This book provides a pathological alteration of neurons and glial cells in congenital hydrocephalus and Arnold Chiari Malformation examined by means of transmission electron microscopy using cortical biopsis of infant patients taken during neurosurgical treatment and immediately fixed in the surgical room to avoid delayed fixation artifacts and postmortem changes. We have described the pathological changes of nerve cell organelles, immature synapses, synaptic plasticity and synaptic degeneration, neuroglial cells and extracellular space. We have systematically related the submicroscopic findings and the pathogenic and pathophysiological mechanisms involved in hydrocephalic edema and intracranial hypertension.