QOL-59. CEREBELLAR MUTISM SYNDROME AND THE SURGICAL RISK FACTORS: A PROSPECTIVE MULTICENTRE STUDY OF 500 PATIENTS UNDERGOING TUMOUR SURGERY IN THE POSTERIOR FOSSA

Abstract OBJECTIVE Cerebellar mutism syndrome (CMS) is a severe neurological complication of tumour surgery in the posterior fossa in childhood. The incidence is reported between 8 and 39%, where CMS sets in within days of surgery and resolves within months, yet long-term sequelae are seen in most patients. This prospective cohort study investigates the course of CMS and the surgical cause of the syndrome. POPULATION AND METHODS We included 500 children with a tumour in the posterior fossa with planned surgery or open biopsy. Enrolment was conducted between 2014 and 2020 in 26 centres in ten European countries. Speech, neurological symptoms and surgical procedure were registered in predefined standardized forms pre-operatively and at three post-operative follow-ups within one year. PRELIMINARY RESULTS A total of 426 children underwent primary surgery and were eligible for analyses. CMS occurred in 56 patients (13.1%) one day (median; IQR: 0–2 days) after surgery and resolved within 38 days (median; IQR: 4–52 days). Another 58 patients (13.6%) had less severe speech impairment. Mutism was associated with lower age (OR: 0.91 [95%CI: 0.85;0.98, p=0.014]), medulloblastoma (OR: 2.5 [95%CI: 1.4;4.7, p=0.0036]) and ATRT (OR: 12.9 [95%CI: 3.4;51.9, p=0.00018]) and tumour location in the fourth ventricle (OR: 4.0 [95%CI: 2.3;7.2, p<0.0001]). Preliminary multivariate analyses revealed no significant association between mutism and surgical access. CONCLUSION CMS is a common complication predominantly seen in younger children after tumour surgery for a medulloblastoma or ATRT in the fourth ventricle. The incidence is not related to the surgical access in this study population.