Hydrocephalus research update--controversies in definition and classification of hydrocephalus.

Classification of hydrocephalus is the most crucial but the most complicated academic challenge within the hydrocephalus research field. The major difficulty in this challenge arises from the fact that the classification is based on almost all subjects in hydrocephalus research, i.e., definition and terminology of hydrocephalus, pathophysiology, hydrocephalus chronology, specific forms of hydrocephalus, associated congenital anomalies/syndrome and underlying conditions, diagnostic procedures for hydrocephalus, and treatment modalities in hydrocephalus. The current status of the classification of hydrocephalus in individual subgroups was reviewed and summarized from publications in the last 60 years (1950-2010), and discussed focusing on the variety of characteristics in hydrocephalus, with more and more new aspects recently disclosed not only in fetal and pediatric but also in adult hydrocephalus. A recently-reported classification of hydrocephalus, "Multi-categorical Hydrocephalus Classification" provides comprehensive coverage of the entire aspects of hydrocephalus with current important classification categories and subtypes.