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Case series
Intravascular Ultrasound in Carotid Web
  1. Sara Hassani1,
  2. Raul G Nogueira2,
  3. Alhamza R Al-Bayati2,
  4. Rajesh Sachdeva3,
  5. Michael McDaniel4,
  6. Diogo C Haussen2
  1. 1 Neurology, Emory University School of Medicine/Marcus Stroke and Neuroscience Center - Grady Memorial Hospital, Atlanta, Georgia, USA
  2. 2 Neurology, Neurosurgery and Radiology, Emory University School of Medicine/Marcus Stroke and Neuroscience Center - Grady Memorial Hospital, Atlanta, Georgia, USA
  3. 3 Cardiology, Morehouse School of Medicine/Grady Memorial Hospital, Atlanta, Georgia, USA
  4. 4 Cardiology, Emory University School of Medicine/Grady Memorial Hospital, Atlanta, Georgia, USA
  1. Correspondence to Dr Diogo C Haussen, Neurology, Neurosurgery and Radiology, Emory University School of Medicine/Marcus Stroke and Neuroscience Center - Grady Memorial Hospital, Atlanta, GA 30303, USA; diogo.haussen{at}emory.edu

Abstract

Background Carotid web (CaW) is a shelf-like linear filling defect in the posterior aspect of the internal carotid bulb, representing an intimal variant of fibromuscular dysplasia. The diagnosis of CaW is traditionally restricted to digital subtraction angiography (DSA), CT/MR angiography (CTA/MRA), and Duplex ultrasonography. In this series of patients with acute ischemic stroke, we evaluated the potential utility of intravascular ultrasound (IVUS) in further characterizing suspected CaWs.

Methods This is a case series of three patients with suspected CaW who underwent DSA for treatment or investigation of large vessel occlusion strokes. In all cases the stroke investigation failed to identify an alternative cause, and the stroke etiology was attributed to a symptomatic CaW. The procedure consisted of positioning a guide catheter in the common carotid artery, navigating the IVUS probe distal to the carotid bulb, and then retracting the probe with a manual pullback. The acquired images were then reviewed in an independent workstation

Results In two of the three cases, IVUS showed an isoechoic-to-hyperechoic focal eccentric area at the posterior carotid bulb, consistent with CaW. The endoluminal protrusion was inconspicuous on IVUS due to the low resolution of ultrasound not allowing a clear differentiation between fibrosis, thrombosis, and atherosclerosis. No abnormalities commonly associated with atherosclerotic disease or dissections were noted. The CaW could not be depicted in the third patient.

Conclusion The use of IVUS in the diagnosis of CaW may have limited relevance. Continued investigation of other imaging modalities for accurate CaW diagnosis is recommended.

  • catheter
  • ultrasound
  • vessel wall
  • angiography
  • technology

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INTRODUCTION

A carotid web (CaW) is a shelf-like protuberance arising from the posterior wall of the internal carotid artery (ICA) bulb.1 CaWs have been associated with large territory ischemic stroke in the young, attributed to embolization from flow stasis/thrombosis within the CaW pocket.1 2 Histologic examination of excised symptomatic webs has noted fibrotic changes predominantly involving the intimal layer, and several authors have suggested a diagnosis of atypical fibromuscular dysplasia (FMD).3 The optimal treatment (antiplatelet or anticoagulation therapy, stenting, or surgery) for secondary prevention of CaW-associated stroke remains unknown.3 4

CaWs have been traditionally diagnosed with digital subtraction angiography (DSA),3 which provides excellent spatial and temporal resolution but is limitedto an endoluminal analysis. Non-invasive imaging techniques, including CT angiography (CTA),5 MRI and angiography (MRI/MRA), as well as Duplex ultrasonography have more recently been used to diagnose and characterize the arterial wall of CaWs.6 7 Despite the quality of these techniques, a definitive diagnosis of CaW may still be difficult to make.

Intravascular ultrasound (IVUS) was first introduced in the early nineties and developed as an adjunct for percutaneous coronary artery interventionsy.8 9 The unique capability of IVUS to deliver real-time endoluminal views has rendered this modality a gold-standard tool in cardiac imaging.10 11 It allows for the assessment of the degree of stenosis, the determination of extent/composition of plaques, the detection of dissection, plaque rupture, or thrombus,12 and can be used to evaluate stent expansion and strut apposition.8 Other studies report superiority of IVUS for the diagnosis of classic renal FMD relative to conventional angiography.13 14 The successful use of intravascular sonography in the coronaries has led to its application within the carotid arteries, but this practice has been very limited in scope. IVUS has been used to identify and characterize carotid artery aneurysms, dissections, and thrombi.15 In atheroscleoric disease, IVUS may reveal residual carotid stenosis post-angioplasty, superficial calcifications, plaque progression, regression, and ulceration.8 16

Here we present three cases of symptomatic CaW and assess the usefulness of IVUS as an adjunctive imaging tool in the evaluation of web morphology and composition.

Methods

This is a case series of patients with suspected CaW who underwent DSA for large vessel occlusion acute stroke therapy or work-up. After the investigation failed to identify alternative causes, the stroke etiology was ultimately attributed to a symptomatic CaW.

In each case, a guide catheter was parked in the common carotid artery (CCA), and the IVUS was navigated into the ICA over a microwire, and positioned distal to the carotid bulb. The IVUS was subsequently withdrawn through the level of the carotid bulb at a constant speed, allowing the reflected ultrasound waves to be processed, reconstructed into images displayed on a monitor, and recorded. This retrospective analysis was approved by the local Institutional Review Board.

Results

Case 1

A quinquagenarian patient with a history of hypertension, hyperlipidemia, and smoking presented with a left middle cerebral artery (MCA) stroke eleven hours after symptom onset. The National Institutes of Health Stroke Scale (NIHSS) score was 4. CTA head and neck showed a proximal left MCA occlusion and a lesion involving the left carotid bulb, which had no calcifications or superimposed thrombus. The patient underwent mechanical thrombectomy and DSA revealed a shelf-like filling defect in the carotid bulb, consistent with a CaW (figure 1). Following thrombectomy, the 9 Fr balloon guide catheter (BGC) was maintained in the CCA. The 018 IVUS probe (Volcano Corporation, San Diego, California, USA) was advanced over a Synchro-2 0.014 inch microwire (Stryker Neurovascular, Fremont, California, USA) under roadmap guidance into the mid-cervical ICA. The microwire was held in place and a manual IVUS pullback was performed. The morphology of the lesion was recorded and analyzed offline. The images demonstrated a thin isoechoic ridge/lesion at the posterior aspect of the carotid bulb, consistent with a CaW (figure 2). No other abnormalities associated with atherosclerosis were noted, such as echolucent areas, acoustic shadows (indicating calcium), fibrous caps, or plaque ulceration. The patient was started on antiplatelet monotherapy (aspirin) and has not experienced recurrent strokes at eight months of follow-up.

Figure 1

Case 1:(A) Lateral digital subtraction angiogram. (B) Post-processed oblique maximum intensity projection CT angiographic image of the lesion.

Figure 2

Case 1: Intravascular ultrasound findings. (A) Intravascular ultrasound (IVUS); (B) Axial cut of CT angiography (CTA) at the level of the carotid bifurcation; (C) Colored IVUS and (D) CTA depicting the carotid web (blue/continuous line). (D) CTA showing the external carotid origin (dotted white line), internal carotid origin (dotted red line), and carotid web pocket (red semi-circle).

Case 2

A quinquagenarian patient with a history of asthma and diabetes mellitus presented with a right MCA syndrome. NIHSS score was 12. CTA head showed an M1 occlusion. Initial read of the CTA neck failed to disclose abnormalities; no calcifications or thrombus were observed. The patient underwent mechanical thrombectomy and a shelf-like abnormality, consistent with CaW in the right carotid bulb, was noted. For further evaluation of the lesion, IVUS images were obtained. A 0.035 IVUS catheter (Volcano Corporation, San Diego, California) was advanced over two 0.014 inch microwires in a monorail fashion, and navigated to the mid cervical ICA through the BGC. Ultrasound images were acquired with a manual pullback of the IVUS probe over the lesion. Gray-scale images delineated an isoechoic-to-hyperechoic focal area/ridge at the posterior carotid bulb, consistent with an underlying CaW (figure 3). As with Case 1, no other features of atherosclerosis were observed. The patient was started on anticoagulation therapy with apixaban, and has not experienced recurrent strokes at six months of follow-up.

Figure 3

Case 2: Angiography and intravascular ultrasound (IVUS) findings. (A) Oblique maximum intensity projection CT angiogram showing the suspected carotid web. (B) Early and (C) late arterial phases of a lateral common carotid angiogram depicting a lesion at the posterior carotid bulb (A) with contrast stagnation (C). (D) IVUS showing a projectile lesion potentially indicating a carotid web (highlighted in E).

Case 3

A sexagenarian patient with a history of hypertension presented with a right MCA syndrome, last known well twelve hours prior. NIHSS score was 16. CTA revealed a proximal right M2 cut-off and bilateral proximal ICA abnormalities, concerning for CaW (Supplemental figure). No superimposed calcifications or thrombosis were noted. The patient was not deemed a suitable candidate for mechanical thrombectomy due to extensive early ischemic changes seen on CT. Five days after admission the patient underwent a diagnostic DSA for further evaluation. The angiogram confirmed bilateral cervical ICA shelf-like irregularities with contrast pooling rostral to the shelf, consistent with bilateral CaW (Supplemental figure). A 6 Fr Envoy guide catheter (Codman & Shurtleff, Raynham, Massachusetts) was advanced over a guidewire into the right common carotid. A high-definition IVUS catheter (Kodama HD IVUS, Ascist, Eden Prairie, Minnesota, USA) was advanced through the Envoy guide catheter over a 0.014 inch microwire, and placed in the mid-cervical right ICA. The IVUS probe was withdrawn. Extensive analysis of the acquired images was inconclusive. No abnormalities consistent with atherosclerosis were noted. The patient was started on dual antiplatelet therapy (aspirin and clopidogrel), and has not experienced recurrent strokes at five months of follow-up.

Discussion

A CaW is a radiologic entity, classically described as a thin, shelf-like endoluminal protrusion at the posterior wall of the carotid bulb on CTA, conventional angiography, MRA with gadolinium, or ultrasonography. These lesions are relatively rare and are often missed or misdiagnosed.3 Diagnostic certainty is further affected by variability in their appearance.

In this report we investigated the potential value of IVUS in complementing the imaging analysis of suspected CaW. The visual interpretation of IVUS relies on the inspection of acoustic reflections of different tissues and layers. The intimal layer of a normal vessel reflects brightly (hyperechoic), the media should be echolucent (hypoechoic), and the adventitia hyperechoic.17 Lipid should generate a hypoechoic (dark) appearance while fibrous (ie, CaW) or calcified tissues are relatively echogenic (calcium additionally causes acoustic shadowing).9 A previous study on fifteen CaWs found that these lesions were generally described as either isoechoic or hyperechoic on carotid ultrasonography.18

Studies that have used IVUS to diagnose renal FMD documented a variety of intraluminal abnormalities such as fibrous tissue bands obstructing the lumen, discrete eccentric ridges of tissue, mobile fluttering membranes, and spiral folds.13 14 19 In the present series involving patients with suspected CaW, the endoluminal protrusion was inconspicuous on IVUS imaging and did not allow for clear differentiation between thrombosis, atherosclerosis, or fibrosis. No abnormalities suggestive of atherosclerosis or medial/classic FMD were noted.

The evaluation may have been limited by several technical factors. Among the parameters affecting the sensitivity of the IVUS imaging are the frequency of the transducer, gain settings, depth of penetration, and focal depth.18 IVUS technology is liable to several inherent types of artifact that can adversely affect the images. Geometric distortion can result from imaging in an oblique (non-perpendicular) plane,20 21 and thus the orientation of the sonography probe within the lumen may have altered the appearance of the carotid wall. It is possible that the so-called lateral impulse response artifacts17 20 22 (which are prone to occur when the transducer is eccentrically placed) may have impacted the images and contributed to the appearance of lamellar pattern. 19 Overall, IVUS proved to be of limited value incharacterizing CaW morphology or wall structure.

A higher resolution imaging modality to evaluate the components of vascular microstructure could offer promise as a method to complement the diagnosis of CaW. Intravascular optical coherence tomography (OCT) represents an exciting technology for imaging vasculature with a resolution not previously attained with IVUS.23 24 OCT is analogous to ultrasound imaging, but it measures the amplitude of backscattered light, not sound, returning from a sample. Studies have shown OCT to have an axial resolution of 10–20 µm, while gray-scale IVUS has a resolution of 100–150 µm,25 giving OCT a 10-fold greater advantage in this regard. The frequency with which artifacts occur would likely be significantly reduced with a higher resolution. Recent studies using OCT have described its usefulness for renal FMD diagnosis and evaluation before and after percutaneous transluminal renal angioplasty26 due to its qualitatively superior delineation of vessel wall morphology. OCT also provides sufficient contrast between lipid, calcium, and fibrous tissue.24 A study using both IVUS and OCT in the coronary arteries reported that intimal thickness could be measured on all OCT images, but could not be identified by IVUS.27 Likewise, in another study the high resolution of OCT facilitated the identification of intimal hyperplasia, the internal and external elastic laminae, and echolucent regions, architecture that is difficult to discern with IVUS.24 Application of OCT technology to the carotid system has similarly yielded encouraging findings with studies reporting superior ability of OCT to visualize the near side of vessel luminal surface pathology, such as intraluminal thrombus or atherosclerotic fibrous cap disruption, and also plaque protrusion after stenting.28–30 From a technical perspective, one of the notable distinctions between IVUS and OCT would be the need to administer contrast media to acquire the high-definition images possible with OCT. However, the higher resolution provided by OCT may make this modality an attractive option to consider for CaW diagnosis.

Conclusions

The use of IVUS in the diagnostic imaging of CaW may have limited relevance. Continued a investigation of other imaging modalities for accurate CaW diagnosis is recommended.

References

Footnotes

  • Contributors SH: acquisition of data, drafting of the manuscript. RN: interpretation of data, critical revision of manuscript. ARA, RS, MM: data acquisition, critical revision of manuscript. DCH: study conception, design of the work, acquisition of data. All authors gave final approval of the version to be published, and are in agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests SH, ARA, RS, MM: none. DCH: Consultant for Stryker and Vesalio, Viz-AI (stock options). RN: Principal Investigator, Stryker Neurovascular (DAWN trial (no compensation), Trevo‑2 trial), Cerenovus/Neuravi (ENDOLOW trial, no compensation); consultant to Stryker Neurovascular; steering committee member, Stryker Neurovascular (no compensation), Medtronic (SWIFT trial, SWIFT Prime trial, no compensation), Cerenovus/Neuravi (ARISE‑2 trial, no compensation); angiographic core lab, Medtronic (STAR trial); executive committee mem­ber, Penumbra (no compensation); Physician advi­sory board, Cerenovus/Neuravi, Phenox, Anaconda, Genentech, Biogen, Prolong Pharmaceuticals, Allm Inc (no compensation), Viz-AI; stock options.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.