CTA for Cerebral Vasospasm
CTA for Cerebral Vasospasm
Abstract & Commentary
Synopsis: Vasospasm is a significant cause of morbidity and mortality in survivors of subarachnoid hemorrhage (SAH). Digital subtraction angiography (DSA) has been the gold standard for diagnosis of vasospasm and also offers the opportunity for endovascular therapeutic intervention. DSA is, however, an invasive procedure with its own set of associated risks. The opportunity to accurately assess spasm using a minimally invasive modality such as CTA could help appropriately triage patients to continued observation or a more invasive test such as DSA. Anderson and colleagues report a prospective comparison of CTA with DSA in the detection and quantification of vasospasm in 17 patients with aneurysmal SAH.
Source: Anderson GB, et al. CT angiography for the detection of cerebral vasospasm in patients with acute subarachnoid hemorrhage. AJNR Am J Neuroradiol 2000; 21:1011-1015.
Dsa has been the standard of reference for detection of vasospasm complicating aneurysmal subarachnoid hemorrhage. The development of minimally invasive methods for imaging the cerebral vasculature (such as CT and MR angiography) raises the question of whether one of these methods could be substituted for DSA. MR-based methods are limited by patient cooperation and also the presence of ferromagnetic aneurysm clips in some patients. Most post-SAH patients undergo follow-up CT when vasospasm is a concern to look for ischemic complications, and CTA can easily be performed in conjunction with a noncontrast head CT. Anderson and colleagues prospectively compared CTA with DSA in their ability to accurately detect cerebral vasospasm in patients with SAH.
A baseline CTA was performed in 17 patients with CT-documented SAH using a helical scanning protocol during bolus injection of contrast material, with coverage from the craniocervical junction to 30 mm above the sellar floor. Five to 10 days later, patients underwent repeat CTA followed within 24 hours by DSA. Maximum intensity projection (MIP) reconstructions were performed on the CTAs by the same experienced investigator. The initial and delayed CTA studies were assessed for spasm by comparing vessel caliber on the two studies, and these results were compared with DSA. Overall, six arterial locations were assessed: four proximal locations (ICA, A1, M1, and basilar) and two distal locations (A2 and M2 segments).
The overall agreement between CTA and DSA for all locations and degrees of vasospasm was 86%. Agreement between CTA and DSA was greater for no spasm and severe (> 50% lumen reduction) spasm than for mild or moderate spasm. CTA was highly accurate for no spasm or severe spasm in proximal locations, and less accurate for distal locations. Nine percent of arteries were not visible at follow-up CTA because of aneurysm clip artifact, and it was noted that titanium clips are not routinely used at Anderson et al’s institution.
Comment by Nancy J. Fischbein, MD
Cerebral vasospasm of varying degrees affects as many as 50% of patients with aneurysmal subarachnoid hemorrhage. Vasospasm typically occurs seven to 10 days following the hemorrhage, and its prompt diagnosis is necessary to institute therapy to avoid complicating ischemic insult to the brain. Patients can be screened noninvasively with transcranial Doppler sonography, but this method is operator dependent and limited in accurately depicting vasospasm at sites other than the proximal middle cerebral artery.1 MRA can depict vasospasm, but it is difficult to perform on severely ill and uncooperative patients and it cannot be performed in patients who have been treated with ferromagnetic aneurysm clips.2 DSA is the gold standard for diagnosis, but it carries a total complication rate of ~5% and ideally would be reserved for those who are likely to require an endovascular therapeutic intervention in combination with diagnostic arteriography. There is therefore a potential need for a modality that can accurately and noninvasively assess the patient at risk for vasospasm such that the patient can be accurately triaged to continued observation or DSA for definitive diagnosis and endovascular therapy, and CTA may offer a solution to this problem. Significant limitations of CTA include the somewhat labor-intensive and operator-dependent postprocessing required for MIP reconstruction, as well as limited visualization of A2 and M2 branches and artifacts related to nontitanium aneurysm clips. Anderson et al’s results demonstrate, however, that a patient with no evidence of spasm on CTA can probably be spared DSA, while for the time being those with evidence of vasospasm can be further evaluated with DSA. Future developments with multidetector scans and automated MIP reconstruction may eventually refine this modality to the point that it can replace DSA for all but therapeutic purposes.
References
1. Okada Y, et al. Comparison of transcranial Doppler investigation of aneurysmal vasospasm with digital subtraction angiographic and clinical findings. Neurosurgery 1999;45:443-450.
2. Tamatani S, et al. Detection of delayed cerebral vasospasm, after rupture of intracranial aneurysms, by magnetic resonance angiography. Neurosurgery 1997;40:748-754.
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