BIOS-02. DIFFERENT GROWTH PATTERN OF VESTIBULAR SCHWANNOMAS IN NEUROFIBROMATOSIS TYPE 2 PATIENTS ACCORDING TO AGE

Abstract The natural growth pattern of vestibular schwannoma (VS) associated with the rare disease neurofibromatosis type 2 (NF2) has not been sufficiently elucidated, and the rationale for proactive treatment for VS in NF2 is not firmly established. This study aimed to uncover the growth pattern of VS associated with NF2 and identify risk factors for rapid growth. A total of 68 VSs from 41 NF2 patients who were diagnosed in Seoul National University Bundang Hospital from July 2006 to July 2023 were retrospectively reviewed. NF2 was clinically diagnosed according to the Manchester criteria. The mean age was 34±16 years (mean ± standard deviation) at diagnosis. The initial tumor volume was a median of 0.263 cm³ (interquartile range [IQR], 0.053-0.754 cm³), and 51 VSs exhibited serviceable hearing classified as Gardner-Robertson grade 1 or 2. Patients were followed for a median of 45 months (IQR, 30-80 months), during which the median volume increased by 0.145 cm³ (IQR, 0.020-0.783 cm³), representing an annual growth rate of 0.044 cm³/yr (IQR, 0.003-0.202 cm³) or 12.4%/yr (IQR, 2.2-27.5%). Patients younger than 25 years (15 patients with 28 VSs) had significantly smaller initial tumor sizes (0.170 cm³ [IQR, 0.031-0.339 cm³] vs. 0.510 cm³ [0.099-1.399 cm³]) but faster tumor growth rates (annual growth rate; 27.3%/yr [IQR, 11.3-81.4%/yr] vs. 4.7%/yr [IQR, 0.0-16.1%/yr]) compared to those 25 years or older (26 patients with 40 VSs). Among the 51 VSs with serviceable hearing at diagnosis, 40 VSs were followed up for more than 12 months. Among them, 13 (32.5%) experienced unserviceable hearing deterioration at a median of 58 months. The risk of hearing loss significantly increased with faster tumor growth rates. The growth rate of NF2-related VS was higher in patients under the age of 25, which may be helpful in determining indications for proactive treatments like radiosurgery for NF2-related VS.