ABSTRACT
The most important concept to underscore as a premise to this chapter is the differential meaning of ventriculomegaly and hydrocephalus. The former is a sign, referring simply to the size of the lateral ventricle(s) that is (are) dilated, regardless of the cause. The term hydrocephalus implies an imbalance in the amount of the cerebrospinal fluid (CSF) within the ventricular system, due to overproduction (rarely) or obstruction (common). In the fetus, the only exceedingly rare cause of CSF overproduction is choroid plexus papilloma. The overwhelming majority of cases of hydrocephalus are obstructive, primarily (aqueductal stenosis) or secondarily (intraventricular hemorrhage, tumors, etc.). Following this fundamental difference between ventriculomegaly (VM) and hydrocephalus, we will address first the sign (VM) and then the pathologic condition (hydrocephalus) in the following sections.
