Intracranial stenoocclusive disease: double-detector helical CT angiography versus digital subtraction angiography

Abstract

Background and purpose: To our knowledge, no large-scale studies comparing the accuracy of CT angiography (CTA) to intraarterial digital subtraction angiography (DSA) of intracranial stenosis have been reported. We attempted to determine the diagnostic value of intracranial CT angiography (CTA) of normal vasculature and variants as well as of stenoocclusive disease.

Methods: One-hundred and twelve patients underwent CTA and intraarterial angiography, and 2205 vascular segments were examined to ascertain presence, visibility, and degree of arterial stenoses (n = 105) as well as anatomic variants. Source, maximum intensity projection (MIP), and MIP-generated multiplanar reformatted (MPR) images were evaluated.

Results: All 55 anatomic variants were identified correctly. Visibility of small-vessel segments was increased from 75% to 83% by using source images. MPR was helpful in differentiating distal vertebral hypoplasia from stenosis and in overcoming artifacts. All 43 occlusive segments were graded correctly (sensitivity = 100%, predictive value = 93.4%) as follows: severely stenotic ([n = 23], sensitivity = 78%, predictive value = 81.8%); moderately stenotic ([n = 36], sensitivity = 61%, predictive value = 84.6%); and mildly stenotic ([n = 3], sensitivity = 66%, predictive value = 28%). Normal segments (n = 2100) had a sensitivity of 99.5%, and CTA evinced a specificity of 99% for detecting stenoocclusive disease. Approximately one-third of wrong assessments were related to the petrous segment of the carotid artery.

Conclusion: CTA with double-detector technology and advanced postprocessing algorithms, including MPR, is about as reliable as MRA in depicting the vasculature of the anterior and posterior circulation and in grading intracranial stenoocclusive lesions, with the exception of the petrous segment of the carotid artery. CTA might be superior to MRA in the evaluation of poststenotic low-flow segments.

fig 1.

CTA with targeted MIP was performed in a 48-year-old man with surgically confirmed pericallosal arterial aneurysm and hypoplasia of A1 segment. A, Anteroposterior (AP) arteriogram of right carotid artery shows hypoplasia of A1 segment (arrow). B, CTA with targeted MIP reveals extended coverage of CTA with double-detector technology. Complete arterial volume is shown by MIP, ranging from the atlas loop to the pericallosal artery. By drawing a freehand line on any selected projection of the volume, targeted MIPs can be created (C and D), avoiding superimposition of vessels. C, Targeted MIP of anterior circulation clearly shows hypoplasia of A1 segment (long arrow) as well as aneurysm (short arrow). D, Targeted MIP of posterior circulation shows normal vasculature.

fig 2.

Severe stenosis of distal segment of left vertebral artery. A, AP of left vertebral artery shows severe stenosis (arrow). B, AP MIP of CTA (right frame) underestimates stenosis (small arrow). MasterCut MPR (arrow) shows more clearly lesion severity and exclusion of reconstruction artifact.

fig 3.

Partial occlusion of ICA. A, Lateral angiogram of right ICA artery shows occlusion of cervical and petrous segments and filling of the carotid siphon and supraclinoid segments (arrow) via collateral flow from ophthalmic artery. B, CTA with Mastercut MPR shows two-frame window. Right frame contains MIP image, and left frame contains a reformatted curved plane (panoramic image) related to white cut line drawn on the MIP image. Start of cut line is marked with asterisk. Owing to reconstruction artifacts caused by vessel contact with bone (especially with petrous segment of carotid artery), vasculature cannot be assessed reliably with MIP images (arrows) alone. The MasterCut MPR image clearly depicts occluded (broad arrows) and open (thin arrows) segments with the same accuracy as the arteriogram. C, CTA with MIP (right) and MasterCut MPR (left) of normal left ICA. Start of the cut line (asterisk) is shown.

fig 4.

Moderate tandem stenoses of right MCA. A and B, AP angiogram (A) and CT angiogram (B) clearly depict stenosis grading (arrows).

fig 5.

A 40-year-old patient with embolic occlusion of right MCA. A, AP angiogram of right carotid artery. B, Axial collapsed CTA enables good visualization of occlusion site (long arrow). Superimposition of veins causes no diagnostic problem (broad arrow).

fig 6.

A 50-year-old woman with moyamoya disease and history of transient ischemic attacks. A and B, AP arteriogram of the right (A) and left (B) carotid artery reveals stenoses of distal carotid artery on both sides as well as high-grade stenoses of the A1 segment (arrow) and occlusion of left M1 segment. Collateral vessels of left M1 segment (arrowheads) cannot be seen by either MRA (C) or CTA (D). C, MRA, oblique AP view, is impaired by poststenotic signal loss, belying an occlusion of the left A1 segment (broad arrow), as well as the right M1 segment (arrowheads). The postocclusive branches of the left MCA are filled by collateral vessels, and very low flow in these segments results in poor MRA signal. Thus, postocclusive segments of the MCA (left) cannot be seen clearly. Notice stenosis of supraclinoid segment of ICA (long arrow). D, CTA, targeted-MIP AP view, correctly shows the right M1 segment as open and presents the clearest depiction of the left distal MCA branches (arrows).

fig 7.

A 54-year-old man with history of aphasia and right upper extremity weakness. A, Axial noncontrast CT 20 hours after onset of stroke shows subtle low density in left nucleus lentiformis and periinsular region. B, AP CTA 8 hours after onset of left hemispheric stroke shows severe stenoocclusive lesion of left M1 segment (arrow) but distal MCA segments are depicted as intense (right), indicating a seemingly good collateral blood flow. C and D, In spite of therapy with intravenous heparine, on follow-up CT 7 days later, a large area of infarction has demarcated on axial noncontrast CT (C). Same-day CTA shows a markedly reduced filling of left MCA vessels (D).