Catheter angiography is an invasive procedure; thus, preoperative planning, as for any surgical procedure, is critical. The indications must be reviewed in light of all previous imaging studies, prior surgical procedures, and evolution of the anatomic pathology. Discussion among the angiographer, referring clinician, consultants, the patient, and the patient’s family should result in consensus on goals and expectations for treatment. It is important that the angiographer obtains a tailored history and physical examination in order to identify specialty-specific factors such as allergies, medications, and renal or hematologic diseases that could delay or alter performance of the angiogram. Preprocedural physical examination including neurologic evaluation is also important so that any changes during the procedure can be quickly recognized and expeditiously treated. Evaluation of the extremities, including lower extremity pulses, is relevant to selection of a site for vascular access. Unique risks to pediatric angiography are the development of leg length discrepancy and claudication due to injury of the femoral artery and femoral capital necrosis due to injury of the foveolar artery. Other complications of diagnostic angiography include stroke, iodinated contrast reaction, renal failure, and puncture site hematoma (15,16,17,18). In general, catheter cerebral arteriography can be performed with a minimum of risk (0.3%) at experienced centers (8).

Prior to embolization of an arteriovenous malformation (AVM), an echocardiogram possibly including a “bubble test” is warranted to evaluate for the presence of right-to-left intracardiac shunts. It is possible for embolic materials or thrombus to pass through an AVM into the normal venous drainage and the right side of the heart. Ordinarily, these small emboli will be filtered by the pulmonary vascular bed and in small numbers without any clinically significant consequences. Intracardiac shunts, common in pediatric patients with certain cerebrovascular malformations, could cause such emboli to pass from the right heart into the left heart and recirculate into the arterial system. The presence of intracardiac shunts means that great care must be undertaken during the embolization procedure to avoid the use of agents likely to pass through the cerebral AVM with resultant embolization to the systemic circulation (19). Pulmonary arteriovenous shunts are also a clinical concern in young patients with hereditary hemorrhagic telangiectasia syndrome (HHT, also known as Osler-Weber-Rendu disease). In such patients, assiduous attention to eliminating all air from venous access lines is required in order to lower the risk of air embolism-induced stroke. Clear communication with practitioners providing anesthesia or intravenous medications preoperatively, intraoperatively, and postoperatively is imperative. The use of air filters on intravenous lines (e.g., 0.22 micron filters) can also reduce the risk or air embolism in patients with intracardiac or pulmonary shunts (20).

The importance of preoperative preparation in regard to the pediatric patient cannot be overemphasized (21,22). Medications (including iodinated contrast) can cause dramatic shifts in intravascular fluid volume and vasomotor tone. An ill child may appear hemodynamically stable but, in actuality, may be exerting maximal physiological mechanisms to maintain blood pressure, systemic, and cerebral perfusion. Administration of sedatives, anesthetics, or vascular contrast can cause hemodynamic collapse in a volumedepleted child. As children undergoing cerebral arteriography may have elevated intracranial pressure (ICP), adequate ventilation is essential to prevent buildup of CO₂ (and consequent elevation of ICP) that could result in herniation syndromes or hinder cerebral perfusion. Occasionally, manipulation of ventilation rate and blood pressure may be necessary to modulate arterial carbon dioxide levels and vasomotor tone. Changes in the pCO₂ can be used to enhance cerebral arteriographic resolution, to reduce the volume of contrast, or to assist distal microcatheter manipulation (23). However, in children with suspected ischemic stroke, especially in the setting of moyamoya disease, blood pressure should be supported while maintaining normal pCO₂. These children will stroke if overventilated. Therefore, the pCO₂ should only be manipulated by highly experienced personnel and in the presence of ICP monitoring in order to prevent cerebral hypoperfusion and herniation syndromes. Careful monitoring during the administration of sedative medications and vascular contrast is essential.

To limit osmotic fluid shift and to reduce the incidence of contrastinduced renal injury, contrast dose (300 mg iodine/mL nonionic contrast) should not exceed 6 cc/kg. For routine digital subtraction angiography, contrast can be diluted by 50% (to 150 mg iodine/mL) if modern fluoroscopic equipment is used. Modern “biplane” neuroangiography equipment allows acquisition of arteriographic series in two projections simultaneously. Evaluation of high-flow arteriovenous shunts may require use of full-strength contrast. In order to get the most angiographic information out of each intra-arterial contrast injection in babies with high-flow intracranial shunts, in addition to standard “first-pass” arterial and venous phase images of the brain, the practitioner can continue to acquire angiographic images through the “second-pass” of contrast once it has gone through the patient’s heart and is now being pumped (albeit in dilute form) through both vertebral arteries and carotid arteries back through the entire brain. Secondpass angiography provides an overview of the relationship between the primary feeders of a vascular malformation and other cerebral vessels. Each catheter, including access sheaths, must be continuously flushed with heparinized saline (1000 units heparin/L) through a flow-regulated system with at least 3 cc/h. However, overly exuberant flushing can cause fluid overload and congestive heart failure (CHF) in small children or children with renal impairment. The anesthesiologist should be informed of the total fluid infusion volume and rate of fluid administration through all catheters. Limitations to contrast and fluid load are a common indication for staging embolization procedures over several sessions in very young children—for example, neonates with high-flow VOGMs—with time in the ICU in-between embolization sessions during which fluid and contrast can be removed either naturally through urinary excretion or, in the sickest children, through dialysis.

Arterial access is the first critical step in performance of any pediatric neuroangiographic procedure. A child’s vessels are small in caliber, prone to spasm, highly mobile, and elastic. These factors often conspire to make arterial access a daunting challenge. Use of real-time ultrasound guidance during micropuncture access to the femoral artery has made a femoral artery puncture significantly easier in the past decade than in prior eras, however. Improper technique can result in laceration or thrombosis of the vessel. Arterial cannulation is facilitated by extension of the legs and elevation of the pelvis to straighten the common femoral artery. Following induction of general anesthesia, systemic blood pressure is often reduced, and manual palpation of the femoral and pedal pulses may become difficult. Marking the skin over the femoral puncture site as well as the foot over the dorsalis pedis and posterior tibialis pulses prior to anesthetic induction can facilitate cannulation and postoperative patient assessment. Proper positioning and padding of pressure points is necessary, particularly in infants and small children. Use of a Micropuncture set and a 3 or 4 French access sheath-catheter system will help to reduce local trauma at the puncture site. Analogous to the concept of ALARA in x-ray dose limitation, keeping the caliber of vascular sheaths placed in the arteries of children as small as possible is key to lowering the risk of arterial injury, access site thrombosis, and distal arterial embolization. Although rare, and often difficult to attribute to a particular angiographic procedure, the potential for adult leg length discrepancy as a late complication of transfemoral angiography in very young children whose lower extremity blood flow could be compromised by femoral artery occlusion or stenosis, should be mentioned to parents during informed consent discussions prior to angiography. It can also be helpful intraprocedurally to have pulse oximeters placed on both great toes: reduced flow to the foot on the side of femoral artery access can be followed intraprocedurally and may be managed with administration of nitropaste, another vasodilating medication, or heparin after access has been achieved.

Systemic heparinization (70 units/kg) during catheterization may also reduce the risk of thrombosis. Assessment of anticoagulation status in the angiography suite is rapidly performed using the activated clotting time (ACT). Depending upon the indication for angiography and other mitigating factors, an ACT 2-3X baseline value is considered therapeutic. In the presence of a recent cerebral hemorrhage or surgical procedure, anticoagulation may be contraindicated. A lower level of anticoagulation for interventional procedures should be considered, if necessary. Following removal of the femoral sheath, access for subsequent arteriographic procedures should alternate between the right and left femoral arteries. In special circumstances, such as neonatal arteriography, the umbilical artery and vein readily provide vascular access for catheter systems sized up to 5 French. If so requested, the neonatology service will maintain umbilical catheters to permit arterial and venous access for endovascular procedures. Umbilical artery access is particularly helpful for the treatment of high-flow intracranial lesions in neonates, as it generally allows multiple embolization sessions with less chance of access site scarring than femoral artery access (24).

The choice of angiographic catheter depends upon the application and patient size. The smallest diameter catheter that readily permits diagnostic arteriography is a 3 French catheter, which is used in neonates and infants. Smaller diameter catheters do not generally allow sufficient injection rate for routine arteriography. Slightly larger (4 French) catheters can be used in older children and provide greatly improved injection rates due to decreased flow resistance. Diagnostic catheters with an intrinsic hockey-stick tip-shape can often be custom-shaped using steam heating to reduce their angulation and allow them to sit less traumatically in the relatively straight cervical vessels of small children without high-flow lesions. For children with high-flow lesions, cervical vessels are often markedly tortuous and more angulation of catheter tips can be advantageous. Although not angulated, the same distal access catheters that have become widespread as intermediate support catheters during stroke intervention in the last decade have also gained popularity as access catheters for intracranial interventions in children either in combination with a short vascular access sheath or as a stand-alone. Manipulation of these catheters without a sheath at the access site with attendant vasospasm and potential damage at the access site, however, may limit their utility in cases wherein extensive navigation between multiple arterial pedicles is necessary. The length of distal access catheters may also limit their utility in small children, as the long segment of these catheters external to the patient needs to be stabilized in order to prevent extracorporeal torque dissipation during catheter navigation. Standard microcatheters can be advanced either through a 4 French diagnostic catheter platform in the cervical vessels or directly through a 4 French access sheath in the femoral artery without coaxial passage into the craniocervical region. Older children and adolescents will tolerate the use of the 4 to 6 French catheter systems commonly used in the adult population. Percutaneous access sheaths are used routinely in our practice to facilitate catheter exchange and to reduce trauma at the puncture site.

The purpose of interventional neuroradiology is the minimally invasive treatment of vascular lesions. The fundamental principle of this treatment is occlusion of pathological vascular channels to improve
the patient’s neurological or cardiovascular condition. Embolization, or endovascular occlusion, requires placement of the tip of a microcatheter in proximity to the abnormal vessels so that these channels can be selectively occluded, sparing normal or other needed vessels. Recent and ongoing developments in catheter technology allow careful and precise placement of embolic materials within the abnormal vascular channels while avoiding embolization of the normal adjacent vessels. A number of embolic materials are currently in use, and many more are under development or employed in clinical practice outside the United States. Table 12-1 lists some characteristics of some of the more commonly used embolic materials. A complete review of the specific applications of these embolic agents is beyond the scope of this text.

At completion of an arteriographic procedure, the femoral access catheter must be removed and the puncture site must be manually compressed. Arterial closure devices generally require an artery that is at least 5 mm in diameter to be deployed safely; these devices are also currently not approved for use in children in the United States. Ideally, the catheter is removed while the patient is still under anesthesia to assure optimal control of the puncture site. Continuous Doppler monitoring of the pedal pulses is recommended to prevent excessive pressure with inadvertent thrombosis of the femoral artery during manual compression. Hemostasis is usually attained within 15 minutes in a patient with normal coagulation parameters. An anticoagulated patient may require the administration of protamine sulfate (10 mg protamine per 1000 units of active heparin in the blood) to reverse the effects of heparin prior to removal of the access catheter. Coagulopathy for other reasons may require administration of blood products or synthesized hemostatic factors. With an ACT below 180 seconds, it is usually possible to obtain arterial hemostasis. Thereafter, the patient should be closely monitored for several hours for evidence of puncture site bleeding, subcutaneous hematoma, or loss of distal pulses. Due to often exuberant arterial vasospasm, delayed access site bleeding appears to be less common in children than in adults. In younger children, keeping a common femoral artery puncture site immobile for several hours can be challenging. One technique to encourage the child not to bend at the hip is to use a soft knee brace or knee immobilizer applied loosely to the knee on the side of the arterial puncture. As most children tend to flex at the knee at the same time they flex at the hip (“frog-leg” movement), keeping the knee straight often reduces the urge to flex at the hip too.