Intracranial aneurysms (IAs) are characteristically rare in the pediatric population and their treatment is often more difficult and complex than that of adults [18]. Additionally, in the pediatric population, ruptured aneurysms are more common than unruptured ones [20]. Management options for pediatric IAs range from observation with serial follow-up imaging to microsurgical or endovascular intervention [15].

Endovascular coil embolization involves placing coils, densely packed inside the aneurysm to induce thrombosis and occlusion. The Pipeline Embolization Device (PED) is a flow-diverting intraluminal device that induces thrombosis and occlusion of the aneurysm with reendothelialization of the device [15,27,30]. The device is approved for use in adults 18 years or older with internal carotid artery (ICA) aneurysms arising from the petrous segment to the terminus. However, it can also be used off-label in pediatric patients with aneurysms that cannot be resolved with traditional endovascular treatments [26]. During flow diversion, a microcatheter is navigated past the aneurysm in the native vessel (without needing to enter the aneurysm). The PED is then deployed across the neck of the aneurysm in the parent blood vessel. If successful, the aneurysm should completely thrombose and occlude in the following 6 weeks to 6 months [6,26].

Aneurysm characteristics in the pediatric population, such as large size, fusiform shape, or dissecting vessel walls make them difficult to treat using conventional microsurgical treatment or endovascular options. This is in part due to the fact that both the blood vessels and the surgical field are smaller in the pediatric population. The pediatric population is also more sensitive to blood loss [6,15],18-20],25]. Thus, choosing the appropriate treatment option between endovascular and microsurgery is controversial; there remains no protocol for IA management in the pediatric population [20]. Despite this, with treatment for aneurysms shifting from microsurgery to endovascular methods in adults, this trend has started to extend to the pediatric population as well [10,35].

Some endovascular options, such as coiling have shown significant rates of recanalization and high mortality and morbidity rates in the general population [16]. Recently, flow diverters have shifted from on-label use in ICA aneurysms only to distal and posterior circulation aneurysms as well [11,16,17,26,31,36,37]. Moreover, flow diverter use has expanded to treat ruptured aneurysms in the acute phase with favorable outcomes despite the need for dual antiplatelet therapies [12]. Flow diverters work by inducing vessel reconstruction. As the parent vessel’s endothelial layer starts remodeling, the aneurysm becomes isolated from the circulation; thus, creating aneurysmal flow disruption and aneurysm thrombosis [8]. The use of flow diverters in the pediatric population is limited to a small number of cases reported in the literature (Table 1) and discussed further below with each underlying etiological aneurysm subtype.

While children do not have chronic exposure to the environmental factors or medical comorbidities associated with aneurysm development as with adults, up to 30% of the pediatric population has underlying conditions related to aneurysm development and growth. These include polycystic kidney disease, Ehlers-Danlos syndrome, fibromuscular dysplasia, infectious endocarditis, and trauma [27,30,32]. Both of our patients did not undergo genetic evaluation, however, given that the first patient has a sibling with a vascular anomaly, he may have had a genetic predisposition.

One etiology of pediatric aneurysms is trauma. Traumatic aneurysms occur due to penetrating or closed trauma of the head [34]. In contrast to adults, the incidence of traumatic aneurysms in pediatrics is very high, reaching 39% in some studies [20]. Furthermore, aneurysm recurrence risk, aneurysmal growth rate, and rupture incidence are higher in the pediatric population, thus raising the importance of early treatment over just observation [20,33]. Similarly, dissecting aneurysms are more common in children, and in contrast to arterial dissection that can heal alone or with medications, dissecting aneurysms tend to grow, thus warranting treatment [13].

Infectious aneurysms, on the other hand, result from the inflammatory reaction to an infectious agent within the adventitia and then muscularis layer, resulting in a very friable, thin-walled aneurysm. Typically these aneurysms appear without a distinguishable neck, so they are considered pseudoaneurysms [14,28]. About 15% of IAs in pediatrics are infectious [21]. Due to their histopathology, infectious aneurysms in pediatric patients have a high risk of rupture along with a latency of complete obliteration. It is additionally challenging to treat infectious aneurysms using flow diversion given the nature of placing an endovascular device in the context of potential bacteremia [4]. Yet, many studies have shown success using flow diverters to treat infectious aneurysms in the pediatric population. Ares et al. reported using PED to treat a two-year-old male with an infectious basilar apex aneurysm; 6-month angiography showed complete obliteration [4]. Another case reported by Appelboom et al. showed complete occlusion of a ten-year-old female’s infectious cavernous carotid aneurysm treated with a flow diverter [3]. A third case reported by Samples et al. showed a 10-year-old female with two reputed, infectious, MCA (middle cerebral artery) aneurysms. The proximal one was treated with coil embolization and the distal one was treated with a flow diverter. Again, 6-month angiogram showed complete obliteration of both aneurysms [29].

While seen to be successful in many case reports, there are four main potential problems related to using flow diverters in pediatrics. First, antiplatelet treatment prior to flow diverters is essential to decrease peri- and post-procedural thromboembolic events [2]. However, due to ADP-induced hyporeactivity, Aspirin-induced Reye syndrome, possible hyper response to antiplatelets and the absence of standard guidelines, using antiplatelets and adjusting their doses is challenging in pediatric patients; additionally, antiplatelet administration is extremely variable [5,7,9]. In a trial studying the appropriate antiplatelet doses in children having heart disease, Li et al. found that to achieve a sufficient therapeutic effect, 0.2 mg/kg of clopidogrel may be enough [23]. The second potential problem of utilizing flow diverters in the pediatric population is that the continuous growth of children raises concerns regarding the presence of a foreign body inside the growing blood vessels and potential long-term complications [5]. Third, the lack of experience in using flow diverters in the pediatric population can pose technical challenges for the operator [22]. Fourth, flow diverters can theoretically increase the risk of developing perforator strokes, particularly after dual antiplatelets are de-escalated to a single antiplatelet [1,24].

Flow diversion has been shown to be a safe endovascular option in treating complex aneurysms in children and can lead to complete occlusion with excellent outcomes. Larger-sized, multicenter trials are encouraged to compare outcomes between flow diversion and other aneurysm treatment options given the rarity of pediatric aneurysms.