From the Guidelines
The most commonly seen finding on chest radiography in a patient with aortic dissection is widening of the mediastinum. This appears as an abnormal broadening of the shadow cast by the central chest structures, particularly the aortic contour. Other radiographic findings may include an abnormal aortic knob contour, pleural effusion (especially on the left side), displacement of intimal calcifications, and tracheal deviation. According to the 2022 ACC/AHA guideline for the diagnosis and management of aortic disease 1, mediastinal widening is a key sign of aortic dissection on chest X-ray findings.
The widened mediastinum occurs because blood accumulates between the layers of the aortic wall during dissection, causing the overall diameter of the aorta to increase beyond normal limits, which is then visible as an enlarged shadow on the radiograph. It's essential to note that chest radiography has limited sensitivity for diagnosing aortic dissection, with up to 20% of patients having normal chest X-rays, as reported in the ACR Appropriateness Criteria for suspected acute aortic syndrome 1. Therefore, definitive diagnosis typically requires advanced imaging such as CT angiography, MRI, or transesophageal echocardiography.
Some key points to consider when evaluating chest radiography in patients with suspected aortic dissection include:
- Mediastinal widening is the most common finding
- Abnormal aortic contour and pleural effusion may also be present
- Chest radiography has limited sensitivity and may not exclude the presence of aortic dissection
- Advanced imaging is often necessary for definitive diagnosis, as recommended by the 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease 1.
From the Research
Aortic Dissection on Chest Radiography
The most common finding on chest radiography in a patient with an aortic dissection is:
- Widened mediastinum This is supported by several studies, including 2, 3, 4, and 5, which highlight the importance of mediastinal widening as a diagnostic criterion for aortic dissection.
Key Findings
Some key points to note about aortic dissection on chest radiography include:
- A study published in 2002 found that widening of the mediastinum on chest radiography had unacceptable sensitivity for predicting aortic injury, with substantial inter-reader variability 2.
- Another study published in 2004 found that chest radiography had a sensitivity of 64% and a specificity of 86% for aortic disease, but sensitivity was lower for pathology confined to the proximal aorta 3.
- A 2012 study found that posteroanterior (PA) chest radiographs were more accurate than anteroposterior (AP) chest radiographs in diagnosing acute nontraumatic thoracic aortic dissection, with a sensitivity of 90% and specificity of 90% for PA radiographs 4.
- A study published in 1980 found that severe chest pain, widened mediastinum, and varying degrees of aortic insufficiency were present in each patient with acute dissection of the ascending aorta 5.
Diagnostic Accuracy
The diagnostic accuracy of chest radiography for aortic dissection can be improved by:
- Using PA chest radiographs instead of AP radiographs 4
- Measuring the maximal mediastinal width and maximal left mediastinal width 4
- Using a lower threshold for proceeding to computed tomography aortogram, especially in elderly patients and those with widened mediastinum on AP chest radiograph 4
- Considering the use of helical computed tomographic evaluation of the mediastinum in high-risk blunt trauma patients, regardless of chest radiographic findings 6