Q. Define Dissection of the Aorta ?

The CXR may be abnormal in upto 80 per cent of patients. The abnormalities include:

i) Widened mediastinum: This is defined as a mediastinal width of more than 8 cm on the AP CXR. A tortuous aorta may be difficult to distinguish from a widened mediastinum. If in doubt, a good PA view is recommended.

ii) Abnormal aortic knob: Loss of definition or a focal widening of the mediastinal contour in the region of the aortic knuckle may be seen.

iii) Ring sign: This describes the displacement of the aorta, > 5 mm past the calcified aortic intima. The presence of this as a new finding on CXR, is considered a very specific radiographic sign.

iv) Left apical cap: This is a result of the pleural effusion that often accompanies an acute dissection.

v) Tracheal deviation and depression of left main stem bronchus or displacement of an NG tube.

Several studies have concluded that it is a combination of several of these findings that lead to suspicion of dissection.