Pediatric Cerebral Aneurysms

Intracranial saccular aneurysms are rare in the pediatric population. In a cooperative study of 6,368 patients with intracranial aneurysms and subarachnoid hemorrhage, only 41 patients (0.6%) were less than nineteen years of age. Although intracranial aneurysms in children are associated with a variety of disorders (See following list), no underlying systemic disorder is detected in the vast majority of affected children. Aneurysms in the pediatric population are more commonly of the large ("giant") type and more commonly arise distal to the circle of Willis than those in the adult population. The distribution of aneurysms within the circle of Willis also differs slightly from that in adults. Most studies indicate that the internal carotid artery bifurcation is the most common location for aneurysms in children. In addition, one third to one half of pediatric aneurysms arise from the posterior circulation (compared with 5-10% in adults. Other studies show a high incidence of intracavernous internal carotid artery aneurysms in children.

Conditions associated with Pediatric Cerebral Aneurysms

  • Polycystic kidney disease
  • Coarctation of the aorta
  • Tuberous sclerosis
  • Hereditary Hemorrhagic Telangiectesis (Osler-Weber-Rendu disease)
  • Alpha-glucosidase deficiency
  • Klippel-Trenaunay-Weber syndrome
  • 3-M syndrome
  • Alpha-1-antitrypsin deficiency
  • Parry-Romberg syndrome
  • Cystic Fibrosis

Older children and adolescents with intracranial aneurysms often present with signs and symptoms of subarachnoid hemorrhage, including severe headache, vomiting, and obtundation, which may progress to coma. About 20% of patients have a history of recurrent headaches. However, headache is uncommon in younger pediatric patients. In the series of Lasjaunias et al, no patient under the age of 5 years presented with signs or symptoms of subarachnoid hemorrhage. Giant aneurysms (diameter greater than 2.5 cm) are found in 20-40% of affected pediatric patients. Patients with giant aneurysms present with focal neurological symptoms and signs as a result of compression of the surrounding brain by the enlarging aneurysm sac. Although aneurysms can sometimes be detected by CT and MR as blood-filled saccular dilatations arising from major intracerebral vessels angiography is essential to detail the precise anatomy (location and size of the neck of the aneurysm, precise size and orientation of the sac) and to locate additional aneurysms.

Treatment
Many pediatric aneurysms can be managed by surgical clipping of the neck of the aneurysm. An alternative treatment when the risks of surgical clipping are unacceptably high or the aneurysm has no definable neck is endovascular occlusion of the aneurysm. Platinum detachable coils can be navigated into the aneurysm and electrolytically detached to occlude the neck and dome. If the aneurysm has a broad neck, it may be occluded with coils using a neck-remodeling technique whereby a temporary balloon occludes the lumen of the parent vessel across the aneurysm neck while detachable coils are deployed into the aneurysm. If the balloon-assisted coiling technique is not possible due to the presence of a fusiform aneurysm, then surgical bypass with vessel occlusion or reconstruction can be undertaken. Alternatively, a balloon test occlusion of the parent vessel can be performed. Test occlusion must be performed in an awake patient to ensure that the patient can tolerate the occlusion. If the test occlusion is tolerated, the parent artery and the aneurysm are permanently occluded with coils or detachable balloons.
Of more than 600 endovascular procedures performed for intracranial aneurysms at our institution, 16 have been in pediatric patients. Four giant aneurysms were treated by balloon occlusion prior to the development of electrolytically detachable coils. Of the remaining 12 patients, 9 were treated with detachable coils. Although the outcomes of these patients are excellent, the long-term results of these endovascular treatments are not yet known.

Mycotic Aneurysms
The term “mycotic” aneurysm refers to those aneurysms resulting from any infectious process and includes bacterial, fungal, and protozoan infections. The most common cause of mycotic aneurysms is an underlying bacterial endocarditis from which infectious thrombi are embolized into the intracranial circulation. The emboli cause a focal arteritis with degeneration of the elastic lamina and muscularis, resulting in a fusiform aneurysmal dilatation. Rupture of a mycotic aneurysm is, in fact, often the presenting sign of subacute bacterial endocarditis. Groups at risk for endocarditis in the pediatric population include those with congenital heart disease (especially right-to-left shunts) and those with rheumatic heart disease. Another important cause of mycotic aneurysms in children is invasion of intracranial vessels by adjacent infections (i.e., middle ear/sinus infection, meningitis, osteomyelitis of the skull, septic cavernous thrombophlebitis). In these patients, the adventitia is involved first, followed by the muscularis and finally, the internal elastic lamina.

When mycotic aneurysms are caused by bacterial endocarditis, the most common presenting symptom is subarachnoid or intracerebral hemorrhage resulting from aneurysmal rupture. Less commonly, symptoms of cerebral ischemia may precede hemorrhage. Those patients with mycotic aneurysm within the cavernous sinus present with symptoms of septic cavernous sinus thrombophlebitis, including fever, orbital edema, venous engorgement, proptosis, chemosis, and ophthalmoplegia.

CT or MR may help to localize the aneurysm by demonstrating adjacent intraparenchymal hemorrhage or by directly visualizing the lesion, especially in the case of intracavernous aneurysms. Associated cerebritis, abscess, edema or infarction may be identified. Cerebral angiography is necessary for definitive diagnosis. On angiograms, mycotic aneurysms appear as fusiform dilatations of the affected vessel. They tend to be located peripherally, most frequently in the distribution of the middle cerebral artery, in contrast to the saccular congenital aneurysms, which tend to be located on the circle of Willis.

Following appropriate antimicrobial therapy, endovascular occlusion of the aneurysm can be considered. The decision regarding when to treat a mycotic aneurysm depends upon the size and location of the aneurysm, the clinical presentation, and observed changes in the patient and the aneurysm over time. Because mycotic aneurysms are typically fusiform, aneurysm treatment often necessitates occlusion of the involved vessel segment immediately proximal to the aneurysm origin. Collateral flow may preserve perfusion of parenchyma distal to the aneurysm. Surgical bypass (either entirely intracranial or extra-cranial to intracranial) with surgical interruption of the vessel proximal to the aneurysm may be indicated to preserve perfusion of eloquent cerebrovascular territory.

Traumatic Aneurysms
Traumatic aneurysms are common in childhood, representing up to 39% of pediatric intracranial aneurysms. They are most commonly caused by penetrating injuries, although blunt trauma, even seemingly mild concussive injury, may also result in damage to the craniocervical vessels. Traumatic aneurysms can be found intracranially or extracranially. The latter are typically associated with flexion/extension/rotation injuries such as from motor vehicle accidents or from projectile injuries causing comminuted fractures at the skull base. Many authors classify traumatic aneurysms as pseudoaneurysms because all layers of the arterial wall are disrupted; flowing blood is confined only by the integrity of the surrounding tissues.

Clinical presentation may be significantly delayed with respect to the traumatic event, and a high index of clinical suspicion is warranted if these lesions are to be identified prior to catastrophic hemorrhage. Immediate arteriographic evaluation has been recommended, and arteriographic re-evaluation is suggested if no lesion is identified or after treatment is completed. Historically, the surgical approach has been difficult because disruption of the tenuous pseudocapsule may result in massive hemorrhage before vascular control can be established. More recently, endovascular occlusion of the feeding vessel or endovascular trapping of inflow and outflow to the aneurysm has proven effective.