A 23-year-old previously healthy man is brought to the emergency department after a stab injury. His friends report that they were "walking down the street minding our own business when a guy jumped out in front of us from behind a dumpster and stabbed him in the chest." They were able to disarm the man after this single attack, and the man then ran off into an alley. The patient is conscious but in distress. Physical examination shows a laterally directed anterior chest wall stab wound at the fifth intercostal space along the left midclavicular line. Which of the following structures is most likely to have been injured in this patient?

Question

A 23-year-old previously healthy man is brought to the emergency department after a stab injury.  His friends report that they were "walking down the street minding our own business when a guy jumped out in front of us from behind a dumpster and stabbed him in the chest."  They were able to disarm the man after this single attack, and the man then ran off into an alley.  The patient is conscious but in distress.  Physical examination shows a laterally directed anterior chest wall stab wound at the fifth intercostal space along the left midclavicular line.  Which of the following structures is most likely to have been injured in this patient?

Quizplus · Accepted Answer

11ec160b_355e_5aed_9249_3324cf38614f_MD0001_00 A penetrating, laterally directed stab wound (possibly from a left-handed assaulter) that involves the fifth intercostal space (ICS) at the left anterior midclavicular line (MCL) would most likely injure the left lung. The lungs occupy most of the volume of the thoracic cavity. The apex of each lung extends into the neck (3-4 cm above the first rib). The lung bases are in direct contact with the diaphragm, which separates the right lung from the right lobe of the liver and the left lung from the stomach, spleen, and (occasionally) left lobe of the liver. The mediastinal surface of each lung has a cardiac impression that accommodates the heart. A deeper (and more medially directed) wound could have injured the left (not the right) ventricle. The heart is located behind the sternum, and its anterior surface is partially covered by the lungs. The cardiac apex is formed by the left ventricle. Depending on heart size, the point of maximal apical impulse can be felt at the fifth left ICS (between the fifth and sixth ribs) at the left MCL. All other heart chambers, including the right ventricle, lie medial to the left MCL and are unlikely to have been affected by the injury. The right ventricle forms the sternocostal (anterior) surface of the heart (Choice E). The diaphragmatic (inferior) surface is formed by the left and right ventricles and is in contact with the central tendon of the diaphragm. The posterior surface of the heart is formed mainly by the left atrium (Choice C). (Choice A) The azygos vein lies in the posterior mediastinum immediately to the right of the midline. It drains blood from the posterior intercostal veins into the superior vena cava. (Choice B) The inferior vena cava is located in the mediastinum, lies to the right of midline, and drains into the right atrium. Educational objective: The left ventricle forms the apex of the heart and can reach as far as the fifth intercostal space at the left midclavicular line (MCL). All other chambers of the heart lie medial to the left MCL. The lungs overlap much of the anterior surface of the heart.

A 23-Year-Old Previously Healthy Man Is Brought to the Emergency