23.1 Introduction

Radiotherapy for vestibular schwannoma (VS) is rarely associated with acute adverse effects. Uncommonly, patients may develop acute transient or delayed progressive ipsilateral trigeminal neuropathy or neuralgia and facial paresis or hemispasm. If the fourth ventricle becomes compressed due to peritumoral edema or cyst formation, then hydrocephalus may also occur (Fig. 23‑1 and Fig. 23‑2 ). The latter complication rarely occurs with small-to-medium-sized tumors, and develops more frequently with tumors greater than 2.5 cm in maximum posterior fossa dimension. In contrast, progressive deterioration of hearing and vestibular function is common after radiotherapy; however, separating the direct effects of radiation and the natural course of disease is somewhat challenging. It is important for the treating physician and patient to be aware of these potential side effects to inform treatment decision making and manage posttreatment care.

23.2 Facial Nerve (CN VII) Paralysis

Modern series reporting outcomes for single-session stereotactic radiosurgery (SRS) performed with Gamma Knife (GK) have reported long-term facial nerve deficits ranging from 0 to 21% (Table 23‑1 ); however, reports of patients treated with a marginal dose of ≤ 13 Gy indicate facial nerve paralysis or hemifacial spasm in 0 to 5% of cases, with the majority of series observing <2% risk of long-term facial paresis. In one of the largest patient series reported, Lunsford and colleaguess. Literatur examined outcomes in 829 patients treated at the University of Pittsburg between 1987 and 2002. In the first 5 years of the series, patients were treated at a higher margin dose (mean, 16 Gy) resulting in 21% of patients experiencing facial nerve dysfunction at 5 years. In contrast, after reducing the margin dose to ≤ 13 Gy, facial nerve dysfunction occurred in less than 1% of cases. Similarly, Hasegawa and colleaguess. Literatur reported their experience of 440 patients with a median follow-up of 12.5 years. For patients receiving doses >13 Gy, long-term facial nerve dysfunction was experienced by 3.5% of patients, while 0% of patients treated to <13 Gy experienced deficits.

A systematic analysis of the literature found that factors affecting facial nerve function preservation following GK radiosurgery included radiation dose, tumor size, and patient age.s. Literatur Analysis of 1,908 patients from 23 published series determined facial nerve function preservation rates of 98.5% for doses ≤13 Gy and 94.7% for doses >13 Gy. Similarly, patients with tumor volumes ≤1.5 cm³ had preservation rates of 99.5% and those with tumor volumes >1.5 cm³ had a 95.5% preservation rate. Finally, patients younger than 60 years had preservation rates of 96.8%, while those older than 60 years experienced a preservation rate of 89.4%. One limitation of this study is that it did not allow for multivariable analysis to determine the impact of the various individual factors. The reader is encouraged to review Chapter 16 for a more in-depth discussion of outcomes after GK radiosurgery for VS.

While much of the early experience with radiosurgical treatment of VSs was delivered with GK, there is a growing literature for treatment outcomes for both single-session and multisession linear accelerator (LINAC)-based radiosurgery. Overall rates of facial nerve paresis for VS treated with single-session LINAC SRS range from 3.2 to 20% (Table 23‑1 ), though series that reported on patients treated with doses <13 Gy generally report deficits in less than 1% of patients.s. Literatur ^,​ s. Literatur Reports of patients treated with multisession hypofractionated or conventionally fractionated radiotherapy demonstrate facial nerve paralysis rates in the range of 0 to 4% (Table 23‑1 ). Differences in dose-fractionation regimens make direct comparison difficult across series, but there appears to be a range of well-tolerated schedules. Combs and colleaguess. Literatur reported on the outcomes of 449 patients treated at three German centers from 1990 to 2012, 291 of whom were treated with multisession conventionally fractionated radiotherapy to a median dose of 57.6 Gy. With a median follow-up of 5.6 years, only 1% of patients developed new facial nerve symptoms. Alternative dose schedules that also appear to be well tolerated include 46.8 Gy in 26 fractions,s. Literatur 50 Gy in 25 fractions,s. Literatur ^,​ s. Literatur and 54 Gy in 30 fractions.s. Literatur ^,​ s. Literatur ^,​ s. Literatur Toxicity outcomes of hypofractionated radiotherapy regimens have also been reported. In one of the largest series, Hansasuta and colleaguess. Literatur reported on 383 patients treated with CyberKnife at Stanford between 1999 and 2007. The majority of patients (90%) were treated to a dose of 18 Gy in three fractions. No patients experienced facial weakness, though 2% of patients reported facial spasm that was transient in all but one case. Alternative hypofractionated radiotherapy regimens with <3% toxicity include 25 Gy in 5 fractionss. Literatur ^,​ s. Literatur ^,​ s. Literatur and 30 Gy in 10 fractions.s. Literatur ^,​ s. Literatur Chapters 17, 18, and 19 provide further detailed discussion regarding LINCAC-based radiosurgery and conventionally fractionated radiation for treatment of VS.

Facial nerve outcomes following proton radiotherapy treatment of VS have been mixed. In the largest series reported of 88 patients treated with single-session radiosurgery using doses of 10 to 18 Gy (median, 12 Gy) (relative biological effectiveness [RBE] 1.1), Weber and colleaguess. Literatur observed new, permanent facial nerve deficits in 8.9% of patients. Similarly, Vernimmen and colleaguess. Literatur reported 9.5% of patients experiencing long-term facial nerve dysfunction after hypofractionated proton treatment to 26 Gy (RBE 1.1) in three fractions. In contrast, Bush and colleaguess. Literatur reported on the outcomes of 29 patients treated at Loma Linda University Medical Center with conventionally fractionated schedules of 54 to 60 Gy (RBE 1.1) in 30 to 33 fractions and observed no patients with long-term facial nerve dysfunction.

Transient facial nerve paresis is more common than a permanent deficit after treatment, occurring in an additional 1 to 5% of patients. Time of symptom onset varies significantly from as early as 2 months up to 2+ years, though most series report onset 3 to 6 months after radiotherapy. When reported, the decrement in facial nerve function is primarily to House–Brackmann grade II, though grade III+ dysfunction has been observed. In patients who develop new or worsening facial nerve paresis following single-session radiosurgery or multisession radiotherapy for VS, the standard management approach is a trial of high-dose steroids with varying tapering schedules depending on treatment response. The above data gathered from multiple, large series of patients treated with various radiosurgical and radiotherapy techniques support the low risk of facial nerve dysfunction following treatment of VS using modern dosing strategies.