Neurosonology and the brain death diagnosis

Created 29/11/2021, last revision 29/04/2023


  • brain death and cerebral circulatory arrest (CCA) are not identical conditions
    • brain death is a clinical diagnosis characterized by the irreversible loss of all brain functions, including the brainstem
    • several mechanisms lead to brain death:  increase in intracranial pressure (ICP), subsequent loss in cerebral autoregulation, ↓ cerebral blood flow, and finally, cerebral circulatory arrest
    • there may be a delay of several hours between the development of circulatory arrest and clinically detectable loss of brain function
  • TCD/TCCD is a non-invasive bedside technique, that allows monitoring or frequent checks in neurocritically ill patients
  • a decrease in intracerebral flow can be detected, progressing to the cerebral circulatory arrest

Intracranial flow patterns

  • the increase of ICP and subsequent decrease of cerebral perfusion pressure (CPP) results in progressive changes in the waveform of the Doppler spectra  → hemodynamics notes
Content available only for logged-in subscribers (registration will be available soon)

Examination procedure

  • the examination should be performed by a trained physician with experience in the ultrasound technique and familiarity with the pathophysiology of brain death
  • a 2MHz diagnostic probe is used
  • basic approaches:
    • transtemporal window
    • transforaminal window (via the foramen magnum)
    • transorbital window
  • proof of cerebral circulation arrest – registration of typical flow patterns (oscillations or systolic spikes) in multiple intracranial arteries (MCA, ACA, PCA, terminal ICA, VA, and BA) is required – at least in MCA bilaterally and in the basilar artery
    • evaluation of ICA alone is not appropriate (possible shunt to ECA without brain perfusion) (Freitas, 2003)
    • assessment of the BA is essential to avoid false-positive results
    • a pathological flow pattern can also be detected in the extracranial arteries (CCA, ICA, VA) or ophthalmic artery (Blanco, 2020)
  • proof of irreversibility of cerebral circulatory arrest:
    • examination showing the above-stated flow pattern lasting ≥ 30 minutes  OR
    • repeated examinations separated by ≥ 30 minutes
    • transitory patterns compatible with cerebral circulatory arrest have been described in patients with SAH rebleeding and after cardiac arrest; a 30-minute interval is sufficient to confirm the irreversibility of the pattern

MAP (Mean Arterial Pressure) should be > 60 mmHg and systolic BP > 90 mmHg during the whole ultrasound examination

 Poor acoustic window

  • use ultrasound contrast agents (up to 98% of patients can be examined this way)
  • use a different approach (incomplete examination should not be used as a confirmatory test of circulatory arrest)

    • transorbital (detect flow in the carotid siphon)
    • extracranial examination (indirect proof of circulatory arrest)

Skull defects

  • patients with clinical brain death who have had large craniectomy or skull fractures, the persistent diastolic flow may be observed (similar to what occurs in children less than 1 year of age in whom the fontanelles are still open)
  • other diagnostic modalities, such as cerebral angiography or radionuclide imaging, may be necessary in these cases to confirm the diagnosis of brain death

Related Content

Send this to a friend
you may find this topic useful:

Neurosonology and the brain death diagnosis