From the Research
The upper limit of normal for mediastinal width on a portable upright chest X-ray is generally considered to be 8 centimeters. This measurement is taken at the widest point of the mediastinum, typically at the level of the aortic knob. A mediastinal width exceeding 8 cm in adults on an upright portable chest X-ray may suggest mediastinal pathology such as aortic injury, mediastinal hemorrhage, lymphadenopathy, or mass. It's essential to consider that this measurement can be affected by factors such as patient positioning, degree of inspiration, and technical aspects of the portable X-ray, as noted in studies such as 1.
The 8 cm threshold is particularly relevant when evaluating for potential aortic injury in trauma patients, where a widened mediastinum may be an indication for further imaging with CT angiography, as discussed in 2. The mediastinal width to chest width ratio is also sometimes used, with a ratio greater than 0.25 (or 25%) considered abnormal, helping to standardize the assessment across different patient body sizes. However, the most recent and highest quality study, 1, highlights the limitations of using mediastinal width as a sole indicator for traumatic injuries, including aortic injury, due to its low specificity and positive predictive value.
Key points to consider:
- The upper limit of normal for mediastinal width is 8 cm on a portable upright chest X-ray.
- Measurements can be influenced by patient and technical factors.
- A widened mediastinum may indicate need for further imaging, especially in trauma cases.
- The mediastinal width to chest width ratio can provide additional assessment criteria.
- Recent studies, such as 1, emphasize the need for cautious interpretation of mediastinal width measurements in the context of trauma.