Long-term follow-up after stereotactic radiosurgery of intracanalicular acoustic neurinoma

Background: The management of solely intracanalicular acoustic neurinoma (iAN) includes observation, microsurgical resection and radiation therapy. Treatment goals are long-term tumor control, hearing preservation and concurrently low side-effects. Stereotactic radiosurgery (SRS) has evolved as an alternative first-line treatment for small AN. Here we report about the long-term follow-up of a unique cohort of patients with iAN after LINAC or Cyberknife (R) based SRS. Methods: In this single center retrospective analysis, we included all patients with iAN who underwent single session LINAC or Cyberknife (R) based SRS between 1993 and 2015, and who had a minimum follow-up period of six weeks. Patient data were analyzed in terms of radiological and clinical tumor control (no further treatment necessary), subjective preservation of serviceable hearing, objective change in pure tone averages (PTA), and adverse events rated by the Common Terminology Criteria for Adverse Events (CTCAE; v4.03). Results: Forty-nine patients (f/m= 21/28, median age 54 +/- 12, range 20-77 years) were identified. Mean tumor volumes were 0.24 +/- 0.12 cm(3) (range, 0.1-0.68 cm(3)), the mean marginal dose was 12.6 +/- 0.6 Gy (range, 11.0-14.0 Gy) and the prescription isodose was 75 +/- 7.4% (range, 47-86%). Mean follow-up time was 65 months (range, 4-239 months). Radiological tumor control was 100% during further follow-up. 17 (35%) out of 49 patients had lost serviceable hearing prior to SRS. Those with preserved serviceable hearing remained stable in 78% (n = 25/32) at the last follow-up (LFU). The median PTA (n = 16) increased from 25.6 dB prior to SRS to 43.8 dB at LFU. Mild adverse events were observed temporarily in two patients (4%): one with CTCAE grade 1 facial nerve disorder after 3 months, resolving three months later, and one with CTCAE grade 2 facial muscle weakness resolving after 12 months. Three patients described permanent mild symptoms CTCAE grade 1 without limiting daily life (facial weakness n = 1, vertigo n = 2). Conclusion: SRS for iAN shows long-term reliable tumor control with a high rate of hearing preservation without considerable permanent side effects, and can be proposed as a safe and effective treatment alternative to microsurgical resection.