Primary Posterior Fossa Lesions and Preserved Supratentorial Cerebral Blood Flow: Implications for Brain Death Determination

Computed Tomography Perfusion for the Diagnosis of Brain Death: A Technical Review

Timely diagnosis of brain death (BD) is critical as it prevents unethical and futile continuation of support of vital organ functions when the patient has passed. Furthermore, it helps with avoiding the unnecessary use of resources and provides early opportunity for precious organ donation. The diagnosis of BD is mainly based on careful neurological assessment of patients with an established underlying diagnosis of neurological catastrophe capable of causing BD.Ancillary testing, however, is tremendously helpful in situations when the presence of confounders prevents or delays comprehensive neurological assessment. Traditionally, four-vessel digital subtraction angiography and computed tomography angiography have been used for blood flow (BF) examinations of the brain. The lack of BF in the intracranial arteries constitutes conclusive evidence that the brain is dead. However, there is an apparent discrepancy between the BF and sufficient cerebral perfusion; several studies have shown that in 15% of patients with confirmed clinical diagnosis of BD, BF is still preserved. In these patients, cerebral perfusion is significantly impaired. Hence, measurement of cerebral perfusion rather than BF will provide a more precise assessment of the brain function.In this review article, we discuss a brief history of BD, our understanding of its complex pathophysiology, current Canadian guidelines for the clinical diagnosis of BD, and the ancillary tests-specifically CT perfusion of the brain that help us with the prompt and timely diagnosis of BD.

The reticular activating system: a narrative review of discovery, evolving understanding, and relevance to current formulations of brain death

A series of landmark experiments conducted throughout the 20th century progressively localized the regions involved in consciousness to the reticular activating system (RAS) and its ascending projections. The first description of the RAS emerged in 1949 through seminal experiments performed by Moruzzi and Magoun in feline brainstems; additional experiments in the 1950s revealed connections between the RAS and the thalamus and neocortical structures. This knowledge has allowed for the explanation of disorders of consciousness with exquisite anatomic precision. The clinical relevance of the RAS is further apparent in modern definitions of brain death/death by neurologic criteria (BD/DNC), which require demonstration of the complete and permanent loss of capacity for consciousness as one of their core criteria. BD/DNC is currently understood across jurisdictions in terms of "whole brain" and "brainstem" formulations. Although their clinical examination between formulations is indistinguishable, policies for BD/DNC declaration may differ in the rare scenario of patients with isolated infratentorial brain injuries, in which ancillary testing is advised in the whole brain formulation but not the brainstem formulation. Canadian guidelines acknowledge that the distinction between whole brain and brainstem formulations is unclear with respect to clinical implications for patients with isolated infratentorial injuries. This has led to variability in Canadian clinicians' use of ancillary testing when the mechanism of BD/DNC is suspected to be an isolated infratentorial injury. The present narrative review highlights these concepts and explores implications for determination of BD/DNC in Canada, with specific emphasis on the RAS and its relevance to both formulations.

Infratentorial brain injury and death by neurologic criteria in Canada: a narrative review

There are two anatomic formulations of death by neurologic criteria accepted worldwide: whole-brain death and brainstem death. As part of the Canadian Death Definition and Determination Project, we convened an expert working group and performed a narrative review of the literature. Infratentorial brain injury (IBI) with an unconfounded clinical assessment consistent with death by neurologic criteria represents a nonrecoverable injury. The clinical determination of death cannot distinguish between IBI and whole-brain cessation of function. Current clinical, functional, and neuroimaging assessments cannot reliably confirm the complete and permanent destruction of the brainstem. No patient with isolated brainstem death has been reported to recover consciousness and all patients have died. Studies suggest a significant majority of isolated brainstem death will evolve into whole-brain death, influenced by time/duration of somatic support and impacted by ventricular drainage and/or posterior fossa decompressive craniectomy. Acknowledging variability in intensive care unit (ICU) physician opinion on this matter, a majority of Canadian ICU physicians would perform ancillary testing for death determination by neurologic criteria in the context of IBI. There is currently no reliable ancillary test to confirm complete destruction of the brainstem; ancillary testing currently includes evaluation of both infratentorial and supratentorial flow. Acknowledging international variability in this regard, the existing evidence reviewed does not provide sufficient confidence that the clinical exam in IBI represents a complete and permanent destruction of the reticular activating system and thus the capacity for consciousness. On this basis, IBI consistent with clinical signs of death by neurologic criteria without significant supratentorial involvement does not fulfill criteria for death in Canada and ancillary testing is required.

What does "brainstem death" mean? A review of international protocols

PURPOSE

The term "brainstem death" is ambiguous; it can be used to refer either exclusively to loss of function of the brainstem or loss of function of the whole brain. We aimed to establish the term's intended meaning in national protocols for the determination of brain death/death by neurologic criteria (BD/DNC) from around the world.

METHODS

Of 78 unique international protocols on determination of BD/DNC, we identified eight that referred exclusively to loss of function of the brainstem in the definition of death. Each protocol was reviewed to ascertain whether it 1) required assessment for loss of function of the whole brain, 2) required assessment only for loss of function of the brainstem, or 3) was ambiguous about whether loss of function of the higher brain was required to declare DNC.

RESULTS

Of the eight protocols, two (25%) required assessment for loss of function of the whole brain, three (37.5%) only required assessment for loss of function of the brainstem, and three (37.5%) were ambiguous about whether loss of function of the higher brain was required to declare death. The overall agreement between raters was 94% (κ = 0.91).

CONCLUSIONS

There is international variability in the intended meaning of the terms "brainstem death" and "whole brain death" resulting in ambiguity and potentially inaccurate or inconsistent diagnosis. Regardless of the nomenclature, we advocate for national protocols to be clear regarding any requirement for ancillary testing in cases of primary infratentorial brain injury who may fulfill clinical criteria for BD/DNC.

Infratentorial Brain Injury Among Patients Suspected of Death by Neurologic Criteria: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

There is a paucity of data on the frequency and prognosis of infratentorial brain injury among patients suspected of death by neurologic criteria (DNC), which likely contributes to scientific uncertainty regarding the role of isolated brainstem death in DNC determination. Our aim was to synthesize the prevalence, characteristics, and evolution of infratentorial brain injury, including isolated brainstem death, among patients suspected of DNC.

METHODS

We conducted a systematic review by searching Medline, Embase, EBM Reviews, CINAHL Complete, and the gray literature from inception to March 26, 2021. We selected cohort and cross-sectional studies, case reports, and case series that included patients suspected of DNC. Two study investigators independently performed study selection, data collection, and risk of bias assessment. Our primary outcomes were the respective prevalence of infratentorial brain injury and isolated brainstem death, which we meta-analyzed using mixed-effects Bayesian hierarchical models with diffuse priors. Our secondary outcomes were the characteristics and evolution of patients with infratentorial brain injury and isolated brainstem death.

RESULTS

Twenty-one studies met the selection criteria, most of which were of moderate to high risk of bias. Among patients suspected of DNC, the prevalence of infratentorial brain injury ranged from 2% to 16% (n = 3,602, mean prevalence: 6.3%, 95% highest density interval [2.4%-14.2%]), whereas the prevalence of isolated brainstem death ranged from 1% to 4% (n = 3,692, mean prevalence: 1.5%, 95% highest density interval [0.5%-3.9%]). A total of 38 isolated brainstem death cases with data on clinical characteristics and/or evolution were included. All had infratentorial strokes. Twenty patients had EEG background activity in the α or θ frequencies, 19 had preserved cerebral blood flow, 2 had preserved supratentorial cerebral perfusion, 2 had cortical responses to visual evoked potentials, and 1 had cortical responses to somatosensory evoked potentials. At the latest follow-up, 28 had progressed to whole-brain death.

DISCUSSION

Studies with moderate to high risk of bias suggest that infratentorial brain injury is relatively uncommon among patients suspected of DNC. Isolated brainstem death is rarer and seems to carry a high risk of progression to whole-brain death. These findings require further high-quality investigation.

Brain herniation on computed tomography is a poor predictor of whether patients with a devastating brain injury can be confirmed dead using neurological criteria

Background

It is unclear if the presence of compartmental brain herniation on neuroimaging should be a prerequisite to the clinical confirmation of death using neurological criteria. The World Brain Death Project has posed this as a research question.

Methods

The final computed tomography of the head scans before death of 164 consecutive patients confirmed dead using neurological criteria and 41 patients with devastating brain injury who died following withdrawal of life sustaining treatment were assessed by a neuroradiologist to compare the incidence of herniation and other features of cerebral swelling.

Results

There was no difference in the incidence of herniation in patients confirmed dead using neurological criteria and those with devastating brain injury (79% vs 76%, OR 1.23 95%, CI 0.56-2.67). The sensitivity and specificity of brain herniation in patients confirmed dead using neurological criteria was 79% and 24%, respectively. The positive and negative predictive value was 81% and 23%, respectively. The most sensitive computed tomography of the head findings for death using neurological criteria were diffuse sulcal effacement (93%) and basal cistern effacement (91%) and the most specific finding was loss of grey-white differentiation (80%). The only features with a significantly different incidence between the death using neurological criteria group and the devastating brain injury group were loss of grey-white differentiation (46 vs 20%, OR 3.56, 95% CI 1.55-8.17) and presence of contralateral ventricular dilatation (24 vs 44%, OR 0.41, 95% CI 0.20-0.84).

Conclusions

Neuroimaging is essential in establishing the cause of death using neurological criteria. However, the presence of brain herniation or other signs of cerebral swelling are poor predictors of whether a patient will satisfy the clinical criteria for death using neurological criteria or not. The decision to test must remain a clinical one.

Brain death: a clinical overview

Brain death, also commonly referred to as death by neurologic criteria, has been considered a legal definition of death for decades. Its determination involves many considerations and subtleties. In this review, we discuss the philosophy and history of brain death, its clinical determination, and special considerations. We discuss performance of the main clinical components of the brain death exam: assessment of coma, cranial nerves, motor testing, and apnea testing. We also discuss common ancillary tests, including advantages and pitfalls. Special discussion is given to extracorporeal membrane oxygenation, target temperature management, and determination of brain death in pediatric populations. Lastly, we discuss existing controversies and future directions in the field.

Jahi McMath, a New Disorder of Consciousness

In this paper, I review the case of Jahi McMath, who was diagnosed with brain death (BD). Nonetheless, ancillary tests performed nine months after the initial brain insult showed conservation of intracranial structures, EEG activity, and autonomic reactivity to the “Mother Talks” stimulus. She was clinically in an unarousable and unresponsive state, without evidence of self-awareness or awareness of the environment. However, the total absence of brainstem reflexes and partial responsiveness rejected the possibility of a coma. Jahi did not have uws because she was not in a wakefulness state and showed partial responsiveness. She could not be classified as a LIS patient either because LIS patients are wakeful and aware, and although quadriplegic, they fully or partially preserve brainstem reflexes, vertical eye movements or blinking, and respire on their own. She was not in an MCS because she did not preserve arousal and preserved awareness only partially. The CRS-R resulted in a very low score, incompatible with MCS patients. mcs patients fully or partially preserve brainstem reflexes and usually breathe on their own. MCS has always been described as a transitional state between a coma and UWS but never reported in a patient with all clinical BD findings. This case does not contradict the concept of BD but brings again the need to use ancillary tests in BD up for discussion. I concluded that Jahi represented a new disorder of consciousness, non-previously described, which I have termed “reponsive unawakefulness syndrome” (RUS).

Neurological Determination of Death Following Infratentorial Stroke: A Population-Based Cohort Study

BACKGROUND

There is international variability in whether neurological determination of death (NDD) is conceptually defined based on permanent loss of brainstem function or "whole brain death." Canadian guidelines are not definitive. Patients with infratentorial stroke may meet clinical criteria for NDD despite persistent cerebral blood flow (CBF) and relative absence of supratentorial injury.

METHODS

We performed a multicenter cohort study involving patients that died from ischemic or hemorrhagic stroke in Alberta intensive care units from 2013 to 2019, focusing on those with infratentorial involvement. Medical records were reviewed to determine the incidence and proportion of patients that met clinical criteria for NDD; whether ancillary testing was performed; and if so, whether this demonstrated the absence of CBF.

RESULTS

There were 95 (27%) deaths from infratentorial and 263 (73%) from supratentorial stroke. Sixteen patients (17%) with infratentorial stroke had neurological examination consistent with NDD (0.55 cases per million per year). Among patients that underwent confirmatory evaluation for NDD with an apnea test, ancillary test (radionuclide scan), or both, ancillary testing was more common with infratentorial compared with supratentorial stroke (10/12 (85%) vs. 25/47 (53%), p = 0.04). Persistent CBF was detected in 6/10 (60%) patients with infratentorial compared with 0/25 with supratentorial stroke (p = 0.0001).

CONCLUSIONS

Infratentorial stroke leading to clinical criteria for NDD occurs with an annual incidence of about 0.55 per million. There is variability in clinicians' use of ancillary testing. Persistent CBF was detected in more than half of patients that underwent radionuclide scans. Canadian consensus is needed to guide clinical practice.

Evaluation of Computed Tomography Angiography as an Ancillary Test to Reduce Confusion After Clinical Diagnosis of Brain Death

BACKGROUND

The diagnosis of brain death (BD) is mainly a clinical diagnosis. Ancillary tests may be used in confusing situations. Although computed tomography angiography (CTA) has high sensitivity and specificity, it can give false-positive results in cases with craniotomy.

OBJECTIVE

The aim of this study is to emphasize the importance of accurate and detailed clinical diagnosis and to reveal that there is organ loss as a result of prolonged supportive tests, especially in developing countries.

MATERIAL AND METHODS

This retrospective study included patients who were diagnosed with BD in the intensive care unit of Van Yüzüncü Yıl University, between September 2014 and August 2017 in Turkey. The study included 14 male and 8 female patients. Patients who did not show any spontaneous respiratory symptoms after the apnea test were diagnosed with clinical BD. Patients on neurodepressant medications who were hypothermic or hypoxic or had a severe endocrine or metabolic disorder were excluded from the study. CTA was used as an ancillary test in compliance with legal requirements. Age, sex, hospitalization days, day of clinical diagnosis of BD, first radiologic evaluation by CTA, clinical diagnosis, and radiologic evaluation were recorded for all patients.

RESULTS

Radiologic evaluation was not compatible with the clinical evaluation in 5 patients. Although 2 of these 5 patients had BD diagnosis clinically, blood flow could be expected during CTA because of cranial injury. Unlike in the literature, false positivity was found in 3 patients with hypoxic ischemic encephalopathy in the present study.

CONCLUSIONS

Proper management of limited resources and the facilitation of cadaver organ donation in developing countries are important and humanitarian global responsibilities. Revision of the country's legal regulations is important and is warranted in this regard.

[Diagnosis of irreversible loss of brain function ("brain death")-what is new?]

The determination of the irreversible cessation of brain function (ICBF) is conducted in Germany according to the guideline of the German Medical Association, which is currently its fourth update issued in July 2015. This article provides an assessment of the current situation including an international comparison. International case reports with allegedly incorrect ICBF diagnosis are reviewed from the point of view of the German guideline. These case reports underpin the validity of the German guideline, especially its following provisions: (1) in patients with known or suspected adaptation to chronic hypercapnia, apnea cannot be diagnosed as usual; therefore in such a case the proof of cerebral circulatory arrest is mandatory; (2) if perfusion scintigraphy is used for proof of cerebral circulatory arrest, only validated lipophilic radiopharmaceuticals are allowed. This is compatible with new research data which indicate that cellular function can be reactivated for several hours after circulatory arrest but not the brain function. The recently updated recommendations of the German Society for Clinical Neurophysiology and Functional Imaging (DGKN) for ancillary testing include editorial adaptations (e.g., the more precise specification of the electrode positions for electroencephalography), standards of display screen with digital electroencephalography and age-related minimum values of mean arterial pressure for Doppler and duplex sonography in children. The novel requirements regarding the institutional organization of ICBF diagnostics in Germany issued in the "Second law on the amendment of transplantation law-improvement of the cooperation and the framework for organ donation" that became effective recently are presented and discussed critically in this review.

Coma and Brain Death

PURPOSE OF REVIEW

This article discusses the diagnostic and therapeutic approach to patients who are comatose and reviews the current knowledge on prognosis from various causes of coma. This article also provides an overview of the principles for determination of brain death as well as advice on how to avoid common pitfalls.

RECENT FINDINGS

Technologic advances have refined our understanding of the physiology of consciousness and the spectrum of disorders of consciousness; they also promise to improve our prognostic accuracy. Yet the clinical principles for the evaluation and treatment of coma remain unaltered. The clinical standards for determination of death by neurologic criteria (ie, brain death) are also well established, although variabilities in local protocols and legal requirements remain a problem to be resolved.

SUMMARY

Effective evaluation of coma demands a systematic approach relying on clinical information to ensure rational use of laboratory and imaging tests. When the cause of coma is deemed irreversible in the setting of a catastrophic brain injury and no clinical evidence exists for brain and brainstem function, patients should be evaluated for the possibility of brain death by following the clinical criteria specified in the American Academy of Neurology guidelines.

Neurological determination of death in isolated brainstem lesions: A case report to highlight the issues involved

The neurological determination of death in patients with isolated brainstem lesions or by disruption of the posterior cerebral circulation is uncommon and many intensivists may never see such a case in their career. It is also the only major difference between the "whole brain" and "brain stem" formulations for the neurological determination of death. We present a case of a patient with infarction of the structures supplied by the posterior cerebral circulation in whom death was diagnosed using neurological criteria, to illustrate the issues involved. We also suggest that international consensus may be achieved if ancillary tests, such as CT angiography, are made mandatory in this situation o demonstrate loss of blood flow in the anterior cerebral circulation as well the posterior circulation.

How should we use imaging in the determination of brainstem death?

Brainstem death is defined as the "irreversible cessation of brainstem function", either due to primary intracranial events or extracranial factors such as hypoxia. The importance of accurate and timely diagnosis of brainstem death in critical care should not be understated, as it allows the withdrawal of treatment when it is no longer deemed to beneficial. Additionally, it may facilitate the process of organ donation. Overall, the diagnosis of brainstem death has four common principles across the world: (1) neurological criteria based on clinical assessment; (2) evidence of irreversible brain damage from known aetiology; (3) demonstrating an absence of a reversible cause; and (4) the use of ancillary studies. The latter in particular has been a controversial issue, with much debate continuing on how imaging should be used. We discuss three key questions surrounding the role of imaging in the diagnosis of brainstem death as well as important issues the radiology community should consider.