Exclusion of echo-lucent plaque using superb micro-vascular imaging: A case report

Background: In the carotid bulb (CB), the vascular morphology can cause a decrease in blood flow velocity near the vessel wall. In addition, the CB is a common site for plaque formation. Particularly, echo-lucent plaques (ELPs) are known to pose a risk for cerebral embolism, requiring careful attention. In carotid ultrasonography (CU), ELPs may be difficult to distinguish from blood flow within the vessel using only B-mode imaging; thus, the use of color Doppler imaging (CDI) is recommended. However, when blood flow is extremely slow, even CDI may fail to differentiate between ELPs and the flow. We encountered a case where superb micro-vascular imaging (SMI) successfully detected extremely low-velocity blood flow, thereby excluding the presence of an ELP that CDI could not discern.

Case description: A 64-year-old male with a history of smoking, hyperlipidemia, and percutaneous coronary intervention for myocardial infarction presented for an atherosclerosis screening. CU with CDI indicated a lesion showing a flow void near the wall of the CB, raising suspicions of significant blood flow stasis or the presence of an ELP or thrombus. He had no neurological findings or carotid bruits. A head magnetic resonance imaging revealed no findings suggestive of cerebral embolization. Using SMI during additional CU, we detected extremely low-velocity blood flow near the wall of the CB, allowing us to exclude an ELP.

Conclusion: When a flow void is observed with CDI in CU, and it is difficult to differentiate between an ELP and extremely low-velocity blood flow, the application of SMI can sometimes detect the extremely low-velocity blood flow. This approach may help avoid invasive examinations such as CU with contrast agents or cerebral angiography.