Likelihood-of-harm/help of Microsurgery Compared to Radiosurgery in Large Vestibular Schwannoma

Introduction: In large vestibular schwannoma (VS), radiosurgery (SRS) as a monotherapy has shown to be inferior with respect to tumor control compared to microsurgical resection (SURGERY) in long-term tumor control. However, SURGERY poses a significantly higher risk of facial palsy. Recent data also has shown that approx. 5% of SRS-treated VS can develop new-onset facial spasm (NOFS), which is often neglected in comparative analyses. We aim to re-evaluate treatment options from an epidemiological point of view applying the concepts of number-needed-to-treat/operate (NNO), number-needed-to-harm (NNH), and likelihood-of-harm/help (LHH) considering treatment-related side-effects.

Methods: This was a retrospective, dual-center cohort study. Tumor size was classified by Koos Classification. Absolute risk reduction (ARR) and risk increase (ARI) were used to derive additional estimates of treatment effectiveness, namely NNO and NNH. LHH was then calculated by a quotient of NNH/NNO to illustrate the risk-benefit-ratio of SURGERY with gross total resection (GTR). Both, facial palsy and new-onset facial spasm have been included as negative treatment-related effect in this analysis.

Results: N=843 patients treated met the inclusion criteria. The incidence of tumor recurrence was significantly higher in SRS (12%), compared to SURGERY (GTR) (3%) resulting in ARR of 8.90% and NNO of 11. At the same time, SURGERY was related to a significant risk of facial palsy resulting in an NNH of 12 (LLH=1.1). However, when NOFS was considered as a treatment-related side-effect of similar significance as facial palsy, NNH was N=46 and LHH was calculated at 4 and was favoring SURGERY as a monotherapy in large VS in this statistical model.

Conclusion : Comparing the effectiveness of two very different treatment modalities such as SURGERY and SRS remains a challenge. The Likelihood-of-harm/help (LLH)-model attempts to include the multifaceted aspects of treatment success and side-effects.