Stereotactic radiosurgery for Koos grade IV vestibular schwannoma: a multi-institutional study
Authors: Pikis Stylianos , Mantziaris Georgios , Kormath Anand Rithika , Nabeel Ahmed M. , Sheehan Darrah , Sheehan Kimball , Reda Wael A. , Tawadros Sameh R. , Abdelkarim Khaled , El-Shehaby Amr M. N. , Emad Eldin Reem , Peker Selcuk , Samanci Yavuz , Kaisman-Elbaz Tehila , Speckter Herwin , Hernández Wenceslao , Isidor Julio , Tripathi Manjul , Madan Renu , Zacharia Brad E. , Daggubati Lekhaj C. , Martínez Moreno Nuria , Martínez Álvarez Roberto , Langlois Anne-Marie , Mathieu David , Deibert Christopher P. , Sudhakar Vivek R. , Cifarelli Christopher P. , Arteaga Icaza Denisse , Cifarelli Daniel T. , Wei Zhishuo , Niranjan Ajay , Barnett Gene H. , Lunsford L. Dade , Bowden Greg N. , Sheehan Jason P. 
Published: July 2022

OBJECTIVE
Though stereotactic radiosurgery (SRS) is an established safe treatment for small- and medium-sized vestibular schwannomas (VSs), its role in the management of Koos grade IV VS is still unclear. In this retrospective multicenter study, the authors evaluated tumor control and the patient outcomes of primary, single-session SRS treatment for Koos grade IV VS.

METHODS
This study included patients treated with primary, single-session SRS for Koos grade IV VS at 10 participating centers. Only those patients presenting with non–life-threatening or incapacitating symptoms and at least 12 months of clinical and neuroimaging follow-up were eligible for inclusion. Relevant data were collected, and the Kaplan-Meier method was used to perform time-dependent analysis for post-SRS tumor control, hearing preservation, and facial nerve function preservation. Univariate and multivariate analyses were performed for outcome measures using Cox regression analysis.

RESULTS
Six hundred twenty-seven patients (344 females, median patient age 54 [IQR 22] years) treated with primary SRS were included in this study. The median tumor volume was 8.7 (IQR 5) cm3. Before SRS, serviceable hearing, facial nerve weakness (House-Brackmann grade > I), and trigeminal neuropathy were present in 205 (33%), 48 (7.7%), and 203 (32.4%) patients, respectively. The median prescription dose was 12 (IQR 1) Gy. At a median radiological follow-up of 38 (IQR 54) months, tumor control was achieved in 94.1% of patients. Early tumor expansion occurred in 67 (10.7%) patients and was associated with a loss of tumor control at the last follow-up (p = 0.001). Serviceable hearing preservation rates at the 5- and 10-year follow-ups were 65% and 44.6%, respectively. Gardner-Robertson class > 1 (p = 0.003) and cochlear dose ≥ 4 Gy (p = 0.02) were risk factors for hearing loss. Facial nerve function deterioration occurred in 19 (3.0%) patients at the last follow-up and was associated with margin doses ≥ 13 Gy (p = 0.03) and early tumor expansion (p = 0.04). Post-SRS, 33 patients developed hydrocephalus requiring shunting. Adverse radiation effects occurred in 92 patients and were managed medically or surgically in 34 and 18 cases, respectively.

CONCLUSIONS
SRS is a safe and effective method of obtaining tumor control in patients with Koos grade IV VS presenting with non–life-threatening or debilitating symptoms, especially those with surgical comorbidities that contraindicate resection. To decrease the incidence of post-SRS facial palsy, a prescription dose < 13 Gy is recommended.