Can Coronary CTA Miss Atherosclerotic Plaque?
Yes, coronary CTA can miss atherosclerotic plaques, particularly small noncalcified plaques, sub-millimeter calcifications, and vulnerable thin-cap fibroatheromas that fall below the resolution limits of current CT technology.
Technical Resolution Limitations
The fundamental constraint of coronary CTA is spatial resolution. The thin fibrous cap of vulnerable plaques measures approximately 70 micrometers, which is 10 times beyond the present in-plane resolution of MDCT (750 micrometers), making it impossible to directly visualize the most dangerous plaque features 1. This represents a critical gap between what matters clinically (plaque vulnerability) and what CT can actually detect.
Specific Plaque Types That Can Be Missed
Sub-millimeter Plaques
Recent head-to-head comparison with optical coherence tomography (OCT) demonstrated that CCTA fails to detect sub-millimeter calcified plaques (≤0.25 mm²) and very small noncalcified plaques, which likely represent very early atherosclerosis 2. While the clinical significance of these tiny plaques remains uncertain, they are definitively present but invisible to CT.
Noncalcified Plaque Detection Challenges
CT shows only 78% sensitivity for detecting soft (hypo-echoic/lipid-rich) plaques when compared to intravascular ultrasound, with 92% specificity 1, 3. The American Heart Association notes that optimal diagnostic image quality cannot be obtained in approximately 15% of coronary vessels, further limiting plaque detection in these segments 1, 3.
Assessment of noncalcified plaque remains limited to studies of very high image quality and may not pertain to average clinical applications 1, 3. This means that in real-world practice, the miss rate for noncalcified plaques is likely higher than research studies suggest.
Plaque Characterization Limitations
Beyond simply missing plaques, overlap between density values makes distinction between fibrous and soft plaques problematic 1, 3. A study comparing MDCT with intravascular ultrasound found moderate correlation (r=0.55) between the two methods for plaque area measurements, with significant tendency toward overestimation by MDCT (8.3±4.8 versus 7.3±3.1 mm³, P<0.001) 1, 3.
More concerning, MDCT substantially underestimates plaque volume per segment compared to IVUS (2435 versus 4360 mm³, P<0.001) 1, 3, meaning CT misses approximately 44% of total plaque burden.
Plaque Size and Vessel Size Dependencies
Noncalcific plaque visualization is limited by both plaque size and vessel size, with smaller plaques located in smaller coronary sections not being accurately characterized 1, 3. This is particularly problematic in distal vessels and branch points where high-risk plaques frequently occur.
Misclassification Errors
Even when plaques are detected, misclassification is common. Misclassification of plaque type accounted for 61% of false negative findings in one study, which was most prevalent among mixed plaques (46%) 2. This means that even "detected" plaques may be incorrectly categorized, potentially leading to inappropriate risk stratification.
Clinical Implications in High-Risk Patients
For patients with diabetes, hypertension, or family history of heart disease, these limitations are particularly relevant. In asymptomatic diabetic patients, 32.7% had noncalcified plaque only seen on CTA despite having a zero calcium score 1. This demonstrates that calcium scoring alone misses significant disease, but even CTA has blind spots.
The 2022 CAD-RADS guidelines acknowledge that high-risk plaque features (positive remodeling, low-attenuation plaque, spotty calcification, napkin-ring sign) have a prevalence of approximately 30% on CCTA, with even higher frequency in the presence of stenosis 1. However, the positive predictive value for identifying future events remains modest 1.
Common Pitfalls to Avoid
Do not rely on plaque characterization from suboptimal quality CT studies 3. Image quality issues from motion artifacts, high heart rates, arrhythmias, obesity, or heavy calcification all increase the likelihood of missing plaques.
Thin maximum-intensity projection images should not be the only data assessed for reporting purposes given the potential for missing coronary lesions due to overlapping high-density structures that may obscure lumen narrowing 1.
The absence of significant stenosis on CT does not exclude risk, as myocardial infarction may result from rupture of a vulnerable plaque without significant luminal stenosis 1, 3.
Overall Diagnostic Performance
Despite these limitations, CCTA demonstrates excellent performance for detecting any plaque identified by OCT with sensitivity of 92%, specificity of 98%, and accuracy of 93% 2. The high negative predictive value (98%) means that when CTA shows no disease, it is highly reliable 1.
However, interobserver variability for plaque volume measurements by MDCT can be as high as 37% 1, 3, indicating substantial measurement uncertainty even when plaques are detected.
When to Consider Alternative or Complementary Imaging
For precise plaque characterization when clinical decisions depend on it, intravascular ultrasound or optical coherence tomography provide more accurate information than CT angiography alone 4, 3. These invasive modalities should be considered when CTA findings are equivocal or when detailed plaque morphology would change management in high-risk patients.