Long-term outcome after Gamma Knife radiosurgery for acoustic neuroma of all Koos grades: a single-center study

Abstract

OBJECTIVE The authors present long-term follow-up data on patients treated with Gamma Knife radiosurgery (GKRS) for acoustic neuroma. METHODS Six hundred eighteen patients were radiosurgically treated for acoustic neuroma between 1992 and 2016 at the Department of Neurosurgery, Medical University Vienna. Patients with neurofibromatosis and patients treated too recently to attain 1 year of follow-up were excluded from this retrospective study. Thus, data on 557 patients with spontaneous acoustic neuroma of any Koos grade are presented, as are long-term follow-up data on 426 patients with a minimum follow-up of 2 years. Patients were assessed according to the Gardner-Robertson (GR) hearing scale and the House-Brackmann facial nerve function scale, both prior to GKRS and at the times of follow-up. RESULTS Four hundred fifty-two patients (81%) were treated with radiosurgery alone and 105 patients (19%) with combined microsurgery-radiosurgery. While the combined treatment was especially favored before 2002, the percentage of cases treated with radiosurgery alone has significantly increased since then. The overall complication rate after GKRS was low and has declined significantly in the last decade. The risk of developing hydrocephalus after GKRS increased with tumor size. One case (0.2%) of malignant transformation after GKRS was diagnosed. Radiological tumor control rates of 92%, 91%, and 91% at 5, 10, and 15 years after GKRS, regardless of the Koos grade or pretreatment, were observed. The overall tumor control rate without the need for additional treatment was even higher at 98%. At the last follow-up, functional hearing was preserved in 55% of patients who had been classified with GR hearing class I or II prior to GKRS. Hearing preservation rates of 53%, 34%, and 34% at 5, 10, and 15 years after GKRS were observed. The multivariate regression model revealed that the GR hearing class prior to GKRS and the median dose to the cochlea were independent predictors of the GR class at follow-up. CONCLUSIONS In small to medium-sized spontaneous acoustic neuromas, radiosurgery should be recognized as the primary treatment at an early stage. Although minimizing the cochlear dose seems beneficial for hearing preservation, the authors, like others before, do not recommend undertreating intracanalicular tumors in favor of low cochlear doses. For larger acoustic neuromas, radiosurgery remains a reliable management option with tumor control rates similar to those for smaller acoustic neuromas; however, careful patient selection and counseling are recommended given the higher risk of side effects. Microsurgery must be considered in acoustic neuromas with significant brainstem compression or hydrocephalus.

Gamma knife surgery in the treatment of intracanalicular vestibular schwannomas

“…Equally good outcomes were reported by Iwai et al who documented an expansion of IVS in only 4% out of 25 patients subjected to low‐dose GKS. Frischer et al obtained an excellent tumor growth control rate (98%) after GKS of vestibular schwannomas representing all Koos grades. Interestingly, in the latter study, the outcomes in patients with Koos grade IV vestibular schwannomas did not differ significantly from the results for tumors with other Koos grades, among them 67 IVS …”

“…In this paper, we present the outcomes of GKS in the largest group of patients with IVS that had been examined thus far (n = 136). Previous studies included markedly smaller groups of patients with IVS, including from 10 to 67 patients . The mean age of patients subjected for gamma knife treatment was 54 years.…”

“…Previous studies included markedly smaller groups of patients with IVS, including from 10 to 67 patients. 31 The mean age of patients subjected for gamma knife treatment was 54 years. This is quite young group of patients, however for IVS, it fits in the age span presented by other authors with range of 48 to 57 years.…”

Hearing preservation after Gamma Knife radiosurgery for cerebellopontine angle meningiomas

“…The hearing preservation rate after SRS for VSs has been reported to be 50%-78%. 10,17,18,25,26,33,37,43 Several factors have been suggested to affect hearing preservation, including tumor volume, pretreatment hearing status, age, cochlear dose, brainstem cochlear nucleus dose, and marginal dose ≤ 13 Gy. 8,9,11,21,26,33,38,43,46 Similarly, we found that patients with Grade I hearing fared better regarding hearing preservation.…”

Progressive Vestibular Schwannoma following Subtotal or Near-Total Resection: Dose-Escalated versus Standard-Dose Salvage Stereotactic Radiosurgery

“…2,3 Microsurgical resection is typically preferred over observation or stereotactic radiosurgery (SRS) for large, symptomatic Koos grade IV VS since SRS does not offer immediate relief from tumor mass effect and may even transiently exacerbate symptomology from iatrogenic peritumoral edeam. [4][5][6][7][8][9] Given the complex nature of advanced VS, rates of macroscopic residual tumor following microsurgery are significantly greater compared with smaller, more easily resectable VS. 10,11 Patients with progressive residual disease following subtotal or neartotal resection are typically appropriate candidates for salvage SRS, which is commonly prescribed to a margin dose of 12 to 13 Gy, the standard radiosurgical dose for primary VS if delivered in a single session. [12][13][14][15][16][17][18] However, local control after salvage SRS appears poor; a recent prospective study demonstrated a local control rate of only 64% following salvage standard-dose SRS for residual VS progressing after subtotal and near-total resection.…”