Intracranial vascular stenosis and occlusive disease: evaluation with CT angiography, MR angiography, and digital subtraction angiography

Abstract

Background and purpose: Although digital subtraction angiography (DSA) provides excellent visualization of the intracranial vasculature, it has several limitations. Our purpose was to evaluate the ability of helical CT angiography (CTA) to help detect and quantify intracranial stenosis and occlusion compared with DSA and MR angiography (MRA).

Methods: Twenty-eight patients underwent CTA, DSA, and 3D time-of-flight (TOF) MRA for suspected cerebrovascular lesions. All three studies were performed within a 30-day period. Two readers blinded to prior estimated or calculated stenoses, patient history and clinical information examined 672 vessel segments. Lesions were categorized as normal (0-9%), mild (10-29%), moderate (30-69%), severe (70-99%), or occluded (no flow detected). DSA was the reference standard. Unblinded consensus readings were obtained for all discrepancies.

Results: A total of 115 diseased vessel segments were identified. After consensus interpretation, CTA revealed higher sensitivity than that of MRA for intracranial stenosis (98% versus 70%, P < .001) and occlusion (100% versus 87%, P = .02). CTA had a higher positive predictive value than that of MRA for both stenosis (93% versus 65%, P < .001) and occlusion (100% versus 59%, P < .001). CTA had a high interoperator reliability. In 6 of 28 patients (21%), all 6 with low-flow states in the posterior circulation, CTA was superior to DSA in detection of vessel patency.

Conclusion: CTA has a higher sensitivity and positive predictive value than MRA and is recommended over TOF MRA for detection of intracranial stenosis and occlusion. CTA has a high interoperator reliability. CTA is superior to DSA in the evaluation of posterior circulation steno-occlusive disease when slow flow is present. CTA results had a significant effect on patient clinical management.

Fig 1.

Example of a DSA false-positive finding for basilar occlusion in a patient with low-flow state due to a severe stenosis of the left vertebral artery. A and B, Frontal (A) and lateral (B) middle arterial phase DSA images show selective injection of dominant left vertebral artery (shown in anatomic orientation). Note the severe stenosis of the left vertebral artery (long arrow) and a small amount of reflux down the nondominant right vertebral artery (short curved arrow in A). The basilar artery distal to the origin of the left anterior inferior cerebellar artery is not opacified and therefore appears occluded (open arrow), even on late arterial and venous images (not shown). C, Lateral projection, left ICA injection, middle arterial phase DSA image shows minimal retrograde filling of the distal basilar artery (arrow) through the posterior communicating artery to the level of the superior cerebellar arteries, suggesting segmental occlusion of the midbasilar artery. D, Corresponding volume-rendered 3D CTA image in anatomic orientation. CTA image was obtained 3 days before DSA and shows a severe left vertebral artery stenosis (black arrow) associated with heavy calcific atheromatous plaque. However, CTA depicts the basilar artery as patent. In addition, the CTA image demonstrates two tandem stenoses of the distal basilar artery (white arrows), which may have contributed to impaired retrograde flow into the basilar artery via the posterior communicating artery upon anterior circulation injection at DSA. There was no change in patient symptoms during the intervening period between the CTA and DSA studies to suggest interval arterial thrombosis.

Fig 2.

Example of a DSA false-positive finding for basilar occlusion in a patient with a low- or balanced-flow state due to a severe stenosis of the basilar artery. A and B, Frontal (A) and lateral (B) middle arterial phase DSA images show selective injection of a dominant left vertebral artery (DSA images shown in anatomic orientation). Note absent cephalad flow in the basilar artery distal to the midbasilar segment (arrow), suggesting basilar artery occlusion. C, Lateral projection, right ICA injection, middle arterial phase DSA image shows minimal retrograde filling of the distal basilar artery (arrow) through the posterior communicating artery. The midbasilar segment is not visualized, suggesting segmental occlusion of the midbasilar artery. D, CTA was performed 12 days before DSA. This volume-rendered 3D CTA image, in anatomic orientation, shows a severe, eccentric, focal midbasilar stenosis (arrow); however, the basilar artery is clearly patent. This was verified on the gray-scale 2D source image. E, Axial 2D curved oblique CTA reformation image, frontal projection, shows focal midbasilar artery stenosis (arrow) with 79% stenosis severity. F, TOF MRA image with frontal oblique MIP shows a focal flow gap in the midbasilar artery (arrow).

Fig 3.

Example of a DSA false-positive finding for basilar occlusion in a patient with a relatively isolated posterior circulation due to bilateral vertebral artery occlusion, a hypoplastic right posterior communicating artery, and a significant left proximal P1 stenosis. A, Frontal late arterial phase DSA image shows selective injection of a dominant right vertebral artery. The basilar artery is not opacified. The right vertebral artery appears to terminate in the right posterior inferior cerebellar artery (arrow). Note that the patent right posterior inferior cerebellar artery supplies some blood flow to the right anterior inferior cerebellar artery and a small tonsillar loop branch to the contralateral left posterior inferior cerebellar artery. B, Frontal middle phase DSA image shows selective injection of the left vertebral artery, which terminates in an extracranial muscular branch near the skull base (arrow). No flow is seen in the intracranial segment of the left vertebral artery indicating occlusion of this vessel segment. C, Lateral projection, right ICA injection, middle arterial phase DSA image shows minimal retrograde filling of the distal basilar artery (arrow) through the posterior communicating artery, but there is absence of flow in the remainder of the basilar artery, suggesting segmental occlusion of this vessel. D, CTA was performed 1 day after DSA. This volume-rendered 3D CTA image in posteroanterior projection (anatomic orientation) shows bilateral distal vertebral artery occlusions (solid black arrows) and significant focal origin stenoses of both the left proximal P1 and the left superior cerebellar artery (white arrow). CTA image also demonstrates minimal flow in what appears to be a small segment of a hypoplastic distal right intracranial vertebral artery, distal to the origin of the right posterior inferior cerebellar artery. The CTA image shows that the basilar artery is entirely patent and stenosis-free (open black arrow). This was verified on the gray-scale 2D source image. E, Volume-rendered 3D CTA image, craniocaudal projection with anatomic orientation, demonstrates a prominent left posterior communicating artery (arrow) and absent right posterior communicating artery. The left P1 is small in caliber. F, Targeted volume-rendered 3D CTA image in the anteroposterior projection demonstrates significant proximal focal left P1 and superior cerebellar artery stenoses (arrow). G, TOF MRA image with frontal MIP shows absent flow signal (arrow) in the expected region of the basilar artery, suggesting occlusion.