Significance of the Tentorial Alignment in Approaching the Trigeminal Nerve through the Suboccipital Retrosigmoid Technique

Abstract

Introduction: In this study, we aimed at assessing the significance of the tentorial alignment in approaching the trigeminal nerve through a suboccipital retrosigmoid craniotomy. Methods: Four parameters were evaluated using preoperative MRI and intraoperative measurements in 34 consecutive patients who underwent microvascular decompression of the trigeminal nerve via a suboccipital retrosigmoid approach: (1) the angle between the tentorium and the line drawn from the hard palate (tentorial angle, TA); (2) the angle between the tentorium and the line connecting the opisthion to the inion (occipital angle, OA); (3) the angle between the lines drawn along the petrous bones ventral to the internal auditory canals (petrous angle, PA); (4) the intraoperative distance between the trigeminal nerve and the acousticofacial bundle (distance, d). Statistical analysis was performed using Pearson's correlation test and t-test as appropriate. Results: Mean values were 50.1 ± 12.2 for TA, 82.3 ± 9.9 for OA, 104.6 ± 12.2 for PA, and 3.2 ± 1.5 mm for d. There was a negative correlation between TA and d (r = − 0.233, p = 0.09): the mean d was 3.7 ± 1.7 mm for TA 51 (p = 0.06). A positive correlation was detected between TA and OA (r = 0.336, p = 0.02). Conclusions: The distance between the trigeminal nerve and the acousticofacial bundle decreases in the presence of a steep tentorial angle. This limits the working field at the petrotentorial sulcus. Awareness of such anatomical features at the time of preoperative planning is of paramount importance to avoid complications during the procedure.