Strategies in the management of extensive descending and thoracoabdominal aortic aneurysms.

T he surgical repair of descending and thoracoabdominal aortic aneurysms began in the early 1950s, and has been traditionally associated with a high mortality rate and a significant risk of paraplegia and multiple organ complications. Crawford classified thoracoabdominal aortic aneurysms into four categories based on the extent of the aneurysm (Figure 1). According to this classification, extent I aneurysms originate distal to the left subclavian artery and involve the visceral arteries. Extent II aneurysms involve the entire aorta distal to the left subclavian. Extent III aneurysms involve the distal half of the descending thoracic aorta and the entire abdominal aorta, and extent IV involve the infradiaphragmatic aorta. Extents I and II are associated with the highest mortality and paraplegia rates. Treatment decisions require balancing the risk of death caused by rupture of the aorta with the risk of mortality and complications from the operation itself. Surgical results have improved significantly over the past 10 years, whereas on the other hand rupture of these aneurysms is invariably fatal. Accurate prediction of the probability of rupture would improve the selection of patients for elective surgery, because rupture rates in patients not treated surgically are high, ranging from 21% to 74%. Specific risk factors that increase the likelihood of rupture have been identified from studies of the natural history of thoracic and thoracoabdominal aortic aneurysms. An individualized yearly risk of rupture can now be calculated, based on specific, easily obtainable dimensional and nondimensional variables. Selected patients whose operative risk is significantly lower than their calculated risk of rupture should be offered elective surgery.