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Endovascular therapy is feasible and relatively safe for many asymptomatic unruptured intracranial aneurysms, according to a registry study published online July 30, 2013, ahead of print in Stroke. But because the risk of procedural failure or complications rises with certain aneurysm sizes and morphologies, careful patient selection is important, the authors say.

Investigators led by Toshiyuki Fujinaka, MD, PhD, of Osaka University (Suita, Japan), analyzed outcomes associated with 4,767 asymptomatic unruptured intracranial aneurysms treated with endovascular therapy. The cohort was derived from 2 Japanese registries: JR-NET (122 neurointerventional centers, 2005-2006) and JR-NET2 (150 neurointerventional centers, 2007-2009).

Of the 45.2% of aneurysms scheduled for embolization, all were treated by intrasaccular coil embolization. The remaining lesions received adjunctive therapies including balloon remodeling, double catheters, and stenting. Intracranial stents, which were not approved in Japan until 2010, were used in only 1.1% of cases.

Endovascular Therapy Highly Successful

Overall, endovascular therapy was successful in 97.9% of cases, with the failure rate decreasing as aneurysm diameter increased (P = 0.003). No difference in failure rates was seen between aneurysms of the anterior and posterior circulation (2.2% vs. 1.9%). The immediate radiographic outcomes of successfully treated aneurysms showed that 57.7% were completely occluded, 31.9% had residual necks, 10.0% had residual domes, and 0.4% ended in unpredicted parent artery occlusion. The rate of residual aneurysm tended to increase annually (P = 0.03).

Procedure-related adverse events occurred in 9.1% of patients, although only 23% of those resulted in worse 30-day modified Rankin scale scores. Intracranial hemorrhagic and ischemic complications developed after 2.0% and 4.6% of procedures, respectively. In particular, 65 aneurysms ruptured during the procedure while only 5 ruptured afterward.

Ischemic complications were more frequent in larger (≥ 10 mm) aneurysms, while hemorrhagic complications were more common in smaller (< 3 mm) aneurysms (P < 0.001 for both). Also, complication rates were lower for aneurysms in the anterior than in the posterior circulation (8.3% vs. 11.2%; P = 0.005). Furthermore, complication rates were lower in aneurysms less than 10 mm in diameter with favorable as opposed to wide necks (6.4% vs. 9.7%; P < 0.001).

At 30 days, rates of morbidity (defined as a deterioration in the modified Rankin Scale score > 0) and procedure-related mortality were 2.12% and 0.31%, respectively. Thirteen deaths were accompanied by hemorrhagic complications (10 aneurysmal ruptures, 2 dissections, and 1 perforation), while 1 was caused by a branch occlusion. No deaths were associated with a systemic condition.

Registry Data Helpful

In a telephone interview with TCTMD, Philip M. Meyers, MD, of Columbia University Medical Center (New York, NY), said the study provides helpful information. “We’re short on good outcome data for endovascular therapy,” he observed.

“The natural history of these aneurysms is somewhat unclear,” Dr. Meyers noted. “It may be that the risk of having an aneurysm just isn’t that great and therefore the treatment has to be pretty successful and low-risk. [This study] provides extra data points from a fairly large registry that shows what happened to almost 5,000 patients who undergo treatment.”

But in a telephone interview with TCTMD, Pascal M. Jabbour, MD, of Jefferson University Hospitals (Philadelphia, PA), said the Japanese data provide little new information. Although the overall complication rate is a little high, he said, actual morbidity and mortality are in line with the literature. It also confirms the large International Study of Unruptured Intracranial Aneurysms (ISUIA) showing low rates of rupture among small aneurysms, as well as other studies linking this subset with higher complications rates.

However, he asserted, neurosurgeons do not believe in the ISUIA’s suggested cutoff of 7 mm, below which anterior circulation aneurysms can simply be observed. “Half of the ruptured aneurysms we see are less than 7 mm,” Dr. Jabbour reported. “With MRA and CTA, we’re detecting more and more small aneurysms, and in our practice the threshold to treat is 5 mm. But that’s not an absolute number. It depends on risk factors such as smoking, familial history of aneurysms, and prior ruptured aneurysm.”

Don’t Treat If You Can’t Beat the Natural History

For Dr. Jabbour, the highlight of the paper is its admonition to be circumspect about treating very small aneurysms. “If we can’t beat the natural history of the disease, we shouldn’t be offering treatment,” he explained. Unfortunately, he added, some patients with tiny aneurysms are so concerned about the dire consequences of rupture that they ignore advice about an unfavorable risk-benefit ratio and demand treatment.

Limiting the applicability of the Japanese results to contemporary US practice, Dr. Jabbour noted, is the fact that most patients received either plain or balloon-assisted coiling, rather than stent-assisted coiling or flow diversion. In fact, he noted, the Pipeline flow diverter device (Covidien, Mansfield, MA) now accounts for roughly 30% of all US endovascular procedures.

Dr. Meyers noted that while Japanese endovascular specialists are generally quite experienced, in the United States the growing adoption of endovascular therapy by a variety of specialists with varying degrees of training has been “a big concern.” This situation can lead both to lower technical skill and questionable patient selection, he added.

Dr. Jabbour agreed. In the United States, with so many physicians having basic endovascular training, “every little community hospital is hiring them, which means there are centers performing 10 or 15 procedures a year. So you have higher complication rates.”

Meanwhile, considerable research is being devoted to inflammatory markers and other ways to discriminate between aneurysms that will and will not rupture, Dr. Jabbour commented, but none has been validated for clinical use.

Study Details

Overall, 80.0% of aneurysms were located in the anterior circulation and 20.0% in the posterior circulation. In terms of maximal diameter, most aneurysms fell within the range of 5 mm to 9 mm (51.9%). At the extremes, however, 12.0% had maximal diameters of 10 mm to 19 mm, with 0.7% wider than 20 mm, while 2.5% had diameters of less than 3 mm. Among aneurysms with diameters of less than 10 mm, 43.6% had narrow necks and 53.4% had wide necks.

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