22.2.1 Tumor Control

Due to current management paradigms, the majority of data available on SRS for vestibular schwannomas using contemporary dosing schedules exist for tumors less than 3 cm in diameter. Since some patients with larger tumors may be medically unfit for surgery and have been treated with SRS, several groups have recently been able to report the results of SRS on tumors greater than 3 cm.s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur ^,​ s. Literatur Tumor control rates in this cohort at 5 years using Kaplan–Meier analyses have ranged from 82 to 92% (Table 22‑1 ).s. Literatur ^,​ s. Literatur ^,​ s. Literatur These rates are lower than those typically reported for SRS-treated patients with tumors ≤ 3 cm in diameter, which are frequently above 95% at 5 years in large series.s. Literatur

Complicating comparative analyses between the outcomes of SRS for small and large vestibular schwannomas is the heterogeneity of the data available. For example, nearly every study on large tumors uses a different threshold to define such lesions (Table 22‑1 ). Outcome data are similarly limited as several studies on large tumors do not perform survival analyses to define tumor control.s. Literatur ^,​ s. Literatur ^,​ s. Literatur Furthermore, the length of follow-up for these studies is typically shorter than reported in studies on smaller tumors. As post-SRS tumor growth can occur up to 6 years after treatment, long-term follow-up is critical.s. Literatur

Some larger studies that have included single institution data on the treatment outcomes of both small and large tumors allow for a more controlled comparison. One such study by Hasegawa and colleagues reported the growth outcomes of Gamma Knife radiosurgery (GKRS) in 427 patients with vestibular schwannomas, including 64 patients with tumors ≥ 10 cm³ (e.g., equivalent to a 2.7-cm-diameter sphere).s. Literatur Progression-free survival (PFS) in the smaller tumor group at 5 and 10 years was 95 and 94%, respectively, while PFS in the larger tumor group was 79 and 77%, respectively. This was statistically significant by univariate (p < 0.0001), but not multivariate (p = 0.17) analysis. However, tumor size by Koos grade was significant on multivariate analysis (p < 0.0001), confirming the relationship between size and outcome. A recent study at the University of Virginia has directly compared the outcomes of GKRS for small to medium tumors (diameter ≤ 3 cm) with those of large tumors (diameter > 3 cm) using a 2:1 matched cohort design.s. Literatur This study revealed an actuarial PFS in the smaller tumor group at 3 and 5 years of 97 and 90%, respectively, while PFS in the larger tumor group was 95 and 82%, respectively (Fig. 22‑2 ).

22.3.1 Comparison with Microsurgery

To determine the relative indications for SRS for vestibular schwannomas, it is important to understand the outcomes of the alternative therapies including microsurgery. Comparative, single-institution studies between SRS and microsurgery in small tumors (<3 cm in diameter) have shown that SRS has a favorable risk–benefit profile when compared with microsurgery.s. Literatur ^,​ s. Literatur ^,​ s. Literatur A similar comparative study for large vestibular schwannomas has not been reported to date. Numerous studies have analyzed the outcomes of microsurgery for large vestibular schwannomas alone, which allows us to understand the relative utility of this therapy. A recent systematic review of microsurgery for vestibular schwannomas has enumerated the risks of microsurgery based on size and approach.s. Literatur With surgery for lesions greater than 3 cm, a retrosigmoid approach resulted in hearing loss in 72% of patients (91 of 127) with serviceable hearing. Facial nerve dysfunction was experienced in 36% of patients (278 of 783). While the rate of other cranial neuropathy was quite low, other complications such as CSF leak and infection may also occur.

Another option for treatment of large vestibular schwannomas is planned subtotal resection followed by SRS. A retrospective analysis of 50 patients treated with this paradigm was recently published by van de Langenberg and colleagues.s. Literatur They found that tumor control was maintained in 90% of patients at last follow-up (median, 33.8 months). Of two patients with preoperative serviceable hearing who underwent a retrosigmoid approach, one maintained useful hearing. Facial nerve function was impaired in nine patients (18%) after treatment, with three patients (6%) having House–Brackmann grade III function or worse. No patient experienced trigeminal neuropathy. Complications included hematoma (two patients, 4%), hydrocephalus (two patients, 4%), lower cranial nerve dysfunction requiring gastronomy tube placement (one patient, 2%), and hemiparesis (one patient, 2%). Overall, this group experienced similar outcomes compared with the group that underwent SRS alone at the same institution (Table 22‑1 , Table 22‑2 ), despite a significantly larger mean tumor volume (14.9 vs. 8.8 cm³).s. Literatur This result, and specifically the requirement for postoperative SRS, must be balanced against the natural history of residual tumor after microsurgery for vestibular schwannomas. Recently, the Gruppo Otologico retrospectively analyzed the behavior of residual tumor after near-total (<2% of tumor remaining) and subtotal (2–5% of tumor remaining) resections.s. Literatur Among 111 patients (mean follow-up, 45.4 months), they reported a 5-year PFS of 92%. Specifically, among the 38 patients with subtotal resection, 7 (18%) experienced regrowth. Based on this result, they proposed that patients with subtotal resections should be followed for a period of 7 to 10 years postoperatively until regrowth is noted. For partial resections (>5% of tumor remaining), they advocated second-stage surgery when possible.