From the Research
An abnormal mediastinal to chest width ratio is typically considered to be greater than 0.38, as defined by a study published in The Journal of Trauma in 1989 1. This ratio is used to assess the width of the mediastinum in relation to the overall chest width on a standard frontal chest X-ray. When this ratio exceeds 0.38, it may indicate underlying pathology, such as aortic aneurysm or dissection, mediastinal masses, mediastinal hemorrhage following trauma, mediastinitis, or significant lymphadenopathy. The measurement of this ratio is crucial, especially in trauma settings, where a widened mediastinum can represent a life-threatening aortic injury. Some studies suggest that a lower threshold, such as 0.25-0.28, may also be indicative of an abnormal mediastinal to chest width ratio 2, 3. However, the most recent and highest quality study on this topic is from 2012, which found that the optimal cutoff levels for mediastinal width ratio were not as reliable as other measurements, such as maximal left mediastinal width (LMW) and maximal mediastinal width (MW) 4. Key points to consider when evaluating the mediastinal to chest width ratio include:
- The ratio is typically measured on an upright posteroanterior chest X-ray
- Portable anteroposterior films may be less reliable due to magnification effects
- Further evaluation with CT imaging is usually recommended when an abnormal ratio is identified
- Common causes of an abnormally widened mediastinum include aortic aneurysm or dissection, mediastinal masses, mediastinal hemorrhage following trauma, mediastinitis, or significant lymphadenopathy.