Incidentally Discovered Unruptured AICA Aneurysm After Radiosurgery for Vestibular Schwannoma: A Case Report and Review of the Literature.

OBJECTIVE: This is a case report and review of the literature of aneurysm formation after stereotactic radiosurgery (SRS) in the posterior fossa. Cerebral aneurysm formation is not a commonly recognized complication of SRS. We present the first case of an unruptured anteroinferior cerebellar artery aneurysm incidentally found at surgery in a patient with trigeminal neuralgia secondary to a vestibular schwannoma (VS) first treated with Gamma Knife radiosurgery. Other cases of posterior fossa aneurysms associated with SRS and the pathogenesis of vascular injury by radiation are discussed. PATIENT: A 57-year-old woman with medically intractable severe trigeminal neuralgia secondary to a 1.4-cm VS treated with SRS 10 years previously at an outside institution. INTERVENTION: The patient underwent a left retrosigmoid craniotomy for tumor debulking. MAIN OUTCOME AND RESULTS: During resection, two small aneurysms on the tumor's ventral side arising from the main trunk of the anteroinferior cerebellar artery were encountered and treated with direct clip ligation, sparing the parent vessel. The patient did well after surgery and was discharged home on Hospital Day 4 at her neurologic baseline, with normal facial nerve function and without trigeminal pain. CONCLUSION: Although aneurysms associated with posterior fossa SRS are rare, there are at least seven reports, including the current case, in the past decade. Because the relationship between radiation and aneurysm formation is unproven and controversial, further study, especially examining long-term effects, is needed. Given the overall rarity and uncertain association between SRS and aneurysm formation, we do not recommend routine aneurysm surveillance screening in patients undergoing Gamma Knife radiosurgery for VS. Surgeons should be aware of the rare possibility of encountering an aneurysm during surgical exploration in patients with VS who fail SRS.