Practice Essentials
Hydrocephalus, a condition first described by Hippocrates, is the abnormal rise in cerebrospinal fluid (CSF) volume and, usually, pressure, that results from an imbalance of CSF production and absorption. Hydrocephalus is classified as communicating hydrocephalus and non-communicating hydrocephalus. In communicating hydrocephalus (also referred to as nonobstructive hydrocephalus), full communication between the ventricles and subarachnoid space exists. Non-communicating hydrocephalus occurs when the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles.
Normal-pressure hydrocephalus (NPH), a form of communicating hydrocephalus, may result from subarachnoid hemorrhage caused by an aneurysm rupture or a traumatic brain injury (TBI), encephalopathy, infection, tumor or complication of surgery. The increase in cerebrospinal fluid in NPH occurs slowly enough that the tissues around the ventricles compensate and the fluid pressure inside the head does not increase. The classic triad of symptoms consists of abnormal gait, urinary incontinence, and dementia. NPH can be mistaken for Alzheimer disease.
Hydrocephalus was not treated effectively until the mid-20th century, when the development of appropriate shunting materials and techniques occurred. At the beginning of the 20th century, doctors (including urologists) attempted to introduce scopes into the ventricular system. Attempts were also made to remove the choroid plexus, which generates much of the CSF, in an attempt to treat hydrocephalus.
Hydrocephalus research and treatment have advanced tremendously in the last 20 years. Today, the focus of hydrocephalus research is on pathophysiology, shunting (eg, new shunt materials and programmable valve design), and minimally invasive techniques of treatment. Areas of research include the following:
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Transplantation of tissue, such as vascularized omentum, to reestablish normal CSF could be the best method for treating communicating hydrocephalus
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Third ventriculostomies and aqueductoplasty eliminate the need for shunting in noncommunicating cases of hydrocephalus; new optics and smaller scopes are expanding this field
For patient education information, see Hydrocephalus Directory.
Pathophysiology
Hydrocephalus can be subdivided into the following three forms:
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Disorders of CSF production - This is the rarest form; choroid plexus papillomas and choroid plexus carcinomas can secrete CSF in excess of its absorption
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Disorders of CSF circulation - This form results from obstruction of the pathways of CSF circulation, which can occur at the ventricles or arachnoid villi; tumors, hemorrhages, congenital malformations (such as aqueductal stenosis), and infections can cause obstruction at either point in the pathways
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Disorders of CSF absorption - Conditions such as the superior vena cava syndrome and sinus thrombosis can interfere with CSF absorption.
Some forms of hydrocephalus cannot be classified clearly. This group includes normal-pressure hydrocephalus and pseudotumor cerebri.
Etiology
The etiology of hydrocephalus in congenital cases is unknown. Very few cases (< 2%) are inherited (X-linked hydrocephalus). The most common causes of hydrocephalus in acquired cases are tumor obstruction, [1] trauma, intracranial hemorrhage, and infection.
Up to one third of patients with a posterior fossa tumor will develop hydrocephalus. [2] Abraham et al found the risk for the development of symptomatic hydrocephalus following posterior fossa tumor surgery were increased in children younger than 6 years and those with a finding of intraventricular blood (IVB) on postoperative CT. [3]
Epidemiology
The overall incidence of hydrocephalus is unknown. When cases of spina bifida are included, congenital hydrocephalus occurs in 2-5 births per 1000. The incidence of acquired types of hydrocephalus is unknown.
Tanaka et al concluded that the incidence of idiopathic NPH was 1.4% in their study of an elderly Japanese population. [4]
Prognosis
In general, outcome is good. A typical patient should return to baseline after shunting, unless prolonged elevated intracranial pressure (ICP) or brain herniation has occurred. The neurologic function of children is optimized with shunting. Infection, especially if repeated, may affect cognitive status.
The best long-term results in the most carefully selected patients are no better than 60% in NPH. Few complete recoveries occur. Often, gait and incontinence respond to shunting, but dementia responds less frequently.
Often, various other neurologic abnormalities associated with hydrocephalus are the limiting factor in patient recovery. Examples are migrational abnormalities and postinfectious hydrocephalus.
In a study of responders and nonresponders to shunt surgery for idiopathic NPH, responders were found to have much higher preoperative pulsatile ICP than nonresponders did. [5]
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Noncommunicating obstructive hydrocephalus caused by obstruction of foramina of Luschka and Magendie. This MRI sagittal image demonstrates dilatation of lateral ventricles with stretching of corpus callosum and dilatation of fourth ventricle.
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Communicating hydrocephalus with surrounding "atrophy" and increased periventricular and deep white-matter signal on fluid-attenuated inversion recovery (FLAIR) sequences. Note that apical cuts (lower row) do not show enlargement of sulci, as is expected in generalized atrophy. Pathologic evaluation of this brain demonstrated hydrocephalus with no microvascular pathology corresponding with signal abnormality (which likely reflects transependymal exudate) and normal brain weight (indicating that sulci enlargement was due to increased subarachnoid cerebrospinal fluid [CSF] conveying pseudoatrophic brain pattern).
