Getting ready for the United States Medical Licensing Examination® (USMLE®) is no easy feat, but we’re sharing expert insights to help give you a leg up. Take a look at the exclusive scoop on this month’s most-missed USMLE test prep question. Think you have what it takes to rise above your peers? Test your USMLE knowledge, and view an expert video explanation of the answer from Kaplan Medical. Once you’ve got this question under your belt, be sure to test your knowledge with other posts in this series.
This month’s question explores pathology and cardiovascular topics. Ready. Set. Go.
Question of the month
A 72-year-old obese woman collapses and is brought to the emergency department. She flew from California to New York three days earlier. She has smoked a pack of cigarettes daily for 50 years. During physical examination, she is unable to respond to questions or follow instructions. Three days later, she becomes hypotensive and dies. Autopsy shows multiple loosely adherent clots within the distal branching arteries of the left middle cerebral artery and in the vertebrobasilar system. Which of the following pathologic conditions would most likely account for the neurologic findings in this patient?
A. Atherosclerosis of penetrating cerebral arteries
B. Endocarditis of the tricuspid valve
C. Patent foramen ovale
D. Pulmonary thromboembolism
E. Trousseau syndrome
The correct answer is C.
Kaplan Medical explains why
Persistence of a patent foramen ovale is found in a significant proportion of healthy subjects. A widely patent foramen ovale may allow emboli originating from the veins in the legs to bypass the pulmonary circulation and reach the systemic arteries, thereby producing infarcts (paradoxical embolism) in the brain and in other organs. Interatrial or interventricular defects can have the same effect. None of the other answer choices would explain the development of embolic infarcts in the cerebral parenchyma. Thrombus formation is associated with Virchow’s triad of hypercoagulability, stasis and endothelial damage. This patient has all of the underlying risk factors, with her obesity, smoking and immobilization during the plane trip.
Note: Another cause of paradoxical embolism in an adult is a small atrial septal defect.
Why you shouldn’t choose the other answers
Read these explanations to understand the important rationale for each answer to help you prepare with future studying.
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Choice A: Atherosclerotic changes are frequently found in the circle of Willis and its major branches, but not in the small caliber penetrating arteries of the brain.
Choice B: Endocarditis of the tricuspid valve which is common in IV drug abusers, may give rise to emboli resulting from fragmentation of valvular vegetations. Emboli from the tricuspid valve, however, would enter the pulmonary circulation, possibly leading to infarcts of the lungs.
Choice D: Pulmonary thromboembolism frequently occurs as a result of deep venous thrombosis, especially after immobilization (as in this patient during her plane trip), bed rest, obstetric delivery and surgery. Thromboemboli that become lodged in the pulmonary arteries, however, cannot pass through the pulmonary capillary filter and cause systemic embolization.
Choice E: Trousseau syndrome, also known as migratory thrombophlebitis, occurs in association with disseminated cancers, especially mucinous adenocarcinomas. This condition is probably caused by release of procoagulant factors by the tumor, and it manifests with recurrent episodes of thrombosis affecting veins (but not arteries) in both limbs and visceral organs.
