Mismatch between TOF MR Angiography and CT Angiography of the Middle Cerebral Artery may be a Critical Sign in Cerebrovascular Dynamics

PURPOSE Although time-of-flight (TOF)-magnetic resonance angiography (MRA) can clearly depict intracranial arteries, the arterial flow of middle cerebral artery (MCA) is occasionally not detected. We evaluated this phenomenon with reference to cerebrovascular dynamics. MATERIALS AND METHODS Seventeen patients with suspected occlusion of MCA or internal carotid artery on TOF-MRA were enrolled. All patients underwent CT angiography (CTA) and quantitative cerebral blood flow (CBF) examination for measurement of resting CBF and cerebrovascular reactivity (CVR). Depending on appearance, patients were categorized into three groups. Group A (n=6) had MCA delineation on both MRA and CTA, while groups B (n=6) and C (n=5) had no signal on MRA, but Group B had a MCA delineation on CTA. RESULTS No significant difference between resting CBF and CBF after the administration of acetazolamide was seen among 3 groups. In contrast, mean CVR in group B was -19.7±18.1%, which was significantly lower than group A [36.4±21.7% (p<0.05)], but not than group C (21.4±35.2%). Furthermore, all patients in group B displayed a so-called steal phenomenon. CONCLUSION This study is the first to show that visualization of MCA on TOF-MRA closely correlates with CVR, and that a vascular pattern showing no MCA signal intensity on MRA but with MCA delineation on CTA indicates a critical cerebrovascular condition.