The vascular pedicle and the vena azygos. Part III: In trauma--the "vanishing" azygos.

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The chest radiographs of 158 patients with widened vascular pedicles were examined. The vascular pedicle was measured and the presence or absence of the right paratracheal stripe and the vena azygos on the radiographs was noted. Increasing the systemic blood volume (or assuming the supine position) causes the vascular pedicle of the heart to widen predominantly to the right, and the vena azygos to enlarge simultaneously. In contrast, extravascular bleeding from aortic damage causes the pedicle to widen predominantly to the left of the midline; at the same time the paratracheal stripe and azygos "vanish." This combination of physiologic and pathologic, and intravascular and extravascular causes of widening of the pedicle. Extravasation of blood or saline from a traumatic right subclavian puncture can cause local bulging of the pedicle to the right and a vanishing azygos. Because the left side of the pedicle remains normal, this can be readily differentiated from an aortic tear.