Topographic anatomical relationship between the trigeminal nerve trunk and superior cerebellar artery in patients with trigeminal neuralgia

Topographic anatomical relationship between the trigeminal nerve trunk (TNT) and superior cerebellar artery (SCA) was investigated in 25 autopsy cases (50 TNTs), in individuals who never suffered from trigeminal neuralgia (TN), by means of injecting colored polymerizing silicone mass into the vertebro-basilar system through one of the vertebral arteries. It was found that the top of SCA loop (formed as its anterior pontomesencephalic segment continues into the lateral pontomesencephalic segment) was situated between TNT and tentorium of the cerebellum, and the lateral pontomesencephalic segment did not intersect the TNT in the vertical plane. The contact between SCA pontomesencephalic segment with the superior surface of TNT in the projection of the entry zone and around it was observed in 16 cases (32%). Close proximity between the SCA and TNT (no more than 2 mm) was observed in 12% of cases, whilst the distance exceeding 2 mm was observed in 56% of cases. In 163 patients with TN, the top of the loop of the dolichoectatic SCA was located below TNT, and its distal part (pontomesencephalic segment) crossed TNT in the region of the entry zone or close to it, causing the traumatizing action. In 121 cases (74%), a single SCA branch was involved and in 42 cases (26%) two branches were involved. Thus, these observations have shown that the contact between SCA and TNT cannot lead to TN development, since traumatizing action on the nerve results not from the pulsation of the wall of artery which touches the nerve, but from the strokes of the distal arm of SCA loop, that unbends during each systole and is located at an angle to TNT. This is the essence of the difference between the neurovascular contact and the neurovascular conflict.