Diagnostic ultrasound ( PDFDrive )

920 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
collagen-rich matrix. 56,57 In vulnerable/ruptured plaques, the
ibrous cap has thinned, exhibiting fewer vascular smooth muscle
cells, decreased collagen, and increased inlammatory cells.
Heterogeneous plaque has been suggested as unstable and
vulnerable, in contrast to homogeneous plaque. Some have
suggested that environmental factors and toxins cause abnormal
low patterns, damaging the internal structure of the vessels. 58
his can lead to intimal proliferation and potential wall ischemia
and the degradation of the vasa vasorum. 58 Because the vasa
vasorum do not have a muscular media, these vessels are subsequently
at risk to rupture, perhaps leading, in part, to intraplaque
hemorrhage. 58 Others have suggested that a bacterial infection
etiology may play a role in inlammatory angiogenesis. 58
Recently, several groups have demonstrated that microRNAs
play a key role in the development and thinning of the ibrous
cap. 59-69 MicroRNAs are a class of noncoding RNAs (ncRNAs)
that are approximately 21 nucleotides in length and are potent
efectors of gene expression, doing so by binding to messenger
RNA and inhibiting protein translation. A role for ncRNA in
cardiovascular diseases is emerging, including microRNAs
(miRNAs) and their inhibition by circular RNA (circRNAs).
MicroRNA-221 and microRNA-222 (miR-221/miR-222) are short
ncRNAs that inhibit the expression of the cyclin-dependent kinase
inhibitor p27 Kip1 , promoting vascular smooth muscle cell proliferation
and intimal thickening. Bazan et al. recently demonstrated
an important role for the downregulation of miR-221/222 in the
shoulder region of carotid plaques shortly ater rupture 70 through
increased p27 Kip1 and propose that vascular smooth muscle cell
volume is lost, leading to intimal thinning.
Ultrasound Plaque Classiication System
Plaque texture is generally classiied as homogeneous or heterogeneous.
14,38,41,45,46,48-50,71-75 he accurate evaluation of plaque can
only be made with gray-scale ultrasound, without the use of
A
B
C
D
FIG. 26.7 Spectrum of Patterns of Homogeneous Plaque. (A) Sagittal and (B) transverse images show homogeneous plaque in left common
carotid artery (type 4). Note the uniform echo texture. (C) Sagittal and (D) transverse images show homogeneous plaque in proximal left internal
carotid artery (type 3). Note the focal hypoechoic area within the plaque, estimated at less than 50% of plaque volume.