Comparison of mediastinal width, mediastinal-thoracic and -cardiac ratios, and "mediastinal widening" in detection of traumatic aortic rupture

Diagnostic accuracy of mediastinal width measurement on posteroanterior and anteroposterior chest radiographs in the depiction of acute nontraumatic thoracic aortic dissection

We aimed to explore the diagnostic accuracy of various mediastinal measurements in determining acute nontraumatic thoracic aortic dissection with respect to posteroanterior (PA) and anteroposterior (AP) chest radiographs, which had received little attention so far. We retrospectively reviewed 100 patients (50 PA and 50 AP chest radiographs) with confirmed acute thoracic aortic dissection and 120 patients (60 PA and 60 AP chest radiographs) with confirmed normal aorta. Those who had prior history of trauma or aortic disease were excluded. The maximal mediastinal width (MW) and maximal left mediastinal width (LMW) were measured by two independent radiologists and the mediastinal width ratio (MWR) was calculated. Statistical analysis was then performed with independent sample t test. PA projection was significantly more accurate than AP projection, achieving higher sensitivity and specificity. LMW and MW were the most powerful parameters on PA and AP chest radiographs, respectively. The optimal cutoff levels were LMW = 4.95 cm (sensitivity, 90 %; specificity, 90 %) and MW = 7.45 cm (sensitivity, 90 %; specificity, 88.3 %) for PA projection and LMW = 5.45 cm (sensitivity, 76 %; specificity, 65 %) and MW = 8.65 cm (sensitivity, 72 %; specificity, 80 %) for AP projection. MWR was found less useful and less reliable. The use of LMW alone in PA film would allow more accurate prediction of aortic dissection. PA chest radiograph has a higher diagnostic accuracy when compared with AP chest radiograph, with negative PA chest radiograph showing less probability for aortic dissection. Lower threshold for proceeding to computed tomography aortogram is recommended however, especially in the elderly and patients with widened mediastinum on AP chest radiograph.

Left Mediastinal Width and Mediastinal Width Ratio Are Better Radiographic Criteria Than General Mediastinal Width for Predicting Blunt Aortic Injury

BACKGROUND

General mediastinal width, left mediastinal width, and mediastinal width ratio were compared as radiographic predictors of aortic injury.

METHODS

A retrospective study investigated the chest radiographs of 51 patients admitted to a level 1 trauma center during a 6-year period for a thorough survey of aortic injury. Mediastinal width (MW >/= 8 cm), left mediastinal width (LMW >/= 6 cm), mediastinal width ratio (MWR >/= 0.60), and a combination of LMW and MWR were compared as predictors of aortic injury. The cutoff points were predetermined by receiver-operator-curve to accommodate 100% sensitivity for each criterion.

RESULTS

Of the 51 patients, 21 had aortic injuries and 30 had normal imaging studies. All criteria had 100% negative predictive value. The specificities and positive predictive values, respectively, were 13.3% and 44.7% (MW), 40.0% and 53.8% (LMW), 43.3% and 55.3% (MWR), and 66.7% and 67.7% (combined LMW and MWR). The positive likelihood ratio of aortic injury was 3.00 when LMW was 6 cm or more and MWR was 0.60 or more.

CONCLUSIONS

Both an LMW of 6 cm or more and an MWR of 0.60 or more are better radiographic criteria than an MW of 8 cm or more for predicting blunt aortic injury. Trauma patients with positive test results based on the combined LMW and MWR criteria should proceed immediately to aortography or helical computed tomography.

Mediastinal Evaluation Utilizing the Reverse Trendelenburg Radiograph

When thoracic aortic rupture is suspected, a 45-degree reverse Trendelenburg (RT) anteroposterior (AP) chest radiograph should place the mediastinal structures in a more appropriate position and allow a more accurate evaluation than a supine AP radiograph. One hundred ninety-one consecutive hemo-dynamically stable adult patients with major blunt thoracic trauma were initially evaluated for mediastinal abnormalities associated with aortic disruption by both supine AP chest radiograph and an AP chest radiograph with the patient in 45-degree RT position. One hundred four patients underwent contrast aortography based on mediastinal abnormalities detected on the supine AP chest radiograph. Twenty of these patients had abnormal aortograms demonstrating traumatic aortic disruption confirmed at surgery. Supine and RT chest radiographs were retrospectively compared in a blinded fashion to evaluate their specificity and positive predictive value for detection of traumatic thoracic aortic rupture. If RT chest radiographic findings had been used to determine the need for further assessment, 29 angiograms (26%) would have been eliminated, specificity would have increased from 52 per cent to 69 per cent, and positive predictive value would have increased from 19 per cent to 27 per cent. Both supine and RT chest radiographs demonstrated mediastinal widening in all 20 patients with abnormal aortograms, with no missed thoracic aortic disruptions (100% sensitivity). This study indicated that the RT chest radiograph may be used instead of the standard supine radiograph as the initial screen for mediastinal evaluation, maintaining a high sensitivity and eliminating the cost and morbidity of many unnecessary aortograms.

Traumatic disruption of the thoracic aorta: a rational approach to imaging

An imaging strategy is crucial in patients who have sustained a traumatic disruption of the thoracic aorta. Of those who reach hospital alive, 70-90 per cent will survive if diagnosed early and treated appropriately. The clinician has many imaging techniques to choose from, but they vary considerably in their degree of accuracy and performance time. Consequently their appropriateness is dependent on the type of injury suspected, the haemodynamic stability of the patient and the availability and experience of the radiologists. This article describes the types and presentation of traumatic thoracic aortic disruption so that the advantages and disadvantages of the various imaging modalities can be explained. It concludes by presenting an imaging strategy for use when this condition is suspected.

Blunt and penetrating chest injuries

The management of chest injuries begins with knowledge of what happened to the patient at the time of the traumatic incident and converting this information into possible diagnoses. The various organs of the chest cavity are discussed emphasizing the controversies that attend the management or diagnosis of each one.

Blunt chest trauma and suspected aortic rupture: reliability of chest radiograph findings

The chest radiographs of 86 patients with suspected aortic rupture from blunt chest trauma were reviewed. Seventy-three patients had no evidence of aortic rupture on aortography or surgical exploration, and 13 patients had surgically confirmed rupture. Sixteen radiographic findings were analyzed for sensitivity and specificity in detecting aortic rupture. The following findings were not statistically significant: hemothorax on either side; rib fractures on either side; pneumothorax on either side; lung contusion; widened left paravertebral stripe; and widening of the mediastinum, along with an increased ratio of mediastinal width to chest width. The most helpful findings leading to suspicion of aortic rupture included nasogastric tube or tracheal deviation to the right at the T4 level; depression of the left mainstem bronchus; and loss of the aortic contour or knob and left apical cap. False positives and false negatives occurred with each radiographic sign, indicating that there is no single finding that is absolutely reliable in predicting or excluding significant injury in every patient with suspected aortic rupture. Analysis of combinations of findings found that when the aortic contour and knob are normal and the nasogastric tube and trachea are not deviated, there was no case of aortic rupture in four consecutive years of experience. These four signs can be used to exclude aortic rupture.