Prediction of Endoscopic Middle Ear Visibility in Relation to the Anatomy and the Optical Angle: Implications for Endoscopic Ear Surgery

By June 7, 2019

Bonali, Marco1; Fermi, Matteo1; Alicandri-Ciufelli, Matteo1; Mattioli, Francesco1; Villari, Domenico1; Presutti, Livio1; Anschuetz, Lukas 2
1 Otolaryngology-Head and Neck Surgery Department, University Hospital of Modena, Modena, Italy;
2 Department of Otorhinolaryngology, Head and Neck Surgery, Inselspital, University Hospital and University of Bern, Bern, Switzerland.

To study the relationship between the endoscopic and radiologic anatomy to middle ear visibility depending on the optical angle used. Moreover, the actual technical limits of transcanal EES were investigated.

Tensor fold, protympanum, facial sinus (FS), sinus tympani (ST), subtympanic sinus (STS), hypotympanum and aditus ad antrum were assessed by means of an exclusive transcanal approach in 33 temporal bones with different angled endoscopes (0°, 45°, 70°) to check for the full visualization of these regions. According to previously published classifications FS, ST and STS were radiologically classified into type A, B and C depending of their extension with respect to the mastoid part of the facial nerve.

The full visibility of the posterior wall of the three different retrotympanic areas was significantly associated to the radiomorphologic classification and the optical angle of the endoscope used. For all the other subsites the rate of full visualization improved thanks to the angled endoscopes.

The complete visibility of middle ear subsites is related to the use of angled endoscopes (45° and 70°). We observed a statistically significant association of full endoscopic visibility to the radiomorphologic classification on preoperative CT and the degree of optical angle used. These results allow the prediction of the endoscopic exposure of the retrotympanum from the preoperative CT and emphasize the  routine use of angled endoscopes during transcanal EES. Despite the experimental use of 70° optical lenses, the retrotympanum remains not fully visible if a posterior and medial extension regarding the FN (Type B and C) is present. This represents a technical limit of exclusive transcanal EES.