Thoracic Aortic Aneurysm

Preliminary Diagnosis: Thoracic Aortic Aneurysm

I. What imaging technique is first-line for this diagnosis

• Computed tomographic angiography (CTA). A non-contrast CT may be necessary to differentiate thrombus calcification, a common finding in aortic aneurysms, from displaced calcified intima associated with aortic dissection.

II. Describe the advantages and disadvantages of this technique for diagnosis of thoracic aortic aneurysm.

Advantages

• Diagnostic and gives precise information regarding the size, shape, and location of the aneurysm

• May diagnose other pathological processes that mimic an aneurysm on a chest radiograph, such as a mass.

• Relatively quick

• Requires minimal patient cooperation and is less susceptible to motion artifact

Disadvantages

• Exposes the patient to a large amount of ionizing radiation.

• Intravenous contrast may cause nephropathy or renal failure.

• Risk of contrast-induced allergic reaction.

III. What are the contraindications for the first-line imaging technique?

• Patients with known contrast allergy.

• Contraindicated in pregnant women, especially within the first two trimesters.

IV. What alternative imaging techniques are available?

• MRI with contrast.

• Transthoracic or transesophageal ultrasound.

• AP and lateral chest radiographs.

• Conventional angiography.

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of thoracic aortic aneurysm.

Magnetic resonance imaging (MRI) with contrast

Advantages

• Does not make use of ionizing radiation.

• Can be used to diagnose or exclude other pathological processes within the chest.

Disadvantages

• Expensive.

• Time-consuming.

• Requires marked patient cooperation to limit motion artifact.

• Difficult study for claustrophobic individuals.

• Requires that patient have good renal function with GFR > 60.

• Intravenous contrast is associated with nephrogenic systemic fibrosis.

Transthoracic or transesophageal ultrasound

Advantages

• May be diagnostic.

• Can distinguish that it is a vascular structure and not a mass.

• Relatively inexpensive.

• Does not use ionizing radiation.

• Transesophageal ultrasound produces better images of the thoracic aorta than transthoracic ultrasound.

Disadvantages

• Resolution may be poor in obese patients.

• Transesophageal ultrasound is relatively invasive and has a risk of esophageal perforation.

AP and lateral chest radiographs

Advantages

• Can demonstrate the prominence of the aorta consistent with an aortic aneurysm, particularly if there are mural calcifications.

• Inexpensive.

• Performed quickly.

Disadvantages

• Much less specific and sensitive than CT.

Conventional angiography

Advantages

• Diagnostic.

• Can be therapeutic if direct intraluminal catheter thrombolysis is indicated.

Disadvantages

• More invasive with higher morbidity, i.e., bleeding, infection, dissection of vessel wall.

• Does not demonstrate anatomical detail beyond vessels of interest like CT or MRI.

• Requires use of iodinated contrast.

• Requires high dose of ionizing radiation.

• Expensive.

• Requires fluoroscopy suite and interventional radiologist to perform the exam.

• Sedation is recommended.

VI. What are the contraindications for the alternative imaging techniques?

MRI with contrast

• Contraindicated in patients with non-MRI compatible devices, i.e., patients with embedded metallic devices not made of titanium, such as cardiac pacers, stents, and other non-MR approved metallic devices which may not enter the magnet for imaging.

Transthoracic ultrasound

• No significant contraindications for transthoracic ultrasound.

Transesophageal ultrasound

• Due to the relatively invasive nature of the exam, prior surgery of the oropharynx or esophagus may be contraindications, particularly if the surgery was recent.

• Due to the relatively invasive nature of the exam, neoplastic, infectious, or inflammatory processes involving the oropharynx or esophagus may be contraindications.

PA and lateral chest radiographs

• No significant contraindications. Some institutions require informed consent for pregnant patients.

Conventional angiography

• Coagulopathy, i.e., bleeding diathesis.

• Pregnancy.

• Creatinine > 1.6.

• Allergy.