Clinical Neurology · Neurosonology
Carotid & Vertebral Ultrasound
Extracranial carotid and vertebral duplex — anatomy, ICA stenosis velocity criteria, plaque, occlusion findings, and special situations.
Carotid & Vertebral Ultrasound
Branches of the ICA (Often Overlooked)
- Caroticotympanic artery — in the petrous portion.
- Vidian artery to the pterygoid canal — in the petrous portion.
- Meningohypophyseal trunk — cavernous portion.
- Inferolateral trunk to the trigeminal ganglia — cavernous portion.
Doppler Parameters — ICA Stenosis Criteria
| Stenosis | PSV | EDV | ICA/CCA |
|---|---|---|---|
| Wake Forest ICA Stenosis Criteria | |||
| < 50% | < 140 | < 40 | < 2 |
| 50–69% | > 140 | < 100 | 2–3 |
| 70–99% | > 140 | > 100 | > 3 |
| Wake Forest Post-Stent Stenosis (revascularized artery has higher velocities due to flow remodeling) | |||
| 50–69% | 175–299 | — | — |
| 70–99% | > 300 | > 140 | > 3.8 |
| US Consortium Criteria | |||
| Normal | < 125 | < 40 | < 2 |
| 50–69% | 125–230 | 40–100 | 2–4 |
| 70–99% | > 230 | > 100 | > 4 |
| Near occlusion | Low | Variable | Variable |
- PSV: used to measure stenosis. PSV > 140 indicates > 50% stenosis. PSV > 140 and EDV > 100 indicates 70–99% stenosis.
- EDV: also used to measure stenosis; if EDV > 100 and PSV > 140 indicates stenosis > 70%. Decreased EDV indicates a resistive waveform.
- ICA/CCA velocity ratio: ICA = highest PSV in ICA; CCA = distal CCA, 2–4 cm before the bulb.
- Side-to-side difference: normal ratio between both sides is 0.7–1.3.
- Waveform analysis.
B-Mode Color Flow
- Stenosis measurement:
- NASCET = (1 − d/n) × 100, where d is the diseased narrow segment and n is the normal distal segment.
- ACAS/WUSH = (1 − minimum lumen diameter / carotid bulb).
- 70% NASCET = 80% ACAS.
- DSA tends to underestimate stenosis.
- Stent stenosis: > 30% reduction in lumen diameter.
- Intima-media thickness.
- Plaque size & characteristics: longitudinal usually overestimates plaques — always check cross sections. 1.1–2 mm is mild, 2.1–4 mm is moderate, > 4 mm is large or severe.
- Dissection, aneurysm, thrombus.
- Slow flow: pulse Doppler is more sensitive for low flow than B-mode. Slow flow may look like no flow on pulse Doppler if PRF is low. On B-mode it may show as “spontaneous echo contrast.”
CCA Volume Flow Rate
- Normal 200–400 ml/min.
- Helps to differentiate true stenotic flow from increased flow for collateral hyperperfusion.
- Case: Right ICA severe stenosis, increased PSV in proximal right ICA (460), flow (118); left ICA with PSV (200), flow (425) — left ICA increased flow due to hyperemia. TCD will show left → right cross flow. Left ICA/CCA PSV ratio < 3 (both are hyperemic, not left ICA stenosis).
Reversed Robin Hood Syndrome (Intracranial Arterial Steal)
- Hypercapnia causes paradoxical reduction in regional CBF within ischemic tissue and augmentation of CBF within normal tissue.
Spectral Broadening
- Can be due to: large insonation angle, large sample volume > 3 mm, large sample volume close to the vessel wall, or high gain settings.
- Typically spectral broadening is expected in TCDs due to the large sample volume (usually 3 or more mm) and is not considered pathological.
ICA Occlusion Findings
- No flow signal.
- High resistive stump waveform.
- Distal ICA & MCA post-stenotic waveform.
Fibromuscular Dysplasia (FMD)
- Usually affects the distal ICA; “string of beads.”
- Long segment stenosis with increased velocities.
Vertebral Arteries
- Numbers: Vertebral — V2: 40–50 cm/s intra-osseous; V1: 60 cm/s at origin.
- Subclavian steal: systolic deceleration; alternating flow / reversed flow at rest.
- Latent subclavian steal: systolic flow deceleration; a second peak velocity.
- Hyperemia test: BP cuff inflated, ask the patient to perform physical exercise. Increased metabolic demands cause vasodilatation. Release the cuff; reversal will show on Doppler.
Ahmed Koriesh, MD