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Anything more aggressive than leaving a tiny unruptured intracranial aneurysm alone may be detrimental to the patient's health, researchers suggested.

How an aneurysm measuring 3 mm or smaller is treated or monitored makes a difference in long-term survival, according to Ajay Malhotra, MD, of Yale School of Medicine in New Haven, Connecticut, in their study published online in JAMA Neurology.

Patients lived the longest if they were steered toward no treatment or preventive follow-up, surviving an average of (QALYs). Other strategies shaved more than a year off that figure:

• MR angiography every 5 years: 18.05 QALYs
• Annual follow-up: 17.93 QALYs
• Biennial follow-up: 17.65 QALYs
• Endovascular coiling: 17.53 QALYs

Malhotra's group drew their conclusions after pulling data from the current unruptured intracranial aneurysm literature, and using it to perform 10,000 simulations based on a 50-year-old with with no history of subarachnoid hemorrhaging.

If tiny non-growing aneurysms have odds of rupture that are lower than 1.7%, no follow-up is the best strategy. Beyond that, coiling can be performed on higher-risk aneurysms.

Yet that 1.7% risk already sets a fairly high ceiling, according to S. Claiborne Johnston, MD, PhD, of University of Texas at Austin, who said in an accompanying editorial that "no study has shown a rate close to this, with a best estimate being 0.23%."

According to the investigators, the 2015 American Heart Association and American Stroke Association guidelines on the management of patients with unruptured intracranial aneurysms give a class I recommendation to intermittent imaging studies at regular intervals to follow-up on aneurysms that are managed conservatively. A first follow-up assessment 6-12 months after initial discovery is recommended, followed by subsequent follow-up yearly or every other year, the guidelines say in a class IIb recommendations.

"No specific guidelines exist regarding the management of tiny, incidentally detected unruptured intracranial aneurysms measuring 3 mm or less," Malhotra's group emphasized. "The incidence of rupture in tiny unruptured intracranial aneurysms in the published literature is low."

It is suggested that harm might be done by endovascular coiling because the procedure is not free from the risk of complications. Whats more, aneurysms might grow back over time.

Sensitivity analyses didn't change the main findings of the present study. The authors acknowledged that they didn't account for the potential effects of age, sex, or aneurysm location, however.

"Our study emphasizes the need for better, more consistent, and longer-term studies reporting the growth and rate of rupture of unruptured intracranial aneurysms to better define the optimal management of small unruptured intracranial aneurysms. Clinical decisions are currently being made based on the limited evidence in the literature," the investigators said.

Limited as it may be, the evidence still points clearly in one direction, Johnston suggested.

"In spite of 2 decades of largely confirmatory evidence for very small aneurysms (arbitrarily set at ≤3 mm in diameter) showing that coil embolization is not as safe as some believe and that rupture and growth rates are extremely low, many continue to recommend treatment for most of these aneurysms."

He added "one can always argue that the underlying studies could be better, but what happened to that oath we all took, 'First do no harm ... ?'"

With the best estimate suggesting we shorten a patient's lifespan by 2 years when we treat a very small aneurysm, we should stop treating now rather than waiting for better data to change course," he urged.