Cerebral aneurysms of all sizes, even small ones below seven millimetres, are 12 times more likely to rupture if they are growing, according to a new study published online in the journal Radiology.
The results of the study counter current guidelines suggesting that small aneurysms pose a low risk for rupture, and it emphasises the need for regular monitoring and earlier treatment.
“Until now, we believed that large aneurysms presented the highest risk for rupture and that smaller aneurysms may not require monitoring,” said the study’s lead author, J Pablo Villablanca, chief of diagnostic neuroradiology, David Geffen School of Medicine, University of California, USA. “Our findings show this is not the case and shed light on additional risk factors for rupture in aneurysms of all sizes.”
In the study, 258 asymptomatic cerebral aneurysms identified either incidentally or during a baseline study of 165 patients (132 women, 33 men) were monitored over time (mean of 2.24 years) with computed tomography angiography (CTA). Patients were scanned with CTA at intervals of six or 12 months.
Over the study period, the researchers observed growth in 46 (nearly 18%) of all the intracranial aneurysms in a total of 38 patients. Three of the growing saccular aneurysms ruptured, and of those, all were less than seven millimeters in size when the patient enrolled in the study.
“Our study shows that the size of the aneurysm is not as important as was once thought,” Villablanca said. “Any aneurysm is potentially capable of growth and thus requires follow-up imaging.”
Current guidelines based on research conducted by the International Study of Unruptured Intracranial Aneurysms and other studies suggest that known aneurysms less than seven millimeters in size have a low risk of rupture and do not need to be monitored with imaging.
Compared to the aneurysms that stayed the same size, the 46 growing aneurysms in the study were associated with a 12-fold higher risk of rupture. The researchers calculated the risk of rupture for growing aneurysms at 2.4% per patient year, vs. 0.2% for aneurysms without growth.
“Our data support the need to perform longitudinal follow-up imaging to monitor for possible growth in all incidental unruptured aneurysms, including small lesions,” Villablanca said.
In a secondary finding, the researchers reported that tobacco smoking and an aneurysm’s initial larger size were independent factors predicting aneurysm growth. These combined risk factors were linked to nearly 80% of all aneurysm growth in the study.
“Our findings correlated a higher risk of rupture to the combined factors of smoking, aneurysm growth and larger aneurysm size,” Villablanca said. “Patients who smoke and have growing aneurysms may require earlier treatment, such as brain surgery or endovascular coiling.”
Observation was the treatment of choice for 194 of 212 (91%) stable aneurysms. When aneurysm growth was discovered by CTA imaging, 50% of the growing aneurysms were treated, while the remaining 50% continued to be observed.