to the underlay cartilage graft), but notably, there is no sensorineural hearing loss. The x-axis represents hearing loss in decibels (dB), while the y-axis indicates frequencies in Hertz (Hz). Please click here to view a larger version of this figure.

Figure 5: Endoscopic view (0° endoscope). (A) This is an immediate pre-surgical view, where the anterior congenital cholesteatoma presses against the intact tympanic membrane. (B) The tympano-meatal flap has been elevated from the malleus, fully exposing the congenital cholesteatoma from the stapedial crus at the rear to the supratubal recess at the front. (C) After cholesteatoma removal, the ossicular chain remains intact. Note the broad scope of the 0° endoscope view, spanning from the Eustachian tube at the front to the stapes at the rear. The black arrowhead in (A) and (B) points to the congenital cholesteatoma, which is removed in (C). Please click here to view a larger version of this figure.

Discussion

This study reports the successful use of a robot-assisted totally endoscopic procedure to remove a stage III congenital cholesteatoma in a 3-year-old child. Total endoscopic ear surgery (TEES) is particularly interesting in the pediatric population, as performing tympanoplasties with a keyhole trans-canal approach reduces healing time and the amount of immediate post-operative care. Regarding cholesteatoma surgery, many studies have now demonstrated that TEES yields similar, if not smaller, residual rates in selected patients compared to microscopic postauricular or endaural approaches^4,5,10.

Stage I or II congenital cholesteatoma (CC) are, of course, ideal cases for TEES, with excellent results. In these cases, there is no ossicular involvement, visibility is often excellent, and the CC does not extend into high-risk areas of residual disease, such as the retrotympanum or anterior epitympanum^4,5,6,7,8. Difficulties may arise in stage III or IV CC, where dissecting ossicles or removing extensive lesions is required with only one hand. In traditional microscopic two-handed surgery, the second hand typically holds a suction device, which can enhance vision by removing blood but also plays a key role in tissue manipulation and ossicular control during dissection.

The robotic endoscope holder represents an innovative and secure solution to combine the advantages of TEES with a two-handed procedure¹¹. This case report demonstrates the feasibility of using this technology in a young 3-year-old child, where a 2.9 mm endoscope, two instruments, and sufficient working space could be accommodated within the child's narrow external auditory canal, enabling work on the stapes and exploration of the epitympanum.

Other systems have been used to combine endoscopic vision with a two-handed approach, facilitating bi-manual manipulation of grafts and prostheses or blood suction^{16,17,18,19,20}. Although some steps during TEES that require a second operative hand can be done with the assistance of another individual (holding the camera or suction), endoscope holders make the entire TEES procedure feasible with two hands, which can be advantageous for surgeons accustomed to this configuration with the microscope. Rigid mechanical endoscope holders may be suitable for short and simple type 1 myringoplasties¹⁸, but they restrict movement, preventing the surgeon from quickly approaching the surgical field or adjusting the view. Therefore, dynamic holders, such as robotic endoscope holders, offer dynamic movement as well as the best precision and security compared to other manually-set dynamic holders^16,20, particularly in a middle ear with an intact ossicular chain. Dangerous head movements may occur during otologic procedures, posing a risk of significant trauma during TEES²¹. As in most otology procedures near the oval window, we recommend securing the head with an adhesive elastic band (as detailed in step 2.4) since the robotic arm cannot automatically move with the patient's head.

The main limitation of the robotic method is the very narrow ear canal in children with craniofacial anomalies (such as Down syndrome), which may render it impossible to simultaneously insert the endoscope and two hand-held instruments. Additionally, diseases that extend posteriorly beyond the lateral semicircular canal may necessitate a larger incision. As previously mentioned (see steps 1.3 and 1.4), careful pre-operative planning and the insertion of a size 3 speculum enable the selection of appropriate candidates for the technique.

Robotic-assisted TEES presents a promising option to expand the use of TEES to complex middle ear lesions while benefiting from the advantages of two-handed surgery and dynamic intra-operative movement. The procedure was successful without adding extra surgical time. A large-scale study on a cohort of patients is required to more precisely determine the limits of robot-assisted TEES and discuss its indications compared to traditional microscopic surgery and one-handed TEES.

Materials

Name	Company	Catalog Number	Comments
0° 2.9 mm 25 cm Endoscope	Collin	RBT-END-0	Endoscope for otoendoscopy
Colorado MicroDissection Needle	Stryker		Pointed electrocautery
Facial nerve monitoring
RobOtol	Collin		Robot dedicated to ear surgery
Space mouse	3DConnexion		RobOtol control arm
Standard otology surgical material			Including amongst standard instruments: speculum, Fisch dissectors