Background: Despite the latest developments in microsurgery, electrophysiological monitoring, and neuroimaging, the surgical management of intrinsic brainstem lesions remains challenging. Several safe entry points have been described to access the different surfaces of the brainstem. Knowledge of this entry zone anatomy is critical to performing a safe and less morbid approach. To access the anterior midbrain surface, a well-known entry point is the anterior mesencephalic (AM) zone. Our aim was to quantify surgical AM zone exposure through the orbitozygomatic (OZ) and subtemporal (ST) approaches. We also analyzed the angular exposure along the horizontal and vertical axis angles for the AM zone.
Methods: Ten cadaveric heads were dissected using the OZ and ST approaches for anterior midbrain surface exposure. A neuronavigation system was used to determine the 3-dimensional coordinates. The area of surgical exposure, angular exposure, and anatomical limits of each craniotomy were evaluated and determined using software analysis and compared for intersection areas and AM safe zone exposure.
Results: The median surgical exposure was 164.7 ± 43.6 mm2 for OZ and 369.8 ± 70.1 mm2 for ST (P = 0.001). The vertical angular exposure was 37.7° ± 9.92° for the OZ and 18.4° ± 2.8° for the ST opening (P < 0.001). The horizontal angular exposure to the AM zone was 37.9° ± 7.3° for the OZ and 47.0° ± 3.2° for the ST opening (P = 0.002).
Conclusions: Although the OZ craniotomy offers reduced surgical exposure, it provides a better trajectory to the AM zone compared with the ST approach.
Keywords: Anterior mesencephalic zone; Brainstem surgery; Orbitozygomatic craniotomy; Safe entry zones; Subtemporal craniotomy; Surgical approaches.
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