Radiologists are often consulted regarding the position of venous access lines. Occasionally, lines may not follow the intended anatomical route, thereby raising the question of whether they are in the correct position or whether an iatrogenic injury has been caused as a result of the procedure. In the present case, a left subclavian vein line was inserted without complication and a chest radiograph requested to confirm its position. Surprisingly, the line was seen continuing down the left sternal edge instead of crossing the midline to enter the right superior vena cava (fig 1). As the line was freely aspirating venous blood, its position within a vessel was confirmed. CT was therefore performed to delineate the intrathoracic anatomy and check the position of the line. A three-dimensional reconstruction demonstrated the presence of a left superior vena cava (LSVC; fig 2).

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Figure 1

A PA (posteroanterior) chest radiograph with the left subclavian vein line continuing down the left sternal edge.

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Figure 2

A three-dimensional reconstruction showing a left superior vena cava.

Persistence of an LSVC is a congenital abnormality which occurs in 0.3% of the general population.1 It forms from a confluence of the left subclavian and left jugular veins, continues inferiorly to lie anterior to the left hilum and drains into the right atrium via a dilated coronary sinus. Its anatomical course reflects retention of the embryologic left anterior and common cardinal veins and the left horn of the sinus venosus; structures that ordinarily regress.2

In conclusion, venous access lines should always be radiographically imaged before they are used to confirm their position. If an abnormality is discovered incidentally, further investigation is required to elucidate the underlying anatomy and distinguish it from serious pathology.