KEY POINTS
■ Surgical repair of thoracic aortic aneurysms and thoracoabdominal aortic aneurysms require a systematic approach in order to prevent devastating complications, especially ischemic spinal cord injury.
■ Treatment decisions are based on balancing the risk of death from aortic rupture with the risk of mortality and complications from the procedure.
■ Some persons with peripheral vascular disease and persons who are at high risk for complications from cardiopulmonary bypass are possible candidates for endovascular repair.
■ Thrombotic or atheromatous debris dislodging into segmental vessels may result in embolization to small end vessels within the spinal cord. This possible mechanism of injury to the spinal cord offsets the benefits of an endovascular repair. Perceived benefits of this procedure are the absence of any aortic occlusion and less hemodynamic instability.
Surgical repair of thoracic aortic aneurysms (TAAs) and thoracoabdominal aortic aneurysms (TAAAs) are challenging procedures that require a systematic approach in order to prevent devastating complications, especially ischemic spinal cord injury. Advances in surgical technique and organ protection have improved the outcomes of these procedures. Standardized protective strategies, such as monitoring somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs), mild hypothermia, distal aortic perfusion, CSF drainage, spinal cord perfusion monitoring, and selective implantation of segmental spinal cord arteries, also improve outcomes. This article describes a current approach to TAA and TAAA repair and analyzes the outcomes.
Classification of aneurysms Surgical repair of TAAs and TAAAs were first performed in the early 1950s. Historically, the procedures are associated with a high mortality rate and a significant risk of paraplegia and multiple organ complications.1 E. Stanley Crawford, MD, and colleagues defined four classifications for TAAAs based on location and the extent of the aneurysm2 (Figure 1). According to the Crawford classification, a type I aneurysm originates distal to the left subclavian artery and involves the visceral arteries. Type II involves the entire aorta distal to the left subclavian artery; type III involves the distal half of the descending thoracic aorta and the entire abdominal aorta; and type IV involves the infradiaphragmatic aorta. Types I and II are associated with the highest rates of mortality and paraplegia.2
Treatment decisions are based on balancing the risk of death from aortic rupture with the risk of mortality and complications from the procedure. Surgical results have improved significantly over the past 10 years. Rupture of these aneurysms is invariably fatal.3,4 Prediction of the probability of rupture may improve selection of patients for elective surgery, as rupture rates in patients not treated surgically are high, ranging from 21% to 74%.5,6 Specific risk factors that increase the likelihood of rupture have been identifi ed from studies of the history of TAAs and TAAAs. An individualized yearly risk of rupture can now be calculated based on specific dimensional and nondimensional variables. Selected patients with an operative risk that is significantly lower than the calculated risk of rupture are candidates for elective surgery.7 Of note, the Crawford classification of aneurysms is commonly mistaken for the DeBakey or Stanford aortic dissection classifications.
Primary care and screening Typically, aneurysms are an incidental finding; a widening of the aorta is noticed on plain radiography of the chest during a workup for something else. The presenting symptoms can be vague, especially in the case of a TAA. However, a history of Marfan syndrome or Ehlers-Danlos syndrome is a reason to suspect an aneurysm because the symptoms can be vague and confused with chest, back, or abdominal pain; therefore, aortic aneurysm should be included in the differential diagnosis. A comprehensive history and astute physical examination should assist in determining the likelihood of an aneurysm. Once aneurysm is diagnosed or suspected, CT angiography should be ordered to establish a definitive diagnosis and a baseline for comparison over time. In addition, referral to an aortic-thoracic surgeon is recommended.