Elsevier

Mayo Clinic Proceedings

Volume 79, Issue 12, December 2004, Pages 1572-1583
Mayo Clinic Proceedings

Symposium on Cerebrovascular Diseases
Pathogenesis, Natural History, and Treatment of Unruptured Intracranial Aneurysms

https://doi.org/10.4065/79.12.1572Get rights and content

Unruptured intracranial aneurysms (UIAs) are a major public health issue. These lesions have become increasingly recognized in recent years with the advent of advanced cerebral imaging techniques. Epidemiological evidence from multiple sources suggests that most intracranial aneurysms do not rupture. Therefore, it is desirable to identify which UIAs are at greatest risk of rupture when considering which to repair. It is important to compare size-, site-, and group-specific natural history rates with size-, site-, and age-specific morbidity and mortality associated with UIA repair because increased natural history risk often is associated with increased risk of aneurysm repair. Patient age is crucial in decision making because of its major effect on operative morbidity and mortality; however, it does not substantially affect natural history. The effect of age is most notable in patients about 50 years of age and older for open surgery and about 70 years of age and older for endovascular procedures. In general, rupture risk is lowest for patients in asymptomatic group 1 (no history of subarachnoid hemorrhage) with UIAs less than 7 mm in diameter in the anterior circulation. Surgical morbidity and mortality are most favorable for asymptomatic patients younger than 50 years who have UIAs less than 24 mm in diameter in the anterior circulation and no history of ischemic cerebrovascular disease. Endovascular morbidity and mortality may be less age dependent, and this could favor endovascular procedures, particularly in patients aged 50 to 70 years. An important issue is determining immediate vs long-term risk regarding treatment effectiveness and durability. This issue emphasizes the importance of long-term follow-up in patients after surgical and endovascular procedures.

Section snippets

PATHOGENESIS

Approximately 80% to 90% of all intracranial aneurysms are classified as saccular or berry aneurysms, which normally appear as small, rounded, berrylike dilatations. Other shapes (sessile, pedunculated, multilobed) also are seen. Multiple aneurysms occur in 20% to 25% of patients with saccular aneurysms, and approximately 20% of patients with saccular aneurysms have a family history of SAH or intracranial aneurysms.14 Various other pathological entities have been associated with intracranial

GROWTH AND RUPTURE OF ANEURYSMS

Much controversy exists about the mechanisms involved with the growth and rupture of intracranial aneurysms. An understanding of such mechanisms is necessary to optimize our knowledge of the clinical behavior of these lesions and to optimize treatment of patients with UIAs.

Because of the risk associated with arteriographic studies over the years, relatively little information regarding serial angiography of UIAs is available.48, 49, 50, 51 Existing data seem to indicate wide variability in the

NATURAL HISTORY STUDIES

Clinical data concerning the natural history of UIAs are best considered separately for patients with UIAs and without prior SAH and patients with UIAs and prior SAH from a different aneurysm.

PATHOPHYSIOLOGY OF ANEURYSMAL DEVELOPMENT, GROWTH, AND RUPTURE

Over the years, some investigators have called attention to patients with small ruptured aneurysms diagnosed after SAH, inferring that small UIAs, even in group 1, may have substantial rupture rates.78 Others have attempted to extrapolate the natural history of UIAs by considering incidence rates of SAH to infer prevalences of UIAs in the population.79 It is important to recognize that ruptured intracranial aneurysms and UIAs constitute distinctly different clinical entities and need to be

TREATMENT CONSIDERATIONS

Patient treatment decisions involve consideration of not only the natural history of UIAs but also the morbidity and mortality rates associated with treatment including direct surgery and endovascular methods.

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