The effects of stereotactic radiosurgery on secondary facial pain.

Twenty-seven patients with tumor-related secondary facial pain were treated by stereotactic radiosurgical procedures between November 1991 and October 1998. They had 14 meningiomas, 11 schwannomas (one trigeminal, 10 vestibular), one nasopharyngeal cancer and one chordoma. The mean maximum dose administered was 26.4 Gy (range 16 to 35 Gy) and the margin of the tumor was encompassed within the 45 to 90% isodose. The patients were analyzed based on their pain relief with a mean follow-up duration of 32.1 months. In 24 patients (85.7%), there was initial pain improvement after radiosurgery, but half had recurrent pain. A pain response was obtained in 12 cases (pain response rate = 42.9%), five were pain free and seven had pain reduction. On the follow-up MRI, a decrease in tumor volume of more than 20% of the preoperative volume occurred in 14 of 25 cases. The mean time interval to initial pain improvement (10.3 months) and pain response (5.7 months) were shorter than for a decrease in tumor volume (18.6 months). Tumor-related secondary facial pain was less responsive to stereotactic radiosurgery than idiopathic trigeminal neuralgia. It would seem that the mechanism of pain relief in radiosurgery is not only trigeminal root decompression secondary to tumor volume reduction, but also other mechanisms involving inactivation of abnormal electrical transmission may be involved.