Abstract
Purpose The purpose of this study is to discuss the long-term effects of radiosurgery for epidermoid tumors, including the symptoms of trigeminal neuralgia and/or facial spasm, which we have originally reported before. Background Intracranial epidermoids are slow-growing tumors that can become symptomatic once they develop into large tumors. The mainstay of the treatment is surgery. However, eradicating the whole tumor is often difficult and some tumors may recur. In addition to their mass effects on the brain, these tumors are often associated with hyperactive nerve dysfunction syndromes such as trigeminal neuralgia, glossopharyngeal neuralgia, and/or facial spasm. Cases and methods We report 13 cases of epidermoid tumors, 12 of which were located in the cerebellopontine angle (CPA), which were treated using 14 radiosurgery procedures. The inclusion criteria for radiosurgery were the presence of well-localized small tumors and/or severe associated neuralgia or facial spasms. The mean target volume ranged from 0.17 to 9.5 cm(3) with a mean of 2.85 cm(3). The lesions were treated with a mean maximum and a marginal dose of 28.2 Gy and 14.2 Gy, respectively. Results Among the 14 gamma knife procedures that were performed in 13 patients, dose planning to ensure total and partial coverage for relief from hyperactive cranial nerve dysfunction (HCND) was performed. Six cases were totally and another eight were partially covered at the dose planning. The irradiated tumors showed a minor decrease or no remarkable changes during a mean follow-up period of 86.1 months. Tumor progression requiring a second surgery was seen in two cases. The trigeminal neuralgias either improved or disappeared soon after the procedure, enabling the discontinuation of the medication. Conclusion Radiosurgery led to a dramatic improvement in HCND. In fact, the immediate cure of neuralgia after the radiosurgery was observed in several cases, even after partial coverage with radiosurgery. The interface between the tumor and the nerve was the main target. The definite mechanisms for this favorable outcome have not been verified yet, but the functional modulation by the radiosurgery could be one. Electrophysiological alteration at the interface between the tumor and nerve has been considered. When the tumors were totally covered with radiosurgery, persistent tumor control was expected. Sufficient tumor control is possible if the tumor can be covered entirely with radiosurgery. Functional modulation of trigeminal neuralgia and facial spasms can also be attained even by partial dose planning for the nerve-tumor interface.