Ipsilateral plaques display higher T1 signals than contralateral plaques in recently symptomatic patients with bilateral carotid intraplaque hemorrhage

Abstract

Background and aims: Prospective studies have shown a strong association between carotid intraplaque hemorrhage (IPH), detected by magnetic resonance imaging (MRI), and cerebrovascular ischemic events. However, IPH is also observed in a substantial number of asymptomatic patients. We hypothesized that there are differences in the characteristics of IPH+ plaques associated with recent symptoms, compared to IPH+ plaques not associated with recent symptoms.

Methods: Patients with recent (≤2 weeks) anterior circulation ischemic events were scanned using a standardized multisequence protocol. Those showing IPH bilaterally were included and analyzed for differences in T1/T2 signals, plaque morphology, and coexisting plaque characteristics between the ipsilateral symptomatic and contralateral asymptomatic sides.

Results: Thirty-one subjects (67 ± 9 years, 97% males) with bilateral IPH were studied. Despite comparable luminal stenosis (53 ± 42% vs. 53 ± 39%, p = 0.99), T1 signal of IPH measured as signal-intensity-ratio compared to muscle was stronger (SIR_{IPH-to-muscle}: 5.8 ± 2.4 vs. 4.7 ± 1.8, p = 0.004) and tended to be more extensively distributed (IPH volume: 150 ± 199 vs. 88 ± 106 mm³, p = 0.071) on the symptomatic side. IPH+ plaques on the symptomatic side were longer (24 ± 6 vs. 21 ± 7 mm, p = 0.026) and associated with larger necrotic core volume (406 ± 354 vs. 291 ± 293 mm³, p = 0.039) than those on the asymptomatic side.

Conclusions: In recently symptomatic patients with bilateral carotid IPH, the symptomatic side showed stronger T1 signals, larger necrotic cores, and longer plaque length than the asymptomatic side. Serial studies on the temporal relationship between these imaging features and clinical events will eventually establish their diagnostic and prognostic value beyond the mere presence of IPH.

Keywords: Carotid artery; Ischemic stroke; Magnetic resonance imaging; Plaque progression.

Fig. 1. Subject with bilateral IPH+ plaques

The slice with the highest T1 signal intensity is shown between the (A) symptomatic and (B) asymptomatic side (SIR_{IPH-to-muscle}: 7.9 vs. 5.2). Original and segmented images are shown. Carotid plaques are delineated by lumen (red) and outer wall (azure) contours. Bilateral plaques demonstrate large necrotic core, IPH (red arrows), and thin fibrous cap (yellow arrows). Necrotic core is detected as non-calcified hypointense areas on T2W (yellow contours). IPH is detected as hyperintense areas on MPRAGE (orange contours). Fibrous cap (not contoured) is by definition the region between necrotic core and carotid lumen and considered thin on both sides as it is partially invisible on T2W. MPRAGE indicates magnetization-prepared rapid acquisition gradient echo; SIR, signal-intensity-ratio; T1W, T1-weighted; T2W, T2-weighted; TOF, time-of-flight.

Fig. 2. Subject with bilateral ulcerated plaques

Surface ulceration, identified as distinct surface depression (white arrows), is present on both the (A) symptomatic and (B) asymptomatic side. Original and segmented images are shown. Carotid plaques are delineated by lumen (red) and outer wall (azure) contours. Bilateral plaques demonstrate remnant necrotic core (yellow), IPH (orange), and ulceration (violet red). There is also a small calcification (dark blue) on the symptomatic side. Abbreviations as in Fig. 1.

Fig. 3. Differences between IPH+ plaques ipsilateral and contralateral to clinical symptoms

The symptomatic side demonstrates (A) stronger T1 signals, (B) longer plaque length, and (C) larger lipid core volume than the asymptomatic side. Short horizontal lines on the line charts indicate mean values.