Implications of Tumor Size on Auditory Brainstem Implant Performance

Introduction: In adult populations, an ABI is most commonly performed in the context of neurofibromatosis type 2 (NF2). Tumor size has demonstrated mixed results in the literature for impacting ABI performance. Study variation in methodology and exclusion criteria of poor performers may have historically underappreciated the impact of larger tumor size on ABI performance. We sought to better understand the implications of tumor size on ABI Categories of Auditory Performance (CAP) score to facilitate more precise patient counselling Methods: Patients >18yo that underwent ABI placement between the years 2009–2023 were included. Patients with prior surgical resection were excluded to reduce the potential of previous cochlear nucleus trauma confounding results. Ipsilateral tumor volume was measured from the pre-operative MRI, and primary endpoint was one-year CAP score. Results: Fourteen patients were included for analysis, with an average age of 35.3 years. The average pre-operative ipsilateral tumor volume was 22.8cm3 (stdev 22.4 cm3). The average post-operative CAP score was 2.7 (stdev 2). A negative association was found between ipsilateral tumor size prior to treatment and CAP score (slope = -0.058, p = 0.010) utilizing a linear regression model. The model accounted for 43.7% of the variance in outcome (r2=0.437, adjusted R2=0.390), with a significant overall model fit (F(1,12)=9.31, p = 0.010). Conclusion: Increased tumor size has a negative correlation with ultimate ABI performance. There were patients in this study with larger tumor size that still benefited from ABI placement. While larger tumor size should not be a contraindication for ABI placement, understanding the role tumor size can have on performance variation can serve to improve tumor management strategies and pre-operative counselling. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany