Surgical and radiosurgical outcomes for Koos grade 3 vestibular schwannomas.

This study aimed to reveal the preferred initial treatment for Koos grade 3 vestibular schwannomas (VS). We performed a two-institutional retrospective study on 21 patients with Koos grade 3 VS undergoing resection at Yokohama Medical Center and 37 patients undergoing radiosurgery at Yokohama Rosai Hospital from 2010 to 2021. Tumor control, complications, and functional preservation were compared. The median pre-treatment volume and follow-up duration were 2845 mm3 and 57.0 months, respectively, in the resection group and 2127 mm3 and 81.7 months, respectively, in the radiosurgery group. In the resection group, 16 (76.2%) underwent gross total resection, and three patients (14.3%) experienced regrowth; however, no one required additional treatment. In the radiosurgery group, the tumor control rate was 86.5%, and three cases (8.1%) required surgical resection because of symptomatic brainstem compression. Kaplan-Meier analyses revealed that tumors with delayed continuous enlargement and large thin-walled cysts were significantly associated with poor prognostic factors (p = 0.0027, p < 0.001). The pre-radiosurgery growth rate was also associated with the volume increase (p = 0.013). Two cases (9.5%) required additional operation due to complications such as post-operative hematoma and cerebrospinal fluid leaks in the resection group, whereas temporary cranial neuropathies were observed in the radiosurgery group. Two patients (9.5%) had poor facial nerve function (House-Brackmann grading grade 3) in the resection group, while no one developed facial paresis in the radiosurgery group. Trigeminal neuropathy improved only in the resection group.Radiosurgery can be considered for the treatment of Koos grade 3 VS for functional preservation. However, resection may also be considered for patients with severe trigeminal neuropathy or a high risk of volume increments, such as large thin-walled cysts and rapid pre-treatment growth.