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On the radiographs, there is moderate enlargement of the right aspect of the cardiac silhouette, dilation of the main pulmonary artery and a focal enlargement of the proximal descending aorta adjacent to the dilated MPA. The majority of the pulmonary vessels are small. The exception is an enlarged and tortuous right caudal artery and slight enlargement of several other pulmonary arteries. The pulmonary parenchyma is normal.

The combination of these findings show a patient with a PDA plus pulmonary hypertension (not overcirculation) and subsequent right heart enlargement.

The majority of candidates were not able to successfully recognize this 6 month-old Maltese dog as a patient with a right-to-left shunting (“reverse”) patent ductus arteriosus.

The manner in which candidates failed this case lends insight into deficits in their study or training. Interestingly, only a few candidates who failed this case were unable to recognize the focal dilation of the proximal descending aorta. The majority of unsuccessful candidates fell into one of two error patterns.

The first group, after identifying the proximal aortic dilation, proceeded to describe findings consistent with a left-to-right shunt despite the actual radiographic findings. Many candidates specifically stated that enlargement of the right caudal pulmonary artery was evidence of pulmonary overcirculation, despite the presence of small pulmonary veins.

The second group included a surprisingly large percentage of candidates who correctly described all important features of the radiographs, but were then unable to come up with the correct diagnosis as a differential diagnosis. Candidates in this group either listed differentials which would not account for all of the findings (including uncomplicated pulmonic stenosis, heartworm disease in this 6 month-old, and primary pulmonary hypertension) or stated that a complex anomaly would be required to fit the findings.

The correct recognition of this condition is crucial to case management (i.e., surgical correction is contraindicated). Generally, this case suggests a deficit of understanding of the expected radiographic appearances of congenital cardiovascular diseases.