Introduction

Intracranial aneurysms (IAs) in the pediatric patient population are rare and challenging. They represent 0.5 to 2% of all IAs. They should not be thought of as aneurysms occurring in little people, but rather regarded as a different entity with different pathophysiology, natural history, treatment options applicable to pediatric patients, and long-term outlook for surviving patients. Caring for pediatric aneurysms, especially very young ones, requires a well-orchestrated collaborative effort that entails neurosurgeons, interventional neuroradiologists, pediatric neurointensivists, and pediatric anesthetists all working in specialized, high-volume neurovascular centers or centers dedicated altogether to caring for pediatric patients. It is also of paramount importance to have the strong presence of a dedicated social worker and spiritual service to support the parents of these children during these difficult times.

Major controversies in decision making addressed in this chapter include:

1. 
   

   Risks of bleeding and rebleeding in pediatric aneurysms.

   
   
2. 
   

   Treatment strategies stratified to different age groups.

   
   
3. 
   

   Technical considerations in open and endovascular management of pediatric aneurysms.

   
   
4. 
   

   Long-term follow-up and screening strategies for pediatric aneurysms.

Whether to Treat

Treatment of IA aims to exclude the whole aneurysm from the blood stream without sacrificing normal blood supply. A ruptured aneurysm should be treated as soon as possible to eliminate the risk of rebleeding. Even for unruptured aneurysms, the highly criticized International Study of Unruptured Intracranial Aneurysms (ISUIA) could not be applied as the conclusion of not treating aneurysms smaller than 7 mm is not universally valid. This is because of the longevity expected in these young children favoring active treatment strategy ( 1 –4 in algorithm ). There is a male predominance throughout the literature in pediatric aneurysm patients although some investigators suggest that among children younger than 2 years of age, the incidence of aneurysms was higher in girls (5:1). Aneurysms in infants are extremely rare. Among patients harboring aneurysms during the first year of life, 20% were reported to have comorbidities such as cutaneous vascular disorder, autosomal-dominant polycystic kidney disease (ADPKD), or brain tumors.

Anatomical Considerations

The most common location for aneurysm in pediatric patients is the internal carotid artery (ICA), typically at the ICA bifurcation and this predilection is seen primarily in juvenile and adolescent cases. In the posterior circulation, the most common locations include midbasilar trunk (31%) and basilar bifurcation (16%). Multiple aneurysms are uncommon among pediatric aneurysm patients. Aneurysm preference for the vertebrobasilar circulation is pronounced among cases occurring within the first 2 years of life. There is also a predilection for middle cerebral artery (MCA) territory, especially distal MCA.

Pathophysiology and Classification

Before we go into the details of management options, we should go first to the classification of pediatric aneurysms as it has a huge bearing on the decision making as the priorities of treatment vary according to the type of aneurysm encountered.

Cerebrovascular accidents in the pediatric population are relatively rare but carry a high rate of mortality. Unlike adult patients, half of these strokes are hemorrhagic with about 15% of these related to cerebral aneurysms, trailing behind arteriovenous malformations (AVMs). Other causes of hemorrhage in young include cavernous malformation, moyamoya disease, and sickle cell disease. The latter two entities are directly associated with aneurysms.

Cerebral aneurysms are generally thought to be an acquired pathology although this notion is challenged at least in part, by the new line of evidence of a significant genetic–environmental interaction leading to the formation of aneurysms in adults. In contrast to the common risk factors known to lead to aneurysm formation in adults, children suffer from distant risk factors that can be classified, according to Aeron et al, into eight pathogenic mechanisms including idiopathic, traumatic, those due to excessive hemodynamic stress, vasculopathic, infectious, noninfectious inflammatory, oncotic, and familial.

Idiopathic aneurysms: Idiopathic IAs are classified by exclusion as these children have no history of trauma, hemodynamic stressors, known acquired or congenital arteriopathies, infections, or tumors, and no family history of IAs. This is the most commonly represented among the different classes accounting for 45% of all pediatric IAs. Even among idiopathic pediatric IAs, differences exist in the phenotype among different age populations. In young children, aneurysms occur at a greater proportion distal to the circle of Willis and an increased frequency of fusiform aneurysm is observed. On the other hand, multiple aneurysms occur in about 15% of teenage and young adult patients and are unusual in young children.

Traumatic aneurysms: Unlike in adults, traumatic aneurysms account for more than 20% of IAs among children, making it the second most common IA in the pediatric patient population. The majority of these occur in males secondary to both blunt and penetrating trauma. They would occur in the spectrum of birth trauma as well. Most traumatic IAs occur in the anterior cerebral circulation, specifically the cavernous segment of the ICA and the pericallosal artery as these two locations are closely intimate with sharp dural folds. More peripheral locations are found to be related to entrapment of the affected vessels in or around skull fractures. The importance of these aneurysms is in that they are multiple in about one-third of the patients and they tend to bleed within the early weeks after the injury. A nonoperative attitude toward these lesions must be accompanied by a close observation as these lesions might grow and bleed after a period of initial stability.

Aneurysms due to excessive hemodynamic stress: Aneurysms can form in the face of hemodynamic stresses that can be classified as (1) flow loading as seen in cerebral arteriovenous shunts or carotid artery occlusion; (2) pressure loading as in juvenile hypertension or abuse of sympathomimetic drugs; (3) vibrational stress as seen in aortic coarctation; and (4) rheologic shear stress as in sickle cell disease. AVMs are the most common of these and the related aneurysms usually present with subarachnoid hemorrhage (SAH) in teenage years.

Vasculopathic aneurysms: Vasculopathic aneurysms caused by congenital cerebral aneurysmal arteriopathies present as part of a diverse spectrum of clinical entities that have in their final common pathway an intrinsic defect in vessel wall that promotes or enables formation of an IA. These defects are considered “permissibility traits” that in the presence of other factors (such as smoking, infection, radiation, etc.) would allow the formation of aneurysms. They represent 10 to 20% of pediatric IAs, manifesting with stroke or hemorrhage within the first decade of life. Unlike other forms of pediatric aneurysms, these have a strong female predominance. They are most often large and of fusiform character. Most of these involve the proximal basal cerebral arteries and are often within or proximal to the circle of Willis and even affecting the extradural segments of the affected arteries.

Infectious aneurysms: Infectious or mycotic aneurysms account for approximately 5% in the pediatric population. Of IAs presenting in the first year of life, 10% are secondary to infections. These occur in immunocompromised children with septicemia or in children with congenital cardiac malformations complicated by endocarditis. Infective emboli are the most implicated mechanism. They could result as peri-infectious aneurysms in cases of infections in the skull base or paranasal sinuses. At presentation, these infectious IAs could be single or multiple and can present with an ischemic stroke or intracranial hemorrhage. Medical management with antibiotic therapy is often the appropriate initial treatment for infectious aneurysms, especially if unruptured. Serial imaging studies and follow-up of inflammatory markers play an important role in monitoring patient response to therapy. Another component in this entity is the relationship between immune deficiency virus and the development of fusiform aneurysms. When facing a pediatric patient with severe dolichoectasia or fusiform aneurysm, it might be indicated to test for human immunodeficiency virus (HIV), especially in high-risk populations, as it will have therapeutic and follow-up implications such as the use of dual antiplatelets with antiretroviral therapy.

Noninfectious inflammatory aneurysms: In children, noninfectious inflammatory IAs are rare. They could be a part of the manifestations of inflammatory central nervous system vasculitis such as Kawasaki′s disease. The significant type includes those affecting children with immunodeficiency syndromes of childhood because they present with a diffuse acquired cerebral aneurysmal arteriopathy. The aneurysms in this arteriopathy are characteristically multifocal with usually long segment fusiform lesions that involve the proximal basal cerebral arteries. The acquired cerebral aneurysmal arteriopathy of HIV infection typically occurs in children aged 8 to 11 years with HIV infection acquired through vertical transmission or perinatal blood transfusion or those affected by diseases requiring frequent blood transfusions.

Oncotic aneurysms: Oncotic aneurysms are extremely rare in pediatric patients. They are intuitively secondary to tumor cell infiltration, but several other mechanisms such as metalloproteinase-mediated cavitation and obliteration of the vasa vasorum have been reported. The spread could be hematogenous (e.g., myxoma, choriocarcinoma, renal cell carcinoma, lung carcinoma) or contagious from adjacent soft tissues (chondrosarcoma of the skull base, glial malignancy). They usually respond or at least stabilize with treatment of the primary disease.