Understanding Hydrocephalus and the ED Management of VP Shunts and Their Complications
Author: Ronald M. Perkin, MD, MA, Professor and Chairman, Department of Pediatrics, Brody School of Medicine at East Carolina University, Greenville, North Carolina
Peer Reviewer: Charles L. Emerman, MD, Chairman, Department of Emergency Medicine, MetroHealth Medical Center, Cleveland Clinic Foundation, Cleveland, Ohio
As technology advances, the emergency department (ED) physician frequently faces the challenges and complications rendered by new devices. Hydrocephalus formerly was a devastating condition. With advances in diagnostic modalities and shunting procedures, children with hydrocephalus now do amazingly well.
Unfortunately, not only do these children get common childhood illnesses, but they also may develop life-threatening complications from their shunting devices that have very similar clinical presentations to common childhood diseases. To effectively and efficiently manage these children, the emergency physician (EP) must have a clear understanding of the technology used and of the potential risks and complications that may develop.— The Editor
Introduction
Hydrocephalus is a pathologic condition in which there are enlarged cerebral ventricles unrelated to cerebral atrophy or dysgenesis. Hydrocephalus is dynamic; there is an active, progressive increase in ventricular volume associated with increased intraventricular pressure due to obstruction of the cerebrospinal fluid (CSF) flow or a mechanical imbalance between CSF production and absorption.
Pathophysiology and Etiologies
CSF continually is produced by the choroid plexus within the lateral, third, and fourth ventricles and as a by-product of cerebral and spinal cord metabolism. CSF formation occurs at a rate of 0.3 mL/min in adults (approximately 400-500cc/day), regardless of intra-cranial pressure (ICP), provided the choroid plexus and the brain itself are perfused.1-3 Age, body mass, and various disease states affect the rate of CSF production. Infants produce less CSF than adults, but these differences are negligible after about 1 year of age.2
The secretion of CSF by the choroid plexus is a metabolically active process involving ion pumps and enzyme systems similar to those found in the distal tubule of the kidney. CSF is indistinguishable from brain extracellular fluid, and because water and electrolytes pass freely in and out of the brain across the ependymal surfaces of the ventricular system, the brain itself is believed to be responsible for a small fraction of total CSF production.
Unlike CSF secretion, CSF reabsorption is a purely passive process driven in a linear fashion by the pressure differential between the subarachnoid space and the venous circulation, specifically, the major dural venous sinuses within the cranial cavity. Thus, the intradural compartment does not stray far from a steady state characterized by equal CSF secretion and reabsorption and an ICP within the normal range. With the rare exception of a choroid plexus papilloma (a tumor of the choroid plexus that causes excessive CSF secretion), the diseases that cause hydrocephalus do so by interfering with CSF reabsorption. A higher pressure gradient is required to drive CSF back into the venous circulation; although all but the most acutely unstable patients with hydrocephalus eventually achieve a steady state between CSF secretion and reabsorption, they do so only at an abnormally high ICP.
Hydrocephalus may be classified as congenital or acquired, communicating or noncommunicating, and intraventricular or extraventricular. The description of communicating vs noncommunicating hydrocephalus may be most helpful in understanding the etiology and treatment options for a particular child (Table 1). Noncommunicating hydrocephalus may result from blockage of any part of the ventricular system, obstructing the passage of CSF from one ventricle into another or from the ventricular system into the subarachnoid cisterns, and results in enlargement of the ventricular system proximal to the site of obstruction. For example, when the aqueduct of Sylvius is obstructed, the lateral and third ventricles enlarge, but the fourth ventricle remains normal in size.4
Table 1. Classification of Obstructive Hydrocephalus
The most common obstruction is congenital aqueductal stenosis at the aqueduct of Sylvius. This obstruction may occur as the result of a perinatal infection (e.g., toxoplasmosis, cytomegalovirus, mumps, syphilis, or meningitis) or compression and obstruction of the aqueduct by a mass (e.g., congenital aneurysm, arachnoid cyst, subdural hematoma, intraventricular or subarachnoid hemorrhage, or early neonatal brain tumors).4,5 Congenital malformations of the brain (e.g., Chiari II malformations, which commonly are associated with myelomeningocele, and Dandy-Walker malformations) also result in noncommunicating or obstructive hydrocephalus with both intra- and extraventricular blockage of CSF. Noncommunicating hydrocephalus may occur as a result of central nervous system (CNS) infections, tumors, trauma, arteriovenous malformations, or systemic bleeding disorders in older children.4,5
Communicating hydrocephalus occurs when CSF flow or absorption is blocked in the subarachnoid spaces, basilar cisterns, and the arachnoid villi. CSF may circulate freely throughout the entire ventricular system and cisterns but may not be absorbed adequately. Communicating hydrocephalus may be associated with meningitis (bacterial or viral), intraventricular hemorrhage, trauma, or a congenital malformation of the subarachnoid spaces. In communicating hydrocephalus, the lateral, third, and fourth ventricles enlarge.4
Other types of hydrocephalus can occur. For example, functional hydrocephalus is secondary to overproduction of CSF by a choroid plexus papilloma. Hydrocephalus ex vacuo is not true hydrocephalus; the ventricles are enlarged, but intraventricular pressure is not increased. The ventricular enlargement is secondary to atrophy of the brain parenchyma as evidenced by enlargement of the sulci and loss of brain tissue on radiologic evaluation and manifested over time by decreased head circumference. Normal pressure hydrocephalus is seen more often in adults and may be due to an incomplete blockage of the normal pathway for the CSF. Dementia, ataxia, and urinary incontinence are classic signs and symptoms of this condition.
The maintenance of normal intracranial pressure (ICP) is important because elevated pressures are associated with cerebral edema, cerebral ischemia, herniation syndromes, and poorer functional outcomes.
Hydrocephalus results from overproduction of CSF, which is rare; a reduction in the amount of CSF absorbed; or obstruction of CSF flow. Shunts allow the diversion of CSF to a body cavity where absorption can occur. They continue to be a mainstay of treatment to reduce the amount of CSF in the brain, decrease pressure, and therefore, minimize the potential damage to the brain parenchyma.
Incidence
The overall incidence of hydrocephalus is unknown. The incidence of infantile hydrocephalus is approximately 3 to 4 per 1000 live births, and aqueductal stenosis is responsible for approximately one-third of the cases.6 The incidence of myelomeningocele varies dramatically from region to region. In the United States, the incidence is approximately 1 per 1000 births.6 Of those children, 80% will develop hydrocephalus that requires shunting during the first year of life and is the result of either a Chiari II malformation or associated aqueductal stenosis.
Hydrocephalus is also a common complication of virtually any insult to the child’s nervous system, including intraventricular hemorrhage, brain tumors, infections, and head trauma. Roughly half of most modern pediatric neurosurgical practices comprise CSF shunting procedures.2
Clinical Presentation
Although the signs and symptoms of hydrocephalus may vary depending upon the etiology, most of the clinical manifestations are associated with increased CSF volume and ICP (Table 2). The presence or absence of an expandable cranium and the volume and compliance of cerebral tissue determine the severity of symptoms.6
Table 2. Signs and Symptoms of Increased ICP
and Progressive Hydrocephalus*
If the accumulation of excessive CSF occurs slowly, an infant or young child may be asymptomatic until the hydrocephalus is advanced. Infants are less likely to become acutely ill because the skull and sutures can expand to accommodate increasing ventricular size, thereby minimizing an elevation in ICP. Full or distended fontanels, frontal bossing, loss or delay of developmental milestones, prominent scalp veins, split sutures, and abnormally rapid head growth are common presenting signs in infancy. Poor feeding, vomiting, irritability and increased tone or hyperreflexia may be apparent, particularly in the lower extremities, as the hydrocephalus progresses. Late signs include lethargy, sixth nerve palsy, and paralysis of upward gaze (i.e., sunsetting).7
Specific signs and symptoms of increased ICP are evident in children older than 18 to 24 months with fused cranial sutures. Such symptoms include headache, nausea, vomiting, and personality changes (i.e., irritability, lethargy, and loss of interest in normal daily activities). Headaches, especially those that awaken the child or occur immediately upon awakening, strongly suggest an elevated ICP.7 Spasticity or ataxia of the lower extremities, as well as urinary incontinence, may occur. Older children may complain of vision problems because increased ICP on the second, third, or sixth cranial nerves result in extraocular muscular paresis and papilledema. Alterations in growth, sexual development, and fluid and electrolyte imbalance may occur if there is increased pressure at the site of the hypothalamus.
Prevention of hydrocephalus and brain herniation is desirable. When hydrocephalus occurs, the frontal and periventricular areas of the brain are more prone to perfusion problems. Herniation syndromes are pathological changes that can permanently damage the brain parenchyma by direct mechanical compression or from increased ICP. Subfalcine herniation occurs when the cingulate gyrus of the frontal lobe is forced across the falx to the contralateral side. Associated changes in mental status, including agitation and coma, can occur. Transtentorial herniation occurs when the midbrain is compressed and the temporal lobe is forced into the tentorial notch; resulting ipsilateral findings that may include a mydriatic and fixed pupil secondary to third cranial nerve compression. Contralateral hemiparesis secondary to cerebral peduncle compression may be seen. With posterior fossa compression, the tonsil of the cerebellum may be forced into the foramen magnum with medullary compression resulting. Bradycardia and respiratory arrest can result.
Radiologic Evaluation
Radiologic evaluation may be helpful to diagnose hydrocephalus. Computed tomography (CT) scans easily can show increased ventricular size. Frontal and temporal horn dilatation can be associated with noncommunicating hydrocephalus. Magnetic resonance imaging (MRI) (T-1 weighted images) is sensitive for periventricular edema. Posterior fossa causes of obstruction are noted better on MRI. Newer techniques to assess the flow of CSF are being refined. Hydrocephalus ex vacuo may be differentiated from true hydrocephalus by the presence of sulci on CT or MRI evaluation. Ultrasonography is most useful in the neonate when the fontanelles are open.
Treatment
Surgical treatment for hydrocephalus is directed at restoring CSF flow by either removing the obstruction to CSF flow or creating a new CSF pathway. The latter usually involves placement of a ventricular catheter or shunt to divert CSF flow to the peritoneal cavity for absorption.
Cerebrospinal Fluid Shunts
Components. CSF shunts consist typically of three parts: a ventricular catheter, a valve, and a distal catheter (Figure 1). The ventricular catheter passes from the ventricle through the cortical mantle out of the skull through a burr hole to reach the external surface of the skull, where it is joined to the inlet of the valve. There is a variety of valve designs that incorporate various mechanical mechanisms, but the purpose of each is to prevent excessive CSF drainage.1 Excessive ventricular drainage can be responsible for troublesome complications (e.g., postural headaches, subdural hemorrhage, and chronic changes in brain compliance) that promote recurrent proximal shunt failure. Most valves include a reservoir that can be punctured percutaneously with a needle for diagnostic purposes. The valve is connected to a distal catheter that carries the CSF to a body site, where it can be reabsorbed into the venous circulation at low pressure. Popular sites for CSF diversion are the peritoneal cavity, the pleural cavity, the gall bladder, the right atrium of the heart, and the internal jugular vein.
Figure 1. Typical Shunt Apparatus
Complications. The attractive feature of the CSF shunt is its almost universal applicability in the management of hydrocephalus, regardless of cause. The burden of the CSF shunt is a high rate of complications, which fall in two broad categories: infection and mechanical failure.
Infection. Infection is believed to be caused most often by contamination of the shunt at surgery.8-9 CSF fistula of the surgical wound, wound dehiscence, and skin breakdown over shunt hardware account for most of the balance of infectious complications. Consequently, most shunt infections present within three months of the surgical procedure, and almost all present within six months. Late CSF shunt infections are curiosities and probably have different mechanisms. Infection rates observed in recent, multicenter surgical trials cluster at 8% to 10% per surgical procedure.1
Mechanical failures. Mechanical failure occurs most commonly from tissue debris plugging the lumen of the shunt, but separation of components, fracture, and migration are other possibilities. Excessive CSF drainage with postural headaches or subdural hemorrhage is also a mode of mechanical failure. Both retrospective and prospective studies consistently have documented that 30% to 40% of shunts fail because of either a mechanical or an infectious basis in the first year after initial placement; an additional 15% fail in the second year.1 After two years, the failure rate drops to 1% and 7% per year, respectively.10-12 The mortality from initial shunt insertion is about 0.1%;1,10 the mortality from shunt failure is approximately 1% to 4%.13,14
Although CSF shunting has dramatically improved the prognosis for children with hydrocephalus, shunts still have inherent problems. Shunt revisions are necessary at some time in almost all children who have been treated for hydrocephalus. Most individuals require two to five revisions during childhood and adolescence.15 Shunts in children with tumors and intraventricular hemorrhage were found to have the highest rate of complications requiring revision.15 The most common complications associated with shunts include blockage (49%), infection (19%), and disconnection (13%).16 Shunt obstruction may occur as a result of chronic or acute inflammation, overgrowth of choroid plexus, accumulation of cellular debris or blood, or occlusion of either the distal or proximal end of the shunt as a result of growth. Repeat shunt failure requiring multiple revisions is a problem for some children. One study found that the interval between revisions became progressively shorter as the number of surgeries increased; it seems that the primary pathology that resulted in hydrocephalus in those children elicited a reactive inflammatory process that was perpetuated by repeat shunt procedures.15 Multiple shunt revisions are traumatic for the child and family and pose physical risk because of surgery and increased ICP; the number of revisions alone, however, has not been correlated with poor neurodevelopmental outcome.17
Third ventriculostomy is an alternative to CSF shunts. The lifelong requirement for surgical maintenance entailed in the use of CSF shunts has driven surgeons to seek alternative treatment strategies. Third ventriculostomy is a surgical opening in the floor of the third ventricle that allows CSF to escape the ventricular system, bypassing obstructive lesions downstream. Third ventriculostomy through a major craniotomy exposure originally was described more than 80 years ago, but recent technologic developments have made endoscopic performance of this procedure through a burr hole feasible and safe. Endoscopic third ventriculostomy (ETV) may be considered for patients with masses or obstructive congenital lesions in the aqueduct, in the fourth ventricle, or at its outlets. About 65% to 70% of the best candidates can avoid initial CSF shunt placement with this technique.18-20 ETV also is being attempted with varying degrees of success in other specific instances, (e.g., CSF shunt failure or infection, hydrocephalus associated with the Chiari malformation type 1, and occasional cases of communicating hydrocephalus), where it is theorized that the obstruction is within the subarachnoid spaces of the posterior fossa. Success rates for those indications are lower (i.e., 23% for neonates with IVH).21 ETV has a higher operative risk than shunt placement. Complications including subarachnoid hemorrhage, basilar artery injury, and hypothalamic/pituitary dysfunction have been reported. Mortality after the procedure has been estimated at 1%.22 Most failures of this therapy occur shortly after the procedure is performed. In one large institutional series, the durability of ETV did not seem to be any better than that of CSF shunts.23 ETV must not be considered by the physician or presented to the family as a permanent cure; patients with hydrocephalus who have undergone ETV require the same lifelong neurosurgical follow-up as patients with CSF shunts.
Recognition of CSF Shunt Complications
The challenge for the EP is the early recognition of CSF shunt failure and distinguishing it from common childhood conditions (e.g., viral respiratory and gastrointestinal syndromes, and otitis). Two nonspecific factors should heighten the pediatrician’s level of suspicion: The first is young age. Infants with shunts making sick visits to the ED are significantly more likely to have shunt failure than older patients with shunts.11 The second is the elapsed time since the most recent shunt operation. Patients making sick visits within six months of surgery are much more likely to have shunt failure than patients who have been without complications for longer than six months.11
The presentations of CSF shunt failure generally fall into one of three modes: acute ICP elevation; chronic, insidiously progressive ICP elevation; and infection. The symptoms and signs of acute ICP elevation are familiar: headache, nausea, vomiting, acute papilledema, and occasionally, VI nerve palsy. Parental descriptions of distention of scalp veins or puffiness around the eyes should not be dismissed, although the physiologic mechanisms and the findings themselves may not be obvious to the physician. Headache that awakens the patient in the early morning is suggestive, as is headache exacerbated by recumbency, straining, or exertion. Symptoms and signs associated with a chronic course of shunt failure include accelerated head growth, loss of developmental milestones or difficulty in school, and chronic papilledema or optic atrophy. In addition to fever, signs that call attention to the possibility of infection are redness and swelling at the surgical sites, drainage of pus, or, more likely, CSF from a wound, nuchal rigidity, abdominal pain, and signs of peritoneal irritation. Patients with related neurologic conditions may manifest CSF shunt failure in ways particular to those underlying conditions. The patient with epilepsy, for example, may present with an otherwise unexplained increase in seizure frequency.24 A patient with myelomeningocele may present with dysphonia, dysphagia, or disturbances of ventilatory regulation related to the underlying Chiari malformation type 2, or with progressive myelopathy related to underlying syringomyelia.
Factors specific to the shunt itself deserve consideration. Patients with pleural CSF shunts may complain of dyspnea and pleuritic pain if CSF reabsorption failure leads to a large pleural collection. Patients who have had atrial CSF shunts in place for many years are at risk for chronic pulmonary thromboembolism and cor pulmonale. Unfortunately, this condition seldom comes to attention before it is irreversible.25 Chronic, indolent infection of a ventriculoatrial shunt can lead to glomerulonephritis, so-called "shunt nephritis", on the basis of antigen-antibody complex deposition.
Physical examination of the shunt sometimes may be informative. Persistence of fluid along the course of the shunt more than two or three weeks after surgery is suspicious for a malfunction. Old shunts can become brittle and fracture, and a palpable gap may be identified between the fracture fragments. Most shunt valves include a pump mechanism for moving fluid through the shunt at the time of surgery. Sometimes attempts are made to extract diagnostic information from the behavior of the pump mechanism. Unfortunately, even in the hands of the pediatric neurosurgeon, pumping the shunt is not a reliable diagnostic test.26,27 A decision to forego further investigation of possible CSF shunt failure must never be made solely on the basis of examination of the valve.
Finally, a symptom generally not associated with shunt failure is the shuntalgia syndrome, focal discomfort at the site of the valve or, commonly, along the distal catheter in the posterior triangle of the neck. There may be associated tenderness; a hard, fibrotic sleeve of subcutaneous scar tissue may be palpable around the shunt catheter, but there is never any associated swelling, fluctuance, or redness. Shuntalgia is most common among adolescents and may be related to tethering of the shunt in the subcutaneous tissues during growth spurts. The syndrome is self-limiting, but the discomfort often is annoying and resistant to nonnarcotic analgesics. It infrequently may herald shunt fracture or separation of shunt components, therefore, neurosurgical reassessment is appropriate.
In this era of evidence-based medicine, the evaluation of the child who may have CSF shunt failure deserves to be put on a rational footing. Unfortunately, research in this area is limited; the available data are not yet applicable to routine pediatric practice.1,28 Estimates of the sensitivity and specificity of certain symptoms, signs, and diagnostic tests are available.
What most practitioners do not know, however, is the prevalence of real CSF shunt failure among those patients presenting for investigation of possible CSF shunt failure. In the jargon of evidence-based medicine, the likelihood ratio attached to some symptom, sign, or test result may be known, but the pretest odds ratio usually is not known. For example, Barnes and colleagues evaluated the clinical presentations of 53 children presenting to a hospital unit dedicated to CSF shunt management. The predictive value of the combination of nausea, vomiting, and drowsiness was high: 82% of patients with this constellation of symptoms were found to have a shunt failure.29 Because of the specialized nature of the unit, however, the high rate of prediction is unsurprising and difficult to translate into a more typical pediatric office or emergency practice, where most children presenting with similar symptoms will have alternative diagnoses.
As in so many areas of pediatric office practice, when a child with hydrocephalus makes a sick visit, the most important question is whether the presenting symptoms reflect a dangerous underlying disease process. If a firm alternative diagnosis can be established on the basis of positive evidence, no further study of the shunt is indicated, but careful observation until symptoms resolve is prudent. The question of shunt failure never is really closed until the patient is well again.
Table 3 lists diagnostic tests that may be used to assess shunt function. As is true of the symptoms and physical signs of shunt failure, these tests each have sensitivities and specificities that are lower than one might wish; there is no definitive standard. Brain imaging deserves particular mention. When a CSF shunt is functioning properly, ventricular volume decreases in comparison with the pretreatment state. When a CSF shunt fails, ventricular volume, usually but not always, increases in comparison with the symptom-free, post-treatment baseline. Brain imaging at the time of symptoms cannot be interpreted without comparison with post-treatment baseline imaging, and although previous images may be available, the changes in the appearance of the brain caused by shunt failure may be subtle or nil. Iskandar reviewed the written interpretations of brain imaging studies in an institutional series of 68 patients with CSF shunt failure confirmed by surgery and subsequent resolution of symptoms. In 24% of the interpretations there was no mention of the possibility of shunt failure.30 In another study, 16% of surgically proven shunt failures had CT scans that were unchanged from previous baseline studies.29 Pediatricians and EPs should not substitute brain imaging for neurosurgical consultation.
Table 3. Diagnostic Measures Useful
in the Evaluation of CSF Shunt Function
EPs are wise to pay attention to the observations of experienced parents. In a review of admissions for possible CSF shunt failure, parents’ opinions were found to have greater diagnostic accuracy than the opinions of referring pediatricians.31 Parents were almost as accurate as brain imaging, although both produced false negatives.
Shunt Infections
Shunt infections are a common complication described in as many as a third of the cases.32,33 Most often the infection occurs within the first few months after surgery.3 Staphylococcus epidermidis, Staphylococcus aureus and gram-negative enteric bacteria are, in order of decreasing incidence, the most common bacterial organisms identified on culture of the CSF. There is an association between the frequency of infection and the number of shunt revisions, the surgeon performing the procedure, longer operative time, children with myelomeningocele, prematurity, and age younger than 6 months.
Presentation often is insidious and may include a change in mental status, fever, irritability, malaise, or nausea; swelling or erythema around the shunt tube, if present, is a more specific sign. Tapping of the shunt may reveal an increased leukocyte count, an elevated protein level, a decreased glucose level, and a culture positive for bacteria. An accurate diagnosis can be made in almost 95% of the cases.34 Results from CSF cultures should be emphasized because the protein and glucose levels and cell count may be normal. A lumbar puncture or ventricular tap is positive less often than a tap of the VP shunt. A lumbar puncture is not advised in a child with a shunt due to the possibility of downward brain herniation and death if there is ventriculomegaly and increased ICP.
Treatment options include antibiotics with or without removal of the shunt. The highest success rates have been reported with shunt removal or externalization combined with antibiotics.33 If a child presents with shunt malfunction and infection, removal of the shunt, external ventricular drainage, and intravenous antibiotics with or without intraventricular antibiotics (depending upon CSF penetration), should be initiated.33,35 Once the CSF is sterile, the shunt should be replaced. In a child who presents with infection and a functioning shunt, it can be left in place, treated initially with antibiotics, and then replaced when the CSF is sterile. However, treatment needs to be individualized. The antibiotics should be broad spectrum and based on Gram stain results of the CSF. Commonly used intravenous antibiotics include second-generation penicillins, third-generation cephalosporins, aminoglycosides, and vancomycin.
Shunt Malfunctions
Shunt malfunction is the most common complication of CSF shunts. The risk for shunt failure is greatest in the first months following placement. The mean survival time for a ventriculoperitoneal shunt is five years; approximately 80% of patients will require a revision in 10 years. Malfunctions occur as the result of obstruction (proximal and distal), infection, over- and underdrainage, mechanical malfunction, and from shunt migration. The most common signs and symptoms of dysfunction include headache, vomiting, nausea, altered mental status, lethargy, and a general feeling of malaise. Many of these findings are age-related (Table 4). The most important caveat to remember is that in any patient with a CSF shunt, the shunt is the source of the problem until proven otherwise.
Table 4. Symptoms of Shunt Malfunction
Obstruction. Obstruction is the most common cause of shunt malfunction. Shunt obstruction may be life-threatening, and it must be recognized and treated immediately. The obstruction may occur at either the proximal end (the portion of the shunt in the ventricle) at the interposed valve, or at the distal end (usually in the peritoneum). Proximal obstruction occurs much more frequently than distal obstruction. It usually is caused by the proximal tip of the catheter becoming occluded with choroid plexus, ependymal cells, glial tissue, brain debris, fibrin, or blood, or if the tip migrates into the brain parenchyma. The valve between the proximal and distal tubing also may become blocked with brain debris or tissue colonization. Distal obstruction may result from kinking of the tubing, disconnection of the shunt tubing, migration of the catheter outside of the peritoneum, intra-abdominal infection, pseudocyst formation, or being clogged with debris. Obstruction also may be associated with an infection in almost one-third of cases.
Disconnections. Disconnections occur at any section of the shunt, but they are especially common at the sites of mobility and with patient growth. Up to 15% of shunt revisions may be attributed to disconnections of shunt components.36
Pseudocyst Formation. CSF pseudocysts also may complicate VP shunts, presenting with an expanding intra-abdominal mass, shunt malfunction, and/or signs of increasing ICP. Pseudocysts may cause acute abdominal complaints with diffuse abdo-minal tenderness, guarding, and distension, and have mimicked such serious intra-abdominal disorders as acute appendicitis with abscess formation, subphrenic abscess, and renal neoplasm.37,38
The diagnosis frequently is made at laparotomy. Abdominal radiographs may suggest a mass, with the cystic nature ascertained by abdominal ultrasound.
The treatment varies and includes percutaneous aspiration with later conversion to a ventriculoatrial shunt, surgical drainage and later VP shunt replacement, or intraoperative drainage of the cyst through the peritoneal catheter with conversion to a ventriculoatrial shunt. Occasionally, the cysts have been infected with S. aureus and required antibiotic therapy.
Catheter Migration. Migration of the distal catheter can occur and has been documented in the following areas: chest, cranium, gastrointestinal tract, scrotum, bladder, liver, rectum, umbilicus, fallopian tube, and vagina (Figure 2).3,39 With increase in height of the child, the distal end of the shunt can become dislodged. Retained shunt fragments occur more often with VP shunts that have been in place for a longer time. If the catheter breaks and there is no evidence of infection or foreign body reaction, this advocates for leaving the catheter in place.
Figure 2. Shunt Migration
Slit Ventricle Syndrome. Slit ventricle syndrome is an uncommon finding noted on CT or MRI of the brain. On radiologic examination, the ventricular system is noted to be smaller than normal, and the child may present with episodic signs of increased ICP and sluggish shunt refill, suggesting proximal shunt malfunction that may be secondary to ventricular collapse against the catheter. Proposed etiologies include decreased intracranial compliance, intermittent shunt malfunction, overdrainage of CSF, or periventricular fibrosis.38 Use of newer valves that have increased resistance during larger flow rates may help prevent overdrainage of the CSF. Treatment options include administration of diuretics or steroids, and craniectomy.
Seizures and Shunts. The percentage of children with VP shunts and seizures is as high as 48%, but there is a high association of seizures with underlying neurologic disorders.40 There is not enough direct evidence of an association between seizures and shunt surgery to warrant routine prophylaxis with antiepileptic drugs.
Seizure activity can be a presenting sign of CSF shunt malfunction.24,41 In many of these patients, it is a first-time seizure.24 Various forms of seizures may be observed: generalized tonic-clonic, focal motor, simple partial, and petit mal.24 With the onset of new seizures in a child with a shunt, an infection and/or obstruction should be excluded, then antiepileptic drugs should be considered.
Other Problems. Subdural hematomas and hygromas may be associated with low intraventricular pressure, which may be associated with damage from small veins and is more likely to occur when the ventricles are large before surgery.
Evaluation and Management
Shunt Obstruction. Patients who present with possible shunt obstruction may show signs of increased ICP, (e.g., headache, nausea, vomiting, lethargy, and papilledema). (See Figure 3.) Other presentations may be more vague and include blurred vision, back or neck pain, gait disturbances, or personality changes. Young infants may demonstrate an enlarging head, poor head control, full bulging fontanel, engorgement of head veins, Macewen’s sign (i.e., a cracked-pot sound heard on percussion over the dilated ventricles), sixth cranial nerve palsy, hyperreactive reflexes, irregular respirations with apnea, and the "setting sun sign" (upward gaze palsy). Seizures also have been noted, but their predictive value for a shunt malfunction is questionable; many children with shunts have underlying CNS disease, which may predispose them to seizures. One should evaluate these patients not only for shunt malfunction, but anticonvulsant levels as well. Patients who present with seizures as a sign of shunt malfunction usually have several other clinical signs, such as headache, vomiting, and respiratory compromise.41
The EP should involve the neurosurgeon early in the evaluation process. Headaches should be considered a sign of shunt malfunction, but it should be remembered that children with hydrocephalus are reported to have migrainous headaches twice as often and nonmigrainous headaches almost three times as often as children without hydrocephalus.42 The incidence of headaches in those children did not decrease with shunt revision and was not associated with seizures or the underlying condition causing the hydrocephalus. These headaches have been called shunt migraines and occur more often in individuals who have very small ventricles after shunting; they are thought to be due to poor brain compliance in response to physiologic variations in ICP.
Shunt malfunction can be partial or variable, depending upon cerebral blood flow, CSF production, and a child’s activity, and may result in periodic episodes of increased ICP. Children with shunts occasionally experience headaches and vomiting in the early morning after sleeping all night.2 These symptoms may be caused by temporary partial blockage of the shunt from cellular debris, inactivity, and the horizontal sleeping position, which negates the beneficial effect of gravity for ventricular drainage. These symptoms usually subside after children have been up for a few hours.
Nausea and vomiting are common clinical symptoms during childhood, often accompanying such diverse conditions as influenza, otitis media, and urinary tract infections. Diarrhea and abdominal pain also are frequent complaints in childhood. Children with hydrocephalus can be expected to have these common complaints as often as other children. When a child has mild gastrointestinal (GI) symptoms, the practitioner must consider the presence or absence of other symptoms and the history of exposure to GI illness. The diagnostic work-up should include an evaluation for shunt infection and GI disease. The primary care provider must recognize that abdominal symptoms may be the presenting symptom of peritoneal shunt malfunction or an acute condition in the abdomen in children with shunts.37
A child with a peritoneal shunt infection may have mild to moderate fever, abdominal pain, anorexia, nausea, vomiting, and diarrhea. He may guard his abdomen and be unwilling to ambulate. Swelling, redness, or inflammation along the catheter tract or at the incision site is highly suggestive of shunt infection. Results of an abdominal ultrasound and CSF cultures should help differentiate between an acute condition in the abdomen and a shunt infection. Specific signs of appendicitis can be demonstrated by a CT scan of the abdomen, but identification of an abdominal pseudocyst is more characteristic of a distal shunt infection.37 Abdominal pseudocysts may develop around the peritoneal end of the VP shunt and usually result from past or current shunt infection. A history of recent or recurrent shunt revisions also substantially increases the risk of infection.
The evaluation of patients with suspected CSF shunt obstruction begins with a complete history and physical examination. An important part of the examination is to palpate over the shunt apparatus and to determine, if possible, the type of shunt and presence of a valve. Once the valve is located, its patency is assessed. An easily depressed valve suggests there is distal patency; a rapid refill of the chamber implies that there is proximal patency as well. Studies have shown that the sensitivity of this examination was only 18% to 20% for shunt obstruction; the value of a negative pumping test (indicating patency) was only 61% to 82%, making this an unreliable sign of shunt malfunction.26
The second portion of the evaluation is to perform an imaging study that includes a shunt series or survey: a lateral radiograph of the skull and a radiograph that includes the neck, thorax, and abdomen. The purpose of this series is to ascertain the location and connections of the shunt apparatus. A head CT scan usually is done; however, it is imperative to have a prior study to evaluate the size of the patient’s ventricles. Ventriculomegaly may persist in some patients despite a functioning shunt; conversely, some patients have shunt malfunctions and high ICP despite small or unchanged ventricles on CT. The evaluating physician must remember that a negative result from a CT scan does not rule out a shunt obstruction.30
After all of the above imaging studies have been completed and the case discussed with a neurosurgeon, an attempt to aspirate fluid from the shunt should be considered only with approval of the neurosurgeon. An elevated opening pressure or the inability to withdraw CSF implies a shunt obstruction. CSF should be obtained for cell count, culture, Gram stain, and a glucose and protein assessment. Once shunt obstruction has been demonstrated, shunt revision is necessary.
If the child is clinically stable and has only mild signs of obstruction, the neurosurgeon may opt to wait 6 to 12 hours to rehydrate the patient before going to the operating room. Because decompensation may occur quickly, the child should be monitored closely in a pediatric intensive care unit, if one is available. Other medical therapies could include the administration of mannitol or furosemide. The child with suspected shunt malfunction must be kept NPO, and intravenous fluid administration must be monitored carefully. Iatrogenic hyponatremia often will have devastating consequences.43-45 The most important factor for hospital-acquired hyponatremia is the administration of hypotonic fluid.44 Administration of excessive amounts of intravenous fluids also may be a factor in the development of hyponatremia.46
Obviously, if the child becomes more obtunded or comatose, has focal neurologic findings, posturing, or autonomic instability (e.g., hypertension and bradycardia), the patient should be resuscitated following the ABCs (airway, breathing, circulation) and the revision performed immediately.
Shunt Infection. There is no characteristic combination of signs and symptoms of shunt infections. Perhaps the most important clinical aspect of identifying a shunt infection is to understand that the presentation is highly variable, and the diagnosis of shunt infection must be sought rather than simply found. Systemic signs and symptoms of infection (e.g., fever, swelling, erythema, warmth, pain, and tenderness) frequently are not present.2 If a focus of infection other than the shunt is identified, it should be treated appropriately. Children being treated for bacterial infection (e.g., otitis media, pneumonia, or streptococcal pharyngitis) should be reassessed carefully in the office or clinic 24 to 48 hours after treatment is initiated. Continued or worsening symptoms may indicate progression of the infection into bacteremia or a CNS infection caused by the increased susceptibility resulting from the shunt. The child with an indwelling CSF shunt who presents with the signs and symptoms of infection involving the intracranial space, the shunt tract, or the abdomen must be presumed to have a shunt infection until proven otherwise;2 a CBC, urinalysis, and blood cultures should be obtained and then a neurosurgeon should be consulted immediately.
Assume that a child who has a very high temperature (i.e., 40° C) and symptoms of moderate to severe illness has a shunt infection until proven otherwise. Consultation with a neurosurgeon is advised. Blood cultures for both aerobic and anaerobic organisms should be drawn, although they often are not initially positive. A CBC also is indicated, but minimal leukocytosis does not rule out shunt infection. CSF should be obtained by the neurosurgeon for culture through the shunt reservoir. Although CSF leukocytosis (i.e., 50 to 200 cells/cm3) is common with shunt infection, an infection can be present despite normal CSF cell count and protein and glucose levels. CSF eosinophilia (i.e., more than 7% of the total CSF white blood cell count) is also indicative of shunt infection.3 Shunt aspiration should be done with meticulous aseptic technique to not contaminate a sterile shunt system or introduce a second organism into an already infected shunt.
A chest radiograph and urine culture are recommended to rule out pneumonia or urinary tract infection. However, if the history and physical findings strongly suggest shunt involvement, the tests may be omitted. The neurosurgeon may prefer that all tests be performed at the hospital because hospitalization often is required to complete the evaluation and treatment process. Throughout the work-up for the source of fever, the EP should be in close communication with the primary neurosurgeon.
Conclusions
As more and more children survive previously life-threatening CNS diseases, the number of shunt-dependent children will increase. The major complications of these shunts include obstruction and infection. The signs and symptoms of obstruction range from mild (e.g., headache and nausea) to life-threatening signs of intracranial hypertension. Fever may be present in only half of those patients with shunt infections. The most important concept to remember is that in any patient with a CSF shunt, the shunt is the problem until proven otherwise. Children with CSF shunts are difficult to evaluate; EPs, pediatricians, and neurosurgeons must work together closely to allow the best possible outcome.
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With advances in diagnostic modalities and shunting procedures, children with hydrocephalus now do amazingly well. Unfortunately, not only do these children get common childhood illnesses, but they also may develop life-threatening complications from their shunting devices that have very similar clinical presentations to common childhood diseases. To effectively and efficiently manage these children, the emergency physician must have a clear understanding of the technology used and of the potential risks and complications that may develop.
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