Pitfalls of CT angiography for acute stroke FILEminimizer

Pitfalls of CT Angiography for Acute Stroke Imaging Assessment MG Matheus, MD, V Jewells, DO, A Felix, MD, S Sen, MD, MS, S Solander, MD, M Castillo, MD University of North Carolina-Chapel Hill Introduction CT is crucial in the workup of acute stroke patients CT angiography (CTA) provides information about tissue and vascular anatomy, adding only a few minutes to overall imaging time Imaging assessment needs to be fast to facilitate triage of appropriate candidates for thrombolytic treatment Size, lesion location and time from symptom onset can guide management decisions CTA is highly accurate in detecting intracranial large vessel occlusion However, image assessment is laborious and attention to technical details and knowledge of stroke dynamic pathophysiology is needed to avoid image misinterpretation Here, we address some technical and physiological pitfalls related to image acquisition and interpretation of CTA in acute stroke patients Approach We retrospectively reviewed studies obtained in the past years in 133 patients with acute stroke symptoms and found 16 patients in whom technical/interpretative problems occurred These studies included: - Non-contrast head CT and CTA CTA consisted of axial mm reconstructed source images after contrast, MIP in three planes and projections volume rendered (VR) images All studies were assessed for: Possible technical problems with regards to imaging acquisition/reconstruction Clinico-pathological patterns of stroke that lead to incorrect image interpretation Results- Technical Pitfalls • VR reconstruction showing vessel overlapping and “kissing” artifacts • Venous contamination causing vascular overlap • VR images techniques masking bone/vessel interface and intravascular densities • Inappropriate window settings masking calcifications and stenosis • Previously VR reformatted images with no visualization of distal vessels • Previously reformatted 3D views without availability of source images to confirm abnormalities Results- Related to Stroke Pathophysiology • Intra-arterial dense material (clot and calcifications) masking occlusions • Primary and secondary collateral flow masking obstruction and stenosis • Stenosis at MCA bifurcation • Anatomical variations Representative Cases Case # Patient presents with stroke symptom of less than hours Non contrast head CT was performed and shows a left dense MCA (arrow) Case # Following the CT of the head, this CTA was performed : Do you consider the left MCA to be occluded? This MIP was interpreted as the MCA being patent Case # Follow-u[ MRA shows that left ICA is occluded Case # Catheter angiogram shows dissected left ICA There is cross filling from right injection to level of occlusion (arrow) Pial collaterals supply territory of left MCA thus filling it with contrast Case # Injection into left vertebral artery shows that it ends in PICA thus the vessel seen on the CTA cannot be the vertebral artery but is probably a vein draining into the marginal sinus Case # 5- Teaching Point Initially, there were discrepant findings between the MIPs and VR images, the latter showing occlusion of both PCAs Catheter angiogram showed occluded left PCA Despite visualization of the presumed left vertebral artery on CTA, angiogram showed it be occluded Moreover, the right vertebral was proximally occluded and recanalized distally The static nature of CTA does not allow one to visualize delay circulation times which may have been related to patient’s symptoms Case # Patient presented to the hospital after a peripheral interventional procedure with signs of a right MCA infarct Embolic infarct was suspected CTA is shown in next slide Case Sequential axial MIPs (on click) showing normal appearing vessels Case # Coronal MIPs show left MCA fenestration (circle) and incompletely seen right M1 segment but with good opacification of the ipsilateral sylvian branches Case # VR images confirm left MCA fenestration (circle) and adequate filling of right MCA despite symptoms corresponding to that side Case # Angiogram confirms left fenestration (circle) On the right, there is a similar fenestration but its superior limb is occluded (arrow) explaining the patients symptoms Case # 6- Teaching Point CTA showed patent right MCA This artery was however fenestrated and the superior limb of the fenestration was occluded resulting in a basal ganglia/capsular infarction The fact that the inferior limb of the fenestration was patent gave the false impression that the entire left MCA was patent This was suspected and lead to catheter angiogram and attempted thrombolysis Case # Patient presented with posterior circulation infarct symptoms and CTA showed an unusual configuration of the top of the basilar artery Case # Sagittal MIP (left) shows irregular basilar artery termination (arrow) This finding cannot be confirmed on the VR image (right) as the basilar artery apex is inseparable from adjacent bone Case # Catheter angiogram shows clot occluding distal basilar artery The definitive diagnosis could be made on CTA and required this study Case # 6- Teaching Point Contrast and/or clot may be of similar density to bone and inseparable from it on VR images This is dependent on window settings and time of study acquisition Some times, changing window setting may solve this problem but others times the problem may persist Suspected defects seen on MIPs may necessitate confirmation by catheter angiography Discussion Stroke is the end product of a dynamic cascade of events that culminates with tissue death CTA information is only a snapshot of entire process CTA may reveal distinct phases of disease process or patient characteristics that serve as confounding factors in imaging, such as     recanalization of prior occlusion intra-arterial clot that is as dense as IV contrast collateral flow that may be primary or secondary symmetrical collateral flow that may be insufficient under hypoperfusion situations Discussion Technical factors such as slice thickness , type of reconstructions, suitable window settings and MIP/VR interactive assessment at the work station may improve assessment of distal branch occlusion and intra-vascular densities Keep in mind, when assessing a patient with acute stroke symptoms, that there is a high likelihood that chronic findings and/or unusual flow patterns may be related to the patient’s symptoms Suggested Image Assessment • • • • • • Assess all acquired imaging settings Alter window level and center when assessing MIPs and VRs to find calcifications, clots, dissections and stenoses that may be either concealed or overestimated Assess 3D images dynamically, changing vessel bifurcations angles Keep in mind that you are dealing with a dynamic disease with possible associated chronic findings; Keep in mind that venous and arterial systems may be contrasted and overlapping Look for possible collateral flow ... catheter angiography Discussion Stroke is the end product of a dynamic cascade of events that culminates with tissue death CTA information is only a snapshot of entire process CTA may reveal distinct...Introduction CT is crucial in the workup of acute stroke patients CT angiography (CTA) provides information about tissue and vascular anatomy, adding... acquisition/reconstruction Clinico-pathological patterns of stroke that lead to incorrect image interpretation Results- Technical Pitfalls • VR reconstruction showing vessel overlapping and “kissing” artifacts