Classification Systems in Neurosurgery

Classification systems abound in the neurosurgical literature. The classification systems themselves, however, have not been systematically classified, and limited guidance is available informing the development of such systems. Some are purely qualitative, and others have quantitative features. Some are purely descriptive, some are explicitly prescriptive in informing treatment, and yet others are predictive or prognostic. In this chapter, we present an initial effort to compile and organize the neurosurgical classification systems in contemporary use and to classify them according to type as well as according to several criteria pertaining to their practical utility. We address features such as consistency, inter-rater reliability, internal validity, external validation, strength of evidence, and generalizability. Our search space was the full text of the current (eighth) edition of Youmans & Winn Neurological Surgery. This comprehensive and collaboratively written and edited textbook of neurosurgery was considered to represent international expert opinion across neurosurgical subspecialties as of 2021. We present the complete list of 489 classification and staging systems, grading and scoring systems, and clinical scales as a reference for readers, cross-referenced into the chapters of the current edition, and annotated with bibliographic information and according to classification type. Of the identified classification systems, 301 (62%) are purely descriptive, 36 (7%) are prescriptive, 120 (25%) are prognostic, and 31 (6%) are comprehensive (descriptive, predictive, and prognostic). We also discuss limitations of this classification effort as well as implications for future refinements.