USMLE Step 1 Question 363

Question:

A 60 year old man with a history of myocardial infarction is receiving an echocardiogram to assess the ejection fraction of his left ventricle. It is discovered that the patient has a dilated left atrium with a visible wall thrombus. He is then started on anticoagulation therapy. Which of the following organs will receive a white (pale) infarct if the left atrial thrombus embolizes?

Correct Answer: A.  Kidney

An infarct describes an area of tissue undergoing coagulative necrosis resulting from decreased blood supply. Embolization of a thrombus can occlude arterial vessels, resulting in infarcted tissue in various organs. Infarcts can be classified into either red (hemorrhagic) infarcts or white (pale) infarcts based upon their gross appearance on pathology. Red infarcts usually occur in loose tissues with collateral circulation or following reperfusion of the infarcted tissue. Pale infarcts usually occur in solid tissues with a single blood supply. Of the listed organs, only the kidney (choice A) has a single blood supply without collateral circulation.

Liver (choice B), Lung (choice C), Small Intestine (choice D), and Large Intestine (choice E) all have more than one blood supply. An infarct in these tissues would tend to be grossly red on pathological examination.