Prevalence of Carotid Web in Youth Assessed by Duplex Sonography: a Cross-Sectional Study
Conditions: Carotid Web
Sponsor: University of Ostrava

Study Protocol 
 
Title: Prevalence of Carotid Web in Youth Assessed by Duplex Sonography: a Cross-
Sectional Study 
 
Short Title: Carotid Web in Youth  
Acronym: CaWY Study 
ID: G25-498516 
Version: 1.4 
Date: October 20, 2025 
Authors: Prof. David Školoudík, M.D., Ph.D. 
                   István Szegedi, M.D., Ph.D. 
                   David Pakizer, MSc., Ph.D. 
Affiliantion: Center for Health Research, Faculty of Medicine, University of Ostrava, Ostrava, 
Czech Republic 
 
 
1) Background and Rationale 
A carotid web (CaW) is a shelf-like, thin, triangular endoluminal projection—typically arising 
from the posterior wall of the internal carotid artery (ICA) bulb—considered by many to be an 
intimal variant of fibromuscular dysplasia and associated with embolic ischemic stroke in 
otherwise low-risk, younger patients. Although CT angiography (CTA) is most frequently used to 
diagnose CaW, characteristic appearances are detectable by carotid duplex ultrasound (DUS) 
on longitudinal B-mode with supportive Doppler findings; microflow/superb microvascular 
imaging can improve conspicuity. Population prevalence in the general young adult population is 
unknown; most estimates come from stroke cohorts (≈2% among symptomatic populations; 
higher within cryptogenic stroke subsets), so a dedicated, population-based sonographic study 
is needed.  
 

2) Objectives and Hypotheses 
Primary objective: Estimate point prevalence of carotid web in a general young adult population 
aged 15–25 years using duplex sonography. 
Secondary objectives: 
• 
Describe CaW laterality and morphology (web thickness, length, and projection angle) 
on ultrasound. 
• 
Estimate prevalence of concomitant ICA/CCA atherosclerotic change or stenosis. 
• 
Assess inter-observer agreement for CaW detection on DUS. 
• 
In an adjudicated subset, compare DUS-suspected CaW with CTA (optional validation). 
Hypothesis: Carotid web is present in 2 % of the general 15–25-year population (two-sided). 
(This is a planning assumption; true prevalence may be lower/higher. Literature in symptomatic 
cohorts ranges roughly 2%, higher in cryptogenic stroke; general-population data are lacking.)  
 
3) Study Design 
Cross-sectional, multi-center, population-based sonographic survey with blinded central image 
adjudication, reported per STROBE guidelines for cross-sectional studies. 
 
4) Study Population 
Inclusion criteria 
• 
Age 15 – 25 years at enrollment. 
• 
Able to provide informed consent. 
Exclusion criteria (for primary analysis; still recorded if present): 
• 
Prior carotid endarterectomy/stenting, neck irradiation, or known vasculopathy with non-
web lesions that preclude assessment. 
• 
Inadequate acoustic window despite optimization (these participants contribute to 
feasibility metrics, not prevalence numerator/denominator). 
Setting & sampling frame 
• 
Community-based recruitment (secondary schools / universities). 

• 
Stratified cluster sampling by sex, age bands (15-17, 18–21, 22–25), and recruitment site 
to approximate the underlying population. 
 
5) Sample Size 
Assumptions 
• 
Expected prevalence p=0.02 (2%) 
• 
Desired absolute precision d=0.01 (±1%) 
• 
Confidence level 95% → Z=1.96 
Formula 
n  =  Z2 p(1−p)d2  =  1.962×0.02×0.980.012  =  752.95n \;=\; \frac{Z^2\, p(1-p)}{d^2} \;=\; 
\frac{1.96^2 \times 0.02 \times 0.98}{0.01^2} \;=\; 752.95n=d2Z2p(1−p)=0.0121.962×0.02×0.98
=752.95  
Required minimum sample size: 753 participants (round up) plus 10% for non-diagnostic/poor-
quality scans and no-shows, i.e. totally 829 participants is needed to screen. 
 
6) Ultrasound Acquisition Protocol 
Equipment & presets 
• 
High-end ultrasound suplex machine Canon Aplio a-series with B-mode, color/power 
Doppler, spectral Doppler, and microflow/superb microvascular imaging. High-
frequency linear transducer PLT-1005BT (5–14 MHz). 
• 
Patient supine, slight neck extension/contralateral head rotation; optimize for the carotid 
bulb/ICA origin. 
Scanning sequence (bilateral) 
1. B-mode: transverse sweep from distal CCA through bulb into proximal ICA and ECA; 
then longitudinal (anterolateral, lateral, posterolateral windows). 
2. Color Doppler: at low PRF to visualize flow separation/recirculation; adjust wall filter 
and gain to avoid overwriting thin intraluminal structures. 
3. Spectral Doppler: with angle correction ≤60°, sample volume 1.5–2.0 mm; measure 
PSV and EDV in standard segments (distal CCA, bulb, proximal ICA). 

4. Microflow imaging: focused on the posterolateral bulb to delineate thin 
shelf/membrane and adjacent flow.  
Image storage 
• 
Mandatory cine loops (≥3 cardiac cycles) in longitudinal and transverse of the bulb/ICA 
origin, plus still frames with and without color, and spectral Doppler waveforms with 
angle annotation ((same as in protocol of ANTIQUE study). 
• 
Label side and projection; record machine make/model, probe, presets. 
 
7) Sonographic Definition of Carotid Web  
Definite carotid web: 
Inclusion criteria: 
1. Focal echogenic lesion in carotid bifurcation (15 mm proximally to flow divider and 15 
mm distally) 
2. The lesion is present (interferes) in the posterior wall 
3. Echogenicity of the lesion is higher than intraluminal blood 
4. Maximal length of lesions 3.0 mm 
5. Minimal intraluminal prominence (width) 2.0 mm 
6. In longitudinal view: Shape of lesion is shelf-like nor valve-like, triangular with the 
sharpest angle proximally with the blood flood direction 
7. In transversal view: Transversal linear defect with echogenic surface projecting in the 
arterial lumen (the shape should be nest-like) 
8. Hemodynamic signature: focal flow separation/recirculation or color aliasing 
immediately distal to the shelf without proportionate atherosclerotic plaque; spectral 
Doppler may be normal or show subtle focal acceleration without classic stenosis 
criteria. 
Exclusion criteria: 
1. The length is greater than the width 
2. Visible only in transversal and not longitudinal view 
3. Presence of carotid plaque (Mannheim consensus) in the posterior wall 

 
Suspected carotid web: 
Inclusion criteria: 
1. Focal echogenic lesion in carotid bifurcation (15 mm proximally to flow divider and 15 
mm distally) 
2. Minimal intraluminal prominence (width) 1.5 mm 
3. One out of these criteria: 
a. In longitudinal view: Shape of lesion is shelf-like nor valve-like, triangular with the 
sharpest angle proximally with the blood flood direction 
b. In transversal view: Transversal linear defect with echogenic surface projecting in the 
arterial lumen (the shape should be nest-like) 
Exclusion criteria: 
1. Presence of carotid plaque (Mannheim consensus) in the posterior wall 
 
Differential sonographic features to record: typical plaque (echogenic/heterogeneous with 
surface calcification), carotid diaphragm, dissection flap (mobile, intramural hematoma), 
carotid web with superimposed thrombus.  
 
7) Sonographic Case Definition of Carotid Web  
Required equipment/settings (if specified in your criteria): 
• 
Probe / frequency: 5-14 MHz 
• 
Settings: MI 1.6, 37 fps, Q scan, dynamic range 70 
• 
Patient position: supine position, slight neck extension/contralateral head rotation 
Diagnostic categories (tick all that apply): 
• 
Definite CaW — must meet morphology, location, hemodynamics criteria and 
exclusions ruled out (plaque, dissection, diaphragm, artifact). 
• 
Probable CaW — meets some morphology criteria and exclusions ruled out (plaque, 
dissection, diaphragm, artifact). 

• 
Not CaW — meets no criteria for CaW. 
Morphologic measurements (standardized): 
• 
Web thickness (mm): ____ (measured at ______) 
• 
Web length/projection into lumen (mm): ____ 
• 
Projection angle (°) relative to vessel wall: ____ 
• 
Distance from flow divider (mm): ____ 
• 
Side: left / right / bilateral 
Hemodynamic signatures (as per your thresholds): 
• 
Color Doppler recirculation/aliasing: present / absent (criteria: ______) 
• 
Spectral Doppler acceleration: PSV ___ m/s (cutoff: ___); ICA/CCA ratio cutoff: ___ 
• 
Microflow imaging pattern: ______ 
Differential exclusion checklist (define image features to rule out): 
• 
Atherosclerotic plaque: ______ 
• 
Dissection flap/intramural hematoma: ______ 
• 
Carotid diaphragm/other membranes: ______ 
• 
Artifact (reverberation, blooming): ______ 
Image acquisition minimums (per side): 
• 
Transverse cine (≥3 cycles) focused on bulb/ICA origin 
• 
Longitudinal cine in ≥2 insonation planes (lat & post-lat) 
• 
Still frames (B-mode ± color) with calipers for all measurements 
• 
Spectral Doppler waveforms (CCA, bulb, proximal ICA) with angle correction ≤60° 
Quality grading (apply your rules): 
• 
Grade 1 (excellent) / 2 (diagnostic) / 3 (limited) — use only Grades 1–2 in primary 
analysis; Grade 3 in sensitivity analysis. 
Reader guidance & adjudication using your criteria: 
• 
Two blinded readers score Definite/Probable/Possible/Not CaW; discrepancies resolved 
by third reader under the same rubric. 

• 
10% repeat reads for κ/ICC. 
CRF add-ons (pre-wired to your criteria) 
• 
Checkboxes for each criterion element (present/absent/not evaluable). 
• 
Auto-calculated category (Definite/Probable/Possible/Not CaW) based on boxes ticked. 
• 
Mandatory image IDs linked to each measurement. 
 
8) Training, Blinding, and Adjudication 
• 
Sonographers undergo a standardized training module with exemplar images and 
checklists. 
• 
Blinding: Operators are blinded to participant clinical data except age/sex; central 
readers (two expert neurosonologists) are blinded to site and each other. 
• 
Adjudication: Disagreements (probable/possible/absent) resolved by a third senior 
reader. 
• 
Reliability: 10% random sample re-read for inter-observer agreement (Cohen’s κ for 
categorical calls; ICC for continuous measures). 
 
9) Data Collection 
• 
Demographics: age, sex, ethnicity (optional), height/weight. 
• 
Vascular risk factors: smoking status, BP at visit, lipid profile if available, personal 
history of stroke/TIA/migraine, OCP use (females), recreational drugs, connective tissue 
disease/FMD history. 
• 
Ultrasound fields: laterality; CaW category (absent/possible/probable), web 
dimensions (length, thickness, projection angle—estimate), distance from flow divider, 
presence of superimposed thrombus, plaque descriptors, standard velocities (CCA, 
bulb, ICA), ICA/CCA PSV ratio, EDV. 
• 
Imaging quality scores and reasons for non-diagnostic studies. 
 
10) Validation Substudy 

• 
Participants with definite or possible CaW on DUS plus 1:2 matched DUS-negative 
controls (matched by age/sex/site) will invited for CTA within 4 weeks to evaluate 
concordance (index test: DUS; reference standard: CTA with thin-slice oblique sagittal 
reconstructions). Outcome: sensitivity/specificity and positive predictive value of DUS 
criteria. (CTA descriptions of CaW as thin, shelf-like posterior bulb defects guide the 
reference call.)  
 
11) Outcomes 
• 
Primary: Point prevalence of probable CaW (participants with ≥1 carotid web / all with 
diagnostic scans), with 95% CI adjusted for sampling design. 
• 
Secondary: 
o 
Prevalence including possible + probable (sensitivity analysis). 
o 
Distribution by side (left/right/bilateral). 
o 
Association between CaW and sex, smoking, BP, OCP use (exploratory). 
o 
Inter-observer agreement metrics. 
o 
In validation substudy: DUS diagnostic accuracy vs CTA. 
 
12) Statistical Analysis Plan 
• 
Weighting: Apply sampling weights for cluster/strata to estimate population prevalence; 
robust SEs (Taylor linearization) or survey-design GLMs. 
• 
Descriptives: Means/SDs or medians/IQRs; counts/% with 95% CIs. 
• 
Primary analysis: Weighted prevalence and exact (Clopper–Pearson) or Wilson CIs for 
rare events; compare strata with Rao–Scott χ². 
• 
Regression (exploratory): Survey-weighted Poisson (log link, robust variance) for 
prevalence ratios of CaW vs candidate covariates. 
• 
Reliability: Cohen’s κ with 95% CI (categorical), ICC(2,1) for continuous measures. 
• 
Missing data: Report flow; use complete-case for primary prevalence; multiple 
imputation for covariate analyses if >5% missing. 

• 
Sensitivity analyses: (i) include possible CaW as positive; (ii) restrict to scans with top 
quality scores; (iii) per-reader estimates. 
 
13) Bias Minimization & Quality Control 
• 
Pre-specified imaging protocol; machine presets harmonized across sites. 
• 
Central training and periodic re-calibration; quarterly site audits of randomly selected 
studies. 
• 
Consecutive sampling within clusters to reduce selection bias; track response rates. 
• 
Maintain blinding; lock image sets before adjudication. 
 
14) Ethics and Safety 
• 
Minimal-risk imaging study; no ionizing radiation in the primary protocol. 
• 
Informed consent; separate consent for optional CTA. 
• 
Participants with incidental significant carotid stenosis or suspected thrombus 
receive counseling and referral per local care pathways. 
• 
Data privacy per GDPR; coded IDs; secure storage. 
 
15) Feasibility & Timeline 
• 
July-December 2025: Finalize SOPs, train sonographers, pilot 50 scans to confirm 
criteria and quality metrics. 
• 
January 2026 – June 2026: Enrollment and scanning. 
• 
May – June 2026: Central reads and adjudication. 
• 
July – December 2026: Analysis, manuscript preparation. 
 
16) Case Report Forms (CRFs) — Core Fields (summary) 
• 
CRF-1 (Eligibility & Consent). 
• 
CRF-2 (Demographics/Risk). 
• 
CRF-3 (Ultrasound Acquisition): device, probe, settings, windows obtained, quality. 

• 
CRF-4 (Ultrasound Findings): CaW category; measurements; Doppler velocities; 
plaque; stenosis category; images saved (IDs). 
• 
CRF-5 (Adjudication): reader A/B calls; consensus; κ. 
• 
CRF-6 (Validation Substudy): CTA done (Y/N), CTA result (CaW Y/N), discordance 
reason. 
 
17) Reporting 
• 
Report per STROBE; include gallery of representative DUS images (longitudinal shelf-like 
lesion, transverse membrane, microflow swirl) and a flow diagram. Explicitly discuss 
limitations: web detection is operator-dependent; ultrasound criteria are less 
standardized than CTA; very low prevalence may limit precision without large samples.  
 
 
Key References (for protocol justification) 
1. Fontaine L, et al. Ultrasound characteristics of carotid web. J Neuroimaging. 2022. 
Describes B-mode/Doppler appearances; microflow imaging improves detection. (PMC, 
PubMed) 
2. Chen H, et al. Carotid webs: pathophysiology, diagnostic approaches, and 
management. J NeuroIntervent Surg. 2024. Overview; ultrasound visualization best in 
longitudinal B-mode. (jnis.bmj.com) 
3. Radiopaedia (review). Carotid web. Emphasizes shelf-like defect at posterior ICA bulb 
and CTA reference standard. (Radiopaedia) 
4. Beach KW, et al. Standardized ultrasound evaluation of carotid stenosis. 2010. 
Acquisition/measurement standards. (PMC) 
5. SRU consensus criteria (summarized). ICA PSV/EDV and ICA/CCA ratios for stenosis 
grading—context for standard carotid reporting alongside web detection. (Radiopaedia) 
6. Yang T, et al. Prevalence and site of predilection of carotid webs (symptomatic cohort). 
Provides symptomatic/asymptomatic estimates within clinical samples. (thejns.org) 
7. Sajedi PI, et al. Carotid Bulb Webs as a Cause of “Cryptogenic” Stroke. 2017. Found 
shelves at posterior bulb in young stroke patients. (PMC)