Importance of Trochlear Nerve Dissection for Tentorial Incision during the Subtemporal Transtentorial Approach: Technical Note

Introduction: The subtemporal transtentorial approach provides excellent exposure of the middle incisural space. Retraction or incision of the tentorial edge improves access to the interpeduncular cistern and the basilar artery. The starting point of the tentorial incision and the tentorial flap geometry is greatly variable. We assessed the impact of freeing the trochlear nerve (TN) from its dural canal (DC) prior to dividing the tentorium.

Methods: We performed a subtemporal transtentorial approach on six hemispheres of cadaveric specimens. Following the exposure of the middle tentorial incisura, the TN is dissected from its DC, allowing a modified tentorial incision technique. Measurements to key anatomic structures were taken before and after tentorial incision.

Results: In each specimen, two sutures are placed along the tentorium edge, posterior to the TN's entrance in its DC. Initially, the TN is dissected free of its DC for a short distance. The tentorial incision is started between both sutures and oriented straight up toward the superior petrosal sinus (SPS). Dissection of the TN's DC is continued anteriorly up to its entry into the cavernous sinus. The tentorial incision is then extended anteriorly, paralleling the trajectory of the SPS. The rostrocaudal exposure of the interpeduncular cistern and basilar artery increased a mean 4.4 mm (SD, 1.7 mm) after completing this extended tentorial incision.

Conclusion: We present a modified technique of tentorial incision in which dissection of the TN from its DC is essential. This technique optimized reflection of the tentorium flap anteriorly and maximized the rostrocaudal exposure allowed via the subtemporal approach.