Plaque and stenosis assessment

The interpretive shift

A coronary report is no longer only a luminogram

Stenosis describes the residual lumen at one site. Plaque burden describes the total atherosclerotic disease carried by the patient. Plaque morphology may refine risk, and physiology asks whether a lesion limits flow. These are related but not interchangeable.

Positive remodelling can preserve the lumen while plaque grows outward, so a patient with little stenosis can still have substantial disease. Conversely, a visually intermediate stenosis may or may not be flow limiting. CCTA should state the anatomical truth and identify when functional information would add value.

One vessel at a time

The segment-by-segment reading sequence

1. Choose the best cardiac phase and confirm overall image quality.
2. Identify origin, course, dominance, branches, stents/grafts, and any non-atherosclerotic abnormality.
3. Trace LM, LAD/diagonals, LCx/OMs, and RCA/PDA/PLV on thin axial plus linked curved MPR.
4. At every plaque, use perpendicular cross-sections to assess wall, lumen, composition, length, and remodelling.
5. Select a nearby normal or least-diseased reference that respects taper and branches.
6. Estimate maximal diameter stenosis; examine more than one plane and phase.
7. Record total plaque burden and high-risk plaque features separately from stenosis.
8. State artifacts, non-evaluable segments, and whether stenosis may be over- or underestimated.
9. Integrate CT-FFR/perfusion only after anatomical quality and lesion localisation are secure.

Composition

Calcified, noncalcified, and partially calcified plaque

Composition is a visual category, not a histology report. Avoid claiming “lipid core” from one attenuation measurement. Low attenuation is affected by kVp, enhancement, reconstruction, noise, partial volume, and measurement method.

The whole-tree signal

Plaque burden predicts risk beyond the tightest stenosis

Qualitatively describe total burden as mild, moderate, severe, or extensive using the entire coronary tree. If a formal method is used, name it.

• Segment involvement score (SIS): number of coronary segments containing any plaque; it captures distribution but not plaque volume within each segment.
• Calcium score: validated marker of calcified burden, but excludes noncalcified plaque.
• Visual CAD-RADS P grade: integrates extent and distribution into P1–P4; learn the formal criteria in Topic 11.
• Quantitative plaque volume: software-derived per-vessel or whole-heart plaque volumes may add precision when technically validated and carefully quality controlled.

Diffuse nonobstructive plaque is not “minor” simply because no focal lesion exceeds 50%. In the impression, make the overall disease burden visible rather than hiding it behind the worst stenosis.

Residual lumen

Grade maximal diameter stenosis consistently

Estimate the narrowest luminal diameter against an appropriate proximal and/or distal reference in a plane perpendicular to the vessel. Report a sensible range rather than false single-percent precision. The formal patient-level CAD-RADS category comes next in Topic 11.

The denominator matters

Choose a reference that is close, normal, and branch-aware

A lesion cannot be graded reliably without a defensible expected vessel diameter. Use the most normal cross-section close to the lesion—often within about 10 mm—while avoiding a major intervening branch. If the proximal segment is ostial or diseased, use a suitable distal reference and account for natural taper.

• Focal disease: compare with adjacent proximal and distal normal segments.
• Diffuse disease: there may be no truly normal reference; state the limitation and use reconstructed expected calibre cautiously.
• Positive remodelling: do not use the enlarged outer wall at the plaque as the reference; compare lumen with normal nearby lumen.
• Bifurcation: respect step-down in calibre after a large branch; do not compare across it as if the vessel were uniform.
• Small vessels: spatial resolution limits percentage accuracy. The 2026 SCCT consensus expects assessment of branches ≥1.5 mm on a good-quality study.

Morphology that refines risk

Four high-risk plaque features

CAD-RADS 2.0 applies the HRP modifier when at least two high-risk features are present. One feature can still be described in prose but does not meet the formal modifier threshold. High-risk morphology is not proof that a plaque is the culprit, nor does it replace symptoms, troponin, ECG, or physiology.

The calcium problem

Blooming can turn moderate disease into apparent severe disease

Dense calcium spreads beyond its true boundary because of limited spatial resolution, partial volume, and reconstruction effects. The residual lumen therefore appears smaller, reducing specificity.

1. Use the sharpest motion-free phase and thin slices.
2. Inspect the lesion in perpendicular short-axis and longitudinal views.
3. Use a small field of view, appropriate sharp kernel, and validated high-resolution/spectral tools if available.
4. Adjust window/level deliberately; never rely on one display setting.
5. Look for visible contrast continuity through the plaque and compare adjacent slices.
6. If the highest plausible grade is reported, explicitly state potential overestimation from blooming.

The subtle plaque

Noncalcified plaque requires wall–lumen–fat discrimination

Use adequate coronary enhancement and a motion-free phase. Confirm plaque as tissue within the coronary wall, bounded by contrast lumen internally and epicardial fat externally. Evaluate it in multiple contiguous slices and planes.

• Avoid placing ROIs across lumen, calcium, or perivascular fat.
• Do not diagnose plaque from a single noisy pixel or one axial slice.
• Positive remodelling can hide stenosis; assess both outer wall and lumen.
• At ostia and bifurcations, distinguish normal wall, valve/aortic-root tissue, and branch flow effects.
• Remember that poor contrast-to-noise can make the lumen look falsely narrowed and plaque falsely low in attenuation.

No visible channel

Describe occlusion, length, distal filling, and chronicity clues

An occlusion is 100% stenosis, but the anatomical report should say more: exact start/end, length, side branches at caps, distal vessel calibre and opacification, calcification, tortuosity, collaterals, and whether the morphology suggests chronic total occlusion (CTO).

• CTO clues: long segment, blunt stump, heavy calcification, negative remodelling, tortuosity, bridging collaterals, and distal reconstitution.
• Acute occlusion: can have a shorter noncalcified filling defect and less established collateralisation, but CT morphology alone cannot date every lesion.
• Slow flow: poor distal enhancement can mimic occlusion; inspect delayed phases if available and correlate with upstream disease.

Confidence belongs in the diagnosis

Recognise what can falsely narrow the lumen

Never upgrade the patient’s worst stenosis from a segment you cannot evaluate. CAD-RADS has an explicit N pathway; Topic 11 covers how non-diagnostic segments interact with the final category.

Anatomy is not flow

Why stenosis and ischaemia can disagree

CT-FFR estimates pressure loss along epicardial coronaries from a high-quality CTCA dataset; CT perfusion measures myocardial contrast delivery under rest/stress conditions. Use functional assessment when it can change management—commonly for anatomically intermediate lesions—not as a rescue for fundamentally non-diagnostic anatomy.

From observation to clinical sentence

The complete lesion statement

Template: [Vessel/segment and branch landmark] contains [composition] plaque of [length/distribution], causing [stenosis range]. [High-risk features]. [Image-quality qualification]. [Distal vessel/physiology if available].

At patient level, separately state the worst stenosis, total plaque burden, HRP modifier when criteria are met, stents/grafts, physiology, and non-diagnostic segments. Topic 11 assembles these into CAD-RADS 2.0.

Reason through the lesion

Worked cases

Case A · Large outward plaque, only 20% narrowing

This is minimal stenosis but not a normal artery. Describe noncalcified/mixed plaque, positive remodelling if measured correctly, and overall burden.

Case B · Dense proximal LAD calcium, apparent 80% narrowing

Review the sharpest phase, orthogonal lumen, windows, and reconstructions. If uncertainty persists, report severe-appearing stenosis with likely blooming overestimation and the degree of confidence/non-evaluability.

Case C · 55% mid-RCA lesion without HRP

Moderate anatomical stenosis. It may or may not be flow limiting; lesion-specific CT-FFR or another functional strategy may help if the result changes management.

Case D · 25% plaque with positive remodelling and low attenuation

Mild narrowing but ≥2 high-risk plaque features. Stenosis and HRP answer different questions; record both.

Case E · Gradual distal CT-FFR decline without focal step

Think diffuse disease/physiological taper rather than assigning the low terminal value to one focal lesion. Interpret the value 1–2 cm distal to each lesion and examine the whole pressure curve.

Active recall

Self-test: answer before opening

Printable quick revision

One-page plaque and stenosis card

• Stenosis: 0 · 1–24 · 25–49 · 50–69 · 70–99 · 100%.
• HRP: positive remodelling · <30-HU focus · napkin ring · spotty calcium; modifier needs ≥2.
• Reference: close + normal + no intervening major branch + respect taper.
• Calcium: assume possible blooming; use phase, cross-section, window, kernel, and honest uncertainty.
• Noncalcified: prove tissue between contrast lumen and epicardial fat across slices/planes.
• Occlusion: map length, caps, calcium, tortuosity, branches, and distal filling.
• Physiology: moderate anatomy does not guarantee ischaemia; low distal flow does not always identify one focal culprit.
• Final rule: describe burden and morphology even when stenosis is small.

Provenance

Sources and scope

This chapter uses the plaque, stenosis, burden, and high-risk morphology teaching from Webinar 4’s CAD-RADS session. Automated captions contain transcription errors; terminology and thresholds were checked against current consensus.

1. SCCT Interpretation and Reporting of CCTA: 2026 Update — segmental interpretation, stenosis ranges, reference selection, plaque burden, calcification limits, and reporting.
2. CAD-RADS 2.0 expert consensus — patient-level stenosis categories, plaque burden, HRP criteria, and modifiers.
3. SCCT CCTA interpretation resource — multi-plane interpretation and structured reporting principles.

Educational material only. Visual grading remains reader- and image-quality-dependent; quantitative plaque tools require vendor-specific validation and manual QC. External references require internet; this chapter works offline.