NEUROIMAGING / NEUROSONOLOGY

Neurosonology and the brain death diagnosis

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

Introduction

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

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)

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

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)

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