Sonographic Findings in Dissection of Extracranial Brain‐Supplying Arteries

Report entitled “Serial Transoral Carotid Ultrasonographic Findings in Extracranial Internal Carotid Artery Dissection” Yakushiji et al.1 In this article, the authors highlight the importance of early diagnosis in extracranial internal carotid artery dissection. They report a case of transient ischemic attack detected clearly with transoral carotid ultrasonography (TOCU) in the early stage of extracranial internal carotid artery dissection. The transoral approach is not frequently applied. The article by Yakushiji et al makes a valuable contribution, especially with regard to obtaining more diagnostic reliability in cases with flow obstruction in the distal extracranial segment of the internal carotid artery below the C1 to C2 vertebral level. Although we do not presently use this technique, we agree with the authors that this approach can be considered, especially if the pathologic findings cannot be imaged directly with extracranial ultrasonography. The reason for this letter is that we would like a clarification of the term “false lumen” used in this report and also in the figures legends. On the basis of our serial examinations of patients with dissection of the extracranial vertebral artery, we suggest the possibility that the structure that was described as a “false lumen” was more likely an “intramural hematoma.” The characteristic ultrasonographic features of a dissection can vary from minor lesions (irregularities and thickening of the vessel wall with a hypoechoic intramural hematoma and/or narrowing of the lumen without hemodynamic alterations) to major structural lesions such as a severe stenosis or occlusion (Figure 1). The vessel lumen may contain hypoechoic structures of varying echogenicity; sometimes it is possible to image a dissecting membrane, which separates the lumen into a trueand false-perfused lumen.2 An intramural hematoma appears in the acute stage as a hypoechoic structure but becomes more echogenic in the further course (Figure 1, A and C). Just such features were also described in the suspected area of a dissection in the article by Yakushiji et al. In contrast, a typical characteristic of a false lumen is that this structure is perfused with blood (ie, a color-coded signal as well as the Doppler signal can be detected in the false lumen of the artery; Figure 1B). This is not visible in the figures shown by Yakushiji et al. The recovery in the size of the true lumen and the normalization of the peak systolic velocity on the affected side would also favor our notion that the intramural hematoma was slowly reabsorbed. This interpretation might have been verified by magnetic resonance imaging (MRI) with a fat suppression technique,