Correspondence

Medical Mystery: Abnormal Chest Film — The Answer

N Engl J Med 2006; 355:1283-1284September 21, 2006

Article

To the Editor:

The medical mystery in the July 27 issue1 involved a chest film (Figure 1AFigure 1Chest Film, Showing a Soft-Tissue Density (Panel A, Arrowheads), and Computed Tomography of the Chest, Showing a Right-Sided Aortic Arch (Panel B, Arrow) and an Aberrant Left Subclavian Artery (Panel C, Arrow).) showing cardiomegaly and a left-sided pacemaker, the leads from which took an unusual course through the mediastinum, to the left of the midline. A persistent left-sided superior vena cava was suspected. A right-sided paratracheal soft-tissue density was also present (Figure 1A, arrowheads). Contrast-enhanced computed tomography (CT) showed that this density was caused by a right-sided aortic arch and not by an aortic-arch aneurysm (Figure 1B, arrow). An aberrant left subclavian artery arising from a dilated diverticulum of Kommerell (Figure 1C, curved arrow) passed posterior to the esophagus. CT without contrast medium confirmed the presence of a persistent left-sided superior vena cava (L in Figure 1C) within the right-sided superior vena cava (R in Figure 1C) owing to the absence of a left brachiocephalic vein. A persistent left-sided superior vena cava occurs in 0.3% of the normal population and is often not recognized unless a central venous line or pacemaker is inserted. A right-sided arch with an aberrant left subclavian artery is the most common type of right-arch anomaly, with an incidence of approximately 1 in 2500.