Combining Computed Tomography Coronary Angiography and Magnetic Resonance Imaging in Assessing Collateral Pathways
A 58-year-old man with a history of bicuspid aortic valve and severe childhood bacterial endocarditis presented to the Radiology Department for further investigation into the complex perivalvular anatomy seen on echocardiography and for assessment of the ascending aorta. Magnetic resonance imaging demonstrated a normal-caliber ascending aorta and a large perivalvular cavity. In addition, however, it showed dilated tortuous coronary arteries and an unusual appearance of the right coronary artery (RCA) origin (Figures 1 through 3⇓⇓). Phase-contrast imaging demonstrated retrograde flow within the mid RCA, presumably caused by large collaterals from the left coronary circulation.
An ECG-gated computed tomography (CT) scan was performed to help further delineate the anatomy. This showed that the large perivalvular space communicated with the left ventricular outflow tract and aortic root through numerous fenestrations. The RCA origin was severely stenotic. Distally, the RCA was supplied by numerous collaterals from the left coronary circulation, as implied by magnetic resonance imaging.
One collateral pathway included a long, tortuous connection from the left circumflex coronary artery through an obtuse marginal branch traveling around the inferior aspect of the heart and communicating through an acute marginal branch with the RCA. The other major collateral pathway passed from the left anterior descending artery across the right ventricular outflow tract to the RCA through the right conus artery. This second collateral is also known by its eponymous name of Vieussens’ collateral pathway.1,2 Also identified in this study is a significant stenosis of the right conus branch near its origin from the RCA, which affected its capacity to act as a collateral pathway.
It is postulated that the clinically documented episode of severe bacterial endocarditis in childhood probably resulted in a perivalvular abscess, leading to the formation of a perivalvular cavity and stenosis of the RCA origin. This in turn eventually led to the formation of these impressive collateral pathways.