Modiolus-Preserving Modified Transcanal Transpromontorial Approach for Treating Internal Auditory Canal Lesions: A Morphometric Anatomical Study

Background: Transcanal transpromontorial approaches may access internal auditory canal (IAC) lesions, but are restricted only for patients with unserviceable hearing. New perimodiolar cochlear implants may offer favorable outcomes after modiolus-preserving tumor resection.

Objective: To propose a modified transcanal transpromontorial approach with modiolus preservation for treating IAC lesions.

Methods: A total of 10 dissections were performed in 5 cadaveric heads: 5 using the exclusive endoscopic (EETTA) and 5 using the modiolus-preserving modified (MMTTA) transcanal transpromontorial approaches. Head CT scans (0.6 mm thick) were obtained before and after the procedures and registered to Brainlab neuronavigation to calculate extent of bone removal and process area of exposure and surgical freedom. Morphometric findings were further compared between the two approaches.[1] [2]

Results: The EETTA was performed as previously reported, by drilling the full promontory and removing the cochlea to access the IAC dura. The MMTTA was performed by drilling from the inferior surface of the spherical recess to the anterior pillar of the round window, exposing the scalae vestibule, intermedia, and tympani of the basal cochlear turn, and then antero-superiorly up to the cochleariform process to expose the IAC dura. The remaining promontory overlying the middle and apical cochlear turns was left intact. Average duration of dissection was 64.8 minutes (±23.4 minutes) for EETTA and 63.8 minutes (±19.43 minutes) for MMTTA (p = 0.943). Partial endoscopic visualization of the tympanic membrane was observed in 3 EETTA (60%) and 4 MMTTA (80%) dissections (p = 0.476). Average distance between the Fallopian canal and the superior surface of the spherical recess was 0.08 mm (±0.27 mm) for EETTA and −0.02 mm (±0.17 mm) for MMTTA (p = 0.507). Average distance between the cochleariform process and the anterior pillar of the round window was 4.46 mm (±0.72 mm) for EETTA and 4.67 mm (±0.83 mm) for MMTTA (p = 0.149). Average extent of bone removal was 38.3 mm³ (±1.37 mm³) for EETTA and 91.03 mm³ (±11.07 mm³) for MMTTA (p < 0.001). Average area of exposure was 15.86 mm² (±4.17 mm²) for EETTA and 10.02 mm² (±4.17 mm²) for MMTTA (p = 0.178). Average surgical freedom was 25.96 mm² (±6.61 mm²) for EETTA and 18.14 mm² (±9.47 mm²) for MMTTA (p = 0.173).

Conclusion: Our proposed MMTTA offers area of exposure and surgical freedom comparable to the standard EETTA for treating IAC lesions. However, it may additionally allow hearing preservation by enabling the implant of perimodiolar cochlear systems. Further clinical studies are required to prove MMTTA's benefits in real clinical scenarios.

Publikationsverlauf

Artikel online veröffentlicht:
01. Februar 2023

• References

• 1 Presutti L, Alicandri-Ciufelli M, Cigarini E, Marchioni D. Cochlear schwannoma removed through the external auditory canal by a transcanal exclusive endoscopic technique. Laryngoscope 2013;123(11):2862–2867
• 2 Plontke SK, Kösling S, Pazaitis N, Rahne T. Intracochlear schwannoma: tumor removal via subtotal cochleoectomy and partial cochlear reconstruction with preservation of semicircular canal function. HNO 2017;65(Suppl 2):158–162