Transcanal Transpromontorial Approach to Lateral Skull Base: Maximal Area of Exposure and Surgical Extensions

Objective: To determine the possible surgical extensions and maximal area of exposure (AOE) achievable through the transcanal transpromontorial approach (TTA) to the internal auditory canal (IAC) and cerebellopontine angle. We hypothesize a possible extension of indication for this minimally invasive approach to the lateral skull base. Methods: In this experimental anatomic study, the expanded TTA was first carried out in 4 temporal bones to define the anatomic boundaries of the maximal exposure, from 2 perspectives, the middle ear and the porus of the IAC. Consecutively, these identified boundaries were translated on segmented 3-dimensional (3D) surface models of 32 temporal bone high-resolution computed tomography scans. Results: The dissections performed were the basis followed during the determination of the AOE on the 3D surface models. The measurements revealed that the AOE at the middle ear was 152.9 ± 33.6 mm2, whereas it was 151.9 ± 24.8 mm2 at the porus of the IAC. The mean superoinferior and anteroposterior extensions at the middle ear were 14.7 ± 2.5 mm and 16.9 ± 2.5 mm, respectively. On the other hand, the mean superoinferior and anteroposterior extensions at the IAC porus were 10.3 ± 1.3 mm and 18.5 ± 1.9 mm, respectively. Conclusions: Consistent with the minimally invasive approaches, the AOE is limited; however, if compared with traditional approaches, it appears of considerable size. Our results may assist the surgeon in the selection process of the appropriate candidates for the TTA and to tailor the approach to the disease.