Mutation in Fibrillin 1 gene leads to decreased tensile strength of the aorta An estimated 75% of patients will have a dilated aortic root Loeys-Dietz Syndrome Aggressive vasculopathy linked to TGFBR1 or 2 mutation Early detection and intervention is important Aortitis Infectious Syphilis (historical), Salmonella, staphylococcal sp, mycobacterium Non-infections/inflammatory More common:
Giant cell and Takaysu’s arteritis Less common: Behcets, Cogans syndrome, replapsing polychondritis Rare: Rheumatoid arthritis, spondyloarthropathies Trauma Typical location is at the aortic isthmus Complications include rupture, pseudoaneurysm, chronic dissection with secondary aneurysm formation Chronic aortic dissection Aneurysm may form due to growth and pressure differential of false lumen

Examples of the various etiologies of thoracic aortic aneurysm disease are listed in Table 11.1. Although the genetics of this disease are multifactorial and not fully elucidated, it is thought that the predominant inheritance of thoracic aortic disease is autosomal dominant with reduced penetrance. Nearly 20% of patients who develop a thoracic aortic aneurysm will have a family history of aortic disease and a familial pattern should be suspected in patients who present at a young age. Younger patients with thoracic aortic dilation should also be evaluated for a bicuspid aortic valve. The presence of a bicuspid valve is highly associated with aneurysm in this population, and these patients may be at higher risk for aortic complications. In older patients, the most common etiology of thoracic aortic aneurysm is degenerative processes associated with increased age; however, hypertension, tobacco abuse, hyperlipidemia, and other genetic factors can result in acceleration of growth. Thoracic aortic aneurysms grow at an average rate of 1–1.5 mm/yr. However, aneurysms that are larger than 5 cm in the ascending aorta and 6 cm in the descending aorta will grow at a faster rate and require more immediate attention.

11.1.2 Clinical Presentation

The vast majority of patients who present with thoracic aortic aneurysms are asymptomatic and the diagnosis is typically made on an imaging test performed for an unrelated indication. Patients may present with chest pain, symptoms of heart failure due to aortic root involvement and subsequent aortic valve insufficiency, local mass effect including compression of trachea or bronchus (wheezing, cough), compression of the esophagus (dysphagia) or hoarseness due to involvement of the recurrent laryngeal nerve. A physical exam may reveal a murmur of aortic valve regurgitation or stenosis, or an early systolic click in the presence of a bicuspid aortic valve.

11.1.3 Evaluation and Diagnostic Studies

Typical chest X-ray findings include a widened mediastinum, deviation of the trachea or displacement of the aortic knob or displaced calcification of the aortic wall. However, none of these findings on chest X-ray are particularly sensitive or specific for thoracic aortic aneurysm. Invasive angiography is the historical gold standard but has largely been replaced by cross-sectional imaging modalities. Table 11.2 highlights the common modalities used to image the thoracic aorta and their respective advantages and disadvantages. Computed tomography (CT) with contrast is typically the most easily accessible and time-efficient modality and is preferred in acute settings (Figure 11.1). Other available modalities for imaging the thoracic aorta include transesophageal and transthoracic echocardiography (Figure 11.2) and magnetic resonance imaging (MRI). Serial imaging utilizing similar imaging modalities is valuable as changes in size over time can dictate the necessity and timing of intervention.

If an aneurysm not requiring surgery is found to involve the aortic root or ascending aorta, then a surface echocardiogram should be performed to evaluate for concomitant aortic valve disease or bicuspid aortic valve disease, which can often be associated with thoracic aortic aneurysms. Once an aneurysm is diagnosed, appropriate surveillance imaging should be performed at 6 months to 1 year for the first year to document aneurysm size stability and then every 1–3 years subsequently depending on the etiology of the aneurysm, the rate of growth and the severity of the concomitant valvular disease.

Table 11.2 Imaging the Thoracic Aorta

11.1.4 Treatment

Since most thoracic aortic aneurysms are asymptomatic, the primary indication for treatment is to prevent the development of life-threatening complications, such as dissection or rupture. The likelihood of these complications depends on the size of the aneurysm and its location as well as the skill of the surgeon. In asymptomatic patients, the thresholds for elective surgical intervention are listed in Figure 11.3. In general, non-genetically mediated aneurysms should be considered for surgical intervention when the size is >5.5 cm. In experienced centers, these thresholds might be lower: e.g. when the ascending aorta and arch are ≥5.0–5.5 cm or ≥5.5–6.0 cm in the descending aorta. In patients with the Marfan syndrome and other genetically triggered conditions, the cutoff is lower (4–5 cm) due to their typically younger ages and higher likelihood of developing life-threatening complications over time.

Figure 11.1 CT angiography demonstrating ascending aortic aneurysm. Note size differential between ascending aorta (*) and descending aorta (^).

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