The protocol followed the guidelines of the local institution's human research ethics committee and was approved by the local institutional review board (KEK-BE 2019-00555). All operations were performed in general anesthesia under controlled hypotension in anti-Trendelenburg positioning with standard otological instruments.

1. Preparation of the surgical site

1. Manually adjust the endoscope screens (see Table of Materials) according to the surgeon's preferred position (sitting or standing).
2. Monitor the facial nerve by checking impedances with a nerve monitoring system (see Table of Materials) and perform a tap test¹³.
3. Disinfect the auricle and the retroauricular region with swabs soaked with commercially available povidone-iodine solution (see Table of Materials).
4. Drape the periauricular region with sterile blankets.
5. Clean and rinse the external auditory canal (EAC) with a blunt syringe and Ringer solution (see Table of Materials).
6. Perform white balancing of the camera with white gauze and apply drops of anti-fog solution to the endoscope lens.

2. Exclusive transcanal endoscopic approach

1. Introduce the 0°, 3mm diameter, and 15cm length endoscope in the EAC (see Table of Materials) and clean the EAC by removing earwax and cutting the hairs in the EAC.
2. Perform local anesthesia with 0.5 mL of diluted epinephrine (1:200.000) injection (see Table of Materials), each using four injection sites in all quadrants of the EAC under endoscopic control. Additionally, inject 0.5 mL of diluted epinephrine (1:200.000) to the vascular strip in the posterior-superior quadrant of the EAC.
3. Inspect the tympanic membrane and the attic region with the 0° endoscope.
4. Elevate a tympanomeatal flap tailored to disease extension using an angled round knife and provide hemostasis with epinephrine (1:1000) soaked cottonoids.
   NOTE: Additional hemostasis may be applied by electrocoagulation using mono- or bipolar cautery; alternatively, radio-frequency-cautery can be used (see Table of Materials). Be careful to use monopolar at the lowest intensities to minimize risks of spread of electricity to the facial nerve.
5. Expose the annulus and, if possible, the chorda tympani; open the middle ear cavity, and evaluate in detail the cholesteatoma extension.
6. Carefully separate the cholesteatoma matrix from the eardrum and from the chorda tympani.
7. Carefully dissect the cholesteatoma involving the middle ear and the incudostapedial area in case of an intact ossicular chain.
8. Perform limited atticotomy using unpowered instruments, bone drilling, or ultrasonic devices (see Table of Materials) by stepwise removal of the lateral portion of the attic and evaluate the extent of cholesteatoma infiltration by following the steps below.
   1. For atticotomy with unpowered instruments: remove small parts of bone, especially the scutum, by a bone curette using rotatory movements or chisel and hammer.
   2. For attico- and antrotomy with bone drilling: remove larger parts of bone either in an underwater technique¹⁴, followed by cutting burrs at low speed (2000-8000 rpm) or cutting or coarse diamond burrs at slow speed with only a little irrigation.
      NOTE: For the underwater technique, the EAC is filled with 0.9% of NaCl solution, and the endoscope lens is inserted into the EAC with the burrs. Subsequently, drilling for attico- and antrotomy is performed directly under visual inspection. Occasional suction is required due to bone dust and reduced visibility. Utmost care has to be applied to prevent damage to surrounding structures by direct or heat damage. The delicate lens and shaft of the endoscope have to be kept away from the rotatory instruments to prevent its damage.
   3. For attico- and antrotomy with ultrasonic devices: remove the larger parts of bone with the curved tip in an underwater technique to prevent heat damage to bone and soft tissues.
      CAUTION: Do not touch the ossicular chain and the cochlea due to possible inner ear hair cell damage due to transmission of micro-vibrations.
9. If the cholesteatoma infiltrates deep into the anterior epitympanum or erodes the incus, remove the incus and, if required, the malleus head to entirely remove the cholesteatoma.
10. Perform stepwise attico- and antrotomy with different devices (see Table of Materials) to follow and completely extirpate the cholesteatoma. Use angled dissectors if appropriate.

3. Middle ear exploration

1. After completion of cholesteatoma resection, an entire middle ear exploration with an emphasis on residual cholesteatoma and functional considerations with the greatest sparing of healthy mucosa is performed. Use first 0° then a 45° angled lens.
   NOTE: If appropriate, a 70° endoscope may also be used.
2. Check anterior epitympanic space, tegmen tympani, posterior epitympanum, antrum until the posterior limit of the lateral semicircular canal.
3. Carefully inspect the retrotympanum, including posterior sinus, sinus tympani, subtympanic sinus, and hypotympanum.
4. Check Eustachian tube, protympanum, supratubar recess, tensor fold, and isthmus; restore the ventilation route by tissue removal in case of obstruction.

4. Reconstruction of the ossicular chain and scutum

1. Perform an incision 5 mm posterior to the tragus edge and cut through to the cartilage, then harvest a large piece of cartilage with perichondrium on both sides.
2. Reconstruct the scutum with a trimmed piece of cartilage and perichondrium for defect closure after attico- and antrotomy.
3. Perform underlay tympanoplasty using a trimmed piece of cartilage with overlapping perichondrium in island-graft technique or temporalis fascia for defect closure of the tympanic membrane. Add perichondrium in case of cartilage use for supporting the construction if necessary.
4. If the stapes is intact, inspect the incus or head of the malleolus for possible malleolar head or incus interposition ossiculoplasty; otherwise, use double-block cartilage (Malafronte technique¹⁵) or PORP (partial ossicular replacement prosthesis).
5. Use a TORP (total ossicular replacement prosthesis) if the stapes supra-structure is also affected by cholesteatoma and needs to be removed.
6. Use resorbable gelatinous sponges to secure the reconstruction, reinforce the reconstruction using a pressed perichondrium layer or cartilage in case of PORP/TORP.

5. Wound closure

1. Reposition the tympanomeatal flap and adapt it to the EAC curvature without sutures.
2. Splint the tympanic membrane with silicone or silk strips of adequate size for defect coverage.
3. Pack the EAC with a resorbable gelatinous sponge and the outer part with an antibiotic (polymyxin, neomycin) and hydrocortisone soaked gauze (see Table of Materials).