Surgical approaches for the lateral mesencephalic sulcus

OBJECTIVE The brainstem is a compact, delicate structure. The surgeon must have good anatomical knowledge of the safe entry points to safely resect intrinsic lesions. Lesions located at the lateral midbrain surface are better approached through the lateral mesencephalic sulcus (LMS). The goal of this study was to compare the surgical exposure to the LMS provided by the subtemporal (ST) approach and the paramedian and extreme-lateral variants of the supracerebellar infratentorial (SCIT) approach. METHODS These 3 approaches were used in 10 cadaveric heads. The authors performed measurements of predetermined points by using a neuronavigation system. Areas of microsurgical exposure and angles of the approaches were determined. Statistical analysis was performed to identify significant differences in the respective exposures. RESULTS The surgical exposure was similar for the different approaches-369.8 +/- 70.1 mm(2) for the ST; 341.2 +/- 71.2 mm(2) for the SCIT paramedian variant; and 312.0 +/- 79.3 mm(2) for the SCIT extreme- lateral variant (p = 0.13). However, the vertical angular exposure was 16.3 degrees +/- 3.6 degrees for the ST, 19.4 degrees +/- 3.4 degrees for the SCIT paramedian variant, and 25.1 degrees +/- 3.3 degrees for the SCIT extreme- lateral variant craniotomy (p < 0.001). The horizontal angular exposure was 45.2 degrees +/- 6.3 degrees for the ST, 35.6 degrees +/- 2.9 degrees for the SCIT paramedian variant, and 45.5 degrees +/- 6.6 degrees for the SCIT extreme-lateral variant opening, presenting no difference between the ST and extreme-lateral variant (p = 0.92), but both were superior to the paramedian variant (p < 0.001). Data are expressed as the mean +/- SD. CONCLUSIONS The extreme-lateral SCIT approach had the smaller area of surgical exposure; however, these differences were not statistically significant. The extreme-lateral SCIT approach presented a wider vertical and horizontal angle to the LMS compared to the other craniotomies. Also, it provides a 90 degrees trajectory to the sulcus that facilitates the intraoperative microsurgical technique.