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The Stroke Council of the American Heart Association (AHA) has formulated recommendations for the management of unruptured intracranial aneurysms. According to the AHA statement, the guidelines are intended to serve as a framework for the development of treatments and for future research on unruptured intracranial aneurysms. The document contains discussions about the natural history of intracranial aneurysms, diagnostic evaluation, surgical treatment and screening for unruptured intracranial aneurysms.

The AHA recommendations appear in the October 31, 2000 issue of Circulation and are also available on the AHA Web site at A single reprint (no. 71-0195) may be obtained by calling 800-242-8721 or by writing to AHA National Center, 7272 Greenville Ave., Dallas, TX 75231-4596.

The AHA council notes that the clinical recommendations are based on cohort and case studies and are therefore flexible. The following summarizes the AHA scientific statement on the management of unruptured intracranial aneurysms.

Natural History

According to the AHA statement, the natural history of unruptured intracranial aneurysms is different in patients who have previously had a subarachnoid hemorrhage from a separate aneurysm than in patients who have not had a subarachnoid hemorrhage. In patients without a previous subarachnoid hemorrhage, the International Study of Unruptured Intracranial Aneurysms (ISUIA) reported a rupture rate of 0.5 percent per year in patients with aneurysms smaller than 10 mm in diameter and a rate of approximately 1 percent per year in those with aneurysms 10 mm or larger in diameter. [ corrected] The follow-up period in the ISUIA study averaged 7.5 years. The rupture rate was 6 percent in the first year among patients with giant (25 mm or larger) aneurysms. When there was no history of subarachnoid hemorrhage, the risk of rupture with posterior communicating, vertebrobasilar/posterior cerebral and basilar tip aneurysms that measured 10 to 24 mm in diameter was approximately 15 percent at 7.5 years. For aneurysms in these locations that measured less than 10 mm, the risk of rupture was approximately 2.5 percent over 7.5 years. The risk of rupture of aneurysms measuring 22 mm or more was approximately 45 percent.

In contrast, patients with a history of subarachnoid hemorrhage and an aneurysm of 10 mm or smaller in diameter had a rupture rate of 0.5 percent per year, a rate 11 times higher than that in patients without a history of subarachnoid hemorrhage. However, for aneurysms of 10 mm or larger in diameter, the rupture rate in patients with a previous subarachnoid hemorrhage was lower than that in their counterparts without a history of subarachnoid hemorrhage (0.65 percent per year versus approximately 1 percent per year). The only clear predictor of future rupture among patients with a history of subarachnoid hemorrhage was a basilar tip location; size alone was not predictive of future rupture. The risk of rupture was approximately 12 percent at 7.5 years in patients with a basilar tip aneurysm smaller than 10 mm in diameter, whereas the risk of rupture was 3 percent for aneurysms of this same size in other locations.

Diagnostic Evaluation

According to the AHA statement, standard computed tomography (CT) with or without contrast agents cannot adequately exclude or confirm the presence of an intracranial aneurysm, particularly an unruptured aneurysm. CT angiography, however, may demonstrate aneurysms as small as 2 to 3 mm and may be useful for monitoring patients during follow-up. Magnetic resonance angiography (MRA) is cited as a useful tool for screening, particularly for aneurysms that measure more than 3 to 5 mm in diameter. The report notes that the gold standard for the diagnostic evaluation of intracranial aneurysms is intraarterial catheter angiography.

Surgical Treatment

The AHA council notes that the patient's age is an important factor that influences the outcome of surgical treatment. Other factors include the presence or absence of symptoms, the patient's medical condition and the size, morphology and location of the aneurysm. According to the report, surgical morbidity is increased when aneurysms have large ill-defined or fusiform necks, arise from atherosclerotic or distended vessels, involve major intracranial bifurcations or are located partially within the cavernous sinus or arise from the midportion of the basilar artery.

Surgical experience also influences outcome. For example, a study in New York state revealed a 53 percent lower mortality rate in 21 hospitals where more than 10 craniotomies were performed per year than the mortality rate in 89 hospitals in which 10 or fewer such operations were performed per year. The mortality rate in hospitals where more than 10 craniotomies were performed annually was 5.3 percent, compared with a mortality rate of 11.2 percent in hospitals where 10 or fewer craniotomies were performed annually.

According to the AHA statement, factors that favor surgery include young age with a long life expectancy, previously ruptured aneurysms, a family history of aneurysm rupture, large aneurysms, symptomatic aneurysms, documentation of aneurysm growth and a low risk associated with treatment.

Summary of Recommendations

The AHA statement makes the following recommendations for the treatment of unruptured intracranial aneurysms:

  • The treatment of small incidental intracavernous aneurysms is not generally indicated. For large symptomatic intracavernous aneurysms, treatment decisions should be individualized on the basis of patient age, the severity and progression of symptoms, and treatment alternatives. The higher risk of treatment and shorter life expectancy in older persons must be considered. Observation of older patients with asymptomatic aneurysms is recommended.

  • Symptomatic intradural aneurysms of all sizes should be considered for treatment, with relative urgency for the treatment of acutely symptomatic aneurysms.

  • Coexisting or remaining aneurysms of all sizes in patients with a history of subarachnoid hemorrhage caused by another treated aneurysm carry a higher risk for future hemorrhage than do similar sized aneurysms in patients without a history of subarachnoid hemorrhage. In such cases, treatment should be considered. Aneurysms located at the basilar apex carry a relatively high risk of rupture. Treatment decisions must take into account the patient's age and medical and neurologic condition and the relative risks of surgical repair. Periodic CT, MRA or selective contrast angiography should be considered when surgical treatment is not undertaken.

  • Treatment of incidental aneurysms measuring less than 10 mm in patients without a history of subarachnoid hemorrhage cannot generally be advocated because the risk of hemorrhage is low in such patients. However, special consideration for treatment should be given if such patients are young. Likewise, treatment should be a consideration for aneurysms that approach 10 mm in diameter, for aneurysms with daughter sac formation and other unique hemodynamic features and for patients with a family history of aneurysms or aneurysmal subarachnoid hemorrhage. Periodic follow-up imaging should be a consideration if the decision is made to manage the patient conservatively.

  • Asymptomatic aneurysms of 10 mm or larger in diameter warrant strong consideration for treatment, taking into account patient age, medical and neurologic condition, and the relative risks of treatment.

Coverage of guidelines from other organizations does not imply endorsement by AFP or the AAFP.

This series is coordinated by Michael J. Arnold, MD, Assistant Medical Editor.

A collection of Practice Guidelines published in AFP is available at

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