Which CTA findings are characteristic of stroke?

Updated: Nov 30, 2018
  • Author: Andrew Danziger; Chief Editor: L Gill Naul, MD  more...
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Answer

The most important purpose of CTA in acute stroke is to detect vessel thrombosis or occlusion. Thrombus characterization is increasingly considered important in predicting treatment success for patients with acute ischemic stroke. [64, 65, 66] CTA source images should always be assessed, in addition to multiplanar reconstruction (MRP) and maximum intensity projection (MIP) images. Proper interpretation requires attention to luminal enhancement to assess vessel patency, intimal flaps to exclude dissection, filling defects and vessel wall calcifications to assess stenosis, and occlusions and focal outpouchings suggestive of aneurysm or pseudoaneurysm (see the image below).

CTA has been demonstrated to be highly reliable for the detection or exclusion of large intracranial vessels, such as the ICA and MCA trunk up to the M2 segment and basilar arteries.

Using multidetector CT with voxel sizes well below 1 mm and postprocessing tools, CTA is highly accurate in measuring vessel diameters adjacent to stenosis and is superior for grading of intracranial stenosis compared with 3D TOF MRA technique. [67]

CTA has the advantage over MRA and DSA of detecting mural calcifications in relation to stenosis. However, in an 11-year retrospective study of patients with CTA-negative subarachnoid hemorrhage (SAH), digital subtraction angiography (DSA) identified vascular pathology in 13% of patients with CTA-negative SAH. Aneurysms or pseudoaneurysms are identified in an additional 4% of patients by repeat DSA following an initially negative DSA. [68]

Use of varied window setting is required to assess luminal patency within the vessel when it is surrounded by calcified thrombus.

In addition to vascular occlusions, CTA source images are able to demonstrate hypoperfused brain parenchyma in acute stroke similar to DWI images.

MIP and surface volume rendered images of the circ MIP and surface volume rendered images of the circle of Willis from a CTA in a 70-year-old female with acute onset right-sided weakness. A high-grade stenosis of the distal left middle cerebral artery (MCA) trunk (red circles) is seen, with filling of the remainder of the MCA territory via an anterior branch near the bifurcation.

In addition to vascular anatomy, regions of parenchymal hypoperfusion can also be assessed with CTA. Regions of diminished flow on CTA source images have also been shown to correlate well with the infarct core (see the image below). [13]

CTA source data can also be useful to assess for a CTA source data can also be useful to assess for areas of hypoperfusion and poor enhancement that may correspond to areas of greatest ischemia. This CTA source image from the patient in the previous case demonstrates significantly diminished enhancement involving the caudate head, lentiform nucleus, and capsular regions. High density noted centrally in this poorly enhancing region represents an area of hemorrhagic transformation.

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