Definition and Epidemiology of Hydrocephalus

Hydrocephalus is one of the more common neurologic sequelae following insult to the central nervous system. It can be congenital or acquired. The incidence of congenital hydrocephalus has been estimated to be 0.48 cases per 1000 live births,¹ whereas the incidence of neonatal hydrocephalus is 3 to 5 cases per 1000 live births.² Table 54-1 lists common causes of pediatric hydrocephalus.³ Acquired causes of hydrocephalus include postintraventricular hemorrhage hydrocephalus, brain tumors, infections, and head injury.³ An estimated 33,000 shunts are placed in patients of all ages annually in the United States, with an estimated shunt prevalence of more than 56,000 in children younger than 18 years.⁴ In the United States, shunt placement accounts for 38,200 to 39,900 hospital admissions and 3.1% of all pediatric hospital charges ($1.4 billion to $2.0 billion).⁵ Hydrocephalus has not been clearly defined but represents a disparity between production and absorption of cerebrospinal fluid (CSF), resulting in raised intracranial pressure with or without ventricular dilatation.

Table 54-1 Common Causes of Hydrocephalus in 344 Pediatric Patients³

Clinical and Radiologic Features

The diagnosis of hydrocephalus is based on clinical features, radiologic appearances, and occasionally invasive intracranial pressure recordings. As seen in Table 54-2,³ children most commonly present with symptoms of irritability, delayed development, and vomiting. For infants, examination often reveals an increasing head circumference and a bulging fontanelle. Seizures are an uncommon presentation. Papilledema, when present, is highly suggestive of raised intracranial pressure. Papilledema is not particularly sensitive for acute raised intracranial pressure but is specific. If seen, it is highly suggestive of raised intracranial pressure; however, it has been shown to be absent in 86% of patient with shunt blockage.⁶ Sixth nerve palsy or loss of upward gaze may be a false localizing sign indicative of raised intracranial pressure.

Table 54-2 Presenting Clinical Features of Hydrocephalus in Pediatric Patients³

Imaging that is commonly used in the primary assessment of a child with suspected hydrocephalus includes ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI). The aim of imaging is to assist in the diagnosis and the etiology of hydrocephalus. MRI provides superior resolution to other imaging modalities and thus is useful when assessing the etiology of hydrocephalus. In addition, T2-weighted sequences such as fast imaging employing steady-state acquisition (FIESTA) and time-spatial labeling inversion pulse sequences⁷ provide information of fluid movement within the ventricles.

Ultrasound through the open anterior fontanelle is quite practical in critically ill premature infants with intraventricular hemorrhage or in patients with myelomeningocele in whom the cause is not in doubt. In patients with mild ventricular enlargement, evidence of transependymal flow of CSF usually suggests that the process is more acute. Other signs of progressive hydrocephalus—enlargement of the temporal horns, dilation of the third ventricle, and effacement of the sulci—are not absolutely specific. In cases in which there is doubt, careful observation with serial images, rather than subjecting the patient to the known risks of shunt failure, is prudent.

The risk of radiation from CT has prompted increased interest in limited-sequence or “quick” MRI.⁸ When evaluating patients with potential shunt dysfunction, brain imaging in conjunction with radiographs of the shunt tubing, known as a shunt series, should be obtained. A shunt series consists of two views of the head, neck, chest, and abdomen so that the whole shunt system is imaged. The current ventricular size in a patient with a possible shunt blockage based on contemporary imaging is not necessarily a good indicator of shunt blockage. Comparison to a previous scan when the patient was well with the same valve in place is far more reliable in terms of diagnosis of shunt blockage.

Physiology and Pathophysiology of CSF Circulation

Historically, it has been suggested that CSF is produced by the choroid plexus in the lateral and fourth ventricles, flows out through the foramina of Luschka and Magendie, and is absorbed by the arachnoid granulations near the venous sinuses. This model has been called into question for two main reasons:

Recently, there has been a different approach to the pathology of hydrocephalus.^9,11 The CSF can be seen as extracellular fluid. The choroid plexus is the driving force for circulating the CSF along the pathway described earlier, but the absorption and, to a lesser extent, the production occur in the subarachnoid spaces and Virchow-Robin spaces. Regional changes in capillary bed caliber and permeability may affect this absorptive mechanism. When an obstruction develops, be it at the level of the aqueduct, the fourth ventricle, or the arachnoid on the brain surface, the absorptive capacity is reduced; therefore, a higher hydrostatic pressure is required to reach equilibrium between absorption and production. More research is required to substantiate these theories.

History of Shunts

The history of hydrocephalus is a fascinating one and dates back to the dawn of civilization. A good summary of the history is presented by McCullough.¹² Early 20th-century attempts at achieving closed ventricular drainage included gold, glass, silver, and rubber tubes, as well as catgut and linen threads passed from the ventricle to the subdural space.^12–15 Similar techniques were used to connect the lumbar thecal sac to the peritoneum or renal pelvis.^16–18 After attempts at third ventriculostomy by Dandy¹⁹ and by Mixter²⁰ and choroid plexectomy by Dandy,²¹ shunts from the lateral ventricle to cisterna magna (Torkildsen shunts²²) and shunts from the lumbar spine to the ureter came into more widespread use.

The treatment of hydrocephalus was revolutionized when Nulsen and Spitz²³ reported in 1952 the successful use of a ventriculojugular shunt using a spring and stainless-steel ball valves. The two valves were housed in rubber intravenous tubing, which acted as a flushing device, and connected to polyethylene tubing at either end. Unfortunately, occlusion of the venous catheter by blood clot was a frequent problem.

Holter’s shunt was the first to use silicone, and he designed a multislit valve out of silicone for use in his son, who had developed hydrocephalus.²⁴ About the same time, Pudenz²⁵ concluded that silicone was the best material and designed two valves to use as ventriculoatrial (VA) shunts.

Principles

Once the decision to implant or revise a shunt is made, the surgeon should begin planning the procedure. Informed consent discussing the rationale for the procedure, the potential complications, and the potential outcome should be sought in a timely fashion prior to surgery. The surgeon should pick out the shunt hardware prior to surgery. The following are important patient factors to consider when planning:

VP Shunts

For a parieto-occipital VP shunt insertion, positioning is important. Once the patient is under general anesthesia and following administration of antibiotics on induction of anesthesia, we use the horseshoe headrest with a bolster placed under the shoulder ipsilateral to the ventricular catheter insertion site for positioning. The head is tilted such that the cranial incision site is accessible. This is usually achieved by rotation and lateral flexion of the neck to the contralateral side (Fig. 54-1A). This position is optimal for tunneling because it keeps the skin around the neck under some traction, provides a straight line from the cranial incision to the abdominal incision, and allows good access to the both abdominal and cranial incisions.

FIGURE 54-1 Sequential steps on shunt insertion. A, Patient positioning and marking of incisions. B, Draping. C, Making a small incision that will not cross over shunt equipment. D, Passing a blunt dissector into the peritoneal cavity. E, Using an abdominal trocar. F, A tunneling device. G, Cannulating the ventricle according to landmarks. H, Using ultrasound guidance to place the ventricular catheter. I, Using a shunt scope to place the ventricular catheter. J, Making the subcutaneous pocket for the valve. K, Silastic-sleeved forceps coaxing the tubing onto the connector. L, Placing the valve into its pocket. M, Suturing the valve to the pericranium.

For patients in whom a laparoscopic peritoneal insertion with an abdominal trocar is being used, the bladder should be emptied. Hair is clipped (not shaved) in the operating room to prevent hair from becoming tangled within the wound. The site of the bur hole and abdominal incisions should be selected and marked before draping.

Many techniques have been described to determine the appropriate location for the bur hole.²⁹ For example many people measure distances from either the ear or the midline to approximate the site of the bur hole. Whichever method is chosen, it is important to correlate the projected bur hole location with the optimal location on the preoperative imaging. Measurements made from CT scan are probably more accurate than choosing the site of the bur hole based on arbitrary surface landmarks. It is important to obtain localization in two planes. The use of neuronavigation removes all guesswork in localization of the optimal bur hole location but may increase cost and time. Furthermore, rigid cranial fixation is usually required, and this can hamper tunneling. Newer neuronavigation techniques such as electromagnetic-based systems eliminate the requirement for head fixation in pins, thus allowing easier tunneling.³⁰

For frontal bur hole placement, the patient is usually positioned supine with the head tilted to the contralateral side. The bur hole site is usually just anterior to the coronal suture 2 to 3 cm from the midline (the midpupillary line is a good estimation). Preparation of a small intervening incision just posterior to the ear is important because it is usually required to tunnel through the subcutaneous tissue plane from the frontal region to the abdomen.

The skin is meticulously prepared with an antiseptic solution such as povidine–iodine or chlorhexidine. We use disposable, adhesive drapes to cover the patient and the operating table entirely, except for a small band of skin from the bur hole site to the abdomen (Fig. 54-1B). We use iodine-impregnated transparent adhesive drapes, although there is no evidence to suggest that shunt infection rates are reduced with this technique.

During the “time out,” we ensure that an appropriate dose of prophylactic antibiotics has been administered to achieve desired tissue concentrations and that we are operating on the correct patient, are operating on the correct side, and have the scans and equipment available. We do not infiltrate the wound with local anesthetic mixed with adrenaline, because this has the potential to increase the number of punctures of the skin and reduce blood supply to the wound. We use a horseshoe incision (Fig. 54-1C) that has its pedicle based on the direction the shunt will initially be tunneled. It is important to keep this pedicle wide and large so that no shunt equipment lies under the incision and blood supply to the flap is not restricted. For frontal bur holes, this may mean an obliquely oriented pedicle.

The size of the bur hole should be adequate to insert the ventricular catheter. We insert all our ventricular catheters under direct, real-time ultrasound guidance so that the bur hole required is quite large and allows access to the probe and the ventricular catheter simultaneously.³¹ In infants, particularly if premature, an opening between the splayed sutures at either frontal or occipital sites is often all that is required for dural access. A small dural incision just large enough to allow passage of the ventricular catheter is optimal, because this may reduce the risk of CSF extravasation into the subgaleal space. This is especially true in patients with thinned cortical mantle. The brain pia is cauterized and opened.

The abdominal incision is simultaneously opened by the second operator. There is no evidence that any specific location on the abdomen results in reduced complications. We avoid umbilical incisions because it is difficult to clean the umbilicus. The peritoneum should be approached by dissection in layers. It is vital to confirm that the peritoneum has been entered, for example, by observation of intraperitoneal contents such as bowel and liver, by flooding the field and watching fluid drain into the peritoneum, or by passing a blunt dissector into the abdominal cavity (Fig. 54-1D). The use of abdominal trocars to enter the peritoneum is a safe and acceptable technique, although we tend to ask our general surgical colleagues to assist when performing this maneuver (Fig. 54-1E).

Tunneling is a potentially dangerous maneuver. The aim is to ensure the tunneling device is subcutaneous throughout its course. There is no evidence that the direction of tunneling, be it cranial to caudal or caudal to cranial, affects complications. A preassembled valve and tubing may not pass in the direction required because you have tunneled in an incorrect direction; hence, planning is important. Potential errant entries while tunneling include the skin, the peritoneum and its contents, the pleural space and lung, the heart and the great vessels of the neck, and the skull base, including the foramen magnum. As a rule, the tip of the trocar should be palpable below the skin at all times and the tip should pass superficial to the ribs and the clavicle. A common site of resistance to tunneling is at the deep cervical fascia of the neck (Fig. 54-1F). If you feel excessive force is required to pass the tunneler, a separate incision should be made and retunneling should commence from that location. If passing to a frontal bur hole, an intervening incision is usually required behind the ear. When tunneling along the chest wall, especially in neonates, there is potential to affect ventilation. The anesthetist should be made aware when tunneling, and the time during which the tunneler is subcutaneous should be kept to a minimum. The peritoneal tubing, with the attached valve, is then passed along the tube, attaching suction to the distal end and irrigating. The valve should then be irrigated to fill it with fluid. It is important to connect the valve in the correct direction (according to manufacturer’s instructions). We make a subcutaneous pocket to seat the valve (Fig. 54-1J).

The ventricular catheter trajectory is then determined according to external landmarks or using some form of image guidance, be it ultrasound or neuronavigation (Fig. 54-1G and H). From a frontal bur hole, traditional landmarks for the foramen of Monro are the intersection of the planes through the midline and just anterior to the external auditory meatus (or simply perpendicular to the skull). If the patient’s head is tilted, these landmarks can be difficult to appreciate, so palpable electrocardiogram electrodes placed at these points prior to draping may be of assistance. From the occipital location, a target at the midpoint of the forehead just at the normal hairline ensures that the catheter proceeds into the frontal horn instead of the temporal horn. For frontal bur holes it is generally accepted that the optimal position of the ventricular catheter tip is just anterior to the foramen of Monro, whereas for occipital bur holes the optimal position is the atrium of the lateral ventricle. In both cases, it is optimal to have the tip of the catheter away from the ventricular walls or choroid plexus. Endoscopic insertion allows visualization of the ventricular catheter in real time (Fig. 54-1I).

The ventricular catheter can often be felt to “pop” once the ependyma is breached with a concomitant “gush” of CSF. This “gush and pop” can be visualized on ultrasound. Gently irrigating the catheter may show pulsatile CSF flow into and out of the catheter. Withdrawing vigorously may draw brain tissue into the catheter and plug the shunt and thus is not recommended. There is no evidence that multiple catheter passes affect outcome; however, making fewer passes is likely to result in having fewer complications. We believe that ultrasound guidance in real time may reduce the number of passes required, thus optimizing catheter position and potentially reducing operating time.

Iatrogenic intraventricular hemorrhage is an uncommon complication that usually occurs as a result of choroid plexus hemorrhage. If the CSF is quite blood stained, it may be more appropriate to convert the operation to an EVD and obtain an urgent CT scan postoperatively.

The ventricular catheter is then connected to the valve and ties are placed along any connections (Fig. 54-1K and M). The valve system is then positioned into the subcutaneous pocket that had been created (Fig. 54-1L). Once in place, the peritoneal catheter should be checked for spontaneous CSF flow. The surgeon should not close until it is clear that the shunt is working. If there is any doubt, the system should be disconnected to verify that both ends are patent.

The distal catheter is then inserted into the peritoneum, with the surgeon making sure that it enters easily and there is enough length to account for patient growth. If the catheter keeps backing out of the abdomen, it may be coiling up in the preperitoneal space or there may be abdominal adhesions. The abdomen is closed in layers, as is the cranial incision. We do not advocate closure of the peritoneum because this layer is often thin and does not contribute to preventing a hernia.

Skin closure is critical. Any CSF leak predisposes to wound breakdown or infection. The rate of shunt infection has been shown to be as high as 57.1% in the presence of perioperative CSF leakage.³² We place an occlusive dressing on the wounds, particularly on young children, who may irritate or pick at their incisions.

Positioning in the postoperative period can be important. Premature infants may be particularly prone to skin ulceration if positioned with the full weight of the head on the valve hardware. In patients with large ventricles, early ambulation may predispose the patient to a subdural hemorrhage. In patients with high-resistance valves, placing them in an upright posture may promote CSF drainage and prevent accumulation under the skin. We allow patients to eat on completion of their surgery and clearance of anesthetics.

The postoperative hospital stay is typically 2 to 3 days. Intravenous prophylactic antibiotics are normally given preoperatively and sometimes postoperatively for two doses only. Shunted patients typically have rapid resolution of acute symptoms. In infants, a sunken fontanelle with standard valves is typical. Low-pressure headache can occur in older patients, particularly if the hydrocephalus is long-standing. Low-pressure headaches can be managed with bed rest, hydration, and simple analgesia. A postoperative scan is important to obtain as a baseline; however, the timing is up to the individual surgeon. Some evidence shows the ventricles do not reach their final size on average until 1 year of age.³³ We tend to scan immediately postoperatively, after 1 year, and then approximately every 5 years in asymptomatic patients.

Ventriculopleural Shunts

Ventriculopleural shunts are an additional option for distal catheter placement. Contraindications include previous chest surgery and adhesions, active pulmonary disease including infection, and borderline pulmonary function in patients in whom a significant pleural effusion might push them into respiratory failure. Infants are more likely to develop a significant effusion temporarily. We recommend a preoperative chest x-ray and pulmonary function testing.

The pleural space can be entered at a variety of sites. A common site is along the anterior axillary line, in the fourth to sixth intercostal space on the right. A muscle-splitting approach along the upper border of the rib (to avoid the neurovascular bundle) reveals the translucent pleura and the lung moving with ventilation.

The pleura is opened sharply. There is no need to ask the anesthetist to collapse the lung; it moves away slightly because it usually is at subatmospheric pressure during inspiration and thus retracts slightly from the chest wall once the pleural space is opened. The distal catheter is then introduced gently and is carefully guided along the chest wall and away from the lung parenchyma. The catheter may need to be cut to avoid putting excess tubing, even allowing for growth, into the chest. A Valsalva maneuver by the anesthetist inflates the lung adequately. At that point, the site should be closed in three layers. Rapidly closing the muscles with a few sutures avoids further air entry into the chest.

A small pneumothorax is usually seen postoperatively on chest x-ray. It resolves over the next few days, whereas the CSF usually accumulates as a small pleural effusion. These patients must be monitored for any evidence of respiratory distress, with serial chest films and continuous oxygen saturation monitoring.^34,35 Usually, the intrapleural fluid disappears over the next several weeks. In patients in whom the pleural fluid progressively accumulates, leading to respiratory distress with significant shift of the mediastinum, percutaneous drainage of the fluid and accessing another site for the tubing are required.

VA Shunts

The right atrium is another alternative to the peritoneum for distal catheter placement. The aim is to place the distal catheter just above the right atrium. Atrial catheters have a slit valve to prevent reflux of blood up the tubing. The patient is placed in the supine position with the head slightly down to avoid air embolus. The anesthetist should be involved throughout the procedure because ventricular ectopic beats are commonly encountered. The ventricular catheter inserted as described in the preceding section. The distal catheter is tunneled to the neck area in the proximity of the site of insertion of the atrial catheter.

There are broadly two methods for performing the distal portion of the procedure: open or percutaneous. For an open procedure, a right-sided neck incision is made to expose the common facial vein, which is tied proximally and held with a stay suture distal to the venotomy site. The catheter is then advanced down the jugular vein into the superior vena cava. Fluoroscopy is used to identify the final position of the tip of the catheter.

The percutaneous method involves cannulating the subclavian vein under color flow Doppler ultrasound guidance. A Seldinger wire is then passed into the vein and progressed to the entrance to the right atrium. A dilator expands the entrance to the subclavian vein. Following this, a peel-away ventricular catheter is inserted. Under fluoroscopic guidance, the tip of the catheter is positioned just above the right atrium.³⁶ The atrial catheter is then connected with a straight connector to the distal catheter, and all incisions are closed in two layers.

Other Sites of Insertion

Other options include reinsertion into the peritoneum, insertion into the gallbladder,³⁷ insertion into the superior sagittal sinus retrograde to the direction of flow,³⁸ and use of the vascular surgeons to assist in insertion into another peripheral vein. We have limited experience in any of these techniques.

Hardware Issues

The primary components of a VP shunt include a ventricular catheter, a valve, and a distal catheter.

Valve Selection

There are many shunt valves available on the market.⁴² They can broadly be categorized into either pressure- or flow-regulated systems. Pressure-regulated valves are either open or closed to CSF flow, depending on the pressure across them (Fig. 54-3A and B). Pressure-regulated valves can be grouped into four design categories:

• Slit valves, where slits within tubing open when the pressure is high enough. This type of valve is commonly used when inserting lumboperitoneal shunts, such as the Spetzler lumbar peritoneal shunt system (Integra NeuroSciences, Plainsboro, NJ).

• Miter valves, where two opposing leaflets are in the closed or open position depending on the pressure differential. Examples include the Mischler Dual chamber valve (Integra NeuroSciences) and the UltraVS cylindrical in-line valve system (Integra NeuroSciences).

• Diaphragm valves, where a mobile flexible membrane moves in response to pressure changes. Examples include the Heyer-Schulte Pudenz flushing valve (Integra NeuroSciences).

• Metallic spring ball valves,²⁸ where a spring moves up and down depending on the pressure. Examples include the Miethke ProGrav valve (BBraun, Melsungen, Germany) and Polaris valve (Sophysa, Orsay Cedex, France).

FIGURE 54-3 Shunt valve designs. A, Standard differential-pressure shunt, spring valve. Flow increases rapidly once opening pressure is exceeded. B, Siphon-reducing device distal to a standard differential-pressure valve, diaphragm type. The effects of gravity are reduced in the upright position. C, Flow-limiting valve with a variable-resistance orifice leading to flow limit, as seen in the flow–pressure curve. D, Two gravity-actuated devices that increase the opening pressure (above) or the resistance (below) in the vertical position. E, Percutaneous adjustable valve that can be completely occluded.

(A to C, Drake JM, Kestle J. Determining the best CSF shunt valve design: The pediatric valve design trial. Neurosurgery 38:604-607, 1996. D and E, Drake JM, Sainte-Rose C. The Shunt Book. New York, Blackwell Scientific, 1995, p 1.)

The pressure at which valves open is termed the opening pressure and is fixed. Typically, there are low, medium, and high designations, which generally correspond to 5, 10, and 15 cm H₂O pressure, respectively, although there are no universal standards.

Flow-regulated valves work by reducing the caliber of the tube through which CSF flows when pressure increases but ensuring that some flow is maintained at all times.⁴³ An example is the OSV II Orbis Sigma valve (Integra NeuroSciences) (Fig. 54-3C). This valve has a variable-diameter pin that partially occludes a ring whose position depends on the pressure. This alters the cross-sectional area through which CSF can flow. Thus, increased pressure would reduce the cross-sectional area; conversely, low pressure would increase it. The result is that, in an idealized system, the flow is constant irrespective of the pressure.

Measures to limit large changes in intracranial pressure based on the patient’s position include siphon-reducing devices. Antisiphon devices have a mobile membrane that moves to narrow an orifice in response to a negative pressure inside the shunt system when the patient is vertical (Fig. 54-3B).^44,45 Examples are the antisiphon device and PS Medical Delta valve (Medtronic, Goleta, CA). Other valves try to reduce the effects of gravity by changing their configuration according to how they are positioned (Fig. 54-3D). In some designs, metallic balls rest on top of a standard spring ball valve to increase the opening pressure when the valve (and patient) is vertical. In another, a single metallic ball rests in an asymmetrical valve seat in upright position, increasing the resistance.

Programmable valves allow the opening pressure to be altered using an externally applied device. Examples include the Miethke ProGrav valve (BBraun), the Polaris valve (Sophysa), the PS Medical Strata valve (Medtronic), and the Codman Hakim valve (DePuy, Raynham, MA). Some factors that are important when evaluating these devices include the ease of assessing the pressure at which the valve is set and ease of altering the pressure. Many of these systems rely on a magnet to alter the setting, so the setting may need to be checked following an MRI (see individual manufacturer guides for details). The newer valves are MRI compatible, with a trade-off of increased difficulty in changing the setting.

Does the Chosen Valve Affect Patient Outcome?

It is generally accepted that a valveless shunt with the diameter of tubing commonly available can cause siphoning, leading to intracranial hypotension with the attendant risk of subdural hematomas. However, there is some evidence that the use of a valveless system with a small internal diameter of tubing and a longer length of tubing may act as a flow-controlled system that prevents overdrainage.⁴⁶ This mechanism by which overdrainage is prevented is similar to the mechanism by which a flow-regulated valve prevents overdrainage. This system exploits the Hagen-Poiseuille equation that states that the flow through a tube is inversely proportional to the radius of the tube,³ the length of the tubing, and the viscosity of the fluid.

There is much debate about the efficacy of flow-controlled valves compared to pressure-controlled valves. Kan et al.⁴⁷ suggested that the incidence of slit ventricle syndrome (described in a later section) is lower in patients who have had a flow-controlled valve inserted compared to differential- and fixed-pressure valves; however, the diagnosis of slit ventricle syndrome was based on radiology, and clinical correlation was not performed. There is no compelling evidence that the shunt obstruction rate is related to whether a flow- or a pressure-controlled system is used.³

Patient Factors

Age appears to be a strong predictor of shunt-related complications. Table 54-4 shows the hazard ratio of shunt-related complications based on age in a cohort of 19,284 patients of all ages. The incidence of shunt-related complications in children in this cohort was in the region of 48%, compared to 27% in adults.³⁹ Tuli et al. also found age to be a significant factor in shunt failure.⁵⁸

The underlying etiology of hydrocephalus is also an important predictor of shunt-related complications. Common causes of hydrocephalus in the pediatric population include aqueduct stenosis, Dandy-Walker malformations, obstruction by tumor, postintraventricular hemorrhage of prematurity, and hydrocephalus associated with myelomeningocele.⁵⁹ Table 54-5 shows the incidence of shunt-related complications based on the condition warranting shunt insertion.

Table 54-5 Shunt-Related Complications Based on the Etiology⁵

It has also been shown that the incidence of shunt failure is greater if multiple shunt revisions have been performed. Shunts are also more likely to fail within 6 months of implantation.³³ The majority of patient risk factors for shunt failure are not alterable, so it is important for the surgeon to be aware of these risk factors when consenting patients.

Surgical Environment and Surgical Technique

The surgical environment has a great potential effect on the outcome of shunt surgery.