Practice Essentials
Hydrocephalus is the abnormal rise in cerebrospinal fluid (CSF) volume and, usually, pressure that results from an imbalance of CSF production and absorption. Worldwide, more than 383,000 new cases occur annually. Hydrocephalus is classified as either communicating (nonobstructive) or noncommunicating (obstructive). In communicating hydrocephalus, as the name indicates, full communication between the ventricles and subarachnoid space exists, whereas in noncommunicating hydrocephalus, the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles. The term ventriculomegaly refers to enlargement of the ventricles.
Normal-pressure hydrocephalus (NPH) is a form of communicating hydrocephalus that typically affects older adults. Although its etiology is unknown, there are several theories. NPH may result from subarachnoid hemorrhage (SAH) caused by an aneurysm rupture or a traumatic brain injury (TBI), encephalopathy, infection, tumor, or complication of surgery. The increase in CSF noted 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 or early Parkinson disease.
Hydrocephalus ex vacuo results from brain damage, typically caused by TBI or an ischemic infarction. In these patients, the brain tissue around the ventricles shrinks, and CSF builds up in the ventricles to fill in the extra space. Although the ventricles increase in size, intracranial pressure (ICP) remains normal, and no treatment is needed.
Hydrocephalus was not treated effectively until the mid-20th century, when appropriate shunting materials and techniques were developed. At the beginning of the 20th century, surgeons attempted to introduce rigid endoscopes into the ventricular system. Attempts were also made to remove or coagulate the choroid plexus, which generates much of the CSF, in an attempt to treat hydrocephalus.
Over the past several decades, research into hydrocephalus and its treatment has yielded major advances. Current research efforts are focused on pathophysiology, shunting (eg, new shunt materials and programmable valve design), and minimally invasive treatment techniques. Areas being investigated include the following:
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Transplantation of tissue (eg, vascularized omentum) to reestablish normal CSF could be the best method for treating communicating hydrocephalus
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Third ventriculostomy and aqueductoplasty could eliminate the need for shunting in cases of noncommunicating hydrocephalus, thanks to advances in optics and the development of smaller neuroendoscopes [1]
Pathophysiology
Hydrocephalus can be subdivided into the following three pathophysiologic types:
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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. Such forms include NPH and idiopathic intracranial hypertension (IIH; also referred to as pseudotumor cerebri).
Etiology
Hydrocephalus may be congenital or acquired.
Congenital hydrocephalus is related to a combination of genetic and environmental factors during fetal development. The most common causes of congenital hydrocephalus are spina bifida and other neural tube defects, narrowing of silvian aqueducts between the third and fourth ventricles (aqueductal stenosis), complications of premature birth (eg, intraventricular hemorrhage [2] [IVH]), and infections during pregnancy (eg, rubella or toxoplasmosis) that can cause inflammation in fetal brain tissue. Very few cases (< 2%) are inherited (X-linked hydrocephalus).
Acquired hydrocephalus can develop at any point after birth and can affect people of all ages. The most common causes of acquired hydrocephalus include TBI, intracranial hemorrhage (ie, SAH), brain tumors, [3] and infections (eg, meningitis or ventriculitis).
As many as one third of patients with a posterior fossa tumor will develop hydrocephalus. [4] Abraham et al found that the risk of symptomatic hydrocephalus developing after posterior fossa tumor surgery was increased in children younger than 6 years and in those with a finding of intraventricular blood on postoperative computed tomography (CT). [5]
Epidemiology
The overall incidence of hydrocephalus is unknown. When cases of spina bifida are included, congenital hydrocephalus occurs at a rate of 2-5 per 1000 births. 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. [6]
Prognosis
In general, outcomes after neurosurgery for hydrocephalus are good. A typical patient should return to baseline after shunting, unless prolonged elevated 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.
Frequently, 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 had. [7]
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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).
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CT scan of a 55-year-old male who presented with progressive decline of his cognitive functions, severe headaches, unstable gait, and lethargy. He was treated with placement of a ventriculoperitoneal shunt. Following the shunt placement, he showed a significant neurological improvement.
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CT scan of a 76-year-old female with NPH who underwent placement of a ventriculoperitoneal shunt. Approximately 10 months postop, she developed a large pseudocyst at the catheter tip. This was treated by laparoscopic fenestration of the pseudocyst and repositioning of the catheter above the liver.
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CT scan of a 79-year-old male status post VP shunt. Approximately a week postop, he suffered a minor trauma and developed a large acute subdural hematoma, requiring surgical evacuation. His initial routine postop CT was unremarkable.
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Postoperative CT scan of a female with NPH who developed a subdural hygroma 6 weeks following a VP shunt. Her shunt was reprogramed to a higher pressure setting with good results.
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Catheter migration and erosion through the skin in an elderly patient with NPH.
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Ventricular catheters used for the treatment of hydrocephalus. Standard ventricular catheter (above) and antibiotic-coated (Bactiseal) ventricular catheter (below).
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Different programmers used for setting up and adjusting hydrocephalus shunts, including the Certas programmer (Integra Lifesciences) (above on left), the Strata programmer (Medronic) (below on left), and the Hakim programmer (Codman) (on right).
