Open Surgical Treatment of Thoracoabdominal Aortic Aneurysms

Classification of Thoracoabdominal Aortic Aneurysms

The classification of thoracoabdominal aortic aneurysms is based on the extent of the involved aorta ( Figure 1 ). Extent I is from the left subclavian to above the most proximal renal artery. Extent II is from the left subclavian artery to below the renal arteries. Extent III is from the sixth intercostal space to below the renal arteries. Extent IV is from T12 to below the renal arteries. Extent V, which was introduced in the last 2 decades, is from T6 to just above the renal arteries. The importance of the classification scheme is that it correlates with the incidence of neurologic deficits and mortality, especially when using the clamp-and-sew technique.

Clinical Manifestations

When symptoms are present before rupture, patients with thoracoabdominal aortic aneurysm complain of vague back or upper abdominal discomfort. Expanding aneurysms can cause pressure on adjacent structures, such as the lung, bronchus, esophagus, or recurrent laryngeal nerve. Axial imaging has largely replaced catheter-based aortography in the diagnostic assessment of thoracoabdominal aortic aneurysms. Computed tomography (CT) and magnetic resonance imaging are now commonplace and essential for assessing aneurysm morphology. Maximal aortic diameter, based on axial imaging or three-dimensional reconstructions, determines the need for operative intervention.

Thoracoabdominal aortic aneurysms can be expected to increase in size by 1 to 3 mm per year. Rupture is uncommon in aneurysms less than 4 cm in diameter. Rupture becomes unpredictable in aneurysms greater than 5 cm, but the risk continues to increase with size. The 5-year risk of rupture is greater than 30% for aneurysms larger than 6 cm. The goal of thoracoabdominal aortic aneurysm repair is prevention of rupture, because the mortality is greater than 90% in the first 24 hours after rupture.

We consider patients for repair of asymptomatic thoracoabdominal aortic aneurysm when maximal diameter is 5 to 6 cm. For patients at low risk of rupture, such as those with aneurysms less than 5 cm, we recommend repeat CT imaging at 6 months. Patients with connective tissue disorders, symptoms, saccular aneurysms, or diameter increases of more than 5 mm in 6 months are also at higher risk for rupture and are considered for earlier repair.

Once operative repair is indicated, preoperative assessment includes pulmonary function testing and echocardiography. Low preoperative left ventricular ejection fraction is a predictor for higher perioperative mortality. Additional testing for coronary artery disease is individualized. Optimal treatment of preoperative asymptomatic coronary artery disease remains controversial. Kidney function is evaluated by estimating the glomerular filtration rate (GFR). Values lower than 90 mL/min per 1.73 m ² body surface area indicate renal impairment. A low GFR is a powerful predictor of adverse outcome that is more sensitive than serum creatinine.