Surgical approaches for the lateral mesencephalic sulcus

Area of Science:

• Neurosurgery
• Surgical Anatomy
• Microsurgery

Background:

• The brainstem is a delicate structure requiring precise surgical access.
• Intrinsic brainstem lesions, particularly those on the lateral midbrain surface, necessitate knowledge of safe entry points.
• The lateral mesencephalic sulcus (LMS) is a key landmark for approaching lateral midbrain lesions.

Purpose of the Study:

• To compare the surgical exposure to the lateral mesencephalic sulcus (LMS) provided by the subtemporal (ST) approach and the paramedian and extreme-lateral variants of the supracerebellar infratentorial (SCIT) approach.
• To evaluate the angles of surgical exposure offered by each approach.
• To determine the optimal surgical corridor for accessing lateral midbrain lesions.

Main Methods:

• Three surgical approaches (ST, paramedian SCIT, extreme-lateral SCIT) were performed on 10 cadaveric heads.
• A neuronavigation system was used to measure predetermined points, areas of microsurgical exposure, and angles.
• Statistical analysis was conducted to compare the exposures and angles between the approaches.

Main Results:

• Surgical exposure areas were similar across all approaches (ST: 369.8 ± 70.1 mm², paramedian SCIT: 341.2 ± 71.2 mm², extreme-lateral SCIT: 312.0 ± 79.3 mm²; p = 0.13).
• Vertical angular exposure was significantly wider with the extreme-lateral SCIT approach (25.1° ± 3.3°) compared to ST (16.3° ± 3.6°) and paramedian SCIT (19.4° ± 3.4°) (p < 0.001).
• Horizontal angular exposure was superior with the ST and extreme-lateral SCIT approaches (45.2° ± 6.3° and 45.5° ± 6.6°, respectively) compared to the paramedian SCIT variant (35.6° ± 2.9°) (p < 0.001).

Conclusions:

• While surgical exposure areas were comparable, the extreme-lateral SCIT approach provides significantly wider vertical and horizontal angles to the LMS.
• The extreme-lateral SCIT approach offers a near 90° trajectory to the LMS, facilitating intraoperative microsurgical technique.
• This approach is advantageous for resecting intrinsic lesions located at the lateral midbrain surface.