Bor ASE, Groenestege ATT, terBrugge KG, Agid R, Velthuis BK, Rinkel GJE, and Wermer MJH. Clinical, Radiological, and Flow-Related Risk Factors for Growth of Untreated,Unruptured Intracranial Aneurysms. Stroke. 2014
Over a year has passed since Dr. Villablanca from UCLA taught us the rate of growth of aneurysms is more important with regard to risk of rupture than the size of the aneurysm. So, needless to say, an understanding of the elements that contribute to the growth of aneurysms has been in greater demand. Researchers from Finland provided some clues about 13 years ago when they published their findings in Stroke (2001) concluding that women are more likely to have aneurysms and smoking cigarettes made their aneurysms grow faster. That study comprised of 87 patients with a total of 111 unruptured aneurysms.
Dr. Bor from the Netherlands and her colleagues expanded significantly on the previous number of patients and aneurysms by analyzing 363 patients with a total of 468 aneurysms. They followed these patients for a median of 2.1 years (total of 1372 patient-years) and performed multivariate Cox regression analysis to come up with their conclusions. Their efforts are commendable and the level of information gathered on these aneurysms is important.
First, they separated the patients into two groups: small aneurysms (< 7mm) and larger ones (≥7mm). They then evaluated the number of aneurysms with and without growth at 2-year intervals and performed analysis to find risk factors for growth. The risk factors they assessed were: sex, age, smoking and hypertension at the time of diagnosis, previous SAH (SAH predating or at the time of diagnosis), presence of multiple aneurysms (ruptured or unruptured), family history of SAH (≥ 2 first degree relatives with an (un)ruptured intracranial aneurysm), initial aneurysm size (maximum aneurysm height or dome width), aneurysm location (posterior versus anterior circulation), multilobarity (multilobar versus unilobar shape), dome>neck ratio (aneurysm dome width larger than aneurysm neck width versus aneurysm dome width smaller than aneurysm neck width), aspect ratio≥median (aspect ratio larger than the median versus aspect ratio smaller than the median), flow direction into the aneurysm (highest versus lowest tertile) and bifurcation angles (highest versus lowest tertile).
In order to increase the level discrimination, the researchers also inserted age (<50, 50-60, >60 years at initial diagnosis), initial aneurysm size (< 2mm, 2-4 mm, 4-7 mm, 7-15 mm and > 15mm), aneurysm location in the anterior circulation: middle cerebral artery versus carotid artery, and anterior communicating/cerebral artery versus carotid artery into the multivariate analysis.
Some of the results were not surprising and were essentially expected since they have been previously shown to be true. For example, the researchers once again confirmed that smoking causes aneurysms to grow faster. They found that about 10% of all aneurysms grow and the initial dome-to-neck ratio was a risk factor as was multilobularity. The greater the dome-to-neck ratio, the more likely the aneurysms were to grow and more lobes meant more growth as well.
However, unlike previous studies that showed female sex to be associated with aneurysm development and growth, Dr. Bor and her colleagues did not find an association. They also did not find any relationship with age, hypertension, familial history of SAH, previous SAH, flow direction into the aneurysm or bifurcation angles.
That was interesting and unexpected. Most clinicians who deal with aneurysms try to avoid hypertension and we were all taught that a previous SAH in a patient who has an aneurysm is a risk for growth and rupture of new aneurysms. But, this study says otherwise. That is why this study is important and deserves discussion.