Clinical History
88-year-old female patient was brought to emergency department with sudden onset of mild chest pain. Patient was awake and cooperative, denied any past history of trauma or cardiac surgeries. At clinical observation no remarkable findings were noticed. ECG, blood pressure and laboratory tests were within normal values (including cardiac enzymes).
Imaging Findings
At emergency department PA-chest radiograph view demonstrated a widened mediastinum predominately to the left-hand that was completed with the lateral view showing an ovalar well-circumscribed opacity behind the heart and overlapping the thoracic vertebrae.
PACS allowed us to have a PA-chest X-ray performed two years before, that merely presented a discrete mediastinal widening. There was no lateral view to compare with and thoracic CT was requested.
CT after intravenous contrast uptake demonstrated a tortuous aortic arch and an extensive aneurysm involving the length of the thoracic descendent aorta with calcified posterior mural thrombus. Multiplanar reconstructions showed saccular aneurysmatic involvement at two different levels: in the aortic arch immediately after subclavia artery origin and in the descending thoracic aorta. In both sites marginal calcifications were noticed and the widest diameter, measured in the descending thoracic aorta, was 6 cm.
Discussion
Thoracic aortic aneurysms correspond to a dilatation of the aortic lumen beyond 4 cm and can be classified as true aneurysms and false aneurysms (pseudoaneurysms). True aneurysms contain all three layers of the aortic wall (intima, media, and adventitia), whereas false aneurysms have fewer than three layers and are contained by the adventitia or periadventitial tissues. [1, 4]
The estimated incidence of aortic aneurysm is 5.9 cases per 100,000 person-years, affecting mostly men (2M:1W) over 60 years old and most commonly described in Caucasian. The cumulative risk of rupturing a thoracic aortic aneurysm (TAA) is related to aneurysm diameter. In a recent series of 133 patients with TAA, risk of rupture at 5 years was 0% for diameter less than 4 cm, 16% for diameter 4-5.9 cm, and 31% for aneurysms greater than 6 cm in diameter. [1, 2, 5]
The aetiology is mostly related to atherosclerosis along with other risk factors (smoking, chronic obstructive pulmonary disease (COPD), hypertension, male gender, older age, high BMI, bicuspid or unicuspid aortic valves, genetic disorders and family history).
Few conditions involving connective-tissue disease such as Marfan syndrome and diseases affecting collagen production namely Ehlers-Danlos syndrome, are considered risk factors to develop thoracic aortic aneurysms. [1]
Plain chest X-ray may show mediastinal widening along with marginal calcifications of the major vessels. [1]
Nonenhanced CT is usually performed first to look for a high-attenuation acute intramural haematoma. The contrast enhanced scanning that follows is the key part of the CT examination. [1]
Multidetector CT is currently used to evaluate an aneurysm in any plane, determine its size and morphologic features, clarify its relationship to branch vessels, evaluate its effect on adjacent structures, and identify complications such as dissection and rupture. [1]
Because some patients referred to the emergency departments with suspected aortic aneurysms versus dissection are old and are unable to undergo CT with contrast administration, some studies are being done to assess MRI protocols to evaluate this condition. MRI findings in a preliminary study with 29 patients, Pereles et al demonstrated that nonenhanced true FISP sequences alone are valid to accurately diagnose aortic dissection or aneurysm in less than 4 minutes. [2] François et al. concluded that in patients who have a contraindication to gadolinium-containing contrast agents, 3D SSFP MRA can be used to evaluate the thoracic aorta. [3]
Diagnostic-angiography is a less popular technique since the advent of CT-angiography brought much more information beyond the aortic lumen itself. [5]
Differential Diagnosis List
Thoracic aortic aneurysm
Aortic dissection
Mass in posterior mediastinal compartment
