All patients (n = 165, median age, 56.9 ± 13.3) who has done both neck CTA and VW MRI in our radiology department, Zhongnan hospital, performed from February 2017 to April 2019 were included. This research was approved by the ethics committee, Zhongnan Hospital of Wuhan University, Wuhan University. Those patient with stent-deployed or poor image quality that cannot be judged (n=12) were excluded. All CTA (n = 153, median age, 56.9 ± 13.3) images were read by two experienced radiologists. All carotids were evaluated in standard and oblique projections (thin cuts) in order to get better view of each carotid arteries. Discrepancies were settled by consensus. Each patients diagnosed with CaWs will be recorded with their characteristics based on following diagnostic criterion.
- Imaging Protocol
- CT angiography
A Siemens Somatom Definition 64 slice CT scanner (Siemens, German) or Philips Ingenuity CT 64 slice CT scanner (Phillips, North America) was use to acquire CTA images. Parameters: tube voltages: 140kv, tube current: 31mAs, thickness 1.5mm, with injection of 1.5ml/kg iopromide contrast material (Bayer Schering Pharma AG).
A 3.0-T system (Prisma; Siemens, German) was used to acquire images using 3D FSE SPACE sequences (black blood) and acquisition parameters are detailed in Table 1. 64-channel head neck coil was used to ensure the good image quality. Each person included three sequences for about thirty minutes scanning. T1 weighted imaging (T1WI), T2 weighted imaging (T2WI) and T1 weighted imaging with fat suppression and contrast enhancement (T1WI-CE) after injection of 0.1 mmol/kg gadolinium-based contrast material (Bayer Schering Pharma AG).
The following parameters were used for T1WI: acquired voxel size, 0.7 × 0.7 × 0.7 mm3; repetition time /echo time, 600ms/13ms; acquisition time, 9 minutes; direction, anterior to posterior. The following parameters were used for T2WI: acquired voxel size, 0.7 × 0.7 × 0.7 mm3; repetition time /echo time 1300ms/124ms; acquisition time, 8 minutes; direction, Right to Left. The following parameters were used for T1 weighted imaging: acquired voxel size, 0.7 × 0.7 × 0.7 mm3; repetition time /echo time, 600ms/13ms; acquisition time, 9 minutes; direction, Anterior to Posterior.
- Diagnostic criterion
- CT angiography
CaW is an intraluminal shelf-like projection within the lumen of the carotid bifurcation (Figure 1) (6, 8, 9, 15). Recent studies have used CTA as the defining imaging modality in series of CaWs. Three features of diagnostic criteria can be summarize into three points:
(1) “A filling-defect “, other description: a shelf-like, a protrusion.
(2) “A thin line or a septum”, dividing the lumen in axial.
(3) “Double-lumen sign”, similar with dissection.
With 5 patients from the Mari E. Boesen’s study, our team summarize six features of CaWs with the following parts (Figure 2):
- “Thickness”: Carotid vessel wall thickness ( isointension )
- Other description: similar with the description of intimal-medial thickness (IMT) in ultrasound
- Diagnosis character: Thickening and signal enhancement of the vessel wall, typically only on the side of the carotid web on Proton density-weighted FSE images (14); sometimes similar with the thickness in plaque, but no fat component or hemorrhage below the vessel wall, which means there is no suppression of signal on fat-saturated series or hyperintension in T1WI, that’s to say usually isointension compared to normal vessel wall.
- Differential diagnosis: A typical atherosclerotic plaque contains several components, including a fibrous cap, calcifications, a necrotic lipid core, hemorrhagic areas, and a fibrous component (10). There is suppression of signal on fat-saturated series or intraplaque hemorrhage in carotid plaque usually.
- “Projection” : derived from posterior wall
- Other description: Focal endoluminal protrusions, protruding lesions in the carotid bifurcation; filling defect similar with CTA(14); shelf-like outgrowth; a linear band of tissue extending into the lumen
- Diagnosis character: Attached to the vessel wall, usually derived from posterior wall, sometimes connect to other side wall. Its MRI signal features: usually isointense without suppression of signal on fat-saturated series or hyperintension beneath the intimal on T1WI; usually isointense or hyperintension on T2WI; it usually has obvious enhancement on T1WI-CE.
- Differential diagnosis: Unlike the well-delineated CaW with its smooth border, surfaces of atherosclerotic lesions are commonly irregular and atherosclerosis may also involve the distal common carotid and areas distal to the bulb (8-10).
- “Value sign”: Value-liked constructer
a) Diagnosis character: The webs derived from two side of lumen with junction in the center.
b) Differential diagnosis:No such image character have been found in other vascular diseases. It may look like vein value or vulnerable intimal flap sometimes.
- “Double lumen sign”: Double-lumen or multi- lumens
a) Diagnosis character: A thin line or a septum dividing the lumen in axial, and may have more than two lumens (14);
b) Differential diagnosis:Similar with carotid dissection sometimes, but there is no mural hematoma (16).
a) Diagnosis character: Residual contrast-enhanced blood accumulation behind the carotid web (14).
b) Differential diagnosis:It need to be distinguish with flow artifacts near the carotid bulb.
CTA was usually selected as defining imaging modality in this study. Each patients’ diagnosis character of each modality were be recorded according to the above-mentioned diagnostic criterion. Discrepant opinions were discussed and settled by consensus. In additions, the degree of stenosis of each patient with CaWs was recorded based on NASCET criteria (mild: 1–29%, low moderate: 30–50%, high-moderate: 50–69%, severe: 70–99%) (13, 14). And any hyperdense focus with relative Hounsfield unit >1,000 was identified as vessel wall calcification.
Statistical Analysis
Interobserver agreement in CTA of detecting carotid webs was checked by using kappa statistics. Two-sided Cohen’s Kappa (κ) coefficient was used to evaluate the inter-rater agreement for the two reader’s diagnostic results.
Sensitivity, specificity, and area under the curve (AUC) of each diagnostic features at CTA and VW MRI were calculated. A P<0.05 was considered statistically significant. Statistical analysis was performed using IBM R SPSS R Statistics 22 (IBM R -Armonk, NY, USA).