Ischemia after Carotid Endarterectomy: Comparison between Transcranial Doppler Sonography and Diffusion-Weighted MR Imaging
Martin Müller
,a,
Werner Reichea,
Philipp Langenscheidta,
Jens Haßfelda and
Thomas Hagena
a From the Departments of Neurology (M.M., J.G.), Neuroradiology (W.R., T.H.), and Surgery (P.L.), University Hospital of the Saarland, Homburg/Saar, Germany.
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FIG 1. The TCD device provides two sample volumes for insonation of the MCA. An embolus streaming down the MCA will be recorded first in the proximal sample volume (depth of insonation, 57 mm [D57]) and with a time delay in the distal sample volume (depth of insonation, 52 mm [D52]). Next to the color-coded decibel scale, the Doppler velocity spectrum after fast Fourier transformation (FFT) of each sample volume is shown. The blood flow direction in both sample volumes is indicated in the proximal sample volume beneath D57 by an arrow directed toward the probe symbol ([), which means that the velocity spectrum of the blood flow in the MCA usually directed toward the probe is imaged above the zero line; the background velocity spectrum can be seen more clearly in the distal sample volume as a band with a signal intensity of 9 to 15 dB (colored slightly blue to green). The signal of the embolus after FFT is overloaded, as indicated by its bidirectional appearance
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FIG 2. A–D, Pre- and postoperative T2-weighted images (A and C) and DWIs (B and D) of a patient in whom a territorial infarct was present on the postoperative images. The small white matter lesions on the preoperative T2-weighted (4000/99/3) image (A) are not present on the preoperative DWI (B) (episequence; 123/1 [TE/excitations]). The corresponding postoperative T2-weighted image (C) and DWI (D) show a medium-sized territorial infarct on the left side, and a small new lesion in the head of the caudate nucleus on the right side. This patient underwent surgery for a tight left-sided stenosis associated with occlusion of the contralateral internal carotid artery
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FIG 3. A–C, Pre- and postoperative images of a patient who had had an episode of amaurosis fugax. The preoperative DWI (A) shows no signal abnormality. The postoperative DWI (B) shows a small cortical lesion in the distribution of the posterior branches of the MCA; on the postoperative T2-weighted image (C), this lesion (arrow) can be seen only in light of the findings on the DWI
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FIG 4. A–D, Pre- and postoperative images of a patient who underwent carotid endarterectomy 14 days after the clinical event. The preoperative T2-weighted (A) and DWI (B) studies show four small cortical lesions and one subcortical lesion (arrow, B). The cortical lesions cannot be detected on the corresponding postoperative DWI (D). The subcortical lesion is still present, but there is a new, smaller territorial infarction nearby as shown on the T2-weighted (C) and DWI (D) studies. These findings may suggest that cortical lesions disappear sooner than subcortical lesions, probably because of the better collateral blood flow in cortical regions as compared with subcortical regions
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FIG 5. A–C, Preoperative CT scan (A) of a patient with an asymptomatic tight stenosis of the right internal carotid artery. In the right parasagittal area, the slight leukoencephalopathy is one aspect of the coincident microvascular disease, which is more clearly present on the other CT sections (not shown). Postoperatively, an infarct in the right precentral gyrus is seen on the axial T2-weighted (B) and DWI (C) studies
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