Section: USMLE

54) A patient arrives in the emergency department after having been stabbed. He has sustained a penetrating wound in the left fourth intercostal space immediately lateral to the sternal border. Which of the following thoracic structures is most likely to have been injured?

1. Left atrium
2. Left ventricle
3. Right atrium
4. Right ventricle
5. Upper lobe of the left lung

The right ventricle forms most of the anterior wall of the heart and extends from approximately the right border of the sternum to approximately 2 inches to the left of the sternum at the level of the fourth intercostal space.

The left atrium forms the posterior wall of the heart. The only portion of the left atrium seen on the anterior surface of the heart is the left auricular appendage, which is at the level of the second intercostal space on the left.

The left ventricle forms most of the left border of the heart and the diaphragmatic surface of the heart. It forms the anterior wall of the heart in a region from approximately 2-3 inches from the left border of the sternum from the third to the fifth intercostal space.

The right atrium forms the right border of the heart. Its anterior surface is on the right side of the sternum from approximately the third rib to the sixth rib.

The left lung is displaced away from the sternum on the left side by the presence of the heart.