Hyperacute Arterial Stroke: CTA/MRA Head

History

Acute change in neurologic status; rule out stroke.

Exam

CTA of the Head
This part of the stroke protocol CTA is performed after the 1st bolus of contrast and is referred to as the initial post contrast head CTA exam. Since there is no recirculation of contrast, it has the advantage of identifying stenoses and short segment occlusions without obscuration by pial collateral. On the other hand, it may underfilling patent, more distal, arteries, which, of course, also reduces the CT-density in the venocapillary pool within brain parenchyma. Thus, the initial post contrast head CTA tends to overestimate the depth of injury in the apparent stroke-zone.

**MRA of the head was performed in Case 9 rather than CTA. The introductory video addresses the imaging differences between MRA of the head versus CTA of the head.

Purpose

1. To define sites of afferent supratentorial arterial thrombosis or flow-limiting high grade stenosis, or less significant luminal narrowing but tandem stenoses, or stenosis plus incomplete circle of Willis with isolated arterial circuit;

2. To define any and all sites of afferent infratentorial arterial thrombosis or flow-limiting high grade stenosis;

3. To determine features of vessel wall and intimal status (nature of stenosis, degree of narrowing, intimal dissection etc.);

4. To assess presence of any combination of proximal stenosis plus an incomplete circle of Willis, which together create an isolated arterial circuit with reduced potential for collateral blood flow;

5. In case of an ICA stenosis/occlusion, is there effective EC-IC collateral (better seen on CTA head than CTA neck);

6 . Is there a watershed stroke zone affecting the usual anastomotic arterial boundary zones;

7. In case of afferent arterial block (occlusion or high-grade stenosis) combined with an incomplete circle of Willis, is there a shift of the expected watershed zone, changing the potential end-of the-line pattern of oligemia (ie: a “shifted watershed zone”);

8. To assess status of retrograde pial collateral for any “pial collateral gap” between a proximal thrombus & the available retrograde pial collateral based on the initial (1st pass) contrast injection;

9. To assess for delayed venous egress (need to prove on post contrast CT head whether it is just delayed or is actually persistently reduced or absent).

Prior Study

CT Head

CT Perfusion

CTA Neck

Findings

Supratentorial Intradural Arterial Circulation

There is a primary or secondary stem intradural ICA occlusion. [Yes/No]

Given an ICA occlusion, there is functional EC-IC collateral. [Yes/No]

The circle of Willis is incomplete. [Yes/No]

Given the circle of Willis is incomplete, is there is a specific vascular territory put at risk.
[Yes/No]

Given there is an extradural ICA occlusion can you estimate the likely end-of the–line watershed location site, based on both the circle of Willis status, available EC-IC collateral, & available pial collateral. [Yes/No]

There is nonocclusive intradural carotid (main trunk) ICA plaque possibly producing stroke in one its branches (ophthalmic, P-com, anterior choroidal). [Yes/No]

There is nonocclusive plaque of A1/2, M1/2 or of the ICA apex, which could cause a supratentorial basal ganglia or caudate perforator stroke. [Yes/No]

There is nonocclusive plaque of P1/2 or of the basilar tip, which could result in supratentorial thalamic or thalmogeniculate perforator stroke. [Yes/No]

Given there is an ACA, MCA, or PCA occlusion (or near occlusion) affecting proximal stem segment (A1/2, M1/2 P1/2), there is a potential “pial collateral gap” between the proximal thrombus and available pial collateral on the initial post contrast head CT. [Yes/No]

Given there is ACA, MCA, PCA occlusion (or near occlusion) of proximal stem segments, trunks, or distal major branches & having assessed state of circle of Willis, there is an end-of the-line watershed component to the stroke. [Yes/No]

Infratentorial Intradural Arterial Circulation

There is high cervical or intradural vertebral artery thrombosis. [Yes/No]

There is wall plaque or thrombus within of all or part of the basilar artery. [Yes/No]

There is thromosis of all or part of the anterior inferior cerebellar artery (AICA). [Yes/No]

There is evidence of stroke in a pontine perforating artery. [Yes/No]

There is thrombosis of all or part of the posterior inferior cerebellar artery (PICA). [Yes/No]

There is thrombosis of all or part of the superior cerebellar artery (SCA). [Yes/No]

Given there is high-grade stenosis or thrombosis of the basilar artery, there is adequate retrograde collateral filling the distal basilar & its branches. [Yes/No]

Given there is high-grade stenosis or thrombosis of the 1st segment of SCA, AICA, or PICA and there is adequate retrograde collateral filling of their distal pial branches, there is evidence of lateral brainstem outer surface perforator infarcts (arising off the occluded 1st segment of SCA/AICA/PICA. [Yes/No]