Epidemiology of Intracranial Aneurysms in Children

Incidence and Prevalence

• Rare condition: The true incidence and prevalence of intracranial aneurysms in children has been challenging to estimate. Pediatric aneurysms are rare and account for 0.5% to 4.6% of cases in large aneurysm series (1,2,7,8). These data have been extrapolated to generate an estimate of one to three cases of pediatric intracranial aneurysm per 1,000,000 population (41).
• No evidence of incidental aneurysms: No incidental aneurysms were found in a large autopsy study of 3,000 children younger than 12 years (3). Moreover, no incidental aneurysms were found in two studies analyzing incidental MRI findings in 225 and 120 neurologically healthy children (4,5).

Age Distribution

• Bimodal age distribution possible, adolescent predominance: Some authors have noted a bimodal age distribution of symptomatic aneurysms in children (two modes: from birth to 6 years, and from 8 years to adolescence) (9). More recently, however, a review of 431 cases revealed no obvious peaks in the overall age distribution of children with ruptured aneurysms, although a higher frequency was noted in adolescence, beginning at age 10 (42). The same study noted an increase in frequency with increasing age in males, but a peak at ages 14 to 15 for females (42).

Sex Predilection

• Male predilection: A review of 431 cases revealed a male-to-female ratio of 1.42:1 (42), and a review of 706 cases revealed a male-to-female ratio of 1.8:1 (43), in contrast to the substantial female predilection in adults (44,45).

Geographic Distribution

• No geographic variation apparent: There are no published reports supporting any variance in incidence as a function of geographic location. Of note, in a large series of aneurysm patients from Finland, a country with a 3-fold increased incidence of subarachnoid hemorrhage, children accounted for 1.3% of patients (46,47). This proportion is comparable to series from other geographical regions, although no true comparisons of regional incidences exist. However, geographical differences in the distribution of head trauma and infectious diseases probably influence the occurrence of traumatic and mycotic aneurysms in certain regions to some degree.

Risk Factors

Children have distinct risk factors for intracranial aneurysms compared with adults, including:

• Modifiable risk factors are not normally a factor in children: The classical modifiable risk factors (such as smoking, alcohol use, and hypertension) are not normally encountered in children (48).
• Children have a higher risk of traumatic aneurysm: A higher risk of developing a traumatic aneurysm has been described in children, predominantly after closed head injury (49).
• Children have a higher risk of infectious aneurysms: Similarly, a higher incidence of infectious aneurysms is observed in children; these account for up to 15% of pediatric aneurysms (50). The origin of these aneurysms is mainly bacterial infection, either by direct involvement of intracranial arteries due to sinus or mastoid air cell infections or by infectious embolization (49). The latter might complicate endocarditis occurring in children with congenital or rheumatic heart disease.
• Children with certain disease states and genetic factors are more likely than similarly affected adults to develop intracranial aneurysms: Other disease states and genetic factors, discussed below, bring an increased risk of intracranial aneurysms to children than adults.

Relationships to Other Disease States and Syndromes

A defined underlying condition can be identified in less than 50% of children presenting with an intracranial aneurysm (49). The following conditions appear to carry an increased risk:

• Renal disorders: Patients with polycystic kidney disease appear to be at increased risk of developing intracranial aneurysms (51,52).
• Cardiovascular disorders: Coarctation of the aorta and interrupted aortic arch increase the risk of intracranial aneurysms (53,54).
• Hematological, inflammatory, and autoimmune disorders: Intracranial aneurysms are more common in children with sickle-cell anemia (55). Systemic vasculitides, such as Kawasaki disease and Takayasu’s arteritis, can also lead to formation of intracranial aneurysms (56,57).

Two aneurysms in a child with sickle cell anemia: (A) MRA revealed an aneurysm of the left paraclinoid segment of the ICA (white arrow) and a relatively small aneurysm of the left A1 segment of the anterior cerebral artery (yellow arrow). (B) DSA demonstrated contrast filling of the unruptured left ICA (white arrow) and left A1 (yellow arrow) aneurysms. (C) The left ICA aneurysm was treated with endovascular flow diversion with adjunctive coiling (white arrow), and the left A1 aneurysm was treated via flow diversion (pipeline embolization device barely visible, yellow arrow). (D) Follow-up MRA revealed interval resolution of the aneurysms, with no evidence of filling of the left ICA aneurysm (white arrow) or left A1 (yellow arrow) aneurysm.

• Phakomatoses: Tuberous sclerosis complex, Klippel-Trénaunay syndrome, and neurofibromatosis type 1 appear to be associated with intracranial aneurysms (58–61).
• Heritable connective tissue disorders: Cerebral aneurysms are reported to occur in children with Ehlers-Danlos and Marfan syndromes (62–64).
• Moyamoya arteriopathy: Intracranial aneurysm formation in moyamoya arteriopathy is common, and ruptured aneurysms in children with this cerebrovascular disease have been reported (65,66).

Three aneurysms in a child with moyamoya arteriopathy and microcephalic osteodysplastic primordial dwarfism type II: (A) DSA with injection of the right ICA demonstrated a saccular aneurysm of the posterior cerebral artery (yellow arrow), an aneurysm of the right ICA terminus (green arrow), and an aneurysm at the right MCA bifurcation (magenta arrow). (B) Right posterior cerebral artery aneurysm was treated using coiling (yellow arrow). (C) Follow-up angiogram showed refilling and enlargement of the right posterior cerebral artery aneurysm, along with growth of the right ICA terminus (green arrow) and right MCA bifurcation (magenta arrow) aneurysms. (D) Rotational angiography revealed a right posterior cerebral artery aneurysm (yellow arrow), right ICA terminus aneurysm (green arrow), and right MCA bifurcation aneurysm (magenta arrow). This child was eventually treated with clipping of the right ICA terminus and right MCA bifurcation aneurysms. Flow diversion is planned to treat the patient’s posterior circulation aneurysm.

• Infection: Children with congenital or rheumatic heart disease are at increased risk of bacterial endocarditis, which can lead to mycotic intracranial aneurysms (67,68).
• Head trauma: Traumatic intracranial aneurysms in children can result from blunt and penetrating trauma to the head (69–71).