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ReplyLetter

Reply:

C. Zhu, X. Tian, A.J. Degnan, J. Lu and Q. Liu
American Journal of Neuroradiology January 2019, 40 (1) E2; DOI: https://doi.org/10.3174/ajnr.A5895
C. Zhu
aDepartment of Radiology and Biomedical Imaging University of California, San Francisco San Francisco, California
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X. Tian
bDepartment of Radiology Changhai Hospital Shanghai, China
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A.J. Degnan
cDepartment of Radiology Children's Hospital of Philadelphia Philadelphia, Pennsylvania
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J. Lu
dDepartment of Radiology Changhai Hospital Shanghai, China
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Q. Liu
dDepartment of Radiology Changhai Hospital Shanghai, China
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We thank Drs Yuan and Sun for their interest in our article1 and their group's recent work on intraplaque hemorrhage (IPH) in carotid plaque.2 While IPH is validated as a high-risk plaque feature in extracranial carotid artery plaque3 due to facile histologic validation from endarterectomy specimens, our current understanding of the role of IPH in intracranial atherosclerotic plaque vulnerability assessment is limited. The characterization of intracranial plaque features by in vivo imaging remains challenging due to the small plaque size and impracticality of histologic validation. The definition of T1-weighted hyperintense signal suggestive of IPH as >150% signal relative to the nearby medial pterygoid muscles on precontrast T1-weighted imaging used in our study was adopted from previous carotid studies and supported by initial studies of IPH within the middle cerebral artery.4

Intracranial IPH is increasingly recognized as a harbinger of elevated stroke risk,5 and our study adds to the literature concerning basilar artery plaque in showing an association with stroke risk independent of the degree of stenosis. We appreciate Drs Yuan and Sun's suggestions on the discussion of imaging sequences for improving the accuracy of intracranial IPH detection. The use of different TR/TE parameters or inversion pulses can alter image contrast, which may partially explain the heterogeneity of prior study results. Histologic validation is preferred to standardize imaging approaches; however, it has practical challenges in intracranial atherosclerotic plaque, which cannot be obtained in vivo. An alternative practical approach to standardize sequences for clinical detection of IPH could be to use phantoms with different T1 values; this method needs to be explored further. In addition, recent studies have increasingly used 3D high-resolution fast spin-echo sequences (sampling perfection with application-optimized contrasts by using different flip angle evolution [SPACE] sequence, Siemens, Erlangen, Germany; CUBE, GE Healthcare, Milwaukee, Wisconsin; or volume isotropic turbo spin-echo acquisition [VISTA], Philips Healthcare, Best, the Netherlands) for intracranial plaque imaging. IPH detection should be used with caution because the long echo-train (>30) induces considerable T2-weighting,6 which alters contrast from traditional 2D T1-weighted fast spin-echo or gradient-echo sequences.

In our study, the degree of stenosis was not associated with stroke symptoms, and the prevalence of IPH was comparable in low- and high-grade stenoses. This finding may reflect IPH as an independent risk factor for stroke symptoms in basilar artery plaque, though the limited sample size in a single-center population could introduce sampling error. Nonetheless, these data highlight the importance of basilar artery IPH even in low-grade stenosis as potentially leading to stroke. High-risk plaque in intracranial arteries with <50% stenosis7 has been recognized as a potential cause of cryptogenic stroke, and identifying these high-risk features, including IPH, may improve the management of these patients. Nonetheless, we agree with Drs Yuan and Sun that both IPH and plaque enhancement should be studied further in a prospective, longitudinal study to better understand potential imaging-related independent risk factors that may predict stroke.

References

  1. 1.
    1. Zhu C,
    2. Tian X,
    3. Degnan AJ, et al
    . Clinical significance of intraplaque hemorrhage in low- and high-grade basilar artery stenosis on high-resolution MRI. AJNR Am J Neuroradiol 2018;39:1286–92 doi:10.3174/ajnr.A5676 pmid:29794236
  2. 2.
    1. Wang X,
    2. Sun J,
    3. Zhao X, et al
    ; CARE-II study investigators. Ipsilateral plaques display higher T1 signals than contralateral plaques in recently symptomatic patients with bilateral carotid intraplaque hemorrhage. Atherosclerosis 2017;257:78–85 doi:10.1016/j.atherosclerosis.2017.01.001 pmid:28110259
  3. 3.
    1. Saam T,
    2. Hetterich H,
    3. Hoffmann V, et al
    . Meta-analysis and systematic review of the predictive value of carotid plaque hemorrhage on cerebrovascular events by magnetic resonance imaging. J Am Coll Cardiol 2013;62:1081–91 doi:10.1016/j.jacc.2013.06.015 pmid:23850912
  4. 4.
    1. Turan TN,
    2. Bonilha L,
    3. Morgan PS, et al
    . Intraplaque hemorrhage in symptomatic intracranial atherosclerotic disease. J Neuroimaging 2011;21:e159–61 doi:10.1111/j.1552-6569.2009.00442.x pmid:19909397
  5. 5.
    1. Yu JH,
    2. Kwak HS,
    3. Chung GH, et al
    . Association of intraplaque hemorrhage and acute infarction in patients with basilar artery plaque. Stroke 2015;46:2768–72 doi:10.1161/STROKEAHA.115.009412 pmid:26306752
  6. 6.
    1. Zhu C,
    2. Haraldsson H,
    3. Tian B, et al
    . High resolution imaging of the intracranial vessel wall at 3 and 7 T using 3D fast spin echo MRI. MAGMA 2016;29:559–70 doi:10.1007/s10334-016-0531-x pmid:26946509
  7. 7.
    1. Cho HJ,
    2. Kim KH,
    3. Kim EJ, et al
    . Clinical implications of basilar artery plaques in the pontine infarction with normal basilar angiogram: a high-resolution magnetic resonance imaging study. J Stroke Cerebrovasc Dis 2018 Sep 12. [Epub ahead of print] doi:10.1016/j.jstrokecerebrovasdis.2018.08.032 pmid:30219629
  • © 2019 by American Journal of Neuroradiology
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