During the developmental phases of MVD, various surgical approaches and decompression techniques were employed as MVD [3–5, 15]. When MVD for TN was first used in Japan, approximately 30 years ago, it was performed using an approach that was almost identical to that used for acoustic tumors, which used the petrosal (lateral) cerebellar surface alone. In 1987, we reported the usefulness of the infratentorial lateral supracerebellar approach for TN, emphasizing utilization of the tentorial (superior) cerebellar surface [9, 10]. In 2000, Fujimaki T et al. reported the combined approach in which both the petrosal and tentorial cerebellar surfaces were used during MVD for TN [1]. From the viewpoint of safe handling of the superior petrosal veins (Sup. Pet. Vs.), the combined approach may be better when performed completely because the offending vessels are decompressed after complete dissection of the arachnoid membrane around all tributaries of the Sup. Pet. V. However, when the combined approach is insufficiently performed and the tentorial cerebellar surface is insufficiently exposed, the offending SCA is decompressed from the posterolateral side on the petrosal cerebellar side. This direction of transposition is unsuitable for shifting the offending SCA medially. The infratentorial lateral supracerebellar approach, conversely, is extremely suitable for medial transposition of SCA [8, 9].

Subsequently, decompression techniques have also been improved. When MVD for TN was initially employed, the interposing method, in which a prosthesis is inserted between an offending vessel and CN V, was generally utilized [4, 14, 15]. However, after experiences of recurrence due to prosthesis adhesion to CN V, interposition was gradually superseded by transposition [5, 14]. Hence, we propose the use of the tentorial stitched sling retraction technique [6–8]. The causes of TN were also clarified as surgical experience increased and are currently considered to include not only offending arteries but also offending veins and/or arachnoiditis [9, 11].

Using the infratentorial lateral supracerebellar approach, surgeons can reach CN V passing on the lateral portion of the tentorial cerebellar surface medial to the vein of the cerebellopontine fissure, the largest common stem of the Sup. Pet. V [7–10]. The approach has the following advantages:

Care must be taken to sufficiently dissect the arachnoid membrane around the Sup. Pet. Vs., particularly the anterolateral marginal vein and the vein of the cerebellopontine fissure.

The entry zone of CN V is located just anteroinferior to the anterior angle, which is the most anterior end of the anterolateral margin separating the tentorial and petrosal cerebellar surfaces (Fig. 11.1a). Therefore, CN V can be reached by following this margin, which is situated parallel to the superior petrosal sinus. One or two common stems of the Sup. Pet. V. usually exist between the porus acusticus internus (PAI) and the Meckel’s cave [13] (Fig. 11.1c). The suprameatal bulging, which is a bulge of the petrous bone between PAI and the Meckel’s cave, is sometimes large and can disturb visualization of the Meckel’s cave [16] (Fig. 11.1b). The lateral pontomesencephalic segment of SCA usually courses medial to CN V, bifurcating into the rostral and caudal trunks and forming a downward loop. When the downward loop is long, it compresses the nerve from the superomedial side and becomes the offending vessel for TN [2, 9] (Fig. 11.1d, e). Because perforators originating from SCA are long, SCA can be easily transposed medially (Fig. 11.1e). An upward loop of AICA courses inferolateral to CN V and sometimes compresses it from the inferolateral side [8, 9] (regarding the anatomy of SCA and AICA, refer to Chap. 3, “Three Cerebellar Arteries: Superior Cerebellar Artery, Anterior Inferior Cerebellar Artery, and Posterior Inferior Cerebellar Artery,” and Chap. 10, “Anatomy for Microvascular Decompression Procedures: Relationships between Cranial Nerves and Vessels, Preoperative Images, and Anatomy for the Stitched Sling Retraction Technique”).