A large survey of adult residents of China has determined that the prevalence of unruptured cerebral aneurysms (UCAs) is 7%, that UCAs increase with age, and that they seem to be more common in women.
This prevalence rate is higher than in previous research, in some cases more than twice as high, probably at least in part because researchers used high-resolution magnetic resonance angiography (MRA) to detect UCAs, said lead author Ming-Hua Li, MD, PhD, professor and chairman of Neuro-radiology, Shanghai Jiao Tong University, China.
Of these, though, only about 8.7% were judged to be at any imminent risk for rupture, they note.
High Diagnostic Accuracy
This new analysis included 4813 residents aged 35 to 75 years from 2 Shanghai districts: Changning, an economically well-developed urban area, and Zhabei, a less developed suburban area. This age group represents the range that is most clinically significant in terms of screening, said Dr. Li. Those younger than 35 years are less likely to have UCAs and those older than 75 have a shorter life expectancy, he said.
Participants completed a standard questionnaire to provide demographic information, personal and family medical history, and lifestyle risk factors, and they underwent a physical examination.
The researchers used 3-dimensional (3D) time-of-flight MRA with a voxel size of less than 0.7 mm. To evaluate UCAs, they applied 3D volume rendering and single artery highlighting. This imaging modality was proven in a previous study by the same research group to have very high diagnostic accuracy for detecting intracranial aneurysms compared with 3D digital subtraction angiography (DSA), said Dr. Li.
In the current study, 3 radiologists who were blinded to participants’ information determined the location and size of the UCAs.
UCAs were defined as abnormal focal dilatations of a cerebral artery with attenuation of the vessel wall or an infundibulum in patients without a history of subarachnoid hemorrhage (SAH). Aneurysms were categorized as less than 3 mm, 3 mm to less than 5 mm, 5 mm to less than 10 mm, or 10 mm or more.
The survey excluded UCAs with a diameter of less than 2 mm because, as Dr. Li explained, aneurysms with such a small diameter are difficult to diagnose with the spatial resolution of the imaging modality used.
Aneurysms were morphologically classified as regular (saccular), irregular (lobular), or fusiform. Sites were classified as internal carotid artery (including the posterior communicating artery), anterior cerebral artery (including the anterior communicating artery), middle cerebral artery (including the MI-2 bifurcation), and vertebrobasilar artery.
The researchers found that 130 men and 206 women had UCAs, with excellent interobserver agreement. The prevalence of UCAs was 7.0% (95% confidence interval, 6.3% to 7.7%).
This is a higher prevalence than in other studies, probably because the researchers used 3D high-resolution MRA, which enabled them to detect small UCAs, Dr. Li speculated. “Those small UCAs could possibly be missed on 2D invasive angiography due to overlapping,” he said. “In addition, we excluded volunteers younger than 35, who are less likely to have UCAs. This could potentially lead to higher prevalence in our survey compared to studies with a wider age range.”
The prevalence of unruptured UCAs in North America is still unknown, said Dr. Li.
The prevalence was higher in women (8.6%) than in men (5.5%) (P < .001). “We hypothesized that decreases in estrogen concentration and estrogen-receptor density may contribute to an increased risk of cerebral aneurysm development in women,” said Dr. Li.
The prevalence of UCAs increased with age and peaked at ages 55 to 64 years in both men and women. This, said Dr. Li, is in line with a meta-analysis published in Lancet Neurology in 2011.
The majority (90.2%) of the UCAs were less than 5 mm in diameter. The mean maximum diameter of the aneurysm sac was 3.5 mm, and the diameter was larger in women.
Most aneurysms (81%) were located in the internal carotid artery (ICA), with more than half (53.9%) in the C5–C6 segments of the ICA. A possible explanation for this, said the authors, is that the study excluded ruptured aneurysms, which are most often located in the anterior or posterior communicating arteries. In addition, the MRA technology allowed for visualization of more UCAs in the siphon segment of the internal carotid artery.
The researchers found that 8.7% of the detected lesions were potentially risky in that they were large, lobulated aneurysms or grew during follow-up and so may have been prone to rupture.
The patients with these aneurysms potentially in danger of rupture are being followed closely, said Dr. Li. “We currently follow up those patients annually by 3D MRA if the lesions remain stable — so no growth or daughter-sac formation. If lesion growth is detected at follow-up, we suggest further treatment accordingly.”
The study did not show an association between the prevalence of aneurysms and hypertension or cardiovascular disease. This was a cross-sectional study that mainly focused on the prevalence of UCAs, explained Dr. Li, adding that the association between risk factors such as hypertension and cardiovascular disease and development of UCAs in Chinese adults needs to be explored in other longitudinal studies.
The findings may not apply to the general population or to populations outside of China, said the authors.
R. Loch Macdonald, MD, PhD, Keenan Endowed Chair in Surgery and head, Division of Neurosurgery, St. Michael’s Hospital, and professor of surgery, University of Toronto, Ontario, Canada, who has a special research interest in cerebral aneurysms, doesn’t believe that the prevalence of aneurysms is any higher in China than elsewhere in the world.
“I suspect they are not more common compared to other geographic regions and ethnicities or races and that the difference is due to a selected older population and more sensitive screening test,” used in the current study, said Dr. Macdonald when approached by Medscape Medical News for a comment.
He pointed to a previously published meta-analysis that found 3% of the population harbored an aneurysm, adjusted to a population with a mean age of 50 years that was 50% male, and expanded on why the numbers in the current study might be much higher.
“They may have found a higher incidence due to inclusion of only patients aged 35 to 75 years,” he added. “Second, the distribution of aneurysms includes many more very small proximal carotid aneurysms. These may not have been diagnosed as frequently before by other methods, so this new screening study may have detected more due to increased sensitivity of the screening method.”