Utility of brain ultrasound is uncertain for many conditions.
A new guideline developed by the American Academy of Neurology specifies only two situations for which the technique's clinical utility has been established: detecting and monitoring vasospasm after subarachnoid hemorrhage, and screening children with sickle cell disease for risk of stroke, said Dr. Michael A. Sloan of Rush University Medical Center, Chicago, and his colleagues (Neurology 62:1468-81, 2004).
For most other potential indications, data show that transcranial Doppler (TCD) ultrasonography provides important insight, but data do not establish that such insight is better than what can be achieved in other ways. In some cases, data suggest that other tests are preferable.
TCD allows noninvasive assessment of the anatomy and hemodynamic status of the cerebral circulation. The guideline authors rated findings from published studies using the American Academy of Neurology rating system for clinical usefulness and predictive value. Research on the range of common indications for performing TCD evaluations were considered, including:
* Diagnosis and follow-up of intracranial steno-occlusive disease.
* Evaluation of the effects of extracranial stenosis on intracranial hemodynamics.
* Monitoring vasospasm following subarachnoid hemorrhage.
* Evaluation of intracranial flow following head trauma and brain death.
* Intraoperative monitoring for emboli detection and hernodynamic changes during major vascular surgery.
* Assessment of vasomotor reactivity.
* Identification of intracranial vasculopathy/stenosis in patients with sickle cell disease.
* Detection/evaluation of severe stenosis in the major basal cerebral arteries.
* Evaluation of supply arteries and flow patterns of arteriovenous malformations.
* Evaluation of posterior circulation and vertebrobasilar pathology.
Only monitoring vasospasm after subarachnoid hemorrhage and screening for sickle cell-related stroke risk met criteria for clinical utility, and those recommendations are qualified. TCD was shown to be useful for detecting and monitoring angiographic vasospasm in the basal segments of the intracranial arteries after subarachnoid hemorrhage, but the sensitivity and specificity of the test compared with cerebral angiography varied from study to study. And not enough data exist to determine whether TCD affects clinical outcomes.
In sickle cell disease, studies have shown that screening affected children between the ages of 2 and 16--a population at risk for occlusive vasculopathy as a result of ischemic cerebral infarction--can reduce stroke risk (by 92% in one large, long-term trial). But data do not provide information on the optimal frequency of testing.
For most other indications, data on clinical utility are insufficient to recommend usage. For example, the collected evidence suggests TCD is "probably useful" for conditions such as cerebral thrombolysis and cerebral microembolism, but the utility relative to other tests is unclear. Data also show TCD to be informative but less appropriate than other techniques for monitoring right-to-left cardiac shunts or evaluating internal carotid artery stenosis.
The guideline includes recommendations for research in ischemic cerebrovascular disease, perioperative and periprocedural monitoring, and monitoring in neurology intensive care units.
BY DIANA MAHONEY
New England Bureau
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|Publication:||Internal Medicine News|
|Date:||Sep 15, 2004|
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