Seriousness depends upon degree.
Small aneurisms are fairly common, and tend to remain the same for long periods, often years, and require no treatment unless change is noted in the examinations.
For many people, once-yearly untrasound (painless, a bit of pushing) followed by its evaluation by the vascular surgeon on your case, is all that is necessary.

If there is more than a small extension that remains constant- the ultrasound shows the situation is changing, then corrective surgery may be necessary.