MR angiography in patients with subarachnoid hemorrhage: adequate to evaluate vasospasm-induced vascular narrowing?

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Abstract
The diagnosis of cerebral vasospasm (CVS) following subarachnoid hemorrhage (SAH) is still challenging. We evaluate the accuracy of time of flight MR angiography (TOF-MRA) to assess the arterial diameters of the circle of Willis in SAH patients with suspected CVS. MR examinations (1.5 Tesla) including 3D TOF-MRA with maximum intensity projections (MIP) and digital subtraction angiography (DSA) were performed within 24 h in 21 patients with acute aneurysmal SAH and suspicion of CVS. Arterial diameters of the circle of Willis including the distal internal carotid artery (ICA) were measured as ratios to the extradural ICA in standard projections. The diagnosis of CVS was established by comparing the luminal size of baseline and follow-up DSA. The correlation between the arterial ratios measured on MIP angiograms and on follow-up DSA was assessed with Pearson's linear regression analysis. Arterial ratios on MIP angiograms were categorized as correct, overestimated, and underestimated compared to the ratios on follow-up DSA. Pearson's correlation coefficient between the ratios of MIP angiograms and DSA was r = 0.5799 and the regression coefficient was b = 0.4775. Highest correlation was found for the category of severe CVS (r = 0.8201). Of all MIP angiograms, 34.9% showed consistent results compared to the DSA, while 44.2% of MIP images overestimated the vascular narrowing. Standard MIP angiograms from TOF-MRA are not accurate to assess vascular narrowing in patients with suspected CVS after aneurysmal SAH. The multifocal arterial stenoses in CVS may induce severe changes in blood flow dynamics, which compromise the diagnostic accuracy of the TOF-MRA.