Considerations for Pediatric Ateriovenous Malformations

29 Considerations for Pediatric Ateriovenous Malformations

Ameet V. Chitale, David M. Sawyer, Ricky Medel, Aaron S. Dumont, and Peter S. Amenta

Abstract

Pediatric arteriovenous malformations (AVMs) differ significantly from those that present in the adult population. Children more frequently present with intracranial hemorrhage, though it is controversial whether there is an increased rate of rupture in these patients. Pediatric AVM patients are faced with a high cumulative lifetime morbidity and, due to plasticity of the still-developing brain, appear to tolerate invasive therapy to a greater degree than adults. Patient- and lesion-specific factors necessitate a multidisciplinary approach to treatment, including surgical resection, radiosurgery, and/or embolization. Surgical resection provides the highest rate of obliteration and is considered the definitive treatment when AVM size, location, and morphology are amenable. The appearance of recurrent AVMs after complete obliteration has been documented in children. The nature of these recurrences is not known, but the risks conferred by them lead many clinicians to perform radiographic follow-up for a longer period of time than in adult patients.

Keywords: pediatric AVM, arteriovenous malformation, congenital AVM, rupture risk, complete obliteration, recurrence, radiographic surveillance

Key Points

Arteriovenous malformations (AVMs) are the most common cause of intracranial hemorrhage in children, leading to high rates of morbidity and mortality.
The morbidity of pediatric AVMs is secondary to the high lifetime hemorrhage risk, seizures, mass effect, and/or hydrocephalus.
Management options include observation and medical control of seizures, surgical resection, endovascular embolization, radiosurgery, or a combination of these modalities.
Size, location, and angioarchitecture are important factors in determining the most effective treatment strategy for an individual lesion.
There is a risk of recurrence after successful obliteration of AVMs in children, which warrants longitudinal radiographic follow-up.

29.1 Introduction

Arteriovenous malformations (AVMs) are considered congenital lesions, with pediatric AVMs representing a subset that present particularly early in life. However, there is evidence to suggest that AVMs presenting in childhood are a qualitatively distinct group. These lesions appear to differ from AVMs diagnosed in adulthood in their clinical presentation, morphologic characteristics, and potential to evolve over time.

About 60 to 85% of pediatric patients present with a hemorrhage,¹^,² and most authors agree that children presenting with AVMs are more likely to do so with a hemorrhage as their initial event than are adults.²^,³^,⁴ However, it is difficult to determine with any precision the actual risk of hemorrhage in pediatric AVM patients, because the baseline prevalence of the disease has not been adequately elucidated.² Estimations of the annual risk of hemorrhage in children harboring AVMs have been derived from retrospective studies, and this value ranges from 2 to 10% per year depending on definition of onset as either the time of diagnosis or birth.⁵ It is therefore unclear whether the risk is greater than the accepted value of 2 to 4% per year in adults. Importantly, there is evidence to suggest AVM rupture in the pediatric population may be more severe and result in higher morbidity and mortality, due to the prevalence of deep-seated AVMs in children.³^,⁶

Pediatric AVMs may be more prone to rupture compared to their adult counterparts for a number of reasons. Multiple series have demonstrated AVM volume to be inversely proportional to the risk of hemorrhage, with smaller lesions showing a greater tendency for hemorrhage.⁶^,⁷^,⁸ AVMs have been observed to enlarge over time, thereby possibly conferring increasing protection against hemorrhage. However, some studies have reported the opposite relationship between volume and risk of bleeding.⁹^,¹⁰^,¹¹ The immaturity of the cerebral vasculature in the pediatric population plays a role in the risk of rupture. Autoregulation of cerebral blood flow is impaired in pediatric patients, leading to labile hemodynamics. In turn, significant fluctuations in flow result in frequent and stronger stresses to the walls of an AVM and increased likelihood of rupture.² An infratentorial location of the AVM, which is associated with an increased risk of bleeding, is also frequent in the pediatric population.¹²

Less commonly, pediatric patients with AVMs will present with a constellation of symptoms, including headache, seizures, and a progressive neurologic deficit. Newborns with large AVMs and vein of Galen malformations have a unique clinical presentation of high-output heart failure as a result of shunting through the lesion.¹³^,¹⁴

29.2 Management of Pediatric Arteriovenous Malformations

29.2.1 Surgery

Complete microsurgical resection of AVMs represents the definitive treatment option and plays a particularly important role in the management of pediatric AVMs (► Fig. 29.1). The prolonged expected lifespan in this population increases the cumulative risk of rupture over a lifetime. Furthermore, the propensity for recurrence or growth of partially treated lesions stresses the importance of complete obliteration when possible. Finally, the high frequency of hemorrhagic presentations results in an increased number of emergent clinical situations, in which open surgery is required to remove space-occupying hematomas and resect the ruptured AVM.

Fig. 29.1 A 13-year-old neurologically intact female patient presenting with headaches. (a) Axial T2-weighted magnetic resonance imaging demonstrating a 1.4 × 1.5 cm left parietal arteriovenous malformation (AVM) with the nidus centered in the postcentral gyrus. (b) Left anterior oblique angiogram shows a relatively compact nidus fed by distal branches of the left middle cerebral artery and anterior cerebral artery. A single large superficial draining vein drains to the superior sagittal sinus. (c) Lateral angiogram demonstrating the AVM. (d) Intraoperative angiogram of the left internal carotid arteries circulation demonstrating complete resection of the AVM. The patient was discharged with mild right hemianesthesia. At 6-month follow-up, the hemianesthesia had resolved; however, the patient complained of persistent right lower extremity diminished proprioception.

Recent retrospective studies have reported on the efficacy and safety of surgical treatment of AVMs in children. Successful treatment is often judged as complete obliteration of the lesion on postoperative angiography. Multiple series pertaining to microsurgical resection demonstrate AVM obliteration rates, as confirmed with angiography, in the range of 65 to 100%, with many studies reporting complete resection in over 80% of cases.¹⁵ Importantly, surgical resection results in immediate obliteration of the lesion and removal of risk of future rupture. The importance of this definitive treatment is amplified in those presenting with rupture, as they have a significant risk of suffering a second bleed within 1 year.¹⁵^,¹⁶ Deep venous drainage seems to contribute to incomplete obliteration of the AVM.¹⁵

Another approach to quantifying outcomes after AVM treatment in children involves comparing preoperative and postoperative neurologic disability by utilizing the modified Rankin scale (mRS). In a series reported by Sanchez-Mejia et al comparing surgical results in children and adults, pediatric patients had mRS values of 0 to 2 (living independently) in 90.6% of cases versus 71.4% in adults. Additionally, 93.8% of pediatric patients had an improvement in mRS compared to 69.8% of adults.¹⁷ This effect was unexplained by measureable differences in the characteristics of the patients or their lesions, leading the authors to suggest that recovery from surgical AVM resection is augmented in children by neural plasticity. Other investigators have noted that the additional benefit of fewer comorbidities in pediatric patients makes them more capable than adults of recovering from catastrophic hemorrhages when treated surgically, reinforcing this notion.¹⁸

Surgical resection of AVMs in children does carry significant morbidity, and complication rates range from 5 to 33%. In particular, questions about the safety of AVM surgery often center on the immediate risk of blood loss and the long-term risk of neurologic deficit. In children, intraoperative blood loss is a particular concern because of their relatively small intravascular volume.¹⁸ However, recent series have shown that intraoperative blood loss can be consistently controlled at acceptable levels under the appropriate conditions.¹⁵ Meticulous hemostasis is maintained during the entire operation and preoperative embolization has a role in obliterating arterial pedicles that are anticipated to be problematic.¹⁸ Additionally, it is important to closely monitor the patient’s hemodynamics and cerebral perfusion during surgery by means of central venous and arterial lines and neurophysiological monitoring.¹⁸

Resection of the entire AVM must be performed to eliminate the risk of rupture, and confirmatory imaging is required to prove that no residual lesion has been left behind. Angiography is the imaging gold standard and intraoperative angiography has been shown to increase the rate of complete microsurgical obliteration.¹⁹ At the conclusion of the resection, angiography can be performed in the operating room or in the angiography suite while the patient remains under general anesthesia. Evidence of residual AVM prompts immediate re-resection and additional angiography until the entire lesion is removed.

Neurologic deficits caused by the resection of brain parenchyma are a known complication of open microsurgery, and can to a certain extent be predicted based on the anatomy of the lesion and the planned surgical approach. Many AVMs can be successfully removed with no permanent deficit or only an expected loss of a visual field, but operating on lesions that reside in eloquent cortex is more likely to produce lasting deficits affecting the functional status of the patient.¹⁵ An important consideration in very young patients is the inability to fixate the head, precluding the use of frameless stereotactic navigation and making resection of complex lesions more difficult.¹⁸ However, newer navigation systems that do not require rigid head fixation may at least overcome some of the historical challenges with navigation.

29.2.2 Radiosurgery

Radiosurgery is used as the primary modality in a select group of pediatric patients with AVMs. In particular, it allows treatment of lesions that would be unsafe to surgically resect, due to either their deep location or proximity to eloquent cortex (► Fig. 29.2).

Fig. 29.2 A 14-year-old neurologically intact male patient presenting with seizures. (a) Axial T2-weighted magnetic resonance imaging demonstrating an unruptured 2.1 × 2.6 cm right frontal arteriovenous malformation (AVM) with a nidus centered in the primary motor strip. (b) Lateral angiogram shows the nidus to be fed by multiple distal right middle cerebral artery branches. Drainage is through superficial draining veins that empty into the superior sagittal sinus and right transverse sinus. (c) Computed tomography angiography used for stereotactic radiosurgery planning.

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