Carotid Thin Fluttering Bands: Fact or Artifact?

We included all patients admitted to our ambulatory for CUS from October 2015 to October 2016. Patients with recent ischemic stroke or transient ischemic attack were excluded to avoid potential confounding ultrasound features (i.e., intimal flap in carotid dissection or plaque’s rupture). Dyslipidemia was defined as Low-Density Lipoprotein (LDL) levels ≥ 130 mg/dL or use of lipid-lowering drugs. Hypertension was defined as values of systolic blood pressure > 140 mmHg and/or > 90 mmHg of diastolic blood pressure. Diabetes was defined as fasting blood glucose of 126 mg/dl or greater. Family history of Coronary Artery Disease (CAD) was defined as a diagnosis of CAD in father/brother aged < 55 years and mother aged < 65 years. Chronic Kidney Disease (CKD) was defined as a Glomerular Filtration Rate (GFR) < 60 ml/min/1.73 m2. Smoke was considered as a risk factor if the patient were a current smoker or an ex-smoker of less than 1 year.

TFB was defined as presence of hyperechoic fluttering band in the carotid lumen in absence of echo graphic pattern of dissection such as visualization of false lumen, low-reflection mural hematoma or thrombus or Doppler high-resistance flow [6]. All studies were performed using GE Vivid E Ultrasound system (GE Healthcare, Horten, Norway) equipped with a dedicated 8L-RS linear array transducer (4-12 MHz) by a single experienced vascular sonographer.

Image was optimized adjusting gain, focus and grey scale parameters. Transverse and longitudinal scans were obtained on the common carotid artery, the carotid bifurcation, internal and external carotid artery by Brightness-mode (B-mode) and color Doppler ultrasound. When longitudinal scan was performed, probe was slowly tilted from lateral to the center. IMT was defined as the distance between the leading edge of the lumen-intima echo and the leading edge of the media-adventitia echo. IMT was measured at a site free of plaque 1 cm proximal to the carotid bulb. The upper limit of normality for IMT was set according to age, gender and race as previously described [7]. We reported the IMT value according to the site of TFB, in case of bilateral TFB mean IMT value was reported. Carotid plaque was defined as the presence of focal wall thickening that is 50% greater than that of the surrounding vessel wall or as a focal region with IMT >1.5 mm echo lucent areas that protrudes into the lumen that is distinct from the adjacent boundary.

TFB was visualized in both longitudinal (Figure 1A, Video 1A), transverse B-mode scan (Figure 1B, Video 1B) and color-doppler scan (Figure 1C, Video 1C); the Motion mode (M-mode) image scan, perpendicularly oriented to the TFB, was also performed in both sections to confirm the intra-vessel location of TFB (Figure 1D). M-mode scan helped in differentiate TFB from reverberation artifacts (Video 2) or venous valve (Figure 2, Video 3).

Figure 1: Long axis view in B-mode show the Thin Fluttering Band (TFB) in the posterior carotid wall (arrow).


Video 1 A: Pancreatoscopy showing floating mucin in the pancreatic duct and the whitish mucin globule.

Video 2: Pancreatoscopy showing floating mucin in the pancreatic duct and the whitish mucin globule.

Video 3: Pancreatoscopy showing floating mucin in the pancreatic duct and the whitish mucin globule.

A total of 915 patients underwent CUS. TFB was identified in 96 patients (10.5%). Mean age of population was 64.14 ± 10.52. Summarizes clinical features (Table 1).

 

	Overall N=96	NP-TFB N=26	P-TFB N=70	p-value*
Age, mean ± SD	64.14 ± 10.52	56.35 ± 11.14	67.03 ± 8.74	0.001
IMT (mm), mean ± SD	1.15 ± 0.14	1.09 ± 0.14	1.17 ± 0.13	0.022
BMI (kg/m2), mean±SD	25.30 ± 0.27	25.10 ± 2.70	25.37 ± 2.54	0.64
Gender male, n (%)	59 (61.5)	12 (46.2)	47 (67.1)	0.060
Smoke, n (%)	49 (51.0)	11 (42.3)	38 (54.3)	0.297
Hypertension, n (%)	55 (57.3)	12 (46.2)	43 (61.4)	0.179
Diabetes, n (%)	16 (16.7)	2 (7.7)	14 (20)	0.22
Dyslipidemia, n (%)	59 (61.5)	14 (53.8)	45 (64.3)	0.35
Family history of CAD, n (%)	26 (27.1)	8 (30.8)	18 (25.7)	0.615
CKD, n (%)	5 (5.6)	1 (3.8)	3 (4.3)	0.059

Table 1: Baseline characteristics of population.
In all patients we found increased intima media thickness (IMT – mean 1.15 ± 0.14); in 70 patients (72.9%) TFB was found in presence of a plaque while in 26 patients (27.1%) no carotid plaque was observed (Figure 3, Video 4). TFB was single in most of patients (n=85, 88.5%) while in 11 patients (11.5%) it was multiple. Total TFBs observed were 109, 61 (56 %) in the right carotid and 48 (44%) in the left carotid. The majority originated in the carotid bulb (82.6%) followed by the internal carotid artery (10.1%) and the common carotid artery (7.3%).

 

Figure 3: A plaque with a TFB is observed in the bulb of a right carotid artery.

 

Video 4: Pancreatoscopy showing floating mucin in the pancreatic duct and the whitish mucin globule

 

Patients with plaque were significantly older (67.03 ± 8.74 vs 56.35 ± 11.14 years, p < 0.001) and cardiovascular risk factors were more prevalent without any statistical significant difference.

In this series we found higher incidence of TFB respect to our previously published study (10.5% vs 2.1%). Lower incidence in our previous report could be due to the learning curve. Indeed, the application of our protocol allowed us to recognize more TFBs than the past. In particular, slow progression from lateral to central position during longitudinal examination and execution of M-mode scan are crucial to evaluate the carotid vessel accurately. Several echo graphic findings differentiate TFB from artifacts such as reverberation or venous valve reflection: 1) TFB is visualized in both transverse and longitudinal section while artifacts typically disappear when changing insonification angle; 2) TFB has a cyclic undulatory motion in B-mode scan and in M-mode scan it shows a peculiar non-consensual motion relative to the surrounding intimal layer while reverberation artifacts are fix in the carotid lumen video 2; conversely, venous valve is thicker than TFB with a different and opposite motion (Figure 2, Video 3).

This study also confirm the previous observation that most of TFBs originated in the carotid bulb, a well known site of disturbed flow where alternation of color doppler are frequently found in presence of TFB (Figure 1C, Video 1C).

Respect to the previously reported series we found higher prevalence of TFBs related to carotid plaque. Ultrasound characteristics of P-TFB are comparable to those found in NP-TFB indeed TFB co-localize with augmented IMT therefore we believe that TFB is not a structure related to the plaque. The increased IMT found in P-TFB group could be explained by the different atherosclerotic stage of patient with carotid plaque respect to those without carotid plaque.

A practical tip that may help in visualize TFB is to tilt slowly the probe from lateral to the center in longitudinal scan when focal augmented IMT is associated with large disturbed flow (alternation of color) in carotid bulb.

Although the pathophysiology of TFB is still unknown, also in this report all patients showed increased IMT, therefore we can speculate that TFB occurs in a precocious stage of atherosclerotic involvement and it could be a dynamic phenomenon of vessel remodeling. Endothelial Shear Stress (ESS) alteration, commonly observed in the carotid bulb, triggers expression of several factors such as adhesion molecules, chemokines and pro-inflammatory cytokines [8-10]. Intimal layer adapts in response to changes in ESS and tensile stress through several dynamic process (REF) that lead to progressive thickening of such tunica, therefore TFB could be the expression of intimal turnover [11].