When the preconditions for the clinical determination of brain death cannot be met, what imaging modalities are recommended to determine absence of intracranial blood flow? What findings in each test confirm brain death?

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College Answer

Test

Positive result

Four vessel angiography

no blood flow above the carotid siphon in the anterior circulation  and no blood flow above the foramen magnum in the posterior circulation

Radionuclide imaging

Tc-99m HMPAO scan demonstrating absent intracranial perfusion

CT angiography

absent enhancement bilaterally of peripheral intracranial arteries and central veins at 60 seconds.
There is less experience with this technique

Discussion

The answer above borrows heavily from the ANZICS Statement on Death and Organ Donation (I have linked to Version 3.2, from 2013).

In brief, the investigations and expected findings are as follows:

Four-vessel arterial digotal subtraction angiography:

  • blood flow should not be demonstrated above the level of the carotid 
    siphon in the anterior circulation, or above the foramen magnum in the posterior circulation

Tc-99m HMPAO radionuclide (SPECT) scan

  • Absent intracranial parenchymal Tc-99m HMPAO uptake

CT angiography

  • Absent contrast enhancement, at 60 seconds following bolus injection, bilaterally and of all of the following vessels:
    • MCA branches beyond the Sylvian branches
    • P2 segment of the PCA
    • pericallosal arteries
    • internal cerebral veins
  • Adequate contrast enhancement of the external carotid artery branches to confirm a technically adequate study.

References

ANZICS Death and Organ Donation Committee, THE ANZICS STATEMENT ON DEATH AND ORGAN DONATION Edition 3.2 2013