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Author Gonzalo Romero (Reviewed by Will Gibson and Yazan Daaboul)
Exam Type USMLE Step 1
Main Category Pathology
Sub Category Cardiology
Prompt A 6-year-old boy is brought to his pediatrician's office for severe headache and nosebleeds over the past six months. The patient complains that his feet become very cold at night for which he has been wearing two pairs of thick socks. At school, he gets occasional cramps in his legs and is easily winded when running in gym class. His blood pressure is 170/95mmHg in the both upper extremities and 100/70 mmHg in both lower extremities, heart rate is 80/min, respiratory rate is 15/min, and temperature is 37 °C (98.6 °F). On physical examination, he has clear breath sounds bilaterally, but a continuous murmur is heard over the inter-scapular area. A chest x-ray demonstrates prominence of the descending aorta compared to the spine. Which of the following findings on chest x-ray is most specific for this patient's condition?
Answer A Kerley B lines
Answer A Explanation [[AnswerAExp::Kerley B lines are abnormal, short, horizontal shadows that are present in the costophrenic angles that are present in thickened interlobular septa in cases of pulmonary edema and neoplasms.]]
Answer B Rib notching
Answer B Explanation The patient's radiologic signs, heart murmur, and symptoms are consistent with post-ductal coarctation of the aorta. Due to increased resistance proximal to the coarctation, collateral arterial circulation often develops. The collateral circulation often manifests as dilated intercostal vessels, which impinge on the inferior surface of ribs. These vessels appear as "rib notching" on X-ray.
Answer C Cardiomegaly
Answer C Explanation [[AnswerCExp::There are many causes of cardiomegaly, including genetic disorders, endocine diseases, infectious processes, toxins, systemic diseases, and iatrogenic causes. In particular, cardiomegaly is not associated with this patient's COA.]]
Answer D Pleural effusion
Answer D Explanation [[AnswerDExp::The most common causes of transudative pleural effusions in the United States are left ventricular failure, pulmonary embolism, and cirrhosis. Conversely, the most common causes of exudative pleural effusions are bacterial pneumonia, cancer (especially lung, breast, and hematological cancers), viral infection, and pulmonary embolism. Therefore, pleural effusion is not a specific finding and is not classically associated with coarctation of the aorta.]]
Answer E Patchy alveolar infiltrates
Answer E Explanation [[AnswerEExp::Patchy alveolar infiltrates are not associated with coarctation of the aorta. Cardiogenic pulmonary edema can be distinguished from non-cardiogenic pulmonary edema by the presence of redistribution of blood flow to the upper lobes and interstitial edema. In contrast, patchy alveolar infiltrates with air bronchograms are more indicative of non-cardiogenic edema.]]
Right Answer B
Explanation [[Explanation::This patient is most likely presenting with symptoms and signs of post-ductal coarctation of the aorta (COA), which is a localized narrowing or abrupt constriction of the aortic arch after the ligamentum arteriosum. COA is commonly associated with aortic aneurysms and bicuspid aortic valve. In severe cases, COA may be present in infancy. Diagnosis may be delayed in less severe narrowing, where patients may be diagnosed during childhood, adolescence, or even early adulthood. It is more common in males than females with a male:female ratio of 2:1.

Clinically, patients often present with headaches, epistaxis, dizziness, syncope, dyspnea, chest pain, cold feet or legs, leg cramps with exercise, significant blood pressure differences in upper and lower extremities, poor growth, and decreased exercise performance. There are 3 potential sources of a murmur: multiple arterial collaterals (continuous murmur), an associated bicuspid aortic valve (systolic ejection click) and the coarctation itself, which can be heard over the left infraclavicular area and under the scapula.

The following are radiologic findings in aortic coarctation: 1. Irregularities or notching of the inferior margins of the posterior ribs that result from collateral flow through dilated and pulsatile intercostal arteries. These collaterals appear after 6 years of age if the coarctation is significant.
2. An inverted "3" sign or a "3" sign on a highly penetrated chest radiograph may be visualized. Post-stenotic dilation of the aorta results in a classic reverse 3 sign on x-ray.
3. Signs of congestive heart failure, including: cardiomegaly, pulmonary edema, and prominent pulmonary vasculature. These signs of congestive heart failure are not specific to this coarctation of the aorta.

Educational Objective: Coarctation of the aorta is characterized by the presence of aortic narrowing proximal or distal to the ligamentum arteriosum. While it may be diagnosed shortly following birth in severe cases, some patients remain undiagnosed until early adulthood. On physical examination, a significant difference between upper and lower extremity blood pressure and a continuous murmur in the inter-scapular area are suggestive of the diagnosis. Chest x-ray often shows a "3" or inverted "3" sign, prominence of descending aorta in relation to the spine, and rib notching due to formation of collaterals.
References: Brown ML, Burkhart HM, Connolly HM, et al. Coarctation of the aorta: lifelong surveillance is mandatory following surgical repair. J Am Coll Cardiol. 2013;62(11):1020-1025.
First Aid 2014 page 283]]

Approved Yes
Keyword Heart, Aorta, Vessels, Vasculature, Coarctation, Cardiology, Pulmonology, Radiology, Chest, Chest X ray
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