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Failure of Cerebrospinal Fluid Shunts: Part II: Overdrainage, Loculation, and Abdominal Complications
Review Article
Failure of Cerebrospinal Fluid Shunts: Part II: Overdrainage, Loculation, and Abdominal Complications Samuel R. Browd, MD, PhD, Oren N. Gottfried, MD, Brian T. Ragel, MD, and John R. W. Kestle, MD, MSc Complications from cerebrospinal fluid shunts are common and can present with a variety of signs and symptoms. In this second part of a two-part review, shunt overdrainage, loculation of the ventricular system in patients with shunts, and abdominal complications related to ventriculoperitoneal shunts are discussed. Familiarity with these types of shunt failure is essential for neurologists and pediatricians because they are often the first to evaluate and triage these children. © 2006 by Elsevier Inc. All rights reserved. Browd S, Gottfried O, Ragel B, Kestle J. Failure of Cerebrospinal Fluid Shunts: Part II: Overdrainage, Loculation, and Abdominal Complications. Pediatr Neurol 2006;34:171-176.
Introduction Shunt failure occurs in 40-50% of patients during the first two years after shunt surgery. The most common causes are obstruction and mechanical failure, both of which were discussed in the first part of this two-part review. Here, a number of less common causes of shunt failure are reviewed: overdrainage, loculations within the ventricular system, and abdominal complications. Overdrainage Overdrainage refers to several scenarios in which a shunt is functioning properly but is removing more fluid than is necessary for that particular patient. This condition
From the Department of Neurosurgery, University of Utah, Primary Children’s Medical Center, Salt Lake City, Utah.
© 2006 by Elsevier Inc. All rights reserved. doi:10.1016/j.pediatrneurol.2005.05.021 ● 0887-8994/06/$—see front matter
can present relatively early after shunt insertion with extra-axial fluid or blood collections (subdural hematoma). More commonly, the excessive drainage occurs over a long period of time (years) resulting in small (“slit”) ventricles. Extra-axial Fluid Collections Early rapid reduction in ventricular size may result in collapse of the brain and accumulation of fluid or blood around the brain. Most commonly, benign cerebrospinal fluid collections are observed; however, subdural hematomas are possible (Fig 1). A common clinical scenario for development of an extra-axial fluid collection is in an older child who undergoes shunt insertion for large ventricles. As the ventricles decrease in size, the brain/ cerebrospinal fluid volume decreases in the cranial vault, allowing a space to develop in the subdural space. Although most practitioners have dealt with this complication of shunting, its occurrence is not common. In the randomized Shunt Design Trial, extra-axial fluid was observed in 12 of 344 (3.4%) patients [1]. Three management options are proposed for extra-axial fluid collections. First, it may be possible to manage these collections conservatively if they are small and possess no component of brain compression or herniation. A second option is to treat the overdrainage by replacing the valve with one with more resistance or inserting an anti-siphon device. The third option is to drain the extra-axial fluid collection either alone or in combination with changing the valve. Drainage may be accomplished by a burr hole and a temporary drain or via a subdural catheter that is spliced
Communications should be addressed to: Dr. Kestle; Division of Pediatric Neurosurgery; Primary Children’s Medical Center; University of Utah; 100 North Medical Drive, Suite 2400; Salt Lake City, UT 84113. E-mail: [email protected] Received December 14, 2004; accepted May 25, 2005.
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Figure 1. Axial noncontrast head computed tomograms depicting examples of shunt overdrainage with subsequent development of extra-axial fluid collections. (A) Bilateral frontoparietal hyperdense extra-axial fluid collections (arrows) consistent with acute subdural hematoma. Asterisk denotes ventricular catheter. (B) Bilateral hemispheric hypodense fluid collections consistent with either cerebrospinal fluid or chronic subdural hematoma. Asterisk denotes ventricular catheter.
into the existing shunt system below the valve. This latter system (i.e., combination intraventricular catheter and spliced subdural catheter) commonly results in reexpansion of the brain with resolution of the extra-axial fluid collections. Reexpansion occurs because of a relative pressure gradient from the ventricular system to the extra-axial fluid space resulting in brain expansion and obliteration of the subdural space. This complication is best prevented by avoidance of overdrainage through selection of appropriate valve systems; additionally, caution should be exercised in shunting an older child with large ventricles.
is also possible with lethargy and coma; fortunately, this is not common [3,4]. Although the incidence of slit ventricle syndrome is low, it accounts for a disproportionate number of shunt revisions and is a common topic in the pediatric neurosurgery literature. DiRocco et al. reported excessive drainage in less than 1% of all newly shunted patients [5]. Long-
Slit Ventricle Syndrome Children who develop very small ventricles in a delayed fashion after shunt insertion may present with symptoms of shunt malfunction with a patent shunt system. This condition has been referred to as “slit ventricle syndrome.” A consistent definition of the syndrome is lacking in the pediatric neurosurgery literature, but the syndrome is characterized by symptomatic small ventricles. Patients with slit ventricles often have had a shunt in place for several years, and radiographic studies demonstrate small ventricular size (Fig 2). Importantly, these patients complain of symptoms suggestive of shunt malfunction, such as headache, with symptoms that are usually repetitive or cyclical in nature. Intermittent headaches can be accompanied by nausea and vomiting as well as other signs and symptoms consistent with elevated intracranial pressure. An important clinical distinction in diagnosing overdrainage vs shunt malfunction is the timing of the symptoms and the patient’s position when headaches occur. In slit ventricle syndrome, the symptoms are commonly postural and patients note improvement when supine for a period of time [2]. An acute presentation
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Figure 2. Axial noncontrast head computed tomogram in a patient with “slit ventricle syndrome.” Bilateral catheters are observed in the anterior frontal horns (asterisks). The patient presented with signs of shunt failure despite the presence of small, slit-like ventricular system.
term follow up to the Shunt Design Trial demonstrated slit ventricle syndrome in only one case out of the 344 patients in the study (follow-up 1.0-5.5 years, median 3 years) [6]. An additional series of 120 patients with ventriculoatrial shunts reported an incidence of 1.8% [7]. The lower incidence documented in some studies may be related to the late onset of the syndrome after shunt insertion. Major et al. reported a mean of 6.5 years from shunt insertion to symptomatic presentation [8]. Sgouros et al. found a 10% incidence of slit ventricle syndrome among 70 patients with 16-year follow-up [9]. Of these patients, all seven required surgical shunt revision to treat symptoms of overdrainage. Conversely, Serlo et al. reviewed their experience in 141 patients and observed that slit ventricles occurred in 75 of 141 (53%) patients in their series [10]. Of the patients with radiographic findings, 52 patients (37%) had symptoms severe enough to warrant surgical management. Although the incidence of slit ventricle syndrome is variable in the literature, it is a known entity that can present years after initial shunt placement, often resulting in the need for shunt revision. Several hypotheses have been proposed regarding the pathophysiology that leads to slit ventricle syndrome. One proposed model suggests that overdrainage caused by siphoning at the distal catheter, either by gravity alone or, in the case of atrial or pleural shunts, by negative pressure at the distal end of the catheter tubing, leads to slit ventricle syndrome. It is hypothesized that overdrainage during the period of brain growth allows the brain to fill the intracranial space completely and, consequently, the ventricles remain collapsed. Overall brain compliance may be reduced and the ventricular catheter can be intermittently obstructed by the collapsed ventricular system. Obstruction may be symptomatic without a measurable change in ventricle size because of poor compensatory mechanisms. Sudden death has been occasionally reported in shunted patients with normal ventricular size demonstrated at postmortem examination. The pathophysiology underlying slit ventricle syndrome may account for these infrequent events. Relatively few shunted patients develop slit ventricle syndrome; however, these children account for a disproportionate number of shunt-related consultations and procedures. Conservative approaches are appropriate in the setting of infrequent symptoms without limitations of daily activities and include observation and medical therapy. In a review by Walker et al., 13 of the 31 patients with the clinical diagnosis of slit ventricle syndrome were managed successfully without surgical intervention [2]. Some patients respond to a scheduled period of supine rest during the day, whereas antimigraine therapy has appeared as an alternative first step in several articles and reviews [2,11,12]. Currently it is unclear whether therapeutic success with antimigraine medications is a reflection of misdiagnosis or of efficacious therapy. In theory, brain compliance is extremely poor in slit ventricle syndrome and any expan-
sion of intracranial volume can lead to worsening symptoms. Antimigraine therapy may stabilize or reduce cerebral blood flow, minimizing the intracranial volume and producing symptomatic relief. Acetazolamide has also been used in the setting of slit ventricle syndrome. If conservative measures fail to provide symptomatic relief, several surgical approaches have been described, including standard shunt revision with higher pressure valves and, more recently, implantation of programmable valve systems [2,4]. Intracranial pressure monitoring may be a helpful preoperative adjunct allowing determination of an ideal pressure setting before valve implantation. In patients with low intracranial pressure during symptomatic periods, changing the valve to one with a higher-pressure setting or adding an antisiphon device may be of benefit. Patients with high intracranial pressure during symptomatic periods are problematic and may require complex procedures such as cranial expansion or subtemporal decompression; however, recent experience suggests shunt revision should be the preferred initial treatment. Shunt revisions in these patients can be difficult, with replacement of the intraventricular catheter being particularly troublesome because of ventricular collapse. Several technical options have been suggested including: (a) dilating the ventricular system under close observation and intracranial pressure monitoring, followed by performing a third ventriculostomy [13]; and (b) using endoscopy, fluoroscopy, or stereotaxis during the revision. Regardless of the operative techniques directed towards slit ventricle syndrome patients, they remain a management dilemma and continue to represent a disproportionate number of the patients requiring multiple shunt revisions.
Loculation Loculation of the ventricular system occurs when separate, noncommunicating fluid pockets develop within the ventricles. As a result, a single shunt does not drain the entire ventricular system and the loculated fluid compartments enlarge, causing symptomatic compression of the surrounding brain. Children with a history of hemorrhage or ventriculitis are most at risk for this. Often loculations are not observed at the time of initial shunt insertion because of ventricular enlargement. Over time, the loculations may develop and mature, resulting in isolated segments of the ventricular system that are not adequately drained. A useful technique for the diagnosis of ventricular loculation and noncommunication among ventricular segments is the iohexol intraventricular dye study. Iohexol injected through an extraventricular device or shunt will diffuse through the ventricular system over 30 minutes to an hour. Loculated segments fail to reveal dye infusion, or sequestration of dye may be observed if it is injected into a catheter residing in a loculated area (Fig 3).
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eter to the existing shunt system; (2) inserting a separate shunt system in the fourth ventricle; (3) fenestrating the fourth ventricle so that it drains to the posterior fossa subarachnoid space; or (4) stenting or fenestrating the aqueduct so that the fourth ventricle drains into the third ventricle. Abdominal Complications Ascites
Figure 3. Axial, nonintravenous contrast head computed tomogram after intraventricular iohexol contrast injection. Right ventricular system was injected with iohexol via external ventricular drain. Note that the iohexol is retained in the right frontal and occipital horns. Normal, communicating ventricles would exhibit the diffusion of dye to all ventricles. Therefore the right ventricular system does not communicate with the third, or left lateral ventricle.
Loculated ventricles present with symptoms of raised intracranial pressure if the loculated compartment is of sufficient size. Treatment is not necessarily required in an asymptomatic child with a loculated compartment that is stable in size, but symptoms or progressive enlargement on imaging usually prompt treatment. The best choice is to create a communication between the loculated compartment and the rest of the ventricular system so that the child can be left with a single shunt. This procedure is usually done endoscopically [14]; rarely an open procedure is warranted. Occasionally patients with a shunt in the lateral ventricle will present with a loculated enlarged fourth ventricle. This syndrome, which is referred to as a “trapped fourth ventricle,” is presumed to occur from secondary closure of the sylvian aqueduct in the face of a functioning supratentorial shunt. As the fourth ventricle expands, patients develop irritability, nausea, vomiting, and symptoms referable to brainstem compression (such as dysconjugate gaze, poor feeding, and swallowing difficulty). Sudden deterioration with cardiorespiratory arrest and death has been reported in one patient in a series of 10 who had an enlarged fourth ventricle [15]. Imaging reveals small or slit-like lateral ventricles, a large, rounded fourth ventricle, with ventral displacement of the brainstem and loss of the posterior fossa subarachnoid spaces (Fig 4). Treatment options are (1) adding a fourth ventricle cath-
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Ascites is a rare complication that can secondarily lead to shunt malfunction. Ascites usually results from a concurrent illness such as cirrhosis, congestive heart failure, nephrosis, or disseminated carcinomatosis. Patients with ascites have abdominal discomfort, and physical findings include altered abdominal contour, fluid wave, or dullness to percussion. Patients with ascites usually have delayed symptoms of underdrainage on presentation. Radiographic diagnosis of ascites is by ultrasound or computed tomographic imaging (Fig 5). Ascitic fluid is observed throughout the peritoneal space and loculated pockets are absent. Peritoneal centesis is the diagnostic modality of choice and can provide information regarding the source of the ascites. Cultures of ascitic fluid usually fail to demonstrate the presence of organisms. Pseudocyst A pseudocyst is a loculated intra-abdominal fluid collection that develops around the peritoneal catheter (Fig 6A and B). Pseudocysts are more common than ascites, and they present as a localized abdominal mass that often enlarges to the point where there is diffuse abdominal
Figure 4. Sagittal T2-weighted magnetic resonance imaging illustrating trapped fourth ventricle syndrome. The patient was a 7-year-old male with myelomeningocele, shunted hydrocephalus, lethargy, and vomiting. The fourth ventricle is elongated and enlarged, and the brainstem is compressed. The lateral ventricles were not enlarged.
Figure 5. Axial, abdominal computed tomogram. Shunt tubing is observed entering abdomen on the right (small arrow). Note the general ascites and edematous bowel (large arrow) caused by colitis, which resulted in intra-abdominal hypertension and poor cerebrospinal fluid drainage and absorption.
tenderness. Symptoms consistent with bowel obstruction can be evident if the pseudocyst is large (Fig 6B). Some authors propose that development of a pseudocyst indicates the presence of a chronic low-grade infection; however, it is not unusual to find sterile fluid within the pseudocyst cavity when it is aspirated. It has also been proposed that children with tumors who have shunts placed are more likely to develop pseudocysts, perhaps because of elevated protein in the cerebrospinal fluid interfering with abdominal absorption. When ascites or a pseudocyst are diagnosed, the peritoneal end of the shunt is externalized and connected to a bedside drainage system. The ascites or pseudocyst fluid is drained at the same time and tested for infection. If the fluid is sterile, the shunt can be replaced and usually a ventriculoatrial system is chosen. Infected fluid requires shunt removal, external ventricular drain insertion, and antibiotics. Perforation Perforation of an abdominal viscus or the bladder is a potential complication of shunt insertion. Although rare, it is a serious complication possibly leading to abdominal infection and sepsis. It may not be recognized at the time of shunt insertion and then presents 2-4 days postoperatively with fever, bowel obstruction, or peritonitis. Clinical examination reveals marked abdominal tenderness, rebound tenderness, and occasionally abdominal guarding. Treatment for acute peritonitis is emergent and involves general surgical exploratory laparotomy to identify and repair any bowel perforation. Antibiotic therapy is instituted immediately upon the suspicion of the diagnosis. Removal of the intra-abdominal portion of the shunt is mandatory and placement of an external ventricular drain is required, until it is demonstrated that the cerebrospinal fluid is sterile, whereupon the shunt can
Figure 6. Axial, abdominal computed tomographic scans depicting examples of abdominal pseudocysts. (A) Moderately sized pseudocyst is observed on the right. Note the loops of shunt tubing within the cerebrospinal fluid collection (arrow). (B) Large pseudocyst filling the entire abdominal cavity and compressing intra-abdominal contents to pericolic gutters. Note the loops of tubing within the large cerebrospinal fluid collection (arrows).
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be replaced in the right atrium. Perforation of the bladder during trocar insertion can be prevented by draining the bladder before surgery using a straight catheter. If the bladder is perforated, urine is usually evident in the trocar lumen. The trocar should be removed immediately and a Foley catheter placed at the conclusion of the surgery. Injury to other intra-abdominal structures is possible, but while these complications are rare, they can carry considerable morbidity and mortality. Erosion of shunt tubing into a hollow viscus can occur distant from the original insertion date and present with a much more indolent course. Peritoneal tubing can erode into a hollow viscus and present, with tubing migrating out of the urethra or coming out of the anus without concurrent symptoms of peritonitis. Unlike an acute episode of peritonitis, the site of entry into the hollow viscus usually heals without intervention once the tubing is removed. Conclusions As outlined above and in the first part of this two-part review, ventriculoperitoneal shunts have many potential complications. Many are prone to failure, and these problems have defied clinical research efforts and elegant shunt designs. It is therefore important that primary care physicians, pediatricians, and neurologists are familiar with these events because they are often the first physicians to evaluate these patients. Continued vigilance and prompt management of these problems are required to optimize the quality of life for hydrocephalic patients.
We thank Kristin L. Kraus for her editorial assistance in preparing these reviews.
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References [1] Drake JM, Kestle JR, Milner R, et al. Randomized trial of cerebrospinal fluid shunt valve design in pediatric hydrocephalus. Neurosurgery 1998;43:294-303; discussion-5. [2] Walker M, Fried A, Petronio J. Diagnosis and treatment of the slit ventricle syndrome. Neurosurg Clin North Am 1993;4:707-74. [3] Epstein F, Lapras C, Wisoff J. Slit-ventricle syndrome’: Etiology and treatment. Pediatr Neurosci 1988;14:5-10. [4] Serlo W, Heikkinen E, Soukkonen A-L, von Wendt L. Classification and management of slit ventricle syndrome. Childs Nerv Syst 1985;1:194-9. [5] Di Rocco C, Marchese E, Velardi F. A survey of the first complication of newly implanted CSF shunt devices for the treatment of nontumoral hydrocephalus. Cooperative survey of the 1991-1992 Education Committee on the ISPN. Childs Nerv Syst 1994;10:321-7. [6] Kestle J, Drake J, Milner R, et al. Long-term follow-up data from the Shunt Design Trial. Pediatr Neurosurg 2000;33:230-6. [7] Vernet O, Campiche R, de Tribolet N. Long term results after ventriculo-atrial shunting in children. Childs Nerv Syst 1995;11: 176-9. [8] Major O, Fedorcsak I, Sipos L, et al. Slit-ventricle syndrome in shunt operated children. Acta Neurochir (Wien) 1994;127:69-72. [9] Sgouros S, Malluci C, Walsh AR, Hockley AD. Long-term complications of hydrocephalus. Pediatr Neurosurg 1995;23:127-32. [10] Serlo W, Saukkonen AL, Heikkinen E, von Wendt L. The incidence and management of the slit ventricle syndrome. Acta Neurochir (Wien) 1989;99:113-6. [11] Nowak TP, James HE. Migraine headaches in hydrocephalic children: A diagnostic dilemma. Childs Nerv Syst 1989;5:310-4. [12] Obana WG, Raskin NH, Cogen PH, Szymanski JA, Edwards MS. Antimigraine treatment for Slit Ventricle Syndrome. Neurosurgery 1990;27:760-3; discussion 3. [13] Reddy K, Fewer HD, West M, Hill NC. Slit ventricle syndrome with aqueduct stenosis: Third ventriculostomy as definitive treatment [see comments]. Neurosurgery 1988;23:756-9. [14] Aldana PR, Kestle JR, Brockmeyer DL, Walker ML. Results of endoscopic septal fenestration in the treatment of isolated ventricular hydrocephalus. Pediatr Neurosurg 2003;38:286-94. [15] James HE. Spectrum of the syndrome of the isolated fourth ventricle in posthemorrhagic hydrocephalus of the premature infant. Pediatr Neurosurg 1990-91;16:305-8.
Failure of Cerebrospinal Fluid Shunts: Part II: Overdrainage, Loculation, and Abdominal Complications Samuel R. Browd, MD, PhD, Oren N. Gottfried, MD, Brian T. Ragel, MD, and John R. W. Kestle, MD, MSc Complications from cerebrospinal fluid shunts are common and can present with a variety of signs and symptoms. In this second part of a two-part review, shunt overdrainage, loculation of the ventricular system in patients with shunts, and abdominal complications related to ventriculoperitoneal shunts are discussed. Familiarity with these types of shunt failure is essential for neurologists and pediatricians because they are often the first to evaluate and triage these children. © 2006 by Elsevier Inc. All rights reserved. Browd S, Gottfried O, Ragel B, Kestle J. Failure of Cerebrospinal Fluid Shunts: Part II: Overdrainage, Loculation, and Abdominal Complications. Pediatr Neurol 2006;34:171-176.
Introduction Shunt failure occurs in 40-50% of patients during the first two years after shunt surgery. The most common causes are obstruction and mechanical failure, both of which were discussed in the first part of this two-part review. Here, a number of less common causes of shunt failure are reviewed: overdrainage, loculations within the ventricular system, and abdominal complications. Overdrainage Overdrainage refers to several scenarios in which a shunt is functioning properly but is removing more fluid than is necessary for that particular patient. This condition
From the Department of Neurosurgery, University of Utah, Primary Children’s Medical Center, Salt Lake City, Utah.
© 2006 by Elsevier Inc. All rights reserved. doi:10.1016/j.pediatrneurol.2005.05.021 ● 0887-8994/06/$—see front matter
can present relatively early after shunt insertion with extra-axial fluid or blood collections (subdural hematoma). More commonly, the excessive drainage occurs over a long period of time (years) resulting in small (“slit”) ventricles. Extra-axial Fluid Collections Early rapid reduction in ventricular size may result in collapse of the brain and accumulation of fluid or blood around the brain. Most commonly, benign cerebrospinal fluid collections are observed; however, subdural hematomas are possible (Fig 1). A common clinical scenario for development of an extra-axial fluid collection is in an older child who undergoes shunt insertion for large ventricles. As the ventricles decrease in size, the brain/ cerebrospinal fluid volume decreases in the cranial vault, allowing a space to develop in the subdural space. Although most practitioners have dealt with this complication of shunting, its occurrence is not common. In the randomized Shunt Design Trial, extra-axial fluid was observed in 12 of 344 (3.4%) patients [1]. Three management options are proposed for extra-axial fluid collections. First, it may be possible to manage these collections conservatively if they are small and possess no component of brain compression or herniation. A second option is to treat the overdrainage by replacing the valve with one with more resistance or inserting an anti-siphon device. The third option is to drain the extra-axial fluid collection either alone or in combination with changing the valve. Drainage may be accomplished by a burr hole and a temporary drain or via a subdural catheter that is spliced
Communications should be addressed to: Dr. Kestle; Division of Pediatric Neurosurgery; Primary Children’s Medical Center; University of Utah; 100 North Medical Drive, Suite 2400; Salt Lake City, UT 84113. E-mail: [email protected] Received December 14, 2004; accepted May 25, 2005.
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Figure 1. Axial noncontrast head computed tomograms depicting examples of shunt overdrainage with subsequent development of extra-axial fluid collections. (A) Bilateral frontoparietal hyperdense extra-axial fluid collections (arrows) consistent with acute subdural hematoma. Asterisk denotes ventricular catheter. (B) Bilateral hemispheric hypodense fluid collections consistent with either cerebrospinal fluid or chronic subdural hematoma. Asterisk denotes ventricular catheter.
into the existing shunt system below the valve. This latter system (i.e., combination intraventricular catheter and spliced subdural catheter) commonly results in reexpansion of the brain with resolution of the extra-axial fluid collections. Reexpansion occurs because of a relative pressure gradient from the ventricular system to the extra-axial fluid space resulting in brain expansion and obliteration of the subdural space. This complication is best prevented by avoidance of overdrainage through selection of appropriate valve systems; additionally, caution should be exercised in shunting an older child with large ventricles.
is also possible with lethargy and coma; fortunately, this is not common [3,4]. Although the incidence of slit ventricle syndrome is low, it accounts for a disproportionate number of shunt revisions and is a common topic in the pediatric neurosurgery literature. DiRocco et al. reported excessive drainage in less than 1% of all newly shunted patients [5]. Long-
Slit Ventricle Syndrome Children who develop very small ventricles in a delayed fashion after shunt insertion may present with symptoms of shunt malfunction with a patent shunt system. This condition has been referred to as “slit ventricle syndrome.” A consistent definition of the syndrome is lacking in the pediatric neurosurgery literature, but the syndrome is characterized by symptomatic small ventricles. Patients with slit ventricles often have had a shunt in place for several years, and radiographic studies demonstrate small ventricular size (Fig 2). Importantly, these patients complain of symptoms suggestive of shunt malfunction, such as headache, with symptoms that are usually repetitive or cyclical in nature. Intermittent headaches can be accompanied by nausea and vomiting as well as other signs and symptoms consistent with elevated intracranial pressure. An important clinical distinction in diagnosing overdrainage vs shunt malfunction is the timing of the symptoms and the patient’s position when headaches occur. In slit ventricle syndrome, the symptoms are commonly postural and patients note improvement when supine for a period of time [2]. An acute presentation
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Figure 2. Axial noncontrast head computed tomogram in a patient with “slit ventricle syndrome.” Bilateral catheters are observed in the anterior frontal horns (asterisks). The patient presented with signs of shunt failure despite the presence of small, slit-like ventricular system.
term follow up to the Shunt Design Trial demonstrated slit ventricle syndrome in only one case out of the 344 patients in the study (follow-up 1.0-5.5 years, median 3 years) [6]. An additional series of 120 patients with ventriculoatrial shunts reported an incidence of 1.8% [7]. The lower incidence documented in some studies may be related to the late onset of the syndrome after shunt insertion. Major et al. reported a mean of 6.5 years from shunt insertion to symptomatic presentation [8]. Sgouros et al. found a 10% incidence of slit ventricle syndrome among 70 patients with 16-year follow-up [9]. Of these patients, all seven required surgical shunt revision to treat symptoms of overdrainage. Conversely, Serlo et al. reviewed their experience in 141 patients and observed that slit ventricles occurred in 75 of 141 (53%) patients in their series [10]. Of the patients with radiographic findings, 52 patients (37%) had symptoms severe enough to warrant surgical management. Although the incidence of slit ventricle syndrome is variable in the literature, it is a known entity that can present years after initial shunt placement, often resulting in the need for shunt revision. Several hypotheses have been proposed regarding the pathophysiology that leads to slit ventricle syndrome. One proposed model suggests that overdrainage caused by siphoning at the distal catheter, either by gravity alone or, in the case of atrial or pleural shunts, by negative pressure at the distal end of the catheter tubing, leads to slit ventricle syndrome. It is hypothesized that overdrainage during the period of brain growth allows the brain to fill the intracranial space completely and, consequently, the ventricles remain collapsed. Overall brain compliance may be reduced and the ventricular catheter can be intermittently obstructed by the collapsed ventricular system. Obstruction may be symptomatic without a measurable change in ventricle size because of poor compensatory mechanisms. Sudden death has been occasionally reported in shunted patients with normal ventricular size demonstrated at postmortem examination. The pathophysiology underlying slit ventricle syndrome may account for these infrequent events. Relatively few shunted patients develop slit ventricle syndrome; however, these children account for a disproportionate number of shunt-related consultations and procedures. Conservative approaches are appropriate in the setting of infrequent symptoms without limitations of daily activities and include observation and medical therapy. In a review by Walker et al., 13 of the 31 patients with the clinical diagnosis of slit ventricle syndrome were managed successfully without surgical intervention [2]. Some patients respond to a scheduled period of supine rest during the day, whereas antimigraine therapy has appeared as an alternative first step in several articles and reviews [2,11,12]. Currently it is unclear whether therapeutic success with antimigraine medications is a reflection of misdiagnosis or of efficacious therapy. In theory, brain compliance is extremely poor in slit ventricle syndrome and any expan-
sion of intracranial volume can lead to worsening symptoms. Antimigraine therapy may stabilize or reduce cerebral blood flow, minimizing the intracranial volume and producing symptomatic relief. Acetazolamide has also been used in the setting of slit ventricle syndrome. If conservative measures fail to provide symptomatic relief, several surgical approaches have been described, including standard shunt revision with higher pressure valves and, more recently, implantation of programmable valve systems [2,4]. Intracranial pressure monitoring may be a helpful preoperative adjunct allowing determination of an ideal pressure setting before valve implantation. In patients with low intracranial pressure during symptomatic periods, changing the valve to one with a higher-pressure setting or adding an antisiphon device may be of benefit. Patients with high intracranial pressure during symptomatic periods are problematic and may require complex procedures such as cranial expansion or subtemporal decompression; however, recent experience suggests shunt revision should be the preferred initial treatment. Shunt revisions in these patients can be difficult, with replacement of the intraventricular catheter being particularly troublesome because of ventricular collapse. Several technical options have been suggested including: (a) dilating the ventricular system under close observation and intracranial pressure monitoring, followed by performing a third ventriculostomy [13]; and (b) using endoscopy, fluoroscopy, or stereotaxis during the revision. Regardless of the operative techniques directed towards slit ventricle syndrome patients, they remain a management dilemma and continue to represent a disproportionate number of the patients requiring multiple shunt revisions.
Loculation Loculation of the ventricular system occurs when separate, noncommunicating fluid pockets develop within the ventricles. As a result, a single shunt does not drain the entire ventricular system and the loculated fluid compartments enlarge, causing symptomatic compression of the surrounding brain. Children with a history of hemorrhage or ventriculitis are most at risk for this. Often loculations are not observed at the time of initial shunt insertion because of ventricular enlargement. Over time, the loculations may develop and mature, resulting in isolated segments of the ventricular system that are not adequately drained. A useful technique for the diagnosis of ventricular loculation and noncommunication among ventricular segments is the iohexol intraventricular dye study. Iohexol injected through an extraventricular device or shunt will diffuse through the ventricular system over 30 minutes to an hour. Loculated segments fail to reveal dye infusion, or sequestration of dye may be observed if it is injected into a catheter residing in a loculated area (Fig 3).
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eter to the existing shunt system; (2) inserting a separate shunt system in the fourth ventricle; (3) fenestrating the fourth ventricle so that it drains to the posterior fossa subarachnoid space; or (4) stenting or fenestrating the aqueduct so that the fourth ventricle drains into the third ventricle. Abdominal Complications Ascites
Figure 3. Axial, nonintravenous contrast head computed tomogram after intraventricular iohexol contrast injection. Right ventricular system was injected with iohexol via external ventricular drain. Note that the iohexol is retained in the right frontal and occipital horns. Normal, communicating ventricles would exhibit the diffusion of dye to all ventricles. Therefore the right ventricular system does not communicate with the third, or left lateral ventricle.
Loculated ventricles present with symptoms of raised intracranial pressure if the loculated compartment is of sufficient size. Treatment is not necessarily required in an asymptomatic child with a loculated compartment that is stable in size, but symptoms or progressive enlargement on imaging usually prompt treatment. The best choice is to create a communication between the loculated compartment and the rest of the ventricular system so that the child can be left with a single shunt. This procedure is usually done endoscopically [14]; rarely an open procedure is warranted. Occasionally patients with a shunt in the lateral ventricle will present with a loculated enlarged fourth ventricle. This syndrome, which is referred to as a “trapped fourth ventricle,” is presumed to occur from secondary closure of the sylvian aqueduct in the face of a functioning supratentorial shunt. As the fourth ventricle expands, patients develop irritability, nausea, vomiting, and symptoms referable to brainstem compression (such as dysconjugate gaze, poor feeding, and swallowing difficulty). Sudden deterioration with cardiorespiratory arrest and death has been reported in one patient in a series of 10 who had an enlarged fourth ventricle [15]. Imaging reveals small or slit-like lateral ventricles, a large, rounded fourth ventricle, with ventral displacement of the brainstem and loss of the posterior fossa subarachnoid spaces (Fig 4). Treatment options are (1) adding a fourth ventricle cath-
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Ascites is a rare complication that can secondarily lead to shunt malfunction. Ascites usually results from a concurrent illness such as cirrhosis, congestive heart failure, nephrosis, or disseminated carcinomatosis. Patients with ascites have abdominal discomfort, and physical findings include altered abdominal contour, fluid wave, or dullness to percussion. Patients with ascites usually have delayed symptoms of underdrainage on presentation. Radiographic diagnosis of ascites is by ultrasound or computed tomographic imaging (Fig 5). Ascitic fluid is observed throughout the peritoneal space and loculated pockets are absent. Peritoneal centesis is the diagnostic modality of choice and can provide information regarding the source of the ascites. Cultures of ascitic fluid usually fail to demonstrate the presence of organisms. Pseudocyst A pseudocyst is a loculated intra-abdominal fluid collection that develops around the peritoneal catheter (Fig 6A and B). Pseudocysts are more common than ascites, and they present as a localized abdominal mass that often enlarges to the point where there is diffuse abdominal
Figure 4. Sagittal T2-weighted magnetic resonance imaging illustrating trapped fourth ventricle syndrome. The patient was a 7-year-old male with myelomeningocele, shunted hydrocephalus, lethargy, and vomiting. The fourth ventricle is elongated and enlarged, and the brainstem is compressed. The lateral ventricles were not enlarged.
Figure 5. Axial, abdominal computed tomogram. Shunt tubing is observed entering abdomen on the right (small arrow). Note the general ascites and edematous bowel (large arrow) caused by colitis, which resulted in intra-abdominal hypertension and poor cerebrospinal fluid drainage and absorption.
tenderness. Symptoms consistent with bowel obstruction can be evident if the pseudocyst is large (Fig 6B). Some authors propose that development of a pseudocyst indicates the presence of a chronic low-grade infection; however, it is not unusual to find sterile fluid within the pseudocyst cavity when it is aspirated. It has also been proposed that children with tumors who have shunts placed are more likely to develop pseudocysts, perhaps because of elevated protein in the cerebrospinal fluid interfering with abdominal absorption. When ascites or a pseudocyst are diagnosed, the peritoneal end of the shunt is externalized and connected to a bedside drainage system. The ascites or pseudocyst fluid is drained at the same time and tested for infection. If the fluid is sterile, the shunt can be replaced and usually a ventriculoatrial system is chosen. Infected fluid requires shunt removal, external ventricular drain insertion, and antibiotics. Perforation Perforation of an abdominal viscus or the bladder is a potential complication of shunt insertion. Although rare, it is a serious complication possibly leading to abdominal infection and sepsis. It may not be recognized at the time of shunt insertion and then presents 2-4 days postoperatively with fever, bowel obstruction, or peritonitis. Clinical examination reveals marked abdominal tenderness, rebound tenderness, and occasionally abdominal guarding. Treatment for acute peritonitis is emergent and involves general surgical exploratory laparotomy to identify and repair any bowel perforation. Antibiotic therapy is instituted immediately upon the suspicion of the diagnosis. Removal of the intra-abdominal portion of the shunt is mandatory and placement of an external ventricular drain is required, until it is demonstrated that the cerebrospinal fluid is sterile, whereupon the shunt can
Figure 6. Axial, abdominal computed tomographic scans depicting examples of abdominal pseudocysts. (A) Moderately sized pseudocyst is observed on the right. Note the loops of shunt tubing within the cerebrospinal fluid collection (arrow). (B) Large pseudocyst filling the entire abdominal cavity and compressing intra-abdominal contents to pericolic gutters. Note the loops of tubing within the large cerebrospinal fluid collection (arrows).
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be replaced in the right atrium. Perforation of the bladder during trocar insertion can be prevented by draining the bladder before surgery using a straight catheter. If the bladder is perforated, urine is usually evident in the trocar lumen. The trocar should be removed immediately and a Foley catheter placed at the conclusion of the surgery. Injury to other intra-abdominal structures is possible, but while these complications are rare, they can carry considerable morbidity and mortality. Erosion of shunt tubing into a hollow viscus can occur distant from the original insertion date and present with a much more indolent course. Peritoneal tubing can erode into a hollow viscus and present, with tubing migrating out of the urethra or coming out of the anus without concurrent symptoms of peritonitis. Unlike an acute episode of peritonitis, the site of entry into the hollow viscus usually heals without intervention once the tubing is removed. Conclusions As outlined above and in the first part of this two-part review, ventriculoperitoneal shunts have many potential complications. Many are prone to failure, and these problems have defied clinical research efforts and elegant shunt designs. It is therefore important that primary care physicians, pediatricians, and neurologists are familiar with these events because they are often the first physicians to evaluate these patients. Continued vigilance and prompt management of these problems are required to optimize the quality of life for hydrocephalic patients.
We thank Kristin L. Kraus for her editorial assistance in preparing these reviews.
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