Transcranial Doppler and Optic Nerve Sonography

Abstract

Transcranial Doppler is a bedside procedure that measures linear cerebral blood flow velocity (CBFV) and the pulsatility index through the intracranial circulation. Transcranial color-coded duplex Doppler (TCCD) provides both CBFV and B-mode functions. In this review they are both referred to as brain ultrasound TCCD. Brain ultrasound can be applied in various environments, including out-of-hospital, emergency room, surgery, intensive care, and ward settings. The most common neurologic disease processes evaluated with TCCD are subarachnoid hemorrhage, traumatic brain injury, and ischemic and hemorrhagic stroke. However, TCCD also is used outside the neuroenvironment for diseases such as sickle cell anemia or for cerebral hemodynamic assessment during the cardiovascular perioperative period. In these applications, TCCD can be used for the detection of cerebral vessel occlusion, estimation of cerebrovascular reactivity, right-to-left cardiac shunts, noninvasive estimation of cerebral perfusion and intracranial pressure, optic nerve sheath diameter, midline shift, hydrocephalus, and the presence of foreign objects. Finally, TCCD has a high accuracy in confirming total cerebral circulatory arrest and has been used as an ancillary test to support clinical diagnosis of brain death. Other indications for TCCD include assessment of collateral blood flow and embolization during carotid endarterectomy, assessment of patterns and extent of collateral circulation in severe stenosis or occlusion, assessment of patent foramen ovale/paradoxical embolism, assessment of arteriovenous malformations and studying their supply arteries and flow patterns, assessment of noncardiac right-to-left shunts, assessment of severe stenosis in the arteries of the circle of Willis, and assessment of vertebral artery dissection.

Keywords: brain injury; brain ultrasound; cerebral autoregulation; cerebral blood flow; flow velocity; hyperemia; intracranial hypertension; midline shift; optic nerve sheath diameter; pulsatility index; stenosis, emboli; transcranial doppler; vasospasm.