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BackgroundThe most widely used classifications of adverse events (AE) in surgical neurology assign a grade to AE that depends on the therapy used to treat them or on new neurologic deficits. Both concepts have substantial shortcomings in grading AE severity. We present a novel multidimensional approach to this challenge and aim at validating the new grading system.MethodsThe new Therapy-Disability-Neurology (TDN) grading system classifies AE into five grades, depending on the associated therapy, disability, and neurologic deficits. We conducted a two-center study on 6071 interventions covering the whole neurosurgical spectrum with data prospectively recorded between January 2013 and September 2019 at the University Hospital Zurich (USZ) and at the Fondazione IRCCS Istituto Neurologico Carlo Besta (FINCB).FindingsUsing data from USZ, a positive correlation was found between the severity of AE and the length of hospital stay (LOS) as well as treatment cost. Each grade was associated with a greater deterioration of the Karnofsky Performance Status Scale (KPS) at discharge and at follow-up. Additionally, there was a correlation between the severity of AE and absolute KPS values. When using the same methods on an external validation cohort from FINCB, correlations between the grade of AE, LOS, and KPS at discharge were even more pronounced.InterpretationOur results suggest that the TDN grade is consistent with clinical and economic repercussions of AE and thus reflects AE severity. It is objective, practical, easily interpreted, and enables comparison between different medical centers. The TDN grade will constitute an important step forward towards a more precise and standardized documentation of AE and ultimately lead to a more critical and patient-centered appraisal of process and outcome measures in surgical neurology.FundingNone.