Introduction

Hydrocephalus is a common neurological condition characterized by impairment of cerebrospinal fluid (CSF) flow with subsequent enlargement of CSF-containing ventricular cavities in the brain. CSF absorption occurs through arachnoid villi into venous sinuses and along cranial and spinal nerves into lymphatics. Enlarging ventricles damage the surrounding brain tissue. In children, hydrocephalus is associated with mental retardation, physical disability, and impaired growth. The pathogenesis of brain dysfunction includes alterations in the chemical environment of brain, chronic ischemia in white matter, and physical damage to axons with ultimate disconnection of neurons. Hydrocephalus is the second most frequent congenital malformation (after spina bifida) of the nervous system, occurring in 5–6 per 10 000 live births. It also develops in 80% of patients with spina bifida, and 15% of premature (< 30 weeks) infants following intraventricular hemorrhage. Hydrocephalus can develop later in childhood or adulthood as a consequence of brain tumors, meningitis, brain injury, or subarachnoid hemorrhage.

For detailed discussions of the pathology of hydrocephalus see previous reviews (references 2 and 3). Briefly summarized, the ependyma lining the ventricles is damaged. In the subependymal layer, reactive gliosis is almost always observed and mitotic activity occurs among subependymal cells. Hydrocephalus can cause reduction in cerebral blood flow and alterations in oxidative metabolism in subcortical regions where white-matter axons and myelin are the main target of damage in hydrocephalus. Imaging studies indicate that the brain is edematous in the periventricular region.