Suprameatal-transzygomatic root endoscopic approach to the geniculate ganglion: an anatomical and radiological study

Purpose To describe the suprameatal-transzygomatic root endoscopic approach (STEA) to the geniculate ganglion (GG), the labyrinthine facial nerve (FN) and epitympanum. Methods The feasibility and limits of the STEA, maintaining the integrity of the ossicular chain, were analysed. Ten human cadaveric ears were dissected. Step-by-step description of the technique and relevant measurements were taken during the approach. The visualization and surgical working field on the anterior and posterior medial epitympanum, GG, greater superficial petrosal nerve, the labyrinthine FN and suprageniculate area were evaluated. The range of motion through the approach and the rate of the decompression of the GG and the labyrinthine portion of the FN were assessed as well. CT-scan measurements were compared with those obtained during the dissection. Results A complete exploration of the epitympanum was possible in every specimen. Decompression of the GG and first portion of the FN was achieved without any trauma to the ossicular chain in nine ears. The endoscope movements were mainly limited by the distance between bony buttress-short process of the incus-tegmen. The working space, during GG and labyrinthine FN decompression, was limited by the distance between malleus head-medial epitympanic wall and malleus head-GG. Radiologic measurements were consistent with those obtained during the dissections. Conclusion The STEA is a promising minimally invasive approach for decompression of the GG and FN's labyrinthine portion. The applications of this corridor include the exploration and surgery of the medial epitympanum, preserving the ossicular chain.