Aneurysms

Intracranial aneurysms are focal enlargements of an arterial wall due to disruption of arterial wall integrity. They can form secondary to trauma (5–10%), infection (15%), or, most commonly, dissection (50%).⁹ Aneurysms may be associated with a predisposing genetic disorder. For example, patients with coarctation of the aorta or polycystic kidney disease have an increased incidence of aneurysms, which usually remain asymptomatic during childhood. While less than 2% of aneurysms are found in pediatric patients,¹⁰ those that do rupture during childhood are most often fatal. Subarachnoid hemorrhage from spontaneous dissection is the most common presenting symptom.

Intracranial aneurysms account for about 10–15% of hemorrhagic strokes in patients younger than 20 years.¹¹ Saccular, or “berry,” aneurysms, which are classically seen in adults, are less common in children. The most common type of aneurysm found in the pediatric population is complex aneurysms including giant, mycotic, traumatic, multiple, or dissecting aneurysms.¹² These types of lesions have significant treatment implications, as their endovascular occlusion and surgical clipping can be more challenging. Endovascular occlusion is considered the first choice and can be utilized for most aneurysms, but microvascular treatment must still be used in some instances, such as when clip reconstruction or bypass is needed.

Preoperative blood pressure control is typically instituted prior to the procedure. This may be achieved with antihypertensive drugs such as labetalol, hydralazine, nicardipine, or even sodium nipride. The use of nimodipine (typical in the adult patient) is controversial in children. Patients may also be on antiepileptic medications as well. If elevated intracranial pressure from a subarachnoid hemorrhage is of concern, an external ventricular drain may be placed to prevent hydrocephalus. Approximately one-third of all subarachnoid hemorrhage (SAH) patients will ultimately require treatment of hydrocephalus, often involving placement of a ventricular shunt.

Anesthetic management again depends on the planned intervention. For aneurysm resection via craniotomy, the usual anesthetic concerns for a craniotomy apply. As expected, adequate intravenous (IV) access should be obtained and arterial waveform monitoring is essential. Preparation for potential sudden and massive blood loss is crucial; blood products should be on hand in the operating room (OR) and ready to administer. Perioperative hemodynamic stability is of utmost importance. Deep preoperative sedation may be preferable to facilitate a smooth induction and avoidance of sudden hypertensive episodes. Adequate depth of anesthesia prior to invasive procedures such as endotracheal intubation or placement of head pins is necessary to prevent precipitous hypertension. The utility of a skull block to attenuate blood pressure swings during head pinning and incision has been demonstrated in the adult population, although its usefulness in smaller children may be limited by threshold of local anesthetic toxicity.¹³ Care should be taken by the surgical team on injection of local anesthetic into the surgical field to avoid excessive use of epinephrine and consequent tachycardia and hypertension. Excessive hypertension during emergence must also be avoided to prevent postoperative bleeding. However, in most cases of aneurysm clipping, a slightly elevated blood pressure may be desirable postoperatively to minimize the risk of vasospasm.

Immediate awakening after aneurysm clipping is particularly important to allow for a neurologic examination. Postclipping, vasogenic cerebral edema with increased intracranial pressure (ICP) or hemorrhage may occur secondary to normal perfusion pressure breakthrough (NPPB). NPPB occurs when vessels surrounding the aneurysm that were chronically maximally dilated are unable to autoregulate (and vasoconstrict) after clipping. Hyperemia then ensues at normal perfusion pressures (or normotension). Thus, moderate hypotension postoperatively (while maintaining CPP) may be desired. Treatment for NPPB may also involve moderate hypothermia and therapy for increased ICP, including diuretics, or head elevation.

Postoperative concerns following aneurysm resection or embolization include vasospasm, serum sodium disturbances, and rehemorrhage. Vasospasm is extremely rare in children, but when it does occur it is typically 4 to 14 days postoperatively. The treatment strategy for vasospasm—which has been extrapolated from the adult literature—includes the calcium channel blocker nimodipine (though controversial in children), “triple-H” therapy (hydration, hemodilution, and hypertension), and angioplasty or intra-arterial vasodilators. If hyponatremia occurs, its exact cause must be identified in order to determine the appropriate treatment. If it is due to cerebral salt wasting syndrome (hypovolemic hyponatremia), treatment is with IV replacement of isotonic fluids. If syndrome of inappropriate antidiuretic hormone (SIADH) is diagnosed (hypervolemic hyponatremia), water restriction should be instituted. Very rarely, rehemorrhage or stroke can occur from faulty clip placement. If this occurs, surgical exploration and evacuation may be necessary. This may involve a reopening of the craniotomy to adjust, reposition, or replace the clip.

Vascular Effects of Trauma and Infection: Carotid Dissection and Cerebral Venous Sinus Thrombosis

Carotid artery dissection (CAD), though rare, is an important cause of acute ischemic stroke in children. The estimated incidence of CAD in children is low at 0.03% after blunt head/neck trauma. However, in children, CAD can be clinically silent, and this frequency may be underestimated.¹⁴ The location of carotid dissections may be extracranial or intracranial. These children will often require an anesthetic for magnetic resonance imaging (MRI) and MRA evaluation of the injury. Extracranial CADs are, overall, the most common location of traumatic vascular dissections of the head and neck in all patients (adults and children).¹⁴ Extracranial CAD is typically a result of trauma to the neck or spine, due to blunt trauma, hyperextension, or rotational injury. Arterial dissection has been associated with a number of other comorbidities including connective tissue diseases (e.g., Ehlers-Danlos syndrome), substance abuse, use of oral contraceptives, and fibromuscular dysplasia. However, CAD can occur in otherwise healthy patients as well. Importantly, dissection may go unnoticed at the time of injury and symptoms of TIA or stroke may be delayed several days after the inciting event. Although intracranial CAD is rare in adults, it is relatively common in children, accounting for 60% of carotid dissections, which are usually spontaneous in nature with no identifiable predisposing risk factors.¹⁴ However, traumatic intracranial CAD may be caused by penetrating soft palate injuries with objects such as pens or sticks and is associated with high morbidity and mortality. Patients presenting with intracranial CAD are also at risk of SAH in addition to embolic stroke.

Treatment of symptomatic extracranial CAD typically involves anticoagulation (in patients without concurrent intracranial dissections). For extracranial CAD, surgical intervention, such as endarterectomy and thrombectomy or carotid ligation, is usually reserved for patients with recurrent transient ischemic attacks (TIAs) or progressive neurologic deficits. In contrast, aggressive surgical intervention such as clipping or resection is typical for most patients with intracranial CAD (though endovascular techniques have been employed successfully).¹⁴

Cerebral venous sinus thrombosis (CVST) is rare, affecting 0.67 per 100,000 children per year, however it accounts for a significant proportion of ischemic strokes in the pediatric population.¹⁵ At approximately 50% of children with CVST, neonates and young infants are among the most commonly affected. The etiology of CVST is often multifactorial and there are many comorbid conditions that have been identified as risk factors. Perinatal complications tend to dominate in the neonatal population. For children outside of the neonatal period, infection is the most commonly associated condition with CVST and prothrombotic disorders are also very frequently encountered. Other common systemic risk factors in toddlers and older children include fever, dehydration, anemia, and various acute and chronic medical conditions (congenital heart disease, autoimmune disease, malignancy, renal disease). Many children have coincident local head or neck pathology, such as head trauma, CNS tumors, recent intracranial surgery, or infections such as otitis media or mastoiditis.¹⁶

Clinical presentation of CVST is highly variable and may be very nonspecific. Presenting symptoms may be subtle and overlap with those of coexisting conditions. Neurologic symptoms may include headache, seizures, altered level of consciousness, encephalopathy, and focal and/or diffuse neurologic deficits.¹⁵

Treatment of CVST first includes supportive care to correct underlying disturbances from coexisting conditions (hydration, antibiotics). Symptomatic measures, such as anticonvulsants to control seizures and surgical or medical therapies to decrease intracranial pressure, are often necessary. Anticoagulation for at least several months with unfractionated heparin, low molecular weight heparin, or warfarin is also often employed—more so in older infants and toddlers—and does not appear to be associated with increased risk of hemorrhage. While thrombolysis, thrombectomy, and surgical decompression have been used successfully, these therapies are poorly studied in the pediatric population. Even with aggressive treatment, many survivors will suffer from long-term motor and cognitive deficits or chronic neurologic symptoms secondary to CVST.¹⁵

Anesthetic management of patients with CAD and CVST includes bearing in mind that these patients are likely to be anticoagulated, and so are at risk for extracranial bleeding complications. If trauma is a suspected or known etiology for either CAD or CVST, appropriate evaluation of the patient should be made and airway precautions should be taken. If CVST occurs in the setting of infection or sepsis, patients may require more aggressive fluid resuscitation or invasive hemodynamic monitoring. Many patients with CVST will show signs of increased ICP and may develop vasogenic edema, both of which may require treatment with diuretics, head elevation, or other measures to lower the ICP.¹⁶

Arteriovenous Malformations

AVMs result from abnormal development of the intervening capillary bed between cerebral arteries and veins, leading to a direct arteriovenous connection. Without the normal capillary bed to slow blood flow, a low resistance vascular interface is created, which leads to a high-flow shunt. This direct arteriovenous (AV) connection also leads to hypertrophy and dilation of the arterial and venous components of the AVM.¹⁷ Over time, the surrounding tissues are deprived of blood supply and nutrients. The surrounding brain parenchyma may atrophy secondary to ischemia as a result of the steal phenomenon.¹⁸ The precise mechanism by which these malformations occur is unclear, however they are thought to form during the third week of embryogenesis.

AVMs are the most common cause of spontaneous intraparenchymal hemorrhage and hemorrhagic stroke in children.² While AVMs are less common in children than in adults, mortality secondary to hemorrhagic events in children is much higher than in adults (20% vs. 6–10%).¹⁹ It is hypothesized that this is related to a higher incidence of posterior fossa and deep-seated (basal ganglia, thalamus) AVMs in children; not only are malformations in these locations more prone to bleeding, but hemorrhage also more frequently results in a catastrophic outcome.²⁰ Nonetheless, most (82%) of AVMs in the pediatric population are supratentorial in location, typically in the distribution of the middle cerebral artery.¹⁹

Malformations that are diagnosed prior to rupture may cause epilepsy, hydrocephalus, or (rarely) congestive heart failure (CHF) in the neonatal period. Unless a malformation is large enough to cause CHF, most remain clinically silent until a stroke or seizure occurs. Unfortunately, the initial presentation in children is typically hemorrhage (80–85%), which may produce symptoms of sudden headache, seizures, nausea/vomiting, or focal neurologic deficits.

Treatment modality depends on the size, complexity, and location of the lesion; options include observation, embolization, radiation, or surgical resection. Surgical resection is the gold standard for smaller, less complex, and accessible malformations. For those located in surgically inaccessible (deep-seated) or eloquent areas, radiation (radiosurgery) with proton beam or gamma knife may be indicated. The evolution of 3D printing has allowed these lesions to be printed preoperatively to help the surgeon better understand the vascular anatomy and hopefully improve ability to facilitate a complete resection. With advances in endovascular technology, embolization has become more useful as an adjuvant therapy, but alone is rarely curative. The intent of embolization is to decrease size and blood flow to the lesion, creating a solid brittle mass that is later surgically resected with less blood loss. After embolization the tissue surrounding the AVM will gradually adjust to changes in perfusion. Occasionally the risk of treatment will outweigh benefit, in which cases observation is the best option. Many AVMs will require multimodality therapy, which has been shown to be an effective strategy for successful obliteration.^{19, 20} Posttreatment, the risk of rebleeding during the first 6 months is approximately 6% and then 3% per subsequent year.

Anesthetic management for AVMs depends on the treatment modality. Embolic procedures in the interventional radiology (IR) suite are typically performed under a standard general anesthetic with appropriate neuromuscular blockade as avoidance of patient movement is crucial. Adequate IV access should be obtained prior to the procedure and blood products should be immediately available. The potential for bleeding from the femoral sheath site should be considered, especially in smaller patients, given that heparinization is required and these procedures may last hours. Euvolemia or slight hypervolemia are recommended, however the potential for fluid overload also exists, given the large volume of heparinized saline that may be administered by the neurointerventionalist.²¹ Large quantities of contrast are often injected, which may contribute to volume overload. These agents may have a high osmolality contributing to a tremendous shift of fluid into the intravascular space. This may result in heart failure or pulmonary edema. Care must be taken to use contrast judiciously and not overadminister. Excessive contrast can precipitate a nephropathy, which can be treated with cessation of contrast, alkalization of urine, and administration of IV fluids. Special attention to volume status is necessary in infants who may already be in high-output CHF and are receiving multiple inotropic agents. Invasive blood pressure monitoring via an arterial line is recommended to facilitate close monitoring and fine control of blood pressure. Should an occlusion occur during embolization, blood pressure should be augmented to maintain perfusion distally. Postprocedurally after partial embolization, abrupt increases in blood pressure should be avoided.¹⁹ Last, in case of a possible rupture, induced hypotension may be required in order to minimize blood loss. One should always be prepared for a possible emergency craniotomy should this occur.

If a surgical resection via craniotomy is performed in the OR, anesthetic goals are in line with those for similar craniotomies: optimize cerebral perfusion pressure (CPP) and oxygen delivery via maintenance of adequate mean arterial pressure and appropriate ventilator parameters. Avoidance of hemodynamic lability is crucial to avoid rupturing the AVM. As with embolization, being prepared for sudden blood loss is essential. As such, adequate IV access and arterial line are helpful. Brain relaxation techniques such as moderate hyperventilation or osmotic diuresis may aid in enhancing surgical exposure.

More modern approaches to interventional treatment of AVMs often involve a combination of embolization in the neurointerventional suite followed by surgical resection. In our institution, we routinely will combine these procedures over two anesthetics (first day is embolization followed by the next day of surgical resection and confirmatory angiography) or under a single anesthetic. The surgical resection can be followed by immediately cerebral angiography to confirm total resection of the AVM. This can then be followed by emergence from anesthesia and transfer to the intensive care unit (ICU).¹⁹

Both inhalational and IV agents have been used safely for the anesthetic for these lesions. Inhalational agents (except N₂O) decrease cerebral metabolic rate and increase cerebral blood flow (vasodilate), while IV agents (except ketamine) decrease cerebral metabolic rate and decrease cerebral blood flow in a dose-dependent manner. It is thought that vasodilating agents may induce a steal phenomenon while vasoconstrictors result in inverse steal. No evidence exists favoring one technique over another in terms of outcome for these patients. As with many aspects of anesthesia and critical care, it is likely that the most important thing is an engaged practitioner who understands both normal and pathological physiology and is able to quickly intervene. Certainly, maintenance of normotension and avoidance of large swings in blood pressure are crucial.

As many patients with AVMs may present with seizures, the patient’s anticonvulsant regimen must be considered when redosing narcotics and muscle relaxants. Because of the upregulation of the cytochrome p450 system induced by many anticonvulsants, these types of drugs (benzodiazepines, some opioids, and muscle relaxants) will likely need to be redosed sooner as they are undergoing accelerated metabolism.²² Anticonvulsants should be continued into the perioperative period. A smooth emergence that avoids significant hypertension is ideal. Often, a technique utilizing higher dose opioid drugs intraoperatively can aid in facilitating a neurologic exam shortly after surgery and prior to extubation.

Perioperative complications may include hydrocephalus, stroke, or rehemorrhage. SAH may result in hydrocephalus and may initially require an external drain to lower CSF volume and monitor ICP. Approximately one-third of all SAH patients will ultimately require a ventricular shunt. Faulty clip placement or a residual AVM may result in rehemorrhage or stroke. Residual lesions should be investigated with postoperative vascular imaging if possible and treated with evacuation of a clot if necessary and/or reopening of the craniotomy and further resection.