Role of computed tomography angiography and perfusion tomography in diagnosing brain death: A systematic review

Computed Tomography Angiography (CTA) in Selected Scenarios with Risk of Possible False-Positive or False-Negative Conclusions in Diagnosing Brain Death

It is widely accepted that brain death (BD) is a diagnosis based on clinical examination. However, false-positive and false-negative evaluation results may be serious limitations. Ancillary tests are used when there is uncertainty about the reliability of the neurologic examination. Computed tomography angiography (CTA) is an ancillary test that tends to have the lowest false-positive rates. However, there are various influencing factors that can have an unfavorable effect on the validity of the examination method. There are inconsistent protocols regarding the evaluation criteria such as scoring systems. Among the most widely used different scoring systems the 4-point CTA-scoring system has been accepted as the most reliable method. Appropriate timing and/or Doppler pre-testing could reduce the number of possible premature examinations and increase the sensitivity of CTA in diagnosing cerebral circulatory arrest (CCA). In some cases of inconclusive CTA, the whole brain computed tomography perfusion (CTP) could be a crucial adjunct. Due to the increasing significance of CTA/CTP in determining BD, the methodology (including benefits and limitations) should also be conveyed via innovative electronic training tools, such as the BRAINDEXweb teaching tool based on an expert system.

Comparison of early- and late-phase CT angiography findings in brain death

BACKGROUND

Late-phase images on computed tomography angiography (CTA), traditionally used for assessing cerebral circulatory arrest in brain death, suffer from suboptimal diagnostic yield due to stasis filling. Herein, we assessed contrast filling in individual intracranial arteries and veins in the early and late phases of CTA in patients with clinically confirmed brain death.

METHODS

Contrast opacification within 28 arterial/venous segments was evaluated in both phases of CTA in 79 patients. This information was combined with reports in the literature to calculate prevalence of contrast filling in different intracranial vessels. Additionally, diagnostic sensitivity of 4-point, 7-point, and 10-point scores defined for brain death were compared among ratings based on early, late, and both phases (arteries rated on early, veins rated on late phase) of imaging.

RESULTS

The median (IQR) number of vessel segments with contrast opacification was 0 (0-2) in early phase and 6 (0-10) in late phase. All segments showed increased prevalence of opacification when evaluated in late phase (p < 0.05). The M4 segments of MCA, internal cerebral veins, and vein of Galen had the lowest percentage of opacification in both phases. The sensitivity of 4-, 7-, and 10-point scoring algorithms increased from 59-91% to 94-99% when ratings were performed using early-phase images rather than based solely on late-phase images.

CONCLUSIONS

The incorporation of early-phase images might be considered as a strategy to improve the sensitivity of CTA as an ancillary test in confirming brain death, especially in patients without missing or questionable elements in clinical examination.

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.

Computed tomography angiography scoring systems and the role of skull defects in the confirmation of brain death

To assess and compare all current computed tomography angiography (CTA) scoring systems for the diagnostic workup of brain death (BD) to digital subtraction angiography (DSA) and clinical tests. Fifty-two patients with a clinical suspicion of BD underwent CTA and subsequently DSA. The diagnostic performance of all current CTA scoring systems was compared to that of DSA, in all patients with a suspicion of BD. A comparison to clinical tests was made only in DSA-positive for BD patients (n = 49), since in DSA-negative BD patients (n = 3) clinical tests were not performed. Further subgroup analysis was performed in relation to skull defects (SDs) stratification. Statistical analysis was conducted by applying statistics-contingency tables, Cochran's-Q test and McNemar's test. The CTA -10, and -7- and all 4-point scoring systems, showed overall sensitivities of 81,6%, 87.8% and 95.9% respectively and 100% specificity, when compared to DSA. In patients with a clinical verification of BD, the CTA -10 and -7-point scoring systems were significantly inferior to clinical tests (p = 0.004 and p = 0.031), while the 4-point scoring systems showed no such difference (p = 0.5). All 4-point scoring systems showed 100% sensitivity in patients with a minor SD or no SD. In patients with a major SD, all CTA scoring systems (- 10, - 7- and all 4-point) were less sensitive (62.5%, 62.5% and 75% respectively). The presence of a major SD was associated with an 8 × relative risk for false negative results in all 4-point scoring systems. CTA showed excellent diagnostic performance in patients with a suspicion of BD. The 4-point CTA scoring systems are the most sensitive for the diagnosis of BD, although in patients with a major SD patient, the role of CTA is ambiguous.

Reliability of CT angiography scoring systems used for brain death and the effect of cranial interventions on the results

OBJECTIVE

To assess vascular opacifications, the efficiency, and interobserver agreement (IOA) of five different computed tomography angiography (CTA) brain death (BD) scoring systems in patients with and without cranial interventions, for determining alternative findings correctly supporting BD diagnosis by CTA even in cranial intervention presence.

METHODS

45 patients clinically identified with BD and evaluated with CTA were included. IOA of five different scoring systems used for CTA BD diagnosis, the effect of intracranial interventions on scoring systems, and vascular opacification were evaluated.

RESULTS

IOA was almost perfect (κ = 0.843-0.911, p < 0.05) and substantial (κ = 0.771-0.776, p < 0.05) in all scoring systems. Significant relationships were observed between craniectomy presence and middle cerebral artery M4 segment and internal cerebral vein (ICV) opacification. No opacification was observed in straight sinus (SS) by observers in any of the craniectomized patients.

CONCLUSION

IOA of CTA scoring systems is adequate. But a significant degree of false-negative results is observed due to ICV filling in craniectomy cases. Opacification presence in SS can give an idea of BD in these cases.

NMR-based metabolomics of human cerebrospinal fluid identifies signature of brain death

INTRODUCTION

Brain death (BD) is the irreversible cessation of all functions of the entire brain, including the brainstem. Cerebrospinal fluid (CSF) is a biological liquid that circulates in brain and spine. Metabolomics is able to reveal the response of biological systems to diverse factors in a specific moment or condition. Therefore, the study of this neurological condition through metabolic profiling using high resolution Nuclear Magnetic Resonance (NMR) spectroscopy is important for understanding biochemical events.

OBJECTIVES

The aim of the current study is to identify the metabolomics signature of BD using ¹H-NMR spectroscopy in human CSF.

METHODS

¹H-NMR spectroscopy has been employed for metabolomic untargeted analysis in 46 CSF samples: 22 control and 24 with BD. Spectral data were further subjected to multivariate analysis.

RESULTS

Statistically significant multivariate models separated subject's samples with BD from controls and revealed twenty one discriminatory metabolites. The statistical analysis of control and BD subjects using Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) model resulted in R²X of 0.733 and Q² of 0.635. An elevation in the concentration of statistically discriminant metabolites in BD was observed.

CONCLUSION

This study identifies a metabolic signature associated with BD and the most relevant enriched selected metabolic pathways.

Absent 18F-FDG Uptake in the Brain-Unsuspected Brain Death

Brain death is the complete, irreversible cessation of brain function, including the capacity for brainstem, respiratory, and vegetative activities. It is a clinical diagnosis that can be supplemented with brain perfusion imaging. Absent cerebral blood flow can be visualized with CT angiography or perfusion scintigraphy. F-FDG PET/CT, visualizing glucose uptake, is another approach that has been shown to indicate brain death in small case series. We here present a case with unsuspected absent F-FDG uptake and thus no metabolic activity, in the brain. The patient was declared brain dead later the same day.

Retrospective analysis of the apnea test and ancillary test in determining brain death

Objective

We investigated the frequency of apnea tests, and the use of ancillary tests in the diagnosis of brain death in our hospital, as well as the reasons for not being able to perform apnea testing and the reasons for using ancillary tests.

Methods

In this retrospective study, the files of patients diagnosed with brain death between 2012 - 2018 were examined. The preferred test was determined if an ancillary test was performed in the diagnosis of brain death. The rate and frequency of use of these tests were analyzed.

Results

During the diagnosis of brain death, an apnea test was performed on 104 (61.5%) patients and was not or could not be performed on 65 (38.5%) patients. Ancillary tests were performed on 139 (82.8%) of the patients. The most common ancillary test was computed tomography angiography (79 patients, 46.7%). Approval for organ donation was received in the meetings with the family following the diagnosis of brain death for 55 (32.5%) of the 169 patients.

Conclusion

We found an increase in the rate of incomplete apnea tests and concordantly, an increase in the use of ancillary tests in recent years. Ancillary tests should be performed on patients when there is difficulty in reaching a decision of brain death, but it should not be forgotten that there is no worldwide consensus on the use of ancillary tests.

Diagnostic accuracy of a revised computed tomography angiography score for brain death confirmation, combining supra-tentorial arteries and infra-tentorial veins

PURPOSE

The 4-point score is the corner stone of brain death (BD) confirmation using computed tomography angiography (CTA). We hypothesized that considering the superior petrosal veins (SPVs) may improve CTA diagnosis performance in BD setting. We aimed at comparing the diagnosis performance of three revised CTA scores including SPVs and the 4-point score in the confirmation of BD.

METHODS

In this retrospective study, 69 consecutive adult-patients admitted in a French University Hospital meeting clinical brain death criteria and receiving at least one CTA were included. CTA images were reviewed by two blinded neuroradiologists. A first analysis compared the 4-point score, considered as the reference and three non-opacification scores: a "Toulouse score" including SPVs and middle cerebral arteries, a "venous score" including SPVs and internal cerebral veins and a "7-score" including all these vessels and the basilar artery. Psychometric tools, observer agreement and misclassification rates were assessed. A second analysis considered clinical examination as the reference.

RESULTS

Brain death was confirmed by the 4-score in 59 cases (89.4 %). When compared to the 4-score, the Toulouse score displayed a 100 % positive predictive value, a substantial observer agreement (0.77 [0.53; 1]) and the least misclassification rate (3.03 %). Results were similar in the craniectomy subgroup. The Toulouse score was the only revised test that combined a sensitivity close to that of the 4-score (86.4 % [75.7; 93.6] and 89.4 % [79.4; 95.6], p-value < 0.001, respectively) and a substantial observer agreement.

CONCLUSIONS

A score including SPVs and middle cerebral arteries is a valid method for BD confirmation using CTA even in patients receiving craniectomy.

Diagnosis of brain death in Brazil

Brain death, defined as the complete and irreversible loss of brain functions, has a history that is linked to the emergence of intensive care units and the advancement of artificial ventilatory support. In Brazil, by federal law, the criteria for the diagnosis of brain death have been defined by the Federal Council of Medicine since 1997 and apply to the entire Brazilian territory. Resolution 2,173/2017 of the Federal Council of Medicine updated the criteria for diagnosing brain death. These changes include the following: the requirement for the patient to meet specific physiological prerequisites and for the physician to provide optimized care to the patient before starting the procedures for diagnosing brain death and to perform complementary tests, as well as the need for specific training for physicians who make this diagnosis. Other changes include the reduction of the time interval between the two clinical examinations, the possibility of continuing procedures in the presence of unilateral ear or eye injury, the performance of a single apnea test and the creation of a statement of brain death determination that includes the recording of all procedures in a single document. This document, despite the controversy surrounding it, increases the safety necessary when establishing a diagnosis of such importance and has positive implications that extend beyond the patient and the physician to reach the entire health system.

Computed tomography angiography accuracy in brain death diagnosis

OBJECTIVE

The present study was designed to answer several concerns disclosed by systematic reviews indicating no evidence to support the use of computed tomography angiography (CTA) in the diagnosis of brain death (BD). Therefore, the aim of this study was to assess the effectiveness of CTA for the diagnosis of BD and to define the optimal tomographic criteria of intracranial circulatory arrest.

METHODS

A unicenter, prospective, observational case-control study was undertaken. Comatose patients (Glasgow Coma Scale score ≤ 5), even those presenting with the first signs of BD, were included. CTA scanning of arterial and venous vasculature and transcranial Doppler (TCD) were performed. A neurological determination of BD and consequently determination of case (BD group) or control (no-BD group) was conducted. All personnel involved with assessing patients were blinded to further tests results. Accuracy of BD diagnosis determined by using CTA was calculated based on the criteria of bilateral absence of visualization of the internal cerebral veins and the distal middle cerebral arteries, the 4-point score (4PS), and an exclusive criterion of absence of deep brain venous drainage as indicated by the absence of deep venous opacification on CTA, the venous score (VS), which considers only the internal cerebral veins bilaterally.

RESULTS

A total of 106 patients were enrolled in this study; 52 patients did not have BD, and none of these patients had circulatory arrest observed by CTA or TCD (100% specificity). Of the 54 patients with a clinical diagnosis of BD, 33 met the 4PS (61.1% sensitivity), whereas 47 met the VS (87% sensitivity). The accuracy of CTA was time related, with greater accuracy when scanning was performed less than 12 hours prior to the neurological assessment, reaching 95.5% sensitivity with the VS.

CONCLUSIONS

CTA can reliably support a diagnosis of BD. The criterion of the absence of deep venous opacification, which can be assessed by use of the VS criteria investigated in this study, can confirm the occurrence of cerebral circulatory arrest.Clinical trial registration no.: 12500913400000068 (clinicaltrials.gov).

Impact of Skull Defects on the Role of CTA for Brain Death Confirmation

BACKGROUND AND PURPOSE

Intracranial pressure modifications caused by a skull defect, such as craniectomy or craniotomy, may change the hemodynamics and decrease the accuracy of CTA to confirm brain death. This study aimed to evaluate the impact of a skull defect and the interpretation criteria of images on this diagnostic test.

MATERIALS AND METHODS

A series of consecutive patients with a clinical diagnosis of brain death underwent CTA (case group), while the control group comprised patients with acute ischemic stroke in the same period. CTA criteria adopted to confirm brain death were the absence of opacification of the M4 branches and internal cerebral veins. The evaluation also included the presence of "stasis filling." Cases were stratified as intact skull, craniotomy, and craniectomy. Three neuroradiologists evaluated all examinations independently.

RESULTS

In the case group, according to the Frampas criteria, the sensitivity of CTA to confirm brain death was 95.5% in patients with intact skull, 87.5% with craniotomy, and 60% with craniectomy. False-negative diagnoses of brain death were 15.6%, related to stasis filling in 71.4% (P < .001). However, according to the "modified Frampas criteria," the sensitivity of CTA to confirm brain death was 100% in patients with intact skull, 93.8% with craniotomy, and 80% with craniectomy. False-negative diagnoses of brain death were found in 6.2% of patients, and there was no stasis filling. CTA showed 100% specificity in the control group. There were no disagreements among observers.

CONCLUSIONS

CTA had a high diagnostic accuracy and reproducibility to confirm brain death in patients with an intact skull. The modified Frampas criteria increased the sensitivity of CTA, particularly in patients with a skull defect. A concurrent skull defect, especially craniectomy, can decrease the sensitivity of CTA to confirm brain death.

Mechanical Roles of F-Actin in the Differentiation of Stem Cells: A Review

In the development and differentiation of stem cells, mechanical forces associated with filamentous actin (F-actin) play a crucial role. The present review aims to reveal the relationship among the chemical components, microscopic structures, mechanical properties, and biological functions of F-actin. Particular attention is given to the functions of the cytoplasmic and nuclear microfilament cytoskeleton and their regulation mechanisms in the differentiation of stem cells. The distributions of different types of actin monomers in mammal cells and the functions of actin-binding proteins are summarized. We discuss how the fate of stem cells is regulated by intra/extracellular mechanical and chemical cues associated with microfilament-related proteins, intercellular adhesion molecules, etc. In addition, we also address the differentiation-induced variation in the stiffness of stem cells and the correlation between the fate and geometric shape change of stem cells. This review not only deepens our understanding of the biophysical mechanisms underlying the fates of stem cells under different culture conditions but also provides inspirations for the tissue engineering of stem cells.

Confirmation of brain death using optical methods based on tracking of an optical contrast agent: assessment of diagnostic feasibility

We aimed to determine whether optical methods based on bolus tracking of an optical contrast agent are useful for the confirmation of cerebral circulation cessation in patients being evaluated for brain death. Different stages of cerebral perfusion disturbance were compared in three groups of subjects: controls, patients with posttraumatic cerebral edema, and patients with brain death. We used a time-resolved near-infrared spectroscopy setup and indocyanine green (ICG) as an intravascular flow tracer. Orthogonal partial least squares-discriminant analysis (OPLS-DA) was carried out to build statistical models allowing for group separation. Thirty of 37 subjects (81.1%) were classified correctly (8 of 9 control subjects, 88.9%; 13 of 15 patients with edema, 86.7%; and 9 of 13 patients with brain death, 69.2%; p < 0.0001). Depending on the combination of variables used in the OPLS-DA model, sensitivity, specificity, and accuracy were 66.7–92.9%, 81.8–92.9%, and 77.3–89.3%, respectively. The method was feasible and promising in the demanding intensive care unit environment. However, its accuracy did not reach the level required for brain death confirmation. The potential usefulness of the method may be improved by increasing the depth of light penetration, confirming its accuracy against other methods evaluating cerebral flow cessation, and developing absolute parameters for cerebral perfusion.

Computed tomography angiography as a confirmatory test for the diagnosis of brain death

OBJECTIVE

For a diagnosis of brain death (BD), ancillary testing is performed if patient factors prohibit a complete clinical examination and apnea test. The American Academy of Neurology (AAN) guidelines identify cerebral angiography (CA), cerebral scintigraphy, electroencephalography, and transcranial Doppler ultrasonography as accepted ancillary tests. CA is widely considered the gold standard of these, as it provides the most reliable assessment of intracranial blood flow. CT angiography (CTA) is a noninvasive and widely available study that is also capable of identifying absent or severely diminished intracranial blood flow, but it is not included among the AAN's accepted ancillary tests because of insufficient evidence demonstrating its reliability. The objective of this study was to assess the statistical performance of CTA in diagnosing BD, using clinical criteria alone or clinical criteria plus CA as the gold-standard comparisons.

METHODS

The authors prospectively enrolled 22 adult patients undergoing workup for BD. All patients had cranial imaging and clinical examination results consistent with BD. In patients who met the AAN clinical criteria for BD, the authors performed CA and CTA so that both tests could be compared with the gold-standard clinical criteria. In cases that required ancillary testing, CA was performed as a confirmatory study, and CTA was then performed to compare against clinical criteria plus CA. Radiographic data were evaluated by an independent neuroradiologist. Test characteristics for CTA were calculated.

RESULTS

Four patients could not complete the standard BD workup and were excluded from analysis. Of the remaining 18 patients, 16 met AAN criteria for BD, 9 of whom required ancillary testing with CA. Of the 16 patients, 2 who also required CA ancillary testing were found to have persistent intracranial flow and were not declared brain dead at that time. These patients also underwent CTA; the results were concordant with the CA results. Six patients who were diagnosed with BD on the basis of clinical criteria alone also underwent CA, with 100% sensitivity. For all 18 patients included in the study, CTA had a sensitivity of 75%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 33%.

CONCLUSIONS

Clinical examination with or without CA remains the gold standard in BD testing. Studies assessing the statistical performance of CTA in BD testing should compare CTA to these gold standards. The statistical performance of CTA in BD testing is comparable to several of the nationally accepted ancillary tests. These data add to the growing medical literature supporting the use of CTA as a reliable ancillary test in BD testing.

Highly water-stable rare ternary Ag-Au-Se nanocomposites as long blood circulation time X-ray computed tomography contrast agents

X-ray computed tomography (CT) is a powerful and widely used medical non-invasive technique that often requires intravenous administration of contrast agents (CAs) to better visualize soft tissues. In this work, we have developed a novel CT contrast agent based on ternary Ag-Au-Se chalcogenide nanoparticles (NP). A facile ligand exchange by using a 3 kDa PEGylated ligand with a dithiol dihydrolipoic acid as an anchor group resulted in highly water-soluble and monodisperse nanoparticles. These PEGylated ternary NPs were tested in vivo in mice, showing slow uptake by the mononuclear phagocyte system, long blood circulation times, low toxicity, and very good X-ray contrast, thus being promising candidates as CT contrast agents for clinical applications.

Guidelines for the assessment and acceptance of potential brain-dead organ donors

Organ transplantation is the only alternative for many patients with terminal diseases. The increasing disproportion between the high demand for organ transplants and the low rate of transplants actually performed is worrisome. Some of the causes of this disproportion are errors in the identification of potential organ donors and in the determination of contraindications by the attending staff. Therefore, the aim of the present document is to provide guidelines for intensive care multi-professional staffs for the recognition, assessment and acceptance of potential organ donors.

Use of Transcranial Doppler Ultrasound for Diagnosis of Brain Death in Patients with Severe Cerebral Injury

Background

The aim of this study was to investigate the use of transcranial Doppler (TCD) for diagnosis of brain death in patients with severe cerebral injury.

Material/Methods

This retrospective study enrolled 42 patients based on inclusion and exclusion criteria. All patients were divided into either the brain death group or the survival group according to prognosis. Blood flow of the brain was examined by TCD and analyzed for spectrum changes. The average blood flow velocity (Vm), pulse index (PI), and diastolic blood flow in reverse (RDF) were recorded and compared.

Results

The data demonstrated that the average speed of bilateral middle cerebral artery blood flow in the brain death group was significantly reduced (P<0.05). However, the PI of the brain death group increased significantly. Moreover, RDF spectrum and nail-like sharp peak spectrum of the brain death group was higher than in the survival group.

Conclusions

Due to its simplicity, high repeatability, and specificity, TCD combined with other methods is highly valuable for diagnosis of brain death in patients with severe brain injury.