X-ray Quiz 11 – Discussion: Mediastinal Widening

X-ray Quiz 11 – Discussion

X-ray chest shows aortic enlargement. Possibilities to be considered are aortic aneurysm, aortic dissection and unfolding of aortic arch in the elderly. In the given clinical scenario of a person presenting with pain in the left scapular region, an aortic dissection has to be considered first. CT Aortogram can confirm the diagnosis of aortic dissection and delineate the extent of dissection to decide on management. A bedside echocardiogram may also show the aortic dissection flap in the ascending aorta if the echo window is good. Echocardiogram is usually considered first because of easy availability in the emergency setting. But a negative echo study does not rule out aortic dissection and CT aortogram should be considered if the clinical situation warrants.

Diagnostic accuracy of supine chest X-ray in the diagnosis of non traumatic Stanford type A aortic dissection has been evaluated in 72 patients in a retrospective case control study [1]. 36 patients with non traumatic Stanford type A dissection and 36 patients without Stanford type A aortic dissection were studied. Maximal mediastinal width in the anteroposterior chest X-ray was measured at the level of the aortic knob in the supine position. Mean width was 100.7 mm in those with non traumatic Stanford type A aortic dissection and 77 mm in those without dissection (P<0.01). An optimal cutoff level was 87 mm with 81% sensitivity and 89% specificity.

Mediastinal hematoma is another lethal sign of Stanford type A aortic dissection [2]. They can present with progressive bruising of the upper half of the body and massive hemoptysis [2,3]. Massive mediastinal hematoma can obstruct the pulmonary artery and superior vena cava and cause sudden death.

Mediastinal width, left mediastinal width and ratio to transthoracic width
Mediastinal width, left mediastinal width and ratio to transthoracic width

Lai et al have assessed the role of AP and PA views in assessment of nontraumatic aortic dissection. They also included maximal left mediastinal width along with maximal mediastinal width and their ratio. Maximal mediastinal width was the maximal width of the mediastinum at the level of the aortic knob from right to left border. Maximal left mediastinal width was the maximal width from the midline of the trachea to the left lateral edge of the aortic knob. As expected, they found that PA projection was more accurate than AP projection. Left mediastinal width and mediastinal width were the most powerful parameters on PA and AP chest X-Rays respectively. Mediastinal width ratio was found to be less useful and less reliable. Optimal cutoff for left mediastinal width was 4.95 cm and that for mediastinal width 7.45 cm in PA view. Corresponding values in AP view were 5.45 cm and 8.65 cm respectively [4].

Others have suggested cut off more than 8 cm for mediastinal width and more than one third of the thoracic distance at the level of the aortic knob in supine AP film, in case of aortic injury.

Back to X-ray Quiz 11

References

  1. Funakoshi H, Mizobe M, Homma Y, Nakashima Y, Takahashi J, Shiga T. The diagnostic accuracy of the mediastinal width on supine anteroposterior chest radiographs with nontraumatic Stanford type A acute aortic dissection. J Gen Fam Med. 2018 Jan 25;19(2):45-49.
  2. Inoue Y, Takahashi R, Kashima I, Tsutsumi K. Mediastinal hematoma: another lethal sign of aortic dissection. Interact Cardiovasc Thorac Surg. 2009 Feb;8(2):275-6.
  3. Minegishi S, Goto H, Yamabi H, Imanaka K. Hemoptysis. Int Heart J. 2018 Sep 26;59(5):1146-1148.
  4. Lai V, Tsang WK, Chan WC, Yeung TW. Diagnostic accuracy of mediastinal width measurement on posteroanterior and anteroposterior chest radiographs in the depiction of acute nontraumatic thoracic aortic dissection. Emerg Radiol. 2012 Aug;19(4):309-15. doi: 10.1007/s10140-012-1034-3. Epub 2012 Mar 14. PMID: 22415593; PMCID: PMC3396328.