Transcranial color-coded duplex sonography for detection of distal internal carotid artery stenosis

BACKGROUND AND PURPOSE: Gradation of high-grade intracranial internal carotid artery (ICA) stenosis poses a challenge to noninvasive neurovascular imaging, which seems critical for angioplasty in the ICA segments C1 and C5. We investigated cutoff values of intracranial ICA stenosis for transcranial color-coded sonography (TCCS) and compared this method with the “gold standard,” digital subtraction angiography (DSA).Materials and METHODS: Forty patients (mean age, 58.9 ± 13.8 years) with intracranial ICA lesions were prospectively examined by using TCCS and DSA. Two standard TCCS coronal imaging planes were used to evaluate the intracranial ICA. In addition, a control group of 128 volunteers without cerebrovascular disease (mean age, 48.8 ± 15.9 years) was investigated to establish standard velocity values.RESULTS: DSA confirmed 96 stenoses and 8 occlusions of the intracranial ICA in the study population. In 9% and 7% of cases, stenosis confined to the C1 or C5 segment was >50% and 70%, respectively. Receiver-operating curves demonstrated cutoff values for >70% stenosis in C1 when the peak systolic velocity (PSV) was >200 cm/s (specificity, 100%; sensitivity, 71%) or the C1/submandibular ICA index was >3 (specificity, 93%; sensitivity, 86%).CONCLUSIONS: TCCS is a reliable adjunctive method to detect and quantify significant stenosis of the intracranial ICA. The assessment of the C1/ICA index and peak systolic velocities maximizes the diagnostic accuracy of C1 stenosis to >70% when extracranial ICA stenosis coexists. Further studies need to be performed to compare the diagnostic accuracies of MR angiography and TCCS with that of DSA.

Detection of atherosclerotic narrowing of intracranial cerebral arteries is important in stroke management and aids in the identification of patients with high risk for vascular events.^1–3 Ischemic stroke due to atherosclerosis of intracranial large arteries has been reported in approximately 8%–29% of adults in general, with a higher prevalence in African and Asian populations.^4–6 The intracranial internal carotid artery (ICA) is the most common location for intracranial stenosis of >50%; such cases compose up to 49% of all intracranial artery stenoses.^1,7 Patients with severe (≥70%) intracranial stenosis have a higher risk of stroke than patients with moderate (50%–69%) intracranial stenosis.⁸ Treatment of significant stenosis relies on antiplatelet and antithrombotic agents as well as on aggressive lipid-lowering therapies.^9,10 Endovascular treatments involving angioplasty for 50%–99% ICA stenosis have also been applied but are considered experimental approaches in need of validation by controlled studies.^11–13Because the course of intracranial ICA is complicated due to its tortuosity and variability, classification of this portion of the vessel may differ between authors,^14–16 in turn complicating interpretation of the data. The “gold standard” used to assess the intracranial ICA remains digital subtraction angiography (DSA). DSA is usually performed only after noninvasive imaging procedures, such as MR angiography (MRA) and, to a lesser degree, conventional transcranial Doppler (TCD) sonography, have suggested intracranial stenosis. With TCD sonography, intracranial ICA stenosis is considered when flow velocities exceed normal values and/or exhibit abnormal flow patterns. Unlike cases of extracranial ICA disease, stenosis gradation of the intracranial ICA has not been calculated.^17,18 With MRA, intracranial ICA stenosis in the C5 as well as the C3 and C1 segments is frequently indicated by flow-void artifacts, especially when using time-of-flight sequences, because of the inherent signal-intensity loss of parallel imaging, which can only be compensated in part by the use of MR imaging contrast agents.¹⁹ Due to these MRA artifacts, calculation of ICA stenosis gradation is difficult, and semiquantitative scales, rather than percentages of stenosis, are frequently used to describe the lesion.²⁰Although the criteria for detecting significant (>50%) stenosis of basal cerebral arteries has been defined for transcranial color-coded sonography (TCCS),^21–24 little data can be found on grading intracranial ICA stenosis. The aim of this study was to elaborate the TCCS criteria for detection and quantification of significant intracranial ICA stenosis and to correlate them with conventional DSA criteria as the standard of reference.