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Difficulty: MediumOrdering Imaging Studies

An emergency response team brings a 59-year-old male to the trauma bay due to the abrupt onset of excruciating pain between his shoulder blades. The patient describes the pain as a "ripping" sensation that started 45 minutes prior to arrival. His medical history includes long-standing hypertension and a severe allergic reaction to iodinated contrast dye five years ago that resulted in anaphylactic shock and required mechanical ventilation. Current vital signs include a heart rate of 112/min, a respiratory rate of 22/min, and blood pressure readings of 205/115 mm Hg in the right arm and 175/95 mm Hg in the left arm. A bedside electrocardiogram reveals sinus tachycardia with left ventricular hypertrophy but no acute ischemic changes. A portable chest radiograph shows a widened mediastinum. Which of the following is the most appropriate next imaging study to establish the diagnosis?

  1. Transesophageal echocardiographyAnswer
  2. B
    Computed tomography angiography of the chest
  3. C
    Magnetic resonance angiography of the chest
  4. D
    Transthoracic echocardiography
  5. E
    Non-contrast computed tomography of the chest

Answer

Transesophageal echocardiography
The patient's clinical presentation of sudden-onset 'ripping' chest pain radiating to the back, asymmetric upper extremity blood pressures, and a widened mediastinum is classic for an acute aortic dissection. Rapid, definitive imaging is required to identify the intimal flap and determine whether the ascending aorta is involved (Type A, requiring emergency surgery) or solely the descending aorta (Type B, typically managed medically). The primary diagnostic modalities are computed tomography angiography (CTA), transesophageal echocardiography (TEE), and magnetic resonance angiography (MRA). CTA is usually the initial test of choice due to its speed and availability; however, it requires intravenous iodinated contrast. Because this patient has a history of severe anaphylaxis to iodine contrast, CTA is contraindicated. TEE is the best next step because it is highly sensitive and specific, avoids contrast administration, and can be performed quickly at the bedside in a potentially unstable patient.

Step-by-Step Solution

1
Analyze the clinical presentation to formulate a differential diagnosis.
The patient presents with sudden, ripping interscapular pain, asymmetric blood pressures, and a widened mediastinum on chest radiograph.
These findings are highly suggestive of an acute thoracic aortic dissection, an emergency requiring rapid diagnosis.
2
Evaluate the patient's specific medical history for contraindications to standard diagnostic testing.
The patient has a history of severe anaphylactic shock and mechanical ventilation due to iodinated contrast media.
Computed tomography angiography (CTA) is the standard first-line test but requires iodinated contrast, making it absolutely contraindicated here.
3
Select the most appropriate alternative imaging modality that balances diagnostic accuracy, speed, and patient safety.
Transesophageal echocardiography (TEE) is selected.
TEE provides high sensitivity and specificity for visualizing the aorta, can be done rapidly at the bedside, and avoids iodinated contrast entirely.

Key Concept

Appropriate selection of imaging for acute aortic dissection in patients with absolute contraindications to standard modalities.
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Ordering Imaging Studies

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