Improved Detection of Anterior Circulation Occlusions: The "Delayed Vessel Sign" on Multiphase CT Angiography

Abstract

Background and purpose: Multiphase CTA, a technique to dynamically assess the vasculature in acute ischemic stroke, was primarily developed to evaluate collateral filling. We have observed that it is also useful in identifying distal anterior circulation occlusions due to delayed anterior circulation opacification on multiphase CTA, an observation we term the "delayed vessel sign." We aimed to determine the usefulness of this sign by comparing multiphase CTA with single-phase CTA.

Materials and methods: All 23 distal anterior circulation occlusions during a 2-year period were included. Ten M1-segment occlusions and 10 cases without a vessel occlusion were also included. All patients had follow-up imaging confirming the diagnosis. Initially, the noncontrast CT and first phase of the multiphase CTA study for each patient were blindly evaluated (2 neuroradiologists, 2 radiology trainees) for an anterior circulation occlusion. Readers' confidence, speed, and sensitivity of detection were recorded. Readers were then educated on the "delayed vessel sign," and each multiphase CTA study was re-examined for a vessel occlusion after at least 14 days.

Results: There was significant improvement in the sensitivity of detection of distal anterior circulation vessel occlusions (P < .001), overall confidence (P < .001), and time taken to interpret (P < .001) with multiphase CTA compared with single-phase CTA. Readers preferred MIP images compared with source images in >90% of cases.

Conclusions: The delayed vessel sign is a reliable indicator of anterior circulation vessel occlusion, particularly in cases involving distal branches. Assessment of the later phases of multiphase CTA for the delayed vessel sign leads to a significant improvement in the speed and confidence of interpretation, compared with single-phase CTA.

Fig 1.

Multiphase CTA and follow-up MR imaging of an 83-year-old woman presenting with acute right upper limb weakness and dysphasia. A, Axial MIP of the first phase demonstrates subtle paucity of vessels in the distribution of the left MCA compared with the right side. B, Axial MIP of the second phase demonstrates the delayed vessel sign (long arrow). There is delayed enhancement of the distal left MCA via pial collateral vessels (short arrows). This vessel is not seen on the first phase due to the presence of an M2 vessel occlusion. C, Axial MIP of the third phase also demonstrates the “delayed” left MCA vessel (long arrow). D, DWI b=1000 image 2 weeks postpresentation demonstrates a recent infarct (arrow) in the same left MCA territory.

Fig 2.

Multiphase CTA in a 65-year-old man with acute left-sided weakness. A, Axial MIP of the first phase without obvious asymmetry. B and C, Axial MIPs of the second and third phases demonstrate the delayed vessel sign (arrow) with opacification of a distal right MCA branch, which was not opacified on the first angiographic phase due to a proximal M2 vessel occlusion. D, DWI b=1000 image 24 hours postpresentation demonstrates an acute infarct (arrow) in the same right MCA territory.

Fig 3.

Multiphase CTA in a 78-year-old man with expressive dysphasia and right-sided weakness. A, Axial source image of the first phase of MPCTA without obvious asymmetry of the intracranial vasculature. B, The delayed vessel sign is identified on the second phase (arrow), indicative of a proximal occlusion. C, Axial source image of the third phase of the MPCTA. D–F, Axial MIPs of the first, second, and third phases of the same patient. The delayed vessel sign is more apparent on MIP image (arrow) of the second phase (E) compared with source images.