Anomalous origin of the left main coronary artery: course determination by computed tomography.

Discr iminat ion between an in terar te r ia l and intraseptal LMCA is important considering their different pathophysiological, surgical and prognostic implications3,4. The interarterial course carries the greatest risk for adverse repercussions among all coronary anomalies; it is linked to the proximal ectopic vessel, which is intussuscepted within the aortic wall media. In contrast, the intraseptal course is considered benign and has been only occasionally correlated with ischemic sequelae; it is linked to muscular compression of the intramyocardial ectopic segment during tachycardia. Computed tomographic coronary angiography may depict anatomic features that are specific to each of these courses, thereby facilitating their differentiation5. Thus, a LMCA with interarterial course is depicted above the pulmonary valve and on coronal images, it is seen en face between the aortic root and pulmonary trunk as an oval structure; the latter is due to the fact that the proximal intussuscepted ectopic segment is hypoplastic and laterally compressed.