Evaluating growth trends of residual sporadic vestibular schwannomas: a systematic review and meta-analysis.

BACKGROUND: Gross total resection remains the gold-standard approach for vestibular schwannomas (VS) when surgery is indicated. In select cases, incomplete resection (IR) becomes a desired alternative to preserve the facial nerve function and the patient's quality of life. While a lot of earlier studies described incompletely resected sporadic VSs as dormant, more recent studies reported a higher growth rate following IR, therefore an evaluation of the residual VS growth rates could have important implications for the follow-up treatment protocols and provide relevant information for neurosurgeons, neuro-otologists, neuropathologists, and radiologists. Although prognostic factors predicting preoperative VS growth have been previously investigated, these factors have not been investigated following IR. Our review aims to examine the growth rate of residual sporadic VS following IR and to examine variables associated with the regrowth of residual VS. METHODS: The review was conducted in accordance with the PRISMA guidelines. Six databases (MEDLINE (Ovid), Embase (Ovid), CINAHL Plus (EBSCO), Cochrane Central Register of Controlled Trials (CENTRAL), WHO International Clinical Trials Registry Platform and UK Clinical Trials Gateway (WHO ICTRP) were searched. Full-text articles analysing growth rates in at least ten patients who had residual VS after IR were assessed. We conducted a meta-analysis using a random-effects model via RevMan. RESULTS: 14 studies totalling 849 patients were included in the analysis. The mean planimetric growth rate was 1.57 mm/year (range 0.16-3.81 mm/year). The mean volumetric growth rate was 281.725 mm3/year (range 17.9-530.0 mm3/year). Age, sex, pre-operative tumour size/volume, cystic tumour sub-type, MIB-1 index, and intracanalicular tumour location were not associated with residual growth. Residual tumour size/volume was statistically significant to growth (OR = 0.65, 95% CI 0.47-0.90, p = 0.01). Radiological re-growth occurred in an average of 26.6% of cases (range 0-54.5%). CONCLUSION: From our analysis, only the residual tumour volume/size was associated with residual VS growth. Therefore, close postoperative surveillance for the first year, followed by an annual MRI scan for at least 5 years, and subsequently extended interval surveillance remains of utmost importance to monitor disease progression and provide timely surgical and adjuvant interventions. Our study shows that future work should be aimed at molecular and histological characteristics of residual VSs to aid prognostic understanding of growth.