Hyperacute Arterial Stroke: CT Perfusion

History

Acute change in neurologic status; rule out stroke.

Exam

CT Perfusion: note CT perfusion is obtained after the 1st bolus (i.e. 1st pass) of contrast and timed based on opacification of normal proximal artery opacification in the head; there is no recirculation effect. Therefore, CT perfusion does not reflect the effects of functional collateralization. Thus, evidence of low CBV and CBF may overestimate the depth of injury in the stroke-zones.

Purpose

1. Evidence of abnormal prolonged TTP/prolonged MTT/ with partially reduced CBQ (flow)/partially reduced CBV (volume) is consistent with oligemia (tissue at risk); this may be improved by collateral on the CTA venocapillary pool analysis, or not.

2. Evidence of abnormal prolonged TTP/prolonged MTT/ with moderately reduced CBF & CBV is consistent with more significant oligemia (ischemic penumbra); this may be partially improved by collateral, or not.

3. Evidence of abnormal prolonged TTP, plus signal dropout within the central part of the prolonged MTT (out of range effect caused by virtually no transcapillary flow), plus markedly reduced or absent CBF & CBV is consistent with advanced oligemia (dense ischemic core). If the MTT signal loss is severe (all black) then venous stasis/venous collapse has probably been added to the afferent arterial block. These cases can end up as sequestered infarctions.

4. Are there findings consistent with the physiologic based hyperemia in the collateral stroke zone with increased TTP/MTT/CBF/CBV; collateral zone changes will be adjacent to the positive diffusion area on MR and do not show contrast leak on CTA.

5. Are there findings more consistent with post ischemic dysautoregulation with increased TTP/MTT but reduced CBV/CBF); these areas may show leak of contrast on CTA and will be within the positive diffusion area on the MR.

6. Final three observations (characteristic of arterial stroke): a. do the areas of oligemia match specific, recognizable, arterial perfusion zones; b. do these zones affect eloquent sites or major white matter tracts; and finally, c. there must be a sharp delineation at the border between the ischemic tissue and the adjacent non ischemic tissue.

7. Note: CT perfusion is insensitive to brainstem infarctions mainly due to beam hardening artifact produced by the skull base.

Prior Study

CT Head

Findings

Initial Evaluation (Technical Aspects)

There is artifact associated with patient motion. [Yes/No]

There is artifact associated with poor cardiac output. [Yes/No]

There is artifact associated with problematic contrast injection. [Yes/No]

Time to Peak (TTP)

There is prolonged (slower flow) TTP in a recognizable arterial perfusion zone. [Yes/No]

There is decreased (shortened) TTP. [Yes/No]

Mean Transit Time (MTT)

There is prolonged (increased) MTT in a recognizable arterial perfusion zone. [Yes/No]

There is decreased (shortened) MTT in a recognizable arterial perfusion zone. [Yes/No]

Cerebral Blood Flow (CBF)

There is reduced CBF in a recognizable arterial perfusion zone. [Yes/No]

There is increased CBF in a recognizable arterial perfusion zone. [Yes/No]

Cerebral Blood Volume (CBV)

There is reduced CBV in a recognizable arterial perfusion zone. [Yes/No]

There is increased CBV in a recognizable arterial perfusion zone. [Yes/No]

Other

Other findings are present more consistent with a diagnosis other than stroke. [Yes/No]

Impression

Hyperacute Stroke - Arterial, Diagnostic: CT Perfusion

There is no evidence of acute stroke.
There is evidence of acute stroke.
There is an abnormality, but it is related to a process other than stroke.