Transcranial and Cervical Ultrasound in Stroke

Introduction

Transcranial Doppler ultrasound (TCD), or transcranial color-coded sonography (TCCS) and duplex ultrasound of extracranial brain supplying vessels are noninvasive methods that can be used at bedside for neurovascular examination ( Fig. 133.1 ). Ultrasound is the safest vessel imaging method that also allows repeated assessments and real-time monitoring. Brightness-mode (B-mode) display has been in clinical use for over four decades to evaluate the vessel wall and plaques in the extracranial arteries. In addition to color flow imaging, spectral Doppler depicts a waveform containing information about velocity, resistance, flow direction vasomotor responses, and presence of emboli .

In many countries, early examination of intracranial arteries is part of benchmarking parameters of an effective acute stroke treatment. With the increasing use of mechanical thrombectomy, there is a trend to perform imaging of cerebral arteries in most acute stroke patients using computed tomography angiography (CTA) or magnetic resonance angiography (MRA). These two modalities of vessel imaging are not often available worldwide on a 24/7 basis. CTA and MRA do not provide information about lesion morphology and real-time hemodynamic information. Thus, the role of ultrasound in stroke patients remains complementary to angiography providing additional important information.

Transcranial Doppler Ultrasonography

TCD uses a 2-MHz probe through the thin portions of the skull (trans-temporal, trans-nuchal (suboccipital) or trans-orbital windows) and can identify proximal basal intracranial arteries that often harbor emergent large vessel occlusions (ELVO) amenable to mechanical thrombectomy. The trans-temporal window is used to examine the M1 and proximal M2 segments of the middle cerebral artery (MCA), A1 segment of the anterior cerebral artery (ACA), terminal internal carotid artery (TICA), and P1/P2 segments of the posterior cerebral artery (PCA) ( Fig. 133.2 ). Trans-orbitally we examine the ophthalmic artery (OA) and ICA siphon. The trans-occipital window ( Fig. 133.3 ) is used to examine both terminal vertebral arteries (VA) and the entire course of the basilar artery (BA) . Cerebellar arteries can also be detected but are not examined due to tortuosity and less predictable course. Key applications of TCD are summarized in Table 133.1 .