|The left superior intercostal vein (aortic nipple) should be less than 4.5 cm on plain film, otherwise further investigation is recommended.|
Shields TW, LoCicero J, M.D. CE et-al. General Thoracic Surgery: Pt. 1. The lung, pleura, diaphragm, and chest wall. Sect. I. Anatomy of the chest wall and lungs. 1. Anatomy of the thorax. Lippincott Williams & Wilkins. (2009).