ABSTRACT
INTRODUCTION Hydrocephalus is a condition in which imbalance of formation, flow, or reabsorption of cerebrospinal fluid (CSF) leads to excess CSF volume/pressure, which then compresses the brain substance and impairs its development and function. Based on its underlying mechanism, hydrocephalus can be classified into noncommunicating (obstructive) and communicating. All this sounds simple, but it is not, and any clinical approach (including clinical imaging) should be humble, as no universal model of hydrocephalus can explain all aspects of this condition (1). This chapter tries to state a few facts and a few concepts that are useful for interpreting the morphological patterns and the causal mechanisms of hydrocephalus, without any dogmatism. Hydrocephalus certainly is a different disease in a child with a medulloblastoma and in a demented elderly patient. Within the pediatric population, it is also very diverse, depending (among other things) on the etiology and on the way the brain responds, which itself depends on the nature and evolutivity of the pathology and on the age/plasticity of the brain.
