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

Cause	Patients
Intraventricular hemorrhage	24.1%
Myelomeningocele	21.2%
Tumor	9.0%
Aqueduct stenosis	7.0%
CSF infection	5.2%
Head injury	1.5%
Other	11.3%
Unknown	11.0%
Two or more causes	8.7%
Total patients	99.0% (344)

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

Symptoms	Children
Irritability	26.6%
Delayed developmental milestone	19.8%
Nausea or vomiting	19.0%
Headache	17.5%
Lethargy	17.5%
New seizures or change in seizure pattern	6.6%
Diplopia	5.8%
Worsening school performance	4.2%
Fever	2.6%
Signs	Infants
Increasing head circumference	81.3%
Bulging fontanelle	70.6%
Delayed developmental milestones	20.9%
Loss of upward gaze	15.8%
Decreased level of consciousness	12.6%
Other focal neurologic deficit	12.4%
Papilledema	12.0%
Sixth nerve palsy	4.6%
Hemiparesis	3.8%
Nuchal rigidity	1.8%

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.

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.

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

Condition	Shunt-Related Complication
Aqueduct stenosis	6.7%
Myelomeningocele	22.8%
Postintraventricular hemorrhage of prematurity	13.6%
Posterior fossa tumor	22.6%
Postinfection	4.8%
Congenital condition	10.8%
Post-trauma	2.3%

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.

Shunt Blockage

No data demonstrate a reliable relationship between the duration of shunt blockage and the speed of clinical deterioration of the patient. Some patients may have clinical symptoms for long before becoming unwell, whereas other patients become unwell quickly. The Birmingham, Alabama, group has analyzed their experience of shunt-related death.⁷⁷ Symptoms of raised intracranial pressure longer than 24 hours prior to death were present in at least 10 of the 28 patients who died. Of these, 5 patients had symptoms for 1 to 4 weeks. They also found that 8 patients died prior to arriving at the hospital. We find that, given that the duration of symptoms prior to a catastrophic event is variable in shunted patients, the safest approach is to review the patient as soon as possible. The Birmingham, Alabama, group’s follow-up study also emphasizes the importance of patient education to prevent such events.⁷⁸

The principles underlying the management of shunt blockage are to make the diagnosis, aim to identify where the blockage is likely to be, and then plan surgery to relieve the blockage by replacing the faulty components. Any obtunded patient with a shunt in situ requires careful evaluation for shunt blockage followed by clear objective evidence that a shunt blockage is not the cause for the reduced level of consciousness.

The diagnosis of shunt blockage is usually made on clinical evaluation combined with a CT/MRI scan and a shunt series (Fig. 54-4). Clinical history in a patient with shunt blockage may reveal symptoms suggestive of raised intracranial pressure. However, subtle deterioration in intellectual performance may be the only symptom of shunt dysfunction. Examination of the site of the shunt may provide some evidence of shunt dysfunction. Fluid around the ventricular site is indicative of proximal shunt blockage or of fracture/disconnection of the shunt apparatus, whereas fluid around the distal catheter and/or ascites is indicative of a CSF malabsorption process.

Although pumping of the shunt reservoir is a time-honored technique, this is often misleading.⁷⁹ Shunts whose reservoirs remain depressed for a long time raise the possibility of proximal shunt obstruction. However, this may simply represent a small ventricular size. A reservoir that is difficult to depress or refills apparently instantaneously frequently indicates a distal obstruction. Some shunt reservoirs contain proximal and distal occluders. By occluding the distal reservoir and depressing and allowing the reservoir to refill, we can infer that the proximal catheter is patent. Similarly, by occluding the proximal reservoir and flushing distally, we can confirm patency of the distal catheter.

Another commonly used preoperative method of shunt interrogation is tapping of the reservoir. Placing a small gauge butterfly needle connected to a manometer provides an evaluation of the pressure required for CSF to flow distal to the reservoir. The valve is usually distal to the reservoir, so we are, in effect, interrogating the valve and the distal tubing. Evaluation of the proximal catheter is more difficult and subjective and requires gentle aspiration of CSF from the butterfly needle. If flow is “easy,” then the probability of a proximal shunt blockage is low. CSF can also be sent for microbiologic examination in the process. The risks of this bedside procedure include introducing infection.

When operating on patients with shunt blockage, it is important to prepare and drape the abdomen, as well as the head, because the only definitive method for diagnosing shunt blockage is operation with the proximal catheter, valve, and distal catheter visible. For this reason, we usually open the cranial incision in the first instance. Careful dissection with the monopolar cautery onto the shunt tubing is an effective method for exposing the tubing without damage (Fig. 54-5A). The components are then systematically disconnected and interrogated. If there is no spontaneous flow from the proximal catheter, then a proximal blockage is diagnosed and the proximal catheter needs revision. It is preferable to remove the catheter and replace it with a new catheter. Often, especially when shunts have been in place for a long time, the ventricular catheter is quite stuck. The catheter should not be pulled out because this is likely to result in intraventricular hemorrhage. It may be possible to free the catheter by placing a stylet through the catheter and using the monopolar cautery to coagulate any choroid plexus occluding the holes at the tip while twisting the catheter (Fig. 54-5B). If this is not possible, the catheter should remain. If the ventricular catheter inadvertently slips into the ventricular system, an endoscopic approach is usually indicated to “fish” the catheter out. CSF should always be obtained and sent for microbiologic examination for all shunt procedures.

For valve and distal catheter blockages, the component or components that are not functioning should be replaced. If the valve is to be replaced and the distal catheter is to remain, the wound needs to be extended to expose a length equivalent to the new valve to avoid kinking and coiling of the distal catheter. For distal revisions, great care must be taken if the same incision site in the abdomen is used because localized adhesions may be present, increasing the risk of bowel perforation.

VP Shunt Infection

Shunt infection is a common complication of shunt surgery. A proportion of patients with shunt infection will have a blocked shunt; hence, it is important to consider shunt infection in anyone who presents with shunt blockage relatively early following VP shunt insertion. The majority of shunt infections occur within 3 months of the shunt surgery. The spectrum of clinical manifestations include the following:

One of the more common and difficult clinical situations to manage is the patient with a VP shunt who has a temperature. If the child is well, other more common causes of a temperature such as a urinary tract infection and upper respiratory tract infection should be excluded. Routine blood tests may reveal a polymorphonuclear leukocytosis and a raised C-reactive protein. Culture of the urine or other obvious sites of infections, for example, the wound, should also be taken. In the absence of another source or in an unwell child, it is prudent to perform a shunt tap as described earlier to diagnose whether the shunt reservoir can be performed preoperatively or by obtaining CSF intraoperatively. In most cases, CSF should be sent for cell count, Gram stain, culture and sensitivity, glucose, and protein. Shunt aspiration should be done using an aseptic technique so as not to iatrogenically contaminate a shunt system. Shunt aspiration provides a high diagnostic yield of shunt infection of approximately 95% and is quite safe.

The most common organisms infecting CSF shunts are staphylococci. Approximately 40% of shunt infections are caused by Staphylococcus epidermidis infections and 20% by S. aureus.^81–83 Other species isolated from infected shunts include the coryneforms, streptococci, enterococci, aerobic gram-negative rods, and yeasts. Propionobacteria acnes is a relatively common organism causing shunt infection but requires prolonged culture to diagnose.⁸⁴ We recommend anaerobic culture with prolonged incubation. Because these organisms are commonly part of the normal skin flora, and shunt infection usually occurs within 2 months of surgery, endogenous spread from the patient or surgical staff is the logical route of infection. Most surgeons would agree that a relatively early shunt infection (i.e., within 6 months of insertion) is seen as a surgical complication.

Bacteria colonize the shunt in the form of a continuous biofilm. This biofilm is composed of bacterial cells, either singly or in microcolonies, all embedded in an anionic matrix of bacterial exopolymers and trapped macromolecules.⁸⁵ The biofilm offers protection against many common antibacterial agents, including antibodies, white blood cells, surfactants, and antibiotics. For this reason, treatment of shunt infections by the exclusive use of systemic or intraventricular antibiotics^82,86 has been generally ineffective, although a recent report in patients without S. aureus infections had reasonable resolution if infections with intraventricular antibiotics were injected into a separate CSF reservoir.⁸⁷

It has been shown that shunt removal with interval antibiotic treatment (usually with EVD) carries the highest shunt infection cure rate and the lowest mortality rate.⁸⁸ CSF shunt removal with immediate replacement carries an almost equal shunt infection cure rate and a higher morbidity and mortality rate. Antibiotic treatment alone has the lowest cure rate and the highest mortality rate. Continuous discussion with the microbiology/infectious disease team members throughout treatment is important. They should advise on isolation of the organism, the appropriate antibiotic based on sensitivity testing, the duration of antibiotic treatment, and when it is appropriate to internalize the shunt. Intrathecal administration is commonly instituted in many units. It is important to ensure that the person administering the antibiotics has been appropriately trained.

When reinserting a VP shunt following shunt infection, we tend to prefer inserting the ventricular catheter in a site that has not been operated on.

Intra-abdominal Pathology

Contamination of the shunt can occur from other general surgical procedures,⁸² such as insertion of a gastrostomy with peritoneal shunts. If a patient presents with obvious peritoneal sepsis (e.g., ruptured appendicitis or perforated bowel), it is generally accepted practice to externalize the shunt by making an incision over the chest wall (i.e., distal to the valve) and connecting the catheter to an external ventricular drainage system. When performing this procedure, the level the drain should be placed at is 0 cm above the foramen of Monro because the valve will still be functioning. Reinternalization should be performed only when the intra-abdominal sepsis has been eradicated. If there is a high chance of bowel adhesions, it may be more prudent to convert to a ventriculopleural or VA shunt. When reinternalizing a distal catheter, it is important to retunnel from an area proximal to the exit site, usually the valve, and to use new catheter tubing. This approach can be applied for the unusual complication where the shunt migrates through the bowel wall and out through the anus.

Patients with VP shunts occasionally present with abdominal swelling. Ultrasound and/or CT may demonstrate intra-abdominal pseudocysts. In this scenario, there is a high chance that a low-grade pseudocyst infection is present. The principles of management include making the diagnosis and treating the infection. The shunt can be externalized over the chest wall and the pseudocyst drained by aspirating from the distal catheter. The fluid should be sent for microbiologic examination, and antibiotic therapy should be initiated. Once the sepsis has been treated, reinsertion at another site, including another part of the abdomen, is appropriate.

Shunt Overdrainage

CSF overdrainage occurs relatively commonly following shunt insertion. Patients with shunt overdrainage may complain of postural headache, lack of energy, and “feeling washed out.” Causes of overdrainage include valve dysfunction or selection of a valve that is inappropriate for that patient. The complication of subdural hematoma is often associated with overdrainage. Treatment involves increasing the pressure in a programmable valve or upgrading to a higher pressure valve. Large subdural hematomas should be treated surgically in the appropriate fashion, in combination with a valve change.

Slit Ventricle Syndrome

A consequence of chronic overdrainage is slit ventricle syndrome. Nomenclature in the literature is confusing. Some authors define the condition as small ventricular size associated with symptoms of intermittent shunt blockage. When the ventricles are very small, the shunt blocks. As the ventricles expand, the shunt unblocks, thus creating a cycle of intermittent shunt blockage.⁸⁹ A product is noncompliant ventricles. There are three theories as to the pathogenesis of noncompliant ventricles; however, it is likely that the true pathophysiology involves more than one mechanism. The first is that ventricular pressure is intimately related to intracranial venous pressure and when CSF pressure drops, uncoupling occurs. This leads to increased venous congestion and increases brain elasticity. The second is that increased pressure with subependymal flow can cause subependymal gliosis and periventricular gliosis with increased ventricular wall stiffness. If this happens, intraventricular pressure would need to be higher than usual to obtain ventricular dilatation. The third proposed mechanism is that low-pressure valves in neonates lead to overshunting with radiologic slit ventricles, the development of microcephaly, and synostosis. This in turn predisposes the ventricular catheter to obstruction and prevents the ventricles expanding in response to obstruction.

This group of patients is among the most difficult to manage. They can be difficult to diagnose because their ventricles do not change significantly in size when the intraventricular pressure is high. The principles of management of a patient with slit ventricles and possible features of shunt blockage include accurate characterization of the intracranial pressure. Careful evaluation of the CT scan may demonstrate subtle changes suggestive of raised pressure, such as reduced CSF over the hemispheres. Intracranial pressure (ICP) monitoring, although invasive, is often required and is the gold standard investigation in the assessment for potential shunt malfunction in the context of complex hydrocephalus. Another recognized technique is to externalize the VP shunt and modulate the pressure according to symptoms. ICP monitoring, if performed, should be continued for 24 to 48 hours, in conjunction with a headache and activity diary, and should be maintained during sleep.

Treatment usually involves shunt revision. Variable pressure valves are often used in this instance so that the pressure can be altered with ease. CSF flow-limiting valves, such as the Orbis Sigma, may also normalize intracranial pressure, possibly by improving intracranial compliance. Intraoperative image guidance is important because the ventricular size is often so small. In cases where multiple shunt revisions have been performed, subtemporal decompression has been shown to be effective. By removing bone (in effect creating a new fontanelle), the defect can act as an alternative pressure relief valve to the shunt, thus increasing intracranial compliance. Endoscopic third ventriculostomy (ETV) and cranial vault expansions have also been attempted.

Management of Patients with Isolated Ventricles

An additional challenge to managing a patient with hydrocephalus occurs when the ventricular system is not one contiguous fluid compartment. This situation occasionally occurs following treatment of ventriculitis or meningitis, but similar principles apply to the management of arachnoid cysts compressing specific parts of the ventricular system. We tend to manage these patients with a combination of endoscopic fenestration of cysts and VP shunting. The aim is to drain as many cysts with as few ventricular catheters as possible. Endoscopic fenestration of the septum pellucidum is a useful method for allowing communication between the two lateral ventricles in the presence of obstruction at the foramen of Monro.

Comatose Patients with Fixed, Dilated Pupils

Patients presenting in coma are fortunately a rare occurrence; however, when seen, management must be prompt. A large bore spinal needle can be placed through the bur hole along the presumed trajectory of the ventricular catheter if the patient is in extremis. Patients presenting in coma should have an EVD inserted, rather than a shunt revision, because if the patient has a VP shunt revision and does not come out of coma immediately, it is difficult to ascertain whether the prolonged coma is caused by blockage of the new shunt or the neurologic damage from the initial presentation was so severe to keep the patient in a comatose condition.

Headaches in Patients with VP Shunts

Headaches are common in patients with VP shunts. There are numerous causes for headaches, and not all headaches are related to the shunt. A detailed history and examination are often necessary. Options for investigation to exclude shunt malfunction include CT, MRI, shunt series, shunt tapping and manometry, altering the valve setting, headache diaries, and ICP monitoring. In the absence of any objective evidence of shunt dysfunction, it is appropriate to refer the patient to your neurology and pain services.

History

The earliest endoscopic treatment for hydrocephalus was choroid plexus fulguration performed by Lespinasse in 1910.⁹¹ Dandy⁹² subsequently described an open technique for third ventriculostomy for the treatment of noncommunicating hydrocephalus. A percutaneous ventriculostomy technique using an endoscope was first described by Mixter in 1923.²⁰ Fay and Grant⁹³ published the first intraventricular photographs that same year, providing the first visual record of endoscopic anatomy. Because of the limited illumination and large size of early endoscopes, open ventriculostomy procedures, as well as percutaneous fluoroscopic and later CT-guided techniques, remained popular for many years. Johns Hopkins provided the technical advances necessary for the revival of neuroendoscopy.⁹⁴ Hopkins’ innovative solid-rod lens and coherent quartz fiber lens systems underlie the basic design of all modern rigid and flexible endoscopic systems. The improved optics and illumination and reduced size of modern endoscopes have greatly increased their utility and reduced their associated morbidity and mortality.

Patient Selection

ETV has been intended to treat noncommunicating hydrocephalus with patent subarachnoid spaces and adequate CSF absorption. Results of ETV have been related to the cause of hydrocephalus encountered, as well as clinical and radiographic features of the individual patient. Table 54-6 lists causes of obstructive hydrocephalus classified according to reported success rates of ETV (see the later section on outcome). Patients with acquired aqueductal stenosis or tumors obstructing third or fourth ventricular outflow have demonstrated the highest success rates, exceeding 75% in carefully selected series of patients.^95–98 Previously shunted patients with or without myelomeningocele and patients with congenital aqueductal stenosis or cystic abnormalities leading to obstruction (i.e., arachnoid cyst or Dandy-Walker malformations) have shown intermediate responses.^{96,97,99–101} Infants presenting with hydrocephalus associated with myelomeningocele, hemorrhage or infection have generally demonstrated poor response to ventriculostomy,^94,102,103 and despite limited reports of success in such patients,^{97,99,100,104–107} they have been more controversial candidates for this procedure. The procedure is not advisable in patients who have undergone prior radiation therapy because of the extremely poor response rates, altered anatomy (i.e., thickened third ventricular floor), and increased risk of bleeding.^97,99,103

Table 54-6 Ventriculostomy Success Rates by Hydrocephalus Cause

High Success Rates (≥75%)

Acquired aqueductal stenosis

Tumor obstructing ventricular outflow • Tectal • Pineal • Thalamic • Intraventricular

Intermediate Success Rates (50%-70%) Myelomeningocele (previously shunted, older patients) Congenital aqueductal stenosis Cystic abnormalities obstructing CSF flow Arachnoid cysts Dandy-Walker malformation Previously shunted patients with difficulties Slit ventricle syndrome Recurrent or intractable shunt infections Recurrent or intractable shunt malfunctions Low Success Rates (<50%) Myelomeningocele (previously unshunted, neonatal patients) Posthemorrhagic hydrocephalus Postinfectious hydrocephalus (excluding aqueductal stenosis of infectious origin)

Several clinical features influence the outcome of ETV (Table 54-7). There appears to be a significant association between increasing patient age and a more favorable outcome.^96,97,99,108 Evidence suggests that this association applies to the age at which hydrocephalus initially developed, as well as the age at the time of ventriculostomy.^97,108 Several studies show success rates of approximately 50% in patients younger than 2 years, regardless of cause.^96,97,100 Results have been reported as even poorer in patients younger than 6 months.¹⁰⁸

Table 54-7 Favorable Clinical and Radiographic Features for ETV

Clinical

Cause of hydrocephalus in high or intermediate success group (see Table 54-6)

Age >6 months at time of hydrocephalus diagnosis

Age >6 months at time of procedure

No prior radiation therapy

No history of hemorrhage or meningitis

Patient previously shunted

Radiographic

Clear evidence of ventricular noncommunication

Obstructive pattern of hydrocephalus

Aqueductal anatomic obstruction

Lack of aqueductal flow void on T2-weighted MRI

Favorable third ventricular anatomy

Width and foramen of Monro sufficient to accommodate endoscope

Rigid >7 mm

Flexible >4 mm

Thinned floor of third ventricle

Downward bulging floor draped over clivus

Basilar posterior to mammillary bodies

Absence of structural anomalies impeding procedure

AVM or tumor obscuring third ventricular floor

Enlarged massa intermedia

Insufficient space between mammillary bodies, the basilar, and the clivus

Basilar artery ectasia

AVM, arteriovenous malformation.

In recent years, the value of endoscopic treatment for hydrocephalus in the developing world has been demonstrated.^109–115 Given the obstacles to urgent access for treatment of shunt malfunction in this environment, shunt dependence is more dangerous in the context of the developing world.¹⁰⁹ However, the low success rate for treatment of infant hydrocephalus by ETV alone has been problematic. The addition of bilateral lateral ventricle choroid plexus cauterization (CPC) to the ETV procedure has significantly increased the likelihood of success for endoscopic treatment of infant hydrocephalus regardless of etiology, thus expanding the applicability of endoscopic treatment for infants in this setting.^110–112 In the extensive experience from Uganda, combined ETV/CPC has been successful in treating hydrocephalus among infants younger than 1 year with postinfectious hydrocephalus (62% success), hydrocephalus associated with myelomeningocele (76% success), and other hydrocephalus of noninfectious origin (72% success). The role of ETV/CPC in treating posthemorrhagic hydrocephalus of prematurity is not apparent from the East African experience, but this is currently under investigation in the United States where, unlike Africa, this is a common cause of infant hydrocephalus.

Many studies had demonstrated a trend toward more successful ventriculostomy outcome in patients with existing shunt systems.^96,100,108 Indeed, ETV has been found to be useful in the treatment of intractable shunt infections and malfunctions and even slit ventricle syndrome refractory to other treatments.^{95,99,116–120} However, other series of ventriculostomy in previously shunted patients have been less promising.^101,113 These contradictory results may reflect the mix of patients in small series. An improved outcome in previously shunted patients was attributed by some to increased CSF absorptive capacity; however, the effect of the shunt itself on CSF absorption is difficult to distinguish from the effect of increased age in these patients. More recently, a history of prior shunt dependence was found to be an independent risk factor for ETV failure in the analysis of a large database from developed countries.¹¹⁴

Formalized methods for predicting the likelihood of ETV success, and thus for improved patient selection, have been recently reported.^114,115,122 An ETV success score based on a large database from developed countries incorporates the parameters of age, etiology, and previous shunt.¹¹⁴ Another success score developed from the Ugandan experience is based on age, etiology, and the extent of CPC as variables that independently influence outcome.¹¹⁵ The presence of scarring in the prepontine cistern has been shown to independently double the risk of ETV failure, whereas an open aqueduct has been shown to increase the risk of failure by 50%.¹²³ Where available, MRI FIESTA (constructive interference in steady state) imaging may prove useful in defining the status of the cistern and of the cerebral aqueduct preoperatively.

Table 54-7 also depicts preoperative radiographic criteria that have been frequently cited for improving outcome and limiting morbidity of ETV. Preoperative MRI optimally demonstrates all relevant anatomic features and should be obtained for all proposed ETV patients. Initially, confirmation of noncommunicating hydrocephalus of favorable cause should be established by the pattern of ventricular dilatation. Anatomic obstruction of CSF pathways between the aqueduct and the fourth ventricular outflow foramina may be visible on T2- or T1-weighted images. Additionally, T2-weighted images may reveal absence of the aqueductal CSF flow void frequently present in normal individuals. Extraventricular sites of obstruction, such as posterior fossa arachnoid scarring, may also cause noncommunicating hydrocephalus.¹²⁴ In addition, ETV has been reported to successfully treat cases in which ventricular outlet obstruction is not apparent, such as idiopathic normal pressure hydrocephalus, as well as communicating hydrocephalus secondary to trauma, hypertensive intracranial hemorrhage, tuberculous meningitis, and subarachnoid hemorrhage.^125–129 Given the significant risk of ETV failure in the face of prepontine cistern scarring,¹²³ preoperative MRI with FIESTA sequences may prove useful in refining patient selection.

Once the patient’s suitability for the procedure has been established, the neurosurgeon must clarify the details of third ventricular anatomy that are likely to affect morbidity. First, the width of the third ventricle and diameter of the foramen of Monro must be sufficient to accommodate the endoscope of choice (see the later section on technique). Additionally, the thickness of the third ventricular floor and the anatomy of the proposed puncture site in relationship to vital structures, particularly the basilar artery and its branches, must be assessed. A downward-bulging third ventricular floor draped over the clivus has been cited as a prerequisite for this procedure in the past, but others have not found this to be necessary.^97,103 Ultimately, the surgeon must be satisfied that there is no structural lesion (i.e., tumor or arteriovenous malformation) or anatomic variation that would render the procedure unduly difficult or hazardous. In cases of doubt, it is reasonable to visualize the floor of the third ventricle and abandon the procedure if the floor is unsuitable.

Technique

An ever-increasing variety of endoscopic equipment is available for neuroendoscopic procedures. For uncomplicated ETV, a 0- or 30-degree rigid scope is most commonly used. This offers superior optics and anatomic orientation. The Gaab endoscope (Johnson & Johnson, Randolph, MA), inserted through a 7-mm rigid cannula, provides the advantage of two working ports with a third for continuous irrigation. A 3.7-mm flexible steerable endoscope (Karl Storz, Tuttlingen, Germany) introduced through a No. 12 French peel-away sheath allows improved maneuverability within the ventricular system, at the expense of some image quality. Alternatively, this endoscope can be passed directly into the lateral ventricle without the use of a sheath in infants with a thin cortical mantle. In addition to performing the ETV, flexible scopes are useful for accessing more remote portions of the ventricular system (i.e., pineal recess or aqueduct), as well as for bilateral cauterization of the lateral ventricular choroid plexus. Several miniature fiberoptic endoscopes are also now available. These scopes can be inserted through a standard ventricular catheter; however, their inferior optics and lack of an irrigating or working channel limit their potential applications (i.e., ventricular catheter placement).

A miniature video camera is attached to the endoscope, and orientation is adjusted before insertion. The monitor should be placed at a comfortable distance and height for viewing throughout the case. Use of the camera allows the senior surgeon, trainee, and operating room staff to view the entire procedure, greatly enhancing the opportunities for learning without added morbidity. Newer cameras have digital filters that can be used to “clean up” the picture when flexible fiberoptic scopes are being used.

Adequate continuous or intermittent irrigation is imperative for proper visualization, particularly if bleeding is encountered. This irrigation is provided by body temperature Ringer’s lactate solution. An uninterrupted release pathway for irrigation fluid is essential to avoid dangerous elevations of intracranial pressure. A separate channel for fluid release can be intermittently or partially blocked to provide transient pressure tamponade for control of bleeding. Direct, gentle pressure using the scope cannula itself, the tip of an instrument such as a Bugby wire, or a balloon compression catheter can also be useful for hemostasis.

ETV can be performed with either a flexible or a rigid endoscope. The patient is positioned supine in a horseshoe headrest with the neck flexed 15 to 20 degrees. A bur hole is made over the right coronal suture, along the midpupillary line. Optimal positioning of the bur hole varies slightly depending on the proposed trajectory, as determined from preoperative MRI. The bur hole is placed more anteriorly to provide access to the posterior third ventricle if desired. The dura is opened in cruciate fashion, and the pial surface is coagulated and incised. A 3-mm-diameter, blunt-tipped brain needle is inserted into the right frontal horn, directed toward the foramen of Monro. After CSF sampling and intracranial pressure assessment, the needle is withdrawn, and the same tract is used for insertion of the endoscope sheath or cannula. This technique allows blunt separation of the ependymal layer and progressive enlargement of this opening, minimizing ependymal bleeding, a common cause of poor intraventricular visualization. In infants, an approach is easily made from the right lateral corner of the anterior fontanel without any bone removal. This allows for formal dural incision and primary closure of the durotomy at the end of the procedure, which minimize the risk of postoperative CSF leakage. Use of this technique is especially important for infants with severe ventriculomegaly and a thin cortical mantle. Infants can be conveniently positioned, prepped, and draped as for a right frontal VP shunt placement in the event that technical failure necessitates shunt placement.

Once insertion of the endoscope into the lateral ventricle has been achieved, the foramen of Monro is located by identification of the choroid plexus and septal and thalamostriate veins (Figs. 54-6A and B and 54-7A). After passage of the endoscope through the foramen of Monro, the optic chiasm, infundibulum, mammillary bodies, massa intermedia, and aqueduct can all be observed along the floor of the third ventricle from anterior to posterior, depending on trajectory (Figs. 54-6C and D and Figs. 54-7B and G). A flexible scope is generally necessary to view the lamina terminalis, suprapineal recess, or third ventricular roof. In cases of obstructive hydrocephalus, a diamond-shaped transparent membrane is commonly seen between the mammillary bodies and the infundibulum. The dorsum sellae, clivus, and basilar artery are often visible through this membrane (Fig. 54-7B). This area of the third ventricular floor between the clivus and the basilar artery is the ideal site for ETV.

Numerous methods of perforating the third ventricular floor have been described that use the scope itself, a cautery unit, laser, or endoscopic instrument.^{96,99,103,130–132} We advise never penetrating the third ventricular floor with cautery or laser because of increased risk of damage to underlying structures, such as the basilar artery. A closed blunt biopsy forceps for initial fenestration can be used, followed by dilation of the stoma with a No. 4 French Fogarty balloon catheter (Fig. 54-7C through E). Care is taken to inflate the balloon with sterile irrigation fluid only under direct vision within the opening, because blindly withdrawing an inflated balloon from the basal cisterns carries a significant risk of injury to perforating vessels. Alternatively, if using a flexible endoscope, the floor can be penetrated with the tip of a Bugby wire, using no electrocautery, and the opening subsequently widened by gentle stretching at the margins of the developing stoma. This is easily accomplished by flexing the steerable tip of the endoscope. After adequate enlargement of the ventriculostomy, the scope can be advanced to inspect the prepontine and interpeduncular cisterns (Fig. 54-7F). The flexible endoscope also allows access to the lamina terminalis, which can be used as an alternative ETV site if technical or anatomic issues preclude use of the third ventricle floor.

Postoperative management of patients after ETV must be individualized to address the unique preoperative and intraoperative details of each case. Infants or patients presenting with subacute hydrocephalus and uneventful procedures may require only short-term postoperative observation, whereas patients with acute presentations, prior shunt dependence, or significant intraoperative bleeding often require an EVD with continuous ICP monitoring in an intensive care unit setting. Patients undergoing a simultaneous endoscopic tumor biopsy or removal of a prior existing shunt system require particularly close observation and monitoring.

In the past, postoperative CSF shunting was recommended to promote expansion of pericerebral CSF spaces and improve absorption.^104,106,113 Compelling evidence suggests, however, that CSF flow through the ventriculostomy maintains its patency, and shunts can lead to closure of the opening.^95,113 We do not recommend a coexisting CSF shunt and ETV.

Choroid Plexus Cauterization

Bilateral lateral ventricle CPC, when performed in combination with ETV, has been demonstrated to be significantly more successful than ETV alone in infants younger than 1 year.^110–112 The combined procedure (ETV/CPC) can be performed with a flexible steerable ventriculoscope via a single approach through the right lateral corner of the anterior fontanel in the midpupillary line, as described earlier. After completing the ETV, attention is turned to the choroid plexus of the right lateral ventricle. Beginning at the right foramen of Monro, the plexus is cauterized with the tip of the Bugby wire (Fig. 54-8A). A monopolar current is used at its lowest effective setting. The tip of the wire is not buried in the substance of the plexus but rather is used to work along its surface, keeping the tip in view. It is imperative to avoid transgressing the ependyma or the choroidal fissure. The plexus is cauterized along its axis back to and including the glomus choroidea (Fig. 54-8B). The superior choroidal vein is typically in view, running along the surface of the plexus, and this is coagulated completely. Care must be taken to avoid injury to the thalamostriate and internal cerebral veins. Once at the atrium, the flexible scope is advanced slightly into the occipital horn posterior to the thalamus, where the tip is flexed and the scope slightly torqued to direct the procedure along the plexus within the temporal horn to its anterior extremity (Fig. 54-9A and B). Once all accessible plexus in the right lateral ventricle has been coagulated and shriveled, the left lateral ventricle is accessed. This requires a septostomy if the septum pellucidum is competent. The point for septostomy is chosen superior to the posterior margin of the foramen of Monro in an avascular region, avoiding the septal vein and its branches. A small circular area is cauterized and then penetrated with the Bugby wire. A cavum septum pellucidum requires deliberate fenestration of each distinct leaf. The scope is passed into the contralateral lateral ventricle, avoiding any contact with the underlying forniceal columns. The contralateral choroid plexus is then easily accessed and cauterized in the same fashion (Fig. 54-9B).

Outcome

The goal of ETV and, to date, the best objectively quantifiable measure of a successful outcome is shunt independence. ETV has yielded a higher success rate with lower morbidity and mortality than earlier methods of third ventriculostomy. Mortality rates for open ventriculostomy procedures varied between 5% and 27%, with success rates of 37% to 75%.^{19,95,103,105,113,133} Percutaneous radiographic and later CT-guided techniques reduced this mortality rate to 2% to 7%, with a 44% to 75% rate of shunt independence.^{95,102,103,106,113,134} Studies using modern endoscopic techniques and equipment, with or without stereotactic CT or MRI guidance, have reported low morbidity (3% to 12%) and essentially no mortality, with success rates greater than 75% for carefully selected patient groups. Table 54-8 depicts the results of earlier ETV studies with success rates by cause where this information is available. The new success prediction scores cited previously have helped define appropriate indications and predict the likelihood of success in an individual patient. Objective measures for postoperative assessment of these patients need to be refined.

One of the most confusing aspects of outcome evaluation in ETV patients is the failure of the ventricles to return to normal size. Most studies report a gradual decrease in the ventricular size over months to years postoperatively, with resolution of periventricular edema and increased extracerebral spaces, coinciding with clinical improvement.^{95–98,113,135} One series of patients treated with either CSF shunts or ETV showed no difference in intellectual outcome despite enlarged ventricles in the ETV group.¹³⁵ A more recent study of infants with myelomeningocele and hydrocephalus demonstrated no difference between patients treated by shunting or those treated by combined ETV/CPC in regard to early developmental outcomes.¹¹³ In that study, there was little difference among shunted patients, patients treated by ETV/CPC, and patients who required no hydrocephalus treatment in regard to ventricular size. Furthermore, no association was demonstrated between ventricle size and developmental outcome. Multiple authors have reported late failures, in which the ventriculostomy closes sometimes years postoperatively.^97,109,136 However, late ETV failure appears to be rare. Importantly, in contrast to the ongoing lifetime risk of shunt failure, the majority of ETV failures have been shown to become apparent within 6 months of the procedure.^112,115,135 Radiographic evaluation of suspected closure is confounded by the presence of persistently enlarged ventricles, and closure must often be suspected solely on the basis of clinical evidence.

Studies detailing the serial measurements of multiple radiographic indices of ventricular size postoperatively show that the third ventricular size responds more quickly (usually within 3 months) than the lateral ventricular size (2 years).^135,137 Additionally, third ventricular size appears to correlate most closely with outcome in these patients.^98,135,137 Several newer modalities appear promising as potential objective measures of ventriculostomy function. MRI detection of T2-weighted flow void around the ventriculostomy has been correlated with clinical outcome in ETV.^138–140 This observation has proved most helpful in confirming ventriculostomy patency postoperatively, particularly in patients with persistent ventriculomegaly.^139,140 Actual quantification of flow velocity through ventriculostomies has also been demonstrated by phase-contrast MRI and Doppler ultrasonography.^141,142 Intraventricular pressure has been observed to return to normal over 3 months in a patient after third ventriculostomy who underwent concurrent implantation of a telemetric ICP monitor.¹⁴³ For patients in whom an EVD is placed postoperatively, such as those undergoing ETV in the face of shunt failure, ICP may take several days to normalize, and serial lumbar puncture has been reported to facilitate this process.¹⁴⁴ We hope that methods of quantifying ventriculostomy function will allow neurosurgeons to refine further the techniques necessary to improve outcome. Radiographic confirmation may also help define indications with more subjective outcomes, for example, the observation of less fulminant shunt malfunctions in patients after ventriculostomy.⁹⁹

Complications

Several series of ETVs report no mortality and low morbidity (Table 54-8).^{95–101,109–112,116,139,145–147} The most common serious complications are related to structures in and around the floor of the third ventricle. In patients with aqueductal obstruction, the third ventricular floor is usually thinned out and transparent and the hypothalamic nuclei displaced laterally. When the floor is not thinned or the ventriculostomy is not performed at the preferred midline site, injury to the hypothalamus or bleeding can result. These complications have been attributed to direct pressure from the perforating instrument, elevated CSF temperature from cautery or the light source, or distention of the third ventricle from continuous irrigation without adequate drainage.⁹⁸ Reported complications from injury to this area include the syndrome of inappropriate secretion of antidiuretic hormone, diabetes insipidus, loss of thirst, amenorrhea, and trancelike states.^136,148 These complications are usually transient. Bradycardia is also observed occasionally, when perforating a thickened third ventricular floor, and a near-fatal cardiac arrest has been reported.¹⁴⁹ Transient postoperative fevers, which frequently occur in these patients, are commonly attributed to irritation of the ependyma from blood or manipulation of the hypothalamus.¹³¹

Other structures at risk in this area include the third and sixth cranial nerves, fornix, and caudate. Injuries to all of these structures, usually transient or clinically silent, have been reported.^136,148 The major life-threatening risk during the procedure is injury to the basilar artery and its branches. The basilar bifurcation is usually visible through the thinned third ventricular floor. Extreme caution should be taken to avoid injuring these vessels, particularly when preoperative imaging suggests a thickened ventricular floor or aberrant location (i.e., anterior to the mammillary bodies) of these vessels. We perform the initial fenestration with a blunt instrument rather than the cautery or laser to minimize the risk of arterial damage. Injury to these vessels can result in catastrophic hemorrhage, stroke, or pseudoaneurysm formation.¹⁵⁰ Other routine complications, associated with most neurosurgical procedures, have also been observed. Superficial wound infections, meningitis and ventriculitis, subdural hematomas, and CSF leaks have all been described.^98,136,148