Imaging

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.

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