Brain death refers to the irreversible end of all brain activity and is usually assessed clinically. As this diagnosis is consider equivalent with cardiac death in many jurisdictions4, and it allows organ donation for transplantation or withdrawal of life support, most countries have specific related legal standards and practice guidelines 2. Radiographic testing may be used as additional support for a clinical diagnosis of brain death, such as when clinical tests are impossible to perform, e.g., ocular trauma precluding brainstem function assessment.
Most tests rely on the absence of cerebral blood flow as a surrogate for brain death. This can be assessed by a number of modalities:
- diffuse cerebral oedema with effacement of the grey-white matter borders
- CT angiography: non-opacification of the cortical middle cerebral arteries and internal cerebral veins are the most sensitive and specific markers on CTA 3
- T1: hypointense, with lost grey-white matter differentiation
- swollen gyri with hyperintense cortex
- expected flow void may be absent in vessels
- DWI: hemispheric high signal, severe ADC drop
- MR angiography: may be interpreted similarly to CT angiography, with nonvisualization of the intracranial vessels5,6
- no forward flow above the terminal ICA; considered gold standard imaging test4
- cerebral perfusion 4,7
- reverberant or ossicilating flow in the MCA vessels has been reported 8
- loss or reversal of diastolic flow in the MCA/ICA
- low acceleration time in the MCA
- on transcranial doppler
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