This chapter presents the existing data concerning the epidemiology of selected forms of hydrocephalus, concentrating on congenital and infantile hydrocephalus and idiopathic and secondary normal pressure hydrocephalus (NPH). The epidemiology of congenital and infantile hydrocephalus has been explored in several studies. Casmiro et al. based the diagnosis on absence of known causes of secondary NPH, impaired gait, and CT scans showing findings indicative of NPH. The chapter explores the epidemiology of idiopathic normal pressure hydrocephalus (iNPH) in a Norwegian county of 220000 inhabitants, by actively informing the public and professional health workers about the condition, asking for referral of suspected individuals on a broad clinical basis. The lack of universally accepted guidelines for the diagnosis of iNPH, and the lack of powerful tests to predict shunt success, probably also contribute to the relative low rate of diagnosis, and consequently, of surgery.

Cerebrospinal fluid (CSF) plays a role in homeostatic hormonal signaling, chemical buffering, circulations of nutrients, and neurodevelopment. The two lateral ventricles drain into the third ventricle through the foramina of Monro. The third ventricle subsequently drains into the fourth ventricle through the narrowest portion of the ventricular system called the cerebral aqueduct. The roof of the fourth ventricle is bounded by the vermis of the cerebellum and the fastigium. CSF production is to a degree dependent on blood perfusion. In instances of increased intracranial pressure (ICP) with subsequent decreased cerebral perfusion, there will be a decrease in CSF production. CSF flows through net bulk flow from the lateral ventricles through the foramen of Monro into the third ventricle, then on into the fourth ventricle through the cerebral aqueduct. The pathways of CSF reabsorption include the ependymal layer of the ventricular system, and endothelial layer of the brain parenchyma.

Normal pressure hydrocephalus (NPH) is characterized by the presence of ventriculomegaly associated with the triad of gait, memory, and urinary problems in the absence of a detectable cause. The characteristic clinical presentation of iNPH, however, also accompanies the insidious onset of hydrocephalus secondary to other processes, such as infection, malignancy, and hemorrhage. This chapter discusses the clinical features, evaluation, and management of secondary and/or compensated hydrocephalus. Most commonly obstruction from aneurysmal subarachnoid hemorrhage, brain malignancy, spinal malignancy, or an infectious etiology can precipitate or directly lead to hydrocephalus. Communicating hydrocephalus is thought to occur in the context of increased cerebrospinal fluid (CSF) production, such as in the case of choroid plexus tumors, or impaired CSF absorption, secondary to leptomeningeal disease or tumor bleeding. Clinical outcomes from endoscopic treatment of neurocysticercosis are better than outcomes after open surgical procedures.

This chapter describes many of the techniques and protocols that can be used to minimize the risk of shunt failure, focusing on the surgical procedure at each anatomic location for proximal and distal catheter placement. It includes the extended discussions of ventricular and lumbar proximal catheters, and peritoneal, atrial, pleural, and other distal catheters. Valves can be divided into four different categories: differential pressure valves, flow-regulated valves, antisiphon valves, and adjustable valves. Antisiphon valves are used to prevent the siphoning of cerebrospinal fluid (CSF) into the distal compartment. Antisiphon devices (ASDs) are primarily used in management of normal pressure hydrocephalus (NPH) patients in the adult population to prevent the formation of subdural hematomas and hygromas, and in the management of hydrocephalus in the pediatric population to prevent the slit ventricle syndrome and proximal catheter obstruction.