New Way to Determine Need for Aneurysm Surgery

A new noninvasive method for predicting abdominal aortic aneurysm (AAA) rupture risk and the need for surgery has been shown to be better than measuring the aneurysm's diameter, used in the past for this purpose. The method was described in the April 2003 issue of the Journal of Vascular Surgery.

More than 100 patients who had computed tomography (CT) scans during the course of routine care had AAA wall-stress analysis. The CT scan is processed through a series of computer programs, including an engineering process called finite element analysis. This breaks the structure into thousands of tiny elements so a computer can calculate the wall stress using the 3-D shape of the AAA from the CT scan, the patient's blood pressure, and the tissue properties of typical AAAs. The result is a computer-generated "stress map” that displays the aneurysm wall stress, the force trying to pull the aneurysm apart and cause rupture.

The patients in the study were generally under observation for their aneurysm because it was too small to repair, or because the risks of repair were felt to be too high compared to the risk of rupture, or because the patient decided not to have the repair. The outcomes of observation were then compared, based on the standard method of determining rupture risk (maximum AAA diameter) versus the maximum stress within the aneurysm wall. The results showed that the new technique predicted the risk of rupture better than maximum AAA diameter, with a 25-fold increase in rupture risk for patients with high AAA wall stress, and only a nine-fold higher increase in risk for patients with a large diameter (over 5.5 cm) aneurysm. Some patients with small aneurysms had high wall stress, while some patients with large aneurysms had low wall stress.

”Another impact of this study may be that blood pressure control in aneurysm patients will be examined with more scrutiny, since blood pressure plays a key role in AAA wall stress. AAA wall stress analysis may be able to prevent rupture in some patients and prevent unnecessary surgery in others,” said Dr. Mark Fillinger, who conducted the study along with colleagues at the Dartmouth-Hitchcock Medical Center (Lebanon, NH, USA).




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