Histologic analysis of a human trigeminal nerve after failed stereotactic radiosurgery: case report.

Background: Stereotactic radiosurgery is an accepted surgery to treat patients with medically intractable trigeminal neuralgia. However, little is known about the mechanism of pain relief after trigeminal neuralgia radiosurgery. We report the histologic findings of a human trigeminal nerve after failed radiosurgery for trigeminal neuralgia.
Case Description: A 74-year-old patient presented with a 10-year history of refractory trigeminal neuralgia. Prior surgeries included an MVD and PRGR. Gamma knife radiosurgery was performed targeting the proximal trigeminal nerve using one 4-mm isocenter (maximum dose, 85 Gy). She experienced good pain relief (no pain, reduced medications) for 16 months. She had no new trigeminal deficits after this procedure. The pain recurred, and she underwent repeat gamma knife radiosurgery targeting the distal trigeminal nerve using one 4-mm isocenter (maximum dose, 70 Gy). The pain continued to escalate until she required hospitalization for pain control and hydration. Three weeks after her second radiosurgical procedure, she underwent a repeat posterior fossa exploration. During that surgery, her trigeminal nerve was partially sectioned, and a small segment of the proximal to midcisternal nerve was sent for histological examination. There was no histologic evidence of nerve damage.
Conclusion: This case supports the contention that trigeminal nerve injury is required to provide long lasting pain relief after trigeminal neuralgia radiosurgery.