Use of intravascular optical coherence tomography to confirm the diagnosis of a carotid web in a patient with recurrent ipsilateral embolic strokes and evaluate the response to stenting

Abstract

A Carotid web (CaW) is defined as a focal shelf-like projection of non-atheromatous, fibrous tissue along the posterior wall of the carotid bulb. CaW are rare and commonly overlooked lesions increasingly recognized as a cause of stroke in otherwise healthy patients. Intravascular imaging modalities such as intravascular ultrasound and optical coherence tomography (OCT) have been proposed as an adjunct to digital subtraction angiography for the evaluation of CaW. However, the use of OCT in CaW has yet to be described. This report investigated the utility of OCT as an adjunct imaging modality in the evaluation of CaW morphology in a young patient with recurrent ischemic strokes.

Introduction

A Carotid web (CaW) is a rare non-atheromatous, focal shelf-like projection of fibrous tissue involving the posterior intimal wall of the carotid bulb. CaW is associated with embolic ipsilateral ischemic strokes secondary to flow stasis and subsequent thrombosis within the CaW pocket. ¹ CaW are commonly overlooked in otherwise young healthy patients with embolic strokes of undetermined source. ² Definitive diagnosis on non-invasive imaging modalities is often delayed due to the rarity and variable appearance of CaW. Intravascular imaging modalities such as intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have been proposed as an adjunct to digital subtraction angiography (DSA) for the evaluation of carotid web. Although IVUS has shown limited utility in the diagnosis of CaW, the use of OCT in CaW has yet to be described. ³ In this report, we investigated the utility of OCT as an adjunct imaging modality in the evaluation of CaW morphology and composition in a young patient with recurrent ischemic strokes. Informed consent was provided by the patient.

Case report

A 43-years-old female non-smoker with a history of recurrent right hemispheric strokes presents for a comprehensive work-up of cryptogenic strokes. The patient had three separate right middle cerebral artery (MCA) territory infarcts commencing at 36 years of age. The first stroke was seven years before presentation and shortly after starting oral contraceptive pills. Given hyperdense MCA sign and possible thrombophilic status, this was deemed embolic in origin and managed with dual antiplatelet agents (Figure 1). The second MCA stroke was three years before presentation despite anticoagulation. Workup at that time revealed a very small patent foramen ovale which was repaired. The third stroke, occurring one month prior to presentation, was complicated by hemorrhagic conversion while on dual antiplatelet therapy. A concurrent right M1 segment occlusion was identified with every ischemic event. Partial recanalization of the presumed embolic M1 occlusions was seen on surveillance MRA in between ischemic events. Retrospective review of neck MRA identified a possible subtle CaW. DSA demonstrated a subtle shelf-like protrusion in the right carotid bulb with significant contrast stagnation within the carotid bulb (Figure 1).

Figure 1.

(A) axial diffusion restriction MRI showing the first ischemic event involving the right insular in the setting of (B) a dense right MCA sign (arrow) on head CT and (C) confirmed occlusion on 3D reconstruction of brain MRA. (D) Initial 3D reconstruction of neck MRA identified a right carotid bulb protrusion (arrow). (E) Lateral right common carotid artery injection showing the CaW (arrow) with (F) significant contrast stasis in the bulb on the late phase (arrow).

Intravascular OCT investigation of the carotid bulb lesion was performed using a 2.7F Dragonfly OCT imaging catheter (Abbott) under complete flow arrest OCT images demonstrated a focal area of intimal fibrous hyperplasia corresponding with the shelf-like protrusion on DSA which confirmed the diagnosis of CaW (Figure 2); no evidence of intramural thrombus or atherosclerosis were seen. The patient was treated with a Carotid Wallstent (Boston Scientific, California, USA) to outwardly displace the CaW against the vessel wall, thereby reducing turbulent flow and stagnation responsible for thrombus formation (Video 1). Control DSA and OCT images demonstrated collapse of the CaW against the vascular wall and satisfactory stent wall apposition (Figure 3). The patient was discharged home on dual antiplatelet agents and remained asymptomatic over 3 months of follow-up.

Figure 2.

(A) baseline lateral right common carotid artery injection with the corresponding OCT cross sectional images: (B) internal carotid artery, (C & D) carotid bulb, and (E) common carotid artery. A hyperdense vessel wall protrusion corresponding with the CaW on DSA was seen at levels C & D.

Figure 3.

(A) control lateral right common carotid artery injection and corresponding cross sectional OCT images following stent deployment showing (C & D) collapse of the CaW by the outward radial force exerted by the stent.

Discussion

CaW is a focal, nonatherosclerotic disease involving the extracranial carotid vasculature. Histopathological analysis of surgically resected CaW demonstrated intimal fibromuscular hyperplasia, with some classifying CaW as a focal variant of fibromuscular dysplasia.^4,5 CaW are rare lesions, historically overlooked or simply misdiagnosed. ⁵ However, more recently, CaW has been increasingly recognized as a cause of stroke in young patients with cryptogenic strokes. ¹

Detection of CaW is influenced by the imaging modality. DSA is widely accepted as the gold standard modality for diagnosis of CaW. Non-invasive vascular imaging, namely CT angiography (CTA), has demonstrated comparable performance to DSA for the diagnosis of CaW. ⁶ The spatial resolution of DSA, though superior to CTA, is limited to endoluminal analysis, lacking direct morphological vessel wall analysis. Intravascular imaging modalities have been proposed as an adjunct to DSA for the diagnosis of suspected CaW. However, the 100–150 μm spatial resolution IVUS is insufficient for diagnosis of CaW, having recently failed to adequately differentiate between atherosclerosis, CaW, and thrombus. ³ OCT provides superior intravascular images with a 10-fold increase in spatial resolution (10–20 μm) resolution by measuring the reflection of near-infrared light. ⁷ The diagnostic accuracy of OCT has been validated through extensive histological analysis in human specimens. ⁸ In coronary vessels, OCT can differentiate between lipid, fibrotic tissue and calcium, eliminating the characteristic calcium shadowing seen with IVUS.^9,10 OCT can reliably identify thin cap fibroatheroma and fibrotic atheromas in carotid artery plaques. ⁷

In this report, we demonstrate the utility of OCT as an adjunct to DSA to confirm the diagnosis of suspected CaW. The CaW was clearly demonstrated on OCT as an endoluminal protrusion corresponding with a “shelf” seen on DSA. The fibrotic appearance of the vessel wall protrusion on OCT helped confirm the diagnosis of a CaW. In addition, OCT demonstrated the ability of radially expanding stents to collapse the web against the vascular wall to decrease flow stagnation. Notwithstanding the high-resolution imaging provided by OCT, it does come with its limitations. Firstly, it is restricted in its depth of view, due to the excessive scattering of light by tissues, which reduces the depth of field to approximately 2 mm. Second, at a clinical level this technology has a circumferential field of view <10mm, resulting in incomplete visualization of large vessels. Thirds, the use of OCT generally requires complete arrest of blood flow through the vessel as blood attenuates the emitted light and hinders image acquisition. Fourth, OCT is subject to extensive artifacts and the identification of subtle findings such as CaW requires expertise. Fifth, OCT is a side-viewing device where post-processed images are generated from rotational pullbacks after crossing potentially unstable lesions. Therefore, the benefits of confirming the diagnosis with this tool must be carefully balanced to the risks of obtaining the images. Finally, as of this publication, the use of OCT in the carotid artery is considered off-label, limiting use to investigational purposes.

Conclusion

Intravascular OCT is a useful adjunct in the diagnosis and treatment of suspected carotid webs.