Fusiform Cerebral Aneurysm Predisposing Factors
Advanced cerebral artery sclerosis (atherosclerosis) is the most common predisposing factor for fusiform cerebral aneurysms in adults, though a significant subset occurs from arterial dissection rather than atherosclerosis.
Primary Etiologies by Population
Adults
- Atherosclerosis is traditionally considered the predominant cause of fusiform cerebral aneurysms in adult populations, particularly in older patients with vascular risk factors 1, 2.
- However, arterial dissection or injury to the internal elastic lamina accounts for the majority (73%) of discrete fusiform aneurysms in younger adults without generalized cerebral atherosclerosis 1.
- In one surgical series of 22 fusiform aneurysms, dissection was identified as the cause in 16 cases (73%), atherosclerosis in 4 cases (18%), and collagen disease or uncertain etiology in 2 cases (9%) 1.
Pediatric Population
- In children, fusiform aneurysms are more commonly idiopathic (45%) or post-traumatic (20%) rather than atherosclerotic 3.
- Children with fusiform aneurysms are more likely to have giant (>25 mm) morphology compared to adults 3.
Other Predisposing Conditions (Less Common)
HIV-Associated Vasculopathy
- HIV vasculopathy causes fusiform aneurysms but remains uncommon, with only 9 pediatric cases reported in the literature as of 1998 4.
- HIV-associated fusiform aneurysms are increasingly recognized in adults with AIDS-defining illnesses, particularly in the setting of immune reconstitution inflammatory syndrome (IRIS) 5.
- These aneurysms can develop in both anterior and posterior circulation and may improve with adherent antiretroviral therapy 5.
Arteriovenous Malformations (AVMs)
- AVMs may coexist with cerebral aneurysms but are not a primary cause of fusiform morphology 3.
- The American Heart Association notes that brain arteriovenous malformations represent concurrent pathology that may predispose to higher hemorrhage risk, but this applies to saccular aneurysms rather than fusiform types 3.
Systemic Aspergillosis
- Systemic aspergillosis is not a recognized predisposing factor for fusiform cerebral aneurysms based on available guideline evidence.
- Mycotic aneurysms from fungal infections typically present as saccular rather than fusiform morphology 3.
Coarctation of the Aorta
- Coarctation of the aorta increases risk for cerebral aneurysm formation generally but is associated with saccular rather than fusiform morphology 3.
- The American Heart Association lists coarctation among at-risk disorders for aneurysm screening, with increased prevalence of intracranial aneurysms in these patients 3.
Clinical Characteristics of Fusiform Aneurysms
Location Patterns
- Fusiform aneurysms show predilection for the posterior circulation (vertebrobasilar system) in non-atherosclerotic cases, with 9 of 11 cases (82%) located posteriorly in one series 2.
- The middle cerebral artery is the most frequent site in atherosclerotic fusiform aneurysms 1.
Morphological Features
- Fusiform aneurysms are characterized by circumferential dilation of the entire arterial segment without a definable neck separating inflow and outflow 3.
- Non-atherosclerotic fusiform aneurysms are often partly or substantially thin-walled despite normal-appearing parent arteries 2.
- Mean dimensions are approximately 16.3 mm in length and 11 mm in width, with 27% containing thrombus 2.
Common Pitfalls
- Do not assume all fusiform aneurysms are atherosclerotic, particularly in younger patients (mean age 37 years) without systemic vascular disease 2.
- Fusiform aneurysms carry rupture risk despite their thick-walled appearance in atherosclerotic cases, with 14-45% presenting with hemorrhage 1, 2.
- These lesions require different treatment approaches than saccular aneurysms, including proximal occlusion, wrapping, or resection with bypass rather than neck clipping or endovascular coiling 2.