Gamma Knife irradiation–induced histopathological changes in the trigeminal nerves of rhesus monkeys

Object The authors' goal was to observe histopathological changes in the trigeminal nerve after Gamma Knife surgery (GKS) in rhesus monkeys, and to investigate the radiobiological mechanism of GKS for primary trigeminal neuralgia. The nerve length–dosage effect of irradiation is also discussed. Methods One of 5 rhesus monkeys randomly served as a control, and the other 4 monkeys were randomly administered a target radiation dose of 60, 70, 80, or 100 Gy (a different dose in each animal). The size of the collimator was 4 mm, and the target point was the trigeminal nerve root. In each experimental monkey, one side was exposed to single-target-point irradiation, and the contralateral side was exposed to double-target-point irradiation. After 6 months, the trigeminal nerve root was examined using light microscopy, transmission electron microscopy, and immunohistochemistry. Results At each radiation dose, the damage to the nerve tissue by single-target-point irradiation was identical to that caused by double-t...