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CT Angiography in the Evaluation of Aneurysmal Subarachnoid Hemorrhage

Summary and Comment |
June 26, 2006

CT Angiography in the Evaluation of Aneurysmal Subarachnoid Hemorrhage

  1. Diane M. Birnbaumer, MD, FACEP

Its role is not yet clear.

  1. Diane M. Birnbaumer, MD, FACEP

The typical approach to evaluating patients for subarachnoid hemorrhage is noncontrast head CT scanning, followed by lumbar puncture if the scan is negative. A positive lumbar puncture typically mandates cerebral CT angiography or magnetic resonance angiography. These authors evaluated the role of head CT angiography when performed without preceding lumbar puncture in patients with suspected subarachnoid hemorrhage.

One hundred sixteen patients underwent noncontrast head CT scans followed immediately by CT angiography with 2.5 mm cuts. If the noncontrast scan was negative, patients got a lumbar puncture. Contrast CT scans were interpreted within 24 hours by radiologists blinded to the patient’s presentation. Further testing (e.g., digital subtraction angiography) was done at the discretion of the consulting neurosurgeon. Ten patients did not complete the study.

An aneurysm was found on CT angiography in six patients (5.1%). Three of these patients had negative findings on noncontrast CT and lumbar puncture. Digital subtraction angiography showed that one of the six positive noncontrast CT scans was a false-positive result.

Comment

The finding that half of patients with cerebral aneurysm had negative lumbar punctures seems surprising until we consider that we would expect CT angiography of 116 asymptomatic people to identify one to three aneurysms. Although promising, use of contrast CT in lieu of lumbar puncture might not be ready for prime time. First, if CT angiography is done in all patients with suspected subarachnoid hemorrhage, rather than just in those with positive lumbar puncture results, many more patients will be subjected to a contrast load and to additional radiation. Second, headache is a frequent emergency department presentation (1%–2% of visits), and only a small fraction of these patients (<5%) will have nontraumatic subarachnoid hemorrhage as the cause of the headache. Applying CT angiography to a larger proportion of patients might detect cerebral aneurysms that are not related to the headache.

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