Endoscopically assisted presigmoid retrolabyrinthine approach to the lateral mesencephalic sulcus: a cadaveric study with comparison to the variant supracerebellar infratentorial approaches

The supracerebellar infratentorial (SCIT) approach is commonly used to gain access to the lateral mesencephalic sulcus (LMS), which has been established as a safe entry point into the posterolateral midbrain. This study describes a lateral variant of the SCIT approach, the supreme-lateral SCIT approach, for accessing the LMS through the presigmoid retrolabyrinthine craniectomy and quantitatively compares this approach with the paramedian and extreme-lateral SCIT approaches. Anatomical dissections were performed in four cadaveric heads. In each head, the supreme-lateral SCIT approach was established on one side, following a detailed description of each step, whereas the paramedian and supreme-lateral SCIT approaches were established on the other side. Quantitative measurements of the exposed posterolateral midbrain, the angles of LMS entry, and the depth of surgical corridors were recorded and compared between the three SCIT approach variants. The supreme-lateral (67.70 ± 23.14 mm 2 ) and extreme-lateral (70.83 ± 24.99 mm 2 ) SCIT approaches resulted in larger areas of exposure anterior to the LMS than the paramedian SCIT approach (38.61 ± 9.84 mm 2 ); the supreme-lateral SCIT approach resulted in a significantly smaller area of exposure posterior to the LMS (65.24 ± 6.81 mm 2 ) than the other two variants (paramedian = 162.75 ± 31.98 mm 2 ; extreme-lateral = 143.10 ± 23.26 mm 2 ; both P