The variable appearance of the left superior intercostal vein.

The authors reviewed several hundred postero-anterior chest radiographs to document the location and appearance of the left superior intercostal vein, which was seen in 9.5% of patients. Variations in the location of this vein when seen end-on as the aortic "nipple", and in the appearance of the "retroaortic" portion (the result of contact with aerated lung), are discussed. The "retroaortic portion" may be seen through the aortic knob.