Brain death

Brain death refers to the irreversible end of all brain activity and is usually assessed clinically. 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. 

As the diagnosis of brain death is considered equivalent with cardiac death in many jurisdictions 4, and it allows organ donation for transplantation or withdrawal of life support, most countries have specific and varied related legal standards and practice guidelines 2,10

Radiographic features

Most imaging tests for brain death rely on the absence of cerebral blood flow as a surrogate for brain death. This can be assessed by a number of modalities including CT, MRI, ultrasound, nuclear medicine examinations, and catheter angiography. 

It is important to note that not all modalities and examinations are approved for the legal determination of brain death and that this will vary from country to country. 

CT
  • 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
MRI
  • T1: hypointense, with lost grey-white matter differentiation
  • T2
    • 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 non-visualization of the intracranial vessels5,6
Angiography (DSA)
  • no forward flow above the terminal ICA; considered gold standard imaging test 4
Nuclear medicine
  • cerebral perfusion 4,7
    • flow images are obtained in the anterior projection; delayed images follow 5 to 10 minutes after the injection
    • hot nose sign: increased external carotid artery perfusion to the nasal region (a cute sign, but of no real diagnostic value) 1
    • empty light bulb sign: absent intracranial uptake 
US
  • reverberant or oscillating 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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Article information

rID: 5240
Synonyms or Alternate Spellings:
  • Cerebral death

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Cases and figures

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    Case 1
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    Absent internal c...
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     Case 3: with hot nose sign
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    Case 4
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    Case 5: CTA
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    Case 8: fused images on SPECT 99mTC
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