Neuronavigation-based quantitative study of the far-lateral keyhole approach following partial removal of the occipital condyle and jugular tubercle.

We aimed to quantitate the exposure of the petroclival area after partial removal of the occipital condyle (OC) and tuberculum jugular (JT) using the far-lateral keyhole approach. Navigation data were obtained for six cadaveric heads, and the OC and jugular tubercle were outlined with different colours. After the retro-condylar keyhole approach was performed, 1/3 and then 1/2 of the OC and then the JT were resected stepwise using neuronavigation. Simultaneously, anatomic structures were observed and the lateral visual field angle (LVFA), exposed clival area and surgical freedom were measured. The mean ± standard deviation (SD) of the LVFA were: 39.2 ± 3.29° (before drilling the OC); 51.46 ± 2.45° (1/3 of the OC drilled); and 57.52 ± 2.66° (1/2 of the OC drilled); these values were significantly different (p<0.01). Exposure of the petroclival area increased significantly after JT removal (p<0.01), whereas surgical freedom increased significantly after removal of both partial OC and JT (p<0.05).We concluded that in the far-lateral keyhole approach, the LVFA is increased by partial drilling of the OC; the middle clivus is further exposed following JT drilling, and surgical freedom is improved significantly after partial removal of the OC and JT.