Original Article
Evaluation of non-stenotic carotid atherosclerotic plaques with combined FDG-PET imaging and CT angiography in patients with ischemic stroke of unknown origin

https://doi.org/10.1007/s12350-020-02511-8Get rights and content

Abstract

Objectives

Non-stenotic plaques are an underestimated cause of ischemic stroke. Imaging aspects of high-risk carotid plaques can be identified on CT angiography (CTA) and 18F-fluoro-deoxyglucose positron emission tomography (FDG-PET) imaging. We evaluated in patients with cryptogenic ischemic stroke the usefulness of FDG-PET-CTA.

Methods

44 patients imaged with CTA and FDG-PET were identified retrospectively. Morphological features were identified on CTA. Intensity of FDG uptake in carotid arteries was quantified on PET.

Results

Patients were imaged 7 ± 8 days after stroke. 44 non-stenotic plaques with increased 18F-FDG uptake were identified in the carotid artery ipsilateral to stroke and 7 contralateral. Most-diseased-segment TBR on FDG-PET was higher in artery ipsilateral vs. contralateral to stroke (2.24 ± 0.80 vs. 1.84 ± 0.50; p < .05). In the carotid region with high FDG uptake, prevalence of hypodense plaques and extent of hypodensity on CTA were higher in artery ipsilateral vs. contralateral to stroke (41% vs. 11%; 0.72 ± 1.2 mm2 vs. 0.13 ± 0.43 mm2; p < .05).

Conclusions

In patients with ischemic stroke of unknown origin and non-stenotic plaques, we found an increased prevalence of high-risk plaques features ipsilateral vs. contralateral to stroke on FDG-PET-CTA imaging suggesting a causal role for these plaques.

Introduction

In up to 40% of patients presenting with ischemic stroke, no definite cause can be established despite extensive work-up.1,2 Non-stenotic complicated carotid atherosclerotic plaques might represent an underestimated cause of ischemic stroke.3, 4, 5 Accurate identification of complicated atherosclerotic plaques causing ischemic stroke is crucial because the prevalence of non-stenotic carotid plaques is high in the population. Culprit carotid lesions have several morphological and biological features that can be identified with non-invasive imaging.6, 7, 8, 9, 10, 11, 12 On CT angiography (CTA), the presence of hypodense regions (< 30 Hounsfield units) or ulcerations have been associated with complicated carotid plaques 13, 14, 15, 16 defined according to the American Heart Association as type VI (AHA-LT6) carotid plaques, characterized by intraplaque hemorrhage (IPH), thrombus, or a ruptured fibrous cap. However, these features lack sensitivity.14 18F-Fluorodeoxyglucose (FDG), a glucose-analogue radiolabeled for positron emission tomography (PET) imaging has demonstrated its value for the non-invasive detection of high metabolic activities in activated macrophages. Strong relationships have been documented between the degree of arterial 18F-FDG uptake and the density of macrophages determined histologically in carotid plaques.17,18

The aim of our study was to investigate, in patients with ischemic stroke of unknown origin and large non-stenotic carotid plaques on CTA, the value of combined morphological (CTA) and functional (FDG-PET) imaging to assess the existence of complicated plaques.

Section snippets

Patient Selection

A total of 188 patients with acute ischemic stroke of unknown origin admitted to the Neurology Department of Bichat University Hospital between 2011 and 2016 were referred for FDG-PET imaging. After excluding patients with absence of carotid plaque on CTA (n = 106, 56.3%) and patients with active vasculitis on FDG-PET imaging (n = 38, 20.2%), 44 patients with large (≥ 3 mm thickness) non-stenotic (< 50% stenosis based on the North American Symptomatic Carotid Endarterectomy Trial - NASCET)

Population of the Study

A total of 44 patients (mean age: 67 ± 15 years; 34% female) with recent acute ischemic stroke of unknown cause were included in the study. Median time between the event and imaging was 7 ± 8 days (1-15 days). Cardiovascular risk factors and patients’ treatment at the time of imaging are displayed in Table 1.

Plaque Characteristics with FDG-PET-CTA

A total of 51 non-stenotic plaques with increased 18F-FDG uptake were detected in carotid arteries of the 44 patients: 44 ipsilateral to the stroke, and additionally contralateral to the

Discussion

In this study, we evaluated retrospectively in a cohort of patients with ischemic stroke of unknown origin the characteristics of non-stenotic carotid plaques on FDG-PET-CTA. We took advantage of FDG-PET imaging to identify hotspots along carotid arteries susceptible to contain culprit lesions and then looked in these hotspots if non-stenotic atherosclerotic plaques with hypodense regions were present on CTA. We found a higher intensity of FDG uptake in the carotid artery ipsilateral to the

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    Pierre Amarenco and Fabien Hyafil Contributed equally / Shared.

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