KEY POINTS
- This retrospective study evaluated 76 treatment-naïve Koos grade III–IV vestibular schwannomas treated with stereotactic radiosurgery: 15 cystic and 61 solid tumors. Mean radiological follow-up was 34 months.
- Cystic tumors were larger at baseline, so inverse probability of treatment weighting was used to adjust for baseline differences, including tumor volume and fractionation.
- At 3–6 months, median volume change was −9.7% for cystic versus +6.8% for solid tumors (p=0.029). At 12–18 months, the corresponding changes were −31.4% versus −1.4% (p=0.031).
- The difference diminished later: beyond 24 months, median volume reduction was −79.7% for cystic versus −48.1% for solid tumors, but this was not statistically significant (p=0.064). After weighting, cystic morphology remained associated with greater early and intermediate shrinkage but not late response.
- Baseline tumor volume, rather than cystic morphology itself, was independently associated with greater reduction at the last follow-up (β −3.1, 95% CI −5.5 to −0.7; p<0.01).
- Local control was 100% in cystic tumors and 98.4% in solid tumors. No patient with a cystic tumor required subsequent surgery, repeat SRS or ventriculoperitoneal shunting.
- The study is limited by the 15-patient cystic cohort, unequal follow-up, heterogeneous radiosurgical fractionation and absence of functional outcomes such as hearing or facial nerve preservation. Residual confounding remained possible despite weighting.
CLINICAL TAKEAWAY
Selected large cystic vestibular schwannomas do not appear intrinsically resistant to radiosurgery; in this cohort, they actually shrank faster than solid tumors during the first 18 months. That supports SRS as a reasonable option in carefully selected patients without an urgent surgical indication, but the study is far too small to establish equivalence to surgery for symptoms or cranial nerve outcomes.