The risk of rupture of abdominal aortic aneurysms (AAAs) is related to the diameter of the lesion and is significantly higher in patients with lesions larger than 50 mm. With AAAs measuring up to 40 mm in diameter, the course is believed to be benign, but these lesions have not been extensively studied. Intervention for smaller AAAs is currently recommended only if the expansion rate is greater than 10 mm per year or the patient becomes symptomatic. As new treatments are developed for AAA, it is increasingly important to clarify the natural progression of smaller lesions.
Biancari and colleagues followed 41 patients who had AAAs with a median diameter of 33 mm (range, 25 to 40 mm). The mean age of these patients was 67 years (range, 42 to 82 years), and the majority of the patients were women, with only five men participating. Because the patients attended a regional university clinic in Finland, complete health and demographic data were available through hospital and national health records. The patients were assessed by abdominal ultrasound examination at three- to six-month intervals for a median period of seven years (range, 1.4 to 11.6 years). During this period, decisions to intervene were based on symptoms, patient preference, aneurysm size, and rate of expansion.
During follow-up, the median linear expansion rate was 2 mm per year (range, 0.0 to 8.4 mm), and this rate was higher in patients with larger lesions at entry to the study. Rupture occurred in three patients (7.3 percent), one of whom died. Open repair was undertaken in 12 patients, and endovascular repair in one patient. In most cases, the lesion had progressed in size, but surgery was also performed because of symptoms, clinical indications, or patient request. One patient died postoperatively. At 10 years, the rate of survival without rupture or repair of AAA was about 70 percent. The median time to rupture was 4.9 years and to repair, 4.5 years, but the range for both events was one to 10 years. The only significant risk factor for rupture or repair was AAA growth rate. Outcomes at 10 years were better in patients taking beta blockers and worse in those with cerebrovascular disease, but these differences were not statistically significant. Smoking and concomitant pulmonary disease did not influence outcomes.
The authors conclude that small AAAs tend to slowly enlarge and can eventually become clinically significant or even life-threatening. They support regular monitoring of these lesions.