Thoraco-Abdominal Aortic Aneurysm

Clinical History

71 year old female patient with acute chest pain radiating to the back.

Imaging Findings

Patient presented with left parasternal chest pain radiating to the back with associated vomiting. She was a known hypertensive patient with ischaemic heart disease. On examination she was unwell, pale, clammy and tachycardic. Upper limb blood pressures were equal bilaterally. There were no other specific findings on examination.
Chest radiograph [Fig. 1] demonstrated a widened mediastinum due to an extensive aneurysm involving the length of the thoracic aorta with tracheal deviation to the right. The lungs were clear of acute pathology. Spiral CT of the thorax and abdomen with contrast [Fig. 2] demonstrated a thoraco-abdominal aortic aneurysm (TAAA) beginning in the ascending aorta just above the aortic valve involving the entire thoracic aorta and extending into the abdominal aorta to end just proximal to the celiac artery. The widest diameter measured 9cm in the ascending thoracic aorta at the same level as the pulmonary trunk.

Discussion

Thoraco-abdominal aortic aneurysms (TAAA) are when thoracic aortic diameter is over 4cm and abdominal aortic diameter over 3cm. They are relatively common, being found in as many as 10% of patients at autopsy [1] and with an incidence of 5.9% per 100 000 person-years [2]. Men are affected more commonly than women. The most common cause is atherosclerotis. Other causes include cystic medial necrosis such as in Marfans, infection, and aortitis. Treatment is indicated when the diameter of the ascending aorta reaches 5.5cm or the descending aorta reaches 6.5cm. This is because the risk of rupture or dissection increases significantly above these sizes.
TAAA are often picked up incidentally on chest radiographs in elderly patients without symptoms. If symptomatic, there may be a variety of symptoms including chest or back pain (especially with acute rupture or dissection), aortic valve incompetence, superior vena cava compression, as well as hoarse voice (left recurrent laryngeal nerve compression), dysphagia (oesophageal compression) or left lower lobe pneumonia (left lower lobe bronchus compression).
Imaging is important in order to define the extent and size of the TAAA as well as the state of the aortic wall and any complications. Chest radiography helps to demonstrate the presence of an aneurysm. If there is a focal aneurysm (usually involving the proximal aorta) a chest radiograph may demonstrate focal mediastinal widening with displacement of which mediastinal structures. This may be difficult to distinguish from a primary lung carcinoma adjacent to the mediastinum. If the aorta is diffusely aneurysmal involving the descending aorta the chest radiograph will demonstrate widening of the mediastinum. There may be difficulty in distinguishing this from a tortuous aorta in an elderly patient but the large size usually helps [3]. Occasionally there may be signs of complication including pleural effusions with rupture and displacement of the wall calcification into the lumen with dissection. However, more complex imaging techniques are necessary to provide the detailed information required to plan management. These include Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Trans-Oesophageal of Trans-Thoracic Echocardiography (TOE or TTE), as well as conventional angiography.
CT is most often used because it is able to provide all necessary information in most cases (particularly with new advanced scanners with multiplanar imaging and CT-angiography) and is quick and readily available [4]. There are drawbacks particularly with contrast reactions and nephrotoxicity of iodine based contrast agents in already seriously ill patients.
MRI is better in this respect because gadolinium contrast agents are much less nephrotoxic and contrast reactions are much less frequent [2]. MRI can demonstrate the structure of the aneurysm better than CT helping to characterise the aetiology of the aneurysm, and it can demonstrate function in the same study [2]. The problem with MRI is that it is not as readily available as CT, takes longer, and patient tolerance is less. If patients are unable to get to CT or MRI or are unsuitable for these imaging techniques TOE or TTE can be used. These techniques also have advantages in that they demonstrate function of valves and blood flow much better. They can also localise a site of a rupture by detecting high velocity jets of blood and intimal flaps that may not be seen on CT or MRI [5]. Unfortunately TOE and TTE like all ultrasound techniques are operator dependent and there is a limited field of view. Also most patients need sedation which may create complications and, finally, angiography is not often used in the diagnosis of TAAA being it reserved for when other techniques have failed. It may be needed in the planning of some stent grafts.

Differential Diagnosis List

Final Diagnosis

Thoraco-Abdominal Aortic Aneurysm

URL:	https://www.eurorad.org/case/2417
DOI:	10.1594/EURORAD/CASE.2417
ISSN:	1563-4086