Subtemporal approach to the tentorial incisura: normative morphometric data based on magnetic resonance imaging scans.

Objective: The tentorial notch can be contained within a transversal line made in front of the cerebral peduncles and another line through the posterior border of the quadrigeminal plate into the anterior, middle and posterior parts. Different approaches to the tentorial incisura have been established. The subtemporal approach represents one of those options. Since morphometrical analyses of this approach in this region have not yet been performed, the aim of the present study was to measure the surgical corridor along these borders.

Methods: Fifty-three magnetization prepared rapid acquisition gradient echo-sequences of individual brains without pathological lesions were analyzed. For this study, an axial section along the pontomesencephalic sulcus and two coronal sections along the above-described borders were measured using a program specially written by one of the coauthors to obtain various parameters. A triangle circumscribing the surgical corridor was delimited by exactly defined anatomic landmarks for the coronal section, and the depths of the temporal lobe at the incisural borders were measured for the axial section.

Results: Various data are given concerning the surgical corridor of a subtemporal approach to the tentorial incisura. The different shapes of this corridor to the incisural region were recorded. According to our measurements, four different types of the temporal lobe could be differentiated.

Conclusion: Knowledge of these distances and various contours of the path is crucial to avoid brain damage during retraction or manipulation. The curvature of the floor of the middle cranial fossa is highly variable and thus determines the surgical path chosen.