Cerebrospinal Fluid Diversion Procedures in the Pediatric Population

Ventriculoperitoneal Shunts

There are many variations in the technique of installing a ventriculoperitoneal shunt. Meticulous attention to detail and thorough planning of the procedure are likely to reduce shunt-related complications, the vast majority of which are related to blockage or infection.

The patient is placed under general endotracheal anesthesia, with the administration of intravenous antibiotics on induction. Antibiotic selection provides coverage for typical organisms of surgical site infections such as staphylococci, with additional coverage if methicillin-resistant Staphylococcus aureus (MRSA) have tested positive preoperatively or there is suspicion of MRSA colonization (i.e. frequent hospitalizations, prior MRSA infection). The bladder should be emptied at the start of the case with either straight catheterization or Foley catheter insertion.

Various techniques have been described to determine the proper location for the burr hole. Many surgeons measure distances from either the ear or the midline to approximate the site of the burr hole. It is important to correlate the projected burr hole location with the optimal location on the preoperative imaging. Measurements made from CT scan images are probably more accurate than choosing the site of the burr hole based on arbitrary surface landmarks. The use of neuronavigation optimizes the burr hole location without any guesswork but may increase the cost of the procedure and the time under anesthesia. Some neuronavigation techniques such as electromagnetic-based systems eliminate the requirement for head fixation in pins, thus allowing for easier positioning and tunneling.

The hair is shaved in the operating room to prevent it from twisting into the wound. A horseshoe headrest is typically used with a bolster placed under the shoulder that is ipsilateral to the ventricular catheter insertion site. In younger children, the head can be positioned on a donut with a small towel rolled underneath the shoulders. For the parieto-occipital burr hole, the head is rotated to the contralateral side and slightly flexed. This position is optimal for tunneling of the distal catheter because it provides a straight line from the cranial incision to the abdominal incision and allows good access to both the cranial and abdominal incisions. For a frontal burr hole, the patient is positioned supine on the horseshoe with the head tilted to the contralateral side ( Fig. 80.1A ). The burr hole is situated approximately 2 to 3 cm from the midline in the midpupillary line just anterior to the coronal suture. A small incision just posterior to the ear is usually required to tunnel through the subcutaneous tissue from the frontal region to the abdomen. The site of the burr hole and abdominal incisions should be selected and marked before draping. For frontal shunts, the postauricular incision should also be marked and prepped. The cranial incision should be made so that the implanted hardware is not placed directly under the incision. The skin is carefully prepped with an antiseptic solution such as povidone-iodine or chlorhexidine. Disposable, adhesive drapes are used to cover the patient and the entire operating table except for a small band of skin from the burr hole site to the abdomen, under which the tunneling will be performed (see Fig. 80.1B ). Iodine-impregnated transparent adhesive drapes are typically used; however, there is no evidence to suggest that shunt infection rates are reduced with this technique. Shunt protocols have been implemented at various institutions with improvements in shunt infection rates. The protocols are variable in terms of surgical preparation, use of antibiotics, draping, gloving, etc. The use of a standardized protocol has been shown to reduce shunt infection rate by several groups with different protocols. The Hydrocephalus Clinical Research Network (HCRN) group found that the implementation of a protocol significantly reduced shunt infection rates across their network. ^, Other groups with different protocols found similar results, where a unified checklist was strictly followed and led to significant reduction in infection rates.

A time-out is performed immediately prior to incision and includes verification of the patient, surgical side, administration of prophylactic antibiotics, and availability of necessary radiographic imaging and equipment. We typically infiltrate the wound with a local anesthetic mixed with epinephrine for improved hemostasis and pain relief at the surgical site. Before incision, all equipment and material needed for surgery are brought into the operating room to prevent traffic in and out of the room during the procedure; a sign requesting not to enter the room is placed on all entry doors.

A curved incision (see Fig. 80.1C ) is typically used with its pedicle in the direction of tunneling. It is important to keep the pedicle wide enough so that no shunt hardware lies under the incision and to ensure adequate blood supply to the wound area. A subgaleal pocket is created to secure the valve and the reservoir. The size of the burr hole is made large enough to insert the ventricular catheter, with consideration of the possible need to change the angle of entry if initial insertion attempts were not successful. The dural incision is minimized as much as possible to allow for the passage of the ventricular catheter only; this decreases the risk of CSF extravasation into the subgaleal space. The pia is opened using bipolar electrocautery at low voltage.

The abdominal incision is made simultaneously by a second operator whenever possible to decrease the operative time. There is no evidence that any specific incision location on the abdomen results in reduced complications. We typically perform an incision at approximately 2 to 3 cm to the right of the midline at a level that is few centimeters superior to the umbilicus. Some surgeons slide the dissector through the peritoneal opening to confirm entry (see Fig. 80.1D ), but this maneuver should be performed with great vigilance so that visceral structures are not injured. A mini-laparotomy or a trocar (see Fig. 80.1E ) may be used to access the peritoneal cavity. Various methods can be used to confirm the opening of and easy access through the peritoneal layer—an important step that should not be overlooked—such as visualization of intraperitoneal contents, flooding the field with warm saline, and watching the fluid as it drains into the peritoneum, and intraoperative lateral fluoroscopy. If general surgery assistance is required due to the presence of abdominal adhesions, direct visualization of entry into the peritoneum can be confirmed via laparoscopy.

Tunneling can either be performed cranial to caudal or vice versa, and it is made easier if the patient is positioned such that the mastoid, clavicle, and xyphoid are co-planar. The goal of tunneling is to stay deep within the subcutaneous tissue but superficial to the thoracic cavity, peritoneum, great vessels of the neck, and skull base. A curved snap may be used to dissect the soft tissue before the insertion of the tunneling device (see Fig. 80.1F ), which may be challenging upon the initial attempts. The device should be palpable below the skin at all times and should be carefully directed superficial to the ribs and clavicle. A common site of resistance to tunneling is the deep cervical fascia of the neck, and a separate incision may be necessary for better control of the tunneling process. The anesthetist should be made aware of the tunneling step due to the increased stimulation and possible changes in ventilation while tunneling along the chest. The peritoneal tubing is then passed through the tunneling sheath; attaching a suction device to the distal end and continuous irrigation can assist in the passage of the tubing.

The ventricular catheter trajectory is determined according to external landmarks or by using image guidance such as neuronavigation or ultrasound (see Fig. 80.1G and 80.1H ). From a frontal burr hole, the traditional landmarks for the foramen of Monro are the intersection of the plane through the midline and the plane just anterior to the external auditory meatus. If the patient’s head is tilted, these landmarks can be difficult to appreciate, thus electrocardiogram (ECG) electrodes placed at the nasion and external auditory meatus prior to draping may help to orient the surgeon. The optimal position for the tip of the catheter is anterior and superior to the foramen of Monro with a catheter length of 5 to 5.5 cm. From an occipital burr hole, an ECG electrode placed at the midpoint of the forehead at the hairline is used to direct the catheter to the frontal horn as opposed to the temporal horn. The catheter length is approximated at 5.5 to 6 cm, and the optimal tip position is the atrium of the lateral ventricle, which causes a “pop” feeling when the ependyma is penetrated, followed by an initial spurt of CSF. There is no evidence that multiple catheter passages affect outcome; however, minimizing the number of passages through the brain parenchyma is likely to decrease the rate of complications such as hemorrhage or future seizures due to gliosis. Endoscopic shunt placement (see Fig. 80.1I ) allows for visualization of the ventricular catheter in real time and can assist in guiding the tip of the catheter away from the ventricular walls or choroid plexus. Ultrasound guidance can identify entry of the catheter into the ventricle and therefore reduce the number of required passages.

After preparing a subgaleal pocket (see Fig. 80.1J ), the ventricular catheter is connected to the valve or valve/reservoir system, and ties are placed along all connections (see Fig. 80.1K ). Placing the suture knot on the underside of the connection sites can help in preventing skin erosions, especially in infants with thin cutaneous tissue. The valve system is positioned deep inside the subgaleal pocket (see Fig. 80.1L ), and the valve is firmly sutured to the pericranium (see Fig. 80.1M ). The peritoneal catheter should be checked for spontaneous CSF flow, and the surgeon should not initiate closure until the shunt is clearly draining CSF. The distal catheter is then inserted into the peritoneum. If the catheter does not cross easily, it may be coiling in the preperitoneal space or there may be abdominal adhesions. If a mini-laparotomy is performed, the abdominal fascia is closed followed by the deep subcutaneous tissue and the dermal layer to prevent the development of herniation through the abdominal wall.

Ventriculopleural Shunts

The ventricular catheter placement and tunneling steps of implanting a ventriculopleural shunt are identical to that of a ventriculoperitoneal shunt. A 3-cm transverse incision is placed along the anterior axillary line in the fourth-to-sixth right intercostal spaces or along the midclavicular line at the second intercostal space, and a muscle-splitting approach through the pectoralis major and intercostal muscles is made along the upper border of the rib to avoid the neurovascular structures. The parietal pleura is identified as a translucent thin membrane covering the lung, which appears to move with ventilation. The anesthetist deflates the lungs, and the pleura is sharply incised for around 2 to 4 mm; the lung retracts from the chest wall as the pleura is cut. After tunneling from the cranial incision, the distal catheter is approximated and cut to a smaller length and adequate CSF flow through the distal end is confirmed. The catheter is then introduced into the pleural space and guided along the chest wall away from the lung parenchyma. Note that, unlike in the peritoneum and to avoid damage to the lung parenchyma, excess catheter is not placed in the pleural space; an intrathoracic length of 30 cm should be sufficient to prevent potential future displacement. A Valsalva maneuver inflates the lung, and under continuous irrigation until air bubbles cease to escape from the pleural space, the site is closed in layers.

Lateral and anteroposterior chest radiographs are performed to confirm the catheter location and usually demonstrate a small pneumothorax as well as a small pleural effusion due to accumulation of CSF. The intrapleural fluid will typically disappear over the next several weeks. However, in select patients the pleural fluid may progressively accumulate and lead to respiratory distress requiring percutaneous drainage of the effusion.

Ventriculoatrial Shunts

The same steps of placing the ventricular catheter for a ventriculoperitoneal or ventriculopleural shunt are used for the ventriculoatrial shunt installation technique. Although some surgeons may prefer to place the distal catheter prior to inserting the ventricular catheter during a ventriculoperitoneal shunt surgery—due to risk of displacement, it is recommended to place the ventricular catheter before the distal one during ventriculoatrial shunting to prevent backflow and clotting of venous blood inside the distal end or dislodgement from the recipient vessel.

Depending on the chosen technique, different vessels can be used as access points to the right atrium. During the open approach, neck dissection is performed until the internal jugular vein (IJV) is exposed. After temporary blockade of the descending venous blood by pulling a rubber band placed around the proximal IJV, a purse-string suture is placed on the anterior part of the distal IJV, followed by a small incision, direct insertion of the catheter into the vein, and tight closure of the suture around the catheter. Alternatively, the transverse facial vein may be sacrificed, and its distal part is used to insert the distal catheter directly into the IJV. One or two sutures may be used to firmly secure the vein around the distal catheter after confirming adequate CSF flow. A minimally invasive technique, the percutaneous approach, is quite similar to installing a central catheter and may also be performed under ultrasonography. A 20/22-gauge cannulating needle is used to cannulate the IJV (1 to 3 cm above the clavicle between the sternal and clavicular heads of the sternocleidomastoid muscle) or the subclavian vein (below the clavicular bone at the junction of the middle and lateral third of the clavicle). This is followed by the passage of a guidewire inside the cannula, preferably under fluoroscopy, until it reaches the superior vena cava or right atrium. The cannula is removed, a nick incision is performed, and the peel-away sheath, with the dilator stacked inside it, is introduced into the vessel along the guide wire. The dilator and the guidewire are then removed, and the distal catheter is passed down the peel-away sheath as far as possible in the right atrium; the peel-away sheath is then removed. Under fluoroscopic guidance, the distal catheter is pulled back to its final position at the middle-to-lower segments of the right atrium (approximated to the T6 vertebral body level in healthy individuals). If the catheter tip is not visualized, injection of a small amount of radiopaque material will be helpful to pull back the catheter into its optimal position. Finally, the distal catheter is flushed with heparinized saline and connected to the valve or directly to the ventricular catheter using a straight connector after verifying adequate CSF flow from the tip of the ventricular catheter.