Abstracts & Commentary
Sources: Wiebers DO, et al; International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms: Natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet. 2003;362:103-110; White PM, Wardlow J. Commentary. Unruptured intracranial aneurysms: Prospective data have arrived. Lancet. 2003;362:90-91.
The management of the patient with an unruptured cerebral aneurysm remains a subject of debate between neurologists and neurosurgeons. Neurologists, citing the results of the retrospective International Study of Unruptured Intracranial Aneurysms (ISUIA),1 hold the opinion that the yearly rupture rate for small anterior circulation cerebral aneurysms is so low, between 0.05 and 0.7%, that in most cases the risks of treatment outweigh the natural history risk for aneurysms less than 1 cm in diameter.
In contrast, neurosurgeons recommend surgery for unruptured cerebral aneurysms as small as 5 mm because of the large proportion of ruptured aneurysms that are small. In one series, more than 60% of ruptured aneurysms were 5 mm or less.2 The discrepancy between reports of the low risk of rupture in small asymptomatic cerebral aneurysms and the large proportion of ruptured aneurysms in this size category remains unexplained.
The present ISUIA report is the largest prospective study of the risk of rupture of unruptured asymptomatic cerebral aneurysm. More than 4000 patients at centers in the United States, Canada, and Europe were assessed. Investigators recorded the 5-year cumulative rupture rates for patients who did not have surgery and assessed morbidity and mortality in those who had either surgical or endovascular procedures. Of the patients enrolled, 1692 did not have aneurysm repair, 1917 had open surgery, and 451 had endovascular procedures.
In patients who did not have a history of subarachnoid hemorrhage (SAH), larger aneurysm size and location were associated with a greater risk of rupture. The 5-year cumulative rupture rates for anterior circulation aneurysms (internal carotid, anterior communicating, anterior cerebral, and middle cerebral arteries) were 0% for those less than 7 mm, 2.6% for those 7-12 mm, 14.5% for those 13-24 mm, and 40% for those 25 mm or greater. For the same size categories, the rupture rates for aneurysms involving the posterior circulation, including the posterior communicating artery, were 2.5%, 14.5%, 18.4%, and 50%, respectively.
These rates often were equaled or exceeded by the risks associated with surgical or endovascular repair of comparable aneurysm. Total morbidity and mortality rates at 1 year in patients with open surgical repair were 12.6% for patients without a history of SAH and 10.1% for patients with SAH from a separate aneurysm. For patients who had craniotomy, variables that were predictive of a poor surgical outcome were age older than 50, aneurysm diameter greater than 12 mm, location in the posterior circulation, previous ischemic cerebrovascular disease, and aneurysm symptoms other than rupture. In the endovascular group, the initial morbidity and mortality rates were 9.1% and 9.5%, respectively. Compared with the surgery group, endovascular patients were older with larger unruptured aneurysms and had a higher proportion of aneurysms in the posterior circulation.
Commentary
The management of patients with unruptured cerebral aneurysms remains complex because of the many factors, such as aneurysm site and size, age of the patient, and specific risk factors, that must be evaluated in each patient. The current prospective data from ISUIA are helpful to clinicians because they indicate a group of patients—those with no history of SAH and an asymptomatic anterior cerebral circulation aneurysm less than 7 mm in diameter—who do not require surgical or endovascular treatment. The study also emphasizes that a patient’s age is especially important because, although older age does not affect the rate of rupture, it has an important effect on surgical morbidity. For example, asymptomatic patients younger than 50 with unruptured anterior circulation aneurysms 24 mm or less in diameter have the lowest rates of surgical morbidity and mortality. In patients older than 50 and in those with posterior circulation aneurysms, endovascular repair is the treatment of choice. Nevertheless, as pointed out by White and Wardlaw in their commentary, in each patient, treatment options and relative benefits and risks need to be discussed with patients and relatives before elective treatment so that full informed consent can be given. — John J. Caronna, MD, Vice-Chairman, Department of Neurology, Cornell University Medical Center; Professor of Clinical Neurology, New York Hospital; Associate Editor, Neurology Alert.
References
1. N Engl J Med. 1998;339:1725-1733.
2. White P, et al. Radiology. 2001;219:739-749.
The present report from the International Study of Unruptured Intracranial Aneurysms is the largest prospective analysis of the risk of rupture of unruptured asymptomatic cerebral aneurysm.
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