Transcranial Doppler assessment of cerebral embolic disorders

Role of Transcranial Doppler in Cardiac Surgery Patients

Abstract

Purpose of Review

This review discusses applications of transcranial Doppler (TCD) in cardiac surgery, its efficacy in preventing adverse events such as postoperative cognitive decline and stroke, and its impact on clinical outcomes in these patients.

Recent Findings

TCD alone and in combination with other neuromonitoring modalities has attracted attention as a potential monitoring tool in cardiac surgery patients. TCD allows not only the detection of microemboli and measurement of cerebral blood flow velocity in cerebral arteries but also the assessment of cerebral autoregulation.

Summary

Neuromonitoring is critically important in cardiac surgery as surgical and anesthetic interventions as well as several other factors may increase the risk of cerebral embolization (gaseous and particulate) and cerebral perfusion anomalies, which may lead to adverse neurological events. As an experimental tool, TCD has revealed a possible association of poor neurological outcome with intraoperative cerebral emboli and impaired cerebral perfusion. However, to date, there is no evidence that routine use of transcranial Doppler can improve neurological outcome after cardiac surgery.

Presumed and confirmed striatocapsular brain infarctions in six dogs

OBJECTIVE

To describe the clinical and diagnostic features of the canine sensorimotor syndrome caused by striatocapsular brain infarctions (SCI).

ANIMALS STUDIED

Six dogs with diagnostic imaging or postmortem evidence of SCI.

PROCEDURES

Medical records of dogs with SCI were retrospectively reviewed and the signalment, history, clinical signs, antemortem clinicopathologic test results, diagnostic imaging findings, case outcomes, and pathologic findings recorded.

RESULTS

All dogs had an acute onset of nonprogressive homonymous visual field deficits and contralateral general proprioceptive (GP) deficits. Contralateral hemiparesis and facial hypalgesia were noted in 5/6 dogs. CT scans were normal in 2/4 dogs, and revealed poorly defined hypoattenuating lesions in the subcortical white matter in two dogs. MRI exams were performed in 5/6 dogs and revealed unilateral, variably sized, striatocapsular lesions consistent with nonhemorrhagic infarctions. Diagnostic imaging (6/6) and postmortem examinations (2/6) suggested that SCI resulted from lesions in the vascular territories of the rostral choriodal (6/6) and lenticulostriate arteries (2/6). Diseases predisposing to infarction were not identified in 5/6 dogs. Improvements in mentation, behavior, proprioceptive deficits, and hemiparesis were seen in surviving dogs, but persistent, symptomatic sensory deficits were noted during the follow-up period.

CONCLUSIONS

SCI should be considered as a differential diagnosis for dogs with acute onset, nonprogressive homonymous hemianopia, contralateral GP deficits or hemiparesis, and facial hypalgesia. MRI is the preferred modality for the antemortem imaging diagnosis of SCI. Although partial recovery occurred in all surviving dogs, visual and facial sensory disturbances persisted.

Embolization in atherosclerosis

Much has been learned about microembolization in the last two decades. The promising blood markers for brain injury will further enhance our future understanding of microembolic events. New surgical techniques, drugs, and devices have substantially reduced microembolization during carotid angioplasty, CEA, and CABG.

Transcranial Doppler in stroke

Transcranial Doppler (TCD) has been extensively used in various clinical situations, and in the last two decades has established its role in the management of patients with cerebrovascular disease and stroke. Based on the Doppler principle, it uses ultrasound waves to insonate the blood vessels supplying the brain to obtain hemodynamic information. Anatomic abnormalities of vascular occlusion, stenosis and spasm can be indirectly derived. Intracranial arterial disease is an important cause of ischemic stroke and TCD can detect these with a fair amount of sensitivity and specificity. In hemodynamically significant extracranial internal carotid artery disease, TCD shows significant abnormalities in flow dynamics of the anterior circulation and abnormalities of cerebral vasomotor reactivity. A distinct advantage of TCD is the ability to monitor blood flow in a blood vessel over prolonged periods of time, which has shown microembolic signals in acute ischemic stroke, carotid artery disease, atrial fibrillation and during angiography. In acute ischemic stroke, TCD can be used to elucidate stroke mechanisms, plan and monitor treatment, and determine prognosis. In an era when stroke is increasingly being recognized as an emergency requiring immediate treatment, TCD may be capable of providing rapid information about the hemodynamic status of the cerebral circulation, within the time frame of the rather small 'therapeutic window'. TCD predicts vasospasm with a high degree of sensitivity and specificity and because of its non-invasive nature repeated assessments can be performed after subarachnoid hemorrhage.