Up until recently, ICA has been considered the gold standard for the evaluation of coronary anomalies. Meanwhile CCTA has emerged as a non-invasive alternative for the evaluation of the coronary architecture, particularly after introduction of modern protocols allowing to perform CCTA with radiation doses substantially lower than that from ICA with improved spatial resolution . We hypothesized that the number of coronary anomalies by CCTA may more closely reflect their real prevalence in the general population. The reported incidences of coronary anomalies were mostly gained by ICA , in which the referral threshold is assumedly higher than for CCTA. Indeed, the number of anomalies identified in our survey by CCTA was remarkably higher compared to previous studies [19, 20]. However, some subgroups of patients underwent CCTA (for example young patients) because of the clinical suspicion of coronary anomalies, while ICA was performed especially for CAD. This issue might partially explain the higher rates of coronary anomalies discovered by CCTA creating a selection bias. Nevertheless the overall prevalence of coronary anomalies detected by CCTA was significantly higher than by coronary angiography (7.85% versus 2.02%; p < 0.01). In this regard, it has to be stated, that the prevalence is also highly dependent on the definition of coronary anomalies. One of the largest clinical data sets which was reported by the Cleveland Clinic Foundation, observed coronary anomalies in 1.3% (n = 1′461) out of 126′595 investigated patients undergoing ICA .
In the present study, coronary anomalies were divided into two groups, i.e. anomalies of the origin/distribution and anomalies of termination. The clinically most relevant coronary anomalies are those with an anomalous course between the large intra-thoracic vessels (aorta and pulmonary artery). In our study, anomalies coursing between the aorta and the pulmonary trunk showed a prevalence of 9.4% by CCTA, which represents a higher occurrence compared to former studies, primarily based on autopsy data [22, 23]. Of note, a discrimination of the course of a potentially malignant anomaly is only of reliable accuracy by CCTA, while ICA is limited by its 2-dimensional projections. Notably, none of our patients with an abnormal course revealed any perfusion defects by myocardial perfusion imaging. At our institution stress testing is usually performed with adenosine unless contraindicated. In this regard some of our patients (n = 5/13) with potentially serious coronary anomalies in the CCTA group were stressed with adenosine, although exercise testing is more physiological as the coronary artery may be squeezed between the pulmonary artery trunc and the aorta. However, these patients were usually referred for a combined investigation with CCTA and SPECT, and incidentally diagnosed with a potentially serious coronary anomaly after the SPECT results. Several studies have reported an increased risk for sudden cardiac death  as such patients showing myocardial ischemia . However, only limited data are available concerning the long-term outcome of such patients without demonstrable myocardial ischemia [3, 26]. Certainly, asymptomatic patients without stress-induced ischemia remain a clinical challenge. There is still controversy concerning the management of these patients. While some favor a surgical approach others recommend a conservative management. Since sudden cardiac death is associated with this anomaly related to severe exercise, patients are recommended to avoid extreme exertion and should be followed medically.
Beside the potential to describe the exact course of aberrant coronary vessels , CCTA offers another important advantage: Radiation dose exposure can be reduced to very low levels by applying novel CT protocols such as prospective ECG-triggering [6–9, 28], tube current modulation  or high-pitch modus . In addition several studies have demonstrated superiority of CCTA over ICA  in detecting coronary anomalies leading to a 100% identification rate of anomalies when analyzed with CCTA compared to 53% with ICA in a small series of 16 patients . CCTA has recently been advocated as first-line method for known or suspected anomalies by the American College of Cardiology, provided appropriate criteria are used .
Interestingly, the most common finding in the CCTA group was myocardial bridging occurring in 43%, while such an anomaly was found in only 21% by ICA. Previous studies have reported myocardial bridging in 1.5-16% when assessed by ICA, while a substantially higher number up to 80% was observed in autopsy series . Thus, myocardial bridging is a very common finding at autopsy even in normal subjects, but is considered clinically significant only when associated with chest pain and myocardial ischemia [34, 35]. In our CCTA patient population, none of the patients with myocardial bridging revealed any perfusion defect in myocardial perfusion studies.
A further very common finding with both imaging modalities was the absence of the left main artery ranging between 12% by CCTA to 36% by ICA. These results are in line with Yamanaka et al. who found this anomaly to be most common (30.4%) among 126′595 patients evaluated by ICA. The prevalence among the general population is considered to be 0.41% . This anomaly is usually regarded as benign, since the distribution of the vessels is normal.
This was a retrospective analysis and not a head to head comparison between two different techniques. Indeed, only a few patients underwent both imaging modalities. Furthermore this study did not include a randomly assigned study population rather than patients who were primarily referred by cardiologists for evaluation of suspected CAD or coronary anomaly which could have attributed to the higher identification of coronary anomalies among CCTA. Finally, young patients are more likely to be referred to a non-invasive imaging study with CCTA than for ICA, which may have introduced a potential selection bias.