Racking the brain: Detection of cerebral edema on postmortem computed tomography compared with forensic autopsy

Post mortem computed tomography meets radiomics: a case series on fractal analysis of post mortem changes in the brain

Estimating the post-mortem interval is a fundamental, albeit challenging task in forensic sciences. To this aim, forensic practitioners need to assess post-mortem changes through a plethora of different methods, most of which are inherently qualitative, thus providing broad time intervals rather than precise determinations. This challenging problem is further complicated by the influence of environmental factors, which modify the temporal dynamics of post-mortem changes, sometimes in a rather unpredictable fashion. In this context, the search for quantitative and objective descriptors of post-mortem changes is highly demanded. In this study, we used computed tomography (CT) to assess the post-mortem anatomical modifications occurring in the time interval 0-4 days after death in the brain of four corpses. Our results show that fractal analysis of CT brain slices provides a set of quantitative descriptors able to map post-mortem changes over time throughout the whole brain. Although incapable of producing a direct estimation of the PMI, these descriptors could be used in combination with other more established methods to improve the accuracy and reliability of PMI determination.

[Postmortem assessment of cerebral edema]

An analysis of literature data on the methods of post-mortem assessment of cerebral edema is presented. Based on the mechanisms of development, two main types of cerebral edema are distinguished: cytotoxic (intracellular) and vasogenic (extracellular). To determine cerebral edema, a number of methods are used, both direct and indirect, invasive and non-invasive assessment. Direct methods for assessing cerebral edema are based on determining the amount of water in its tissue. Indirect methods include morphological and radiation studies. Traditionally, the most evidence-based criteria for the diagnosis of cerebral edema are macroscopic and microscopic changes determined at autopsy. Methods are also indicated for determining the content of water in brain tissue by comparing the mass of wet and dry brain, as well as estimating the specific density of brain tissue.

Head CT: Toward Making Full Use of the Information the X-Rays Give

Although clinical head CT images are typically interpreted qualitatively, automated methods applied to routine clinical head CTs enable quantitative assessment of brain volume, brain parenchymal fraction, brain radiodensity, and brain radiomass. These metrics gain clinical meaning when viewed relative to a reference database and expressed as quantile regression values. Quantitative imaging data can aid in objective reporting and in the identification of outliers, with possible diagnostic implications. The comparison to a reference database necessitates standardization of head CT imaging parameters and protocols. Future research is needed to learn the effects of virtual monochromatic imaging on the quantitative characteristics of head CT images.

Tissue sample analysis for post mortem determination of brain edema

The post mortem evaluation of a brain edema is routinely performed by pathologists based on the macroscopic signs during autopsy. This method represents the current gold standard, but is subjective and observer dependent. Therefore, three post mortem evaluation methods of brain samples were analyzed in this work: histology, wet-dry weight and normalized cerebral weight, which was described in 2020 by Bauer et al. Tissue samples from six different regions of 34 brains were collected and examined both by rating of histological slides and by measuring the water content by using a drying oven. The rating of the histological slides, stained with hematoxylin and eosin, was performed by two pathologists independently. For the water content, the wet weight and the dry weight of each sample were set in relation. The normalized cerebral weight was calculated by dividing the brain weight by the brain volume, which were both determined during autopsy and in computed tomography images, respectively. A fair to moderate interrater agreement was obtained for the histologic evaluation and a significant correlation was present between one rater and the wet-dry weight and the normalized cerebral weight method. When classifying according to the gold standard, a significant difference was detected between the edematous and nonedematous cases by using the wet-dry weight method in the cerebral cortex and by using the normalized cerebral weight method. However, the significant correlations and group differences were limited to the aforementioned results. In conclusion, both the histological and the wet-dry weight method show limited benefits for the classification of brain edema and the histology analysis is highly observer dependent. The normalized cerebral weight method, however, reveals a significant effect between the edematous and nonedematous cases when classifying according to the gold standard. Therefore, we suggest to apply this method for the assessment of brain edema since it is objective and rater independent. Nevertheless, the exact evaluation of brain edema remains a challenging task, especially due to the continuous transition between no edema and edema.

Postmortem Magnetic Resonance Imaging and Postmortem Computed Tomography in Ligature and Manual Strangulation

PURPOSE

The aim of this study was to evaluate magnetic resonance imaging (MRI) findings in cases of fatal manual or ligature strangulation. Verification of strangulation by computed tomography (CT), MRI, and at autopsy as well as its detectability in each modality was assessed.

METHODS

We retrospectively analyzed 6 manual and ligature strangulation cases between 2013 and 2019 who all underwent a whole-body CT, head and neck MRI, and an autopsy. Two radiologists examined head and neck imaging data and compared the data to autopsy findings.

RESULTS

Magnetic resonance imaging showed a high efficiency in verifying intramuscular hemorrhages, which were confirmed in autopsy. Moreover, in one case without a visible strangulation mark, soft tissue injuries associated with strangulation were detected. Fractures, especially thyroid cartilage fractures, were successfully diagnosed by CT.

CONCLUSIONS

As MRI showed a successful detection of soft tissue lesions in relation to strangulation, it can serve as an alternative method or provide additional value to an autopsy. Intramuscular hemorrhages are a common finding in manual and ligature strangulation, providing a useful sign of applied pressure on the neck. However, to evaluate fractures, an additional CT or autopsy is recommended.

Analysis of different post mortem assessment methods for cerebral edema

While cerebral edema is a live-threatening condition in living persons, also an edema-like fluid redistribution can occur post mortem. In deceased, usually macroscopic signs are evaluated during autopsy in order to determine the presence or absence of cerebral edema. As a quantitative and objective classification is beneficial, an already existing method (Radojevic et al., 2017), which is based on a mathematical formula using the intracranial dimensions and the cerebral weight, was compared to the evaluation of macroscopic signs in 31 cases. The results showed an excellent agreement for the comparison between the raters as well as the measurement methods (at opened skull or in CT images). However, both measurement methods only poorly agree with the macroscopic edema evaluation. In order to find a more concordant method, the normalized cerebral weight, which puts the cerebral weight in relation to the intracranial volume, was calculated for 115 cases. This method resulted in an excellent agreement with the macroscopic rating and showed a clear numerical difference between the edematous and nonedematous group. While the influence of the post mortem time and the cooling time was found to be negligible, the age at death might confound the edema classification due to pre-existing cerebral atrophy leading to lower cerebral weights. In summary, the present study compared different assessment methods to classify cerebral edema and developed a rater independent, objective and quantitative classification method, which was as reliable as the rating of the forensic pathologists.

Postmortem imaging findings and cause of death determination compared with autopsy: a systematic review of diagnostic test accuracy and meta-analysis

BACKGROUND

The aim of this study was to evaluate the sensitivity of postmortem computed tomography (PMCT), postmortem magnetic resonance imaging (PMMR) and PMCT angiography (PMCTA) compared with autopsy in cases of adult death investigations.

METHODS

For this systematic review and meta-analysis, Embase, PubMed, Scopus, Web of Science and Medline were searched for eligible studies in October 2016; a follow-up literature search was conducted in March 2018. Studies referring to PMCT, PMCTA and/or PMMR of more than 3 cases with subsequent autopsy were included. Data were extracted from published texts in duplicate. The extracted outcomes were categorized as follows: soft tissue and organ findings, skeletal injuries, haemorrhages, abnormal gas accumulations and causes of death. The summary measure was sensitivity, if 3 or more studies were available. To combine studies, a random effects model was used. Variability and heterogeneity within the meta-analysis was assessed.

RESULTS

Of 1053 studies, 66 were eligible, encompassing a total of 4213 individuals. For soft tissue and organ findings, there was a high pooled sensitivity with PMCTA (0.91, 95% CI 0.81-0.96), without evidence for between-study variability (Cochrane's Q test p = 0.331, I² = 24.5%). The pooled sensitivity of PMCT+PMMR was very high in skeletal injuries (0.97, CI 0.87-0.99), without evidence for variability (p = 0.857, I² = 0.0%). In detecting haemorrhages, the pooled sensitivity for PMCT+PMMR was the highest (0.88, 95% CI 0.35-0.99), with strong evidence of heterogeneity (p < 0.05, I² > 50%). Pooled sensitivity for the correct cause of death was the highest for PMCTA with 0.79 (95% CI 0.52-0.93), again with evidence of heterogeneity (p = 0.062, I² > 50%).

CONCLUSION

Distinct postmortem imaging modalities can achieve high sensitivities for detecting various findings and causes of death. This knowledge should lead to a reasoned use of each modality. Both forensic evidence and in-hospital medical quality would be enhanced.

Pediatric postmortem computed tomography: initial experience at a children's hospital in the United States

Postmortem CT might provide valuable information in determining the cause of death and understanding disease processes, particularly when combined with traditional autopsy. Pediatric applications of postmortem imaging represent a new and rapidly growing field. We describe our experience in establishing a pediatric postmortem CT program and present a discussion of the distinct challenges in developing this type of program in the United States of America, where forensic practice varies from other countries. We give a brief overview of recent literature along with the common imaging findings on postmortem CT that can simulate antemortem pathology.

Postmortem evaluation of brain edema: An attempt with measurements of water content and brain-weight-to-inner-skull-circumference ratio

INTRODUCTION

Postmortem evaluations of cerebral edema typically involve examinations of macroscopic features such as the presence of pressure signs and compression of the ventricles. Global massive edema is easily detectable in an autopsy, but less-extensive edema may be difficult to diagnose.

AIM

The aim of this study was to compare measurements of brain water contents, postmortem CT radiodensity and brain weight to skull size in edematous and nonedematous brains in order to develop an objective method for postmortem evaluations of brain edema.

METHOD

Fifty-four subjects autopsied at Oslo University Hospital underwent a standard forensic postmortem examination, including a computed axial tomography (CT) scan, measurement of brain weight, and macroscopic evaluation of the brain. CT images were used to roughly measure the inner skull circumference. The water content of the brain was determined by excising samples of approximately 1 g of brain tissue from eight different areas of the brain surface, drying them, and measuring their percentage water content.

RESULTS

The main finding was a significant relationship between brain weight and inner skull circumference, with the ratio between these two parameters being significantly higher in cases with severe postmortem brain edema than in cases with very little or no brain edema. The water content did not differ significantly between the edema and nonedema cases. There were no significant changes in radiodensity.

CONCLUSION

This indicates that the brain-weight-to-inner-skull-circumference ratio may serve as a good marker for severe brain edema in postmortem diagnostics, whereas measurements of water content can be misleading.

The gas bubble sign-a reliable indicator of laryngeal fractures in hanging on post-mortem CT

OBJECTIVE

The purpose was to evaluate the presence of gas in the tissue adjacent to the laryngeal structures, "the gas bubble sign", in cases of hanging as a diagnostic indicator of neck trauma.

METHODS

In this study, post-mortem CT (PMCT) scans and autopsies of 35 victims of hanging were examined to reveal age-dependent changes, laryngeal fracture, fracture location and the presence of gas. A matched group with cardiac arrest or intoxication was used as controls (n = 35). An autopsy was performed in each case.

RESULTS

Incomplete suspension was the most common method in hanging. The thyroid horns (90.5%) were identified as the most vulnerable location for fractures. Laryngeal deformity and dislocation, which was only detected on PMCT, was observed in 57.1% and was concomitant with fractures in 83.3%. Laryngeal fractures are more common with advanced age (>40 years, 88.9%) and less common in younger subjects (<40 years, 29.4%). The gas bubble sign with regard to laryngeal fractures yielded a sensitivity of 79.2%, a positive predictive value of 95%, a specificity of 90.9%, a negative predictive value of 34.5% and an accuracy of 83%.

CONCLUSION

The complex evaluation of the larynx is profoundly supported by PMCT and the detection of the gas bubble sign as a diagnostic indicator of neck trauma. This relevant diagnostic finding might aid in not only post-mortem cases but also clinical cases, for patients who survive an assault to the neck. Advances in knowledge: (1) The gas bubble sign is a diagnostic indicator of neck trauma in not putrefied bodies. (2) PMCT supports evaluation of trauma to the neck in hanging tremendously. (3) The diagnostic finding of gas located at the laryngeal structures may not only aid in post-mortem cases but also clinical cases of people who survive an assault to the neck.

Traumatic brain injury: Comparison between autopsy and ante-mortem CT

PURPOSE

The aim of this study was to compare pathological findings after traumatic brain injury between autopsy and ante-mortem computed tomography (CT). A second aim was to identify changes in these findings between the primary posttraumatic CT and the last follow-up CT before death.

METHODS

Through the collaboration between clinical radiology and forensic medicine, 45 patients with traumatic brain injury were investigated. These patients had undergone ante-mortem CT as well as autopsy. During autopsy, the brain was cut in fronto-parallel slices directly after removal without additional fixation or subsequent histology. Typical findings of traumatic brain injury were compared between autopsy and radiology. Additionally, these findings were compared between the primary CT and the last follow-up CT before death.

RESULTS

The comparison between autopsy and radiology revealed a high specificity (≥80%) in most of the findings. Sensitivity and positive predictive value were high (≥80%) in almost half of the findings. Sixteen patients had undergone craniotomy with subsequent follow-up CT. Thirteen conservatively treated patients had undergone a follow-up CT. Comparison between the primary CT and the last ante-mortem CT revealed marked changes in the presence and absence of findings, especially in patients with severe traumatic brain injury requiring decompression craniotomy.

CONCLUSION

The main pathological findings of traumatic brain injury were comparable between clinical ante-mortem CT examinations and autopsy. Comparison between the primary CT after trauma and the last ante-mortem CT revealed marked changes in the findings, especially in patients with severe traumatic brain injury. Hence, clinically routine ante-mortem CT should be included in the process of autopsy interpretation.

State of the art in post-mortem forensic imaging in China

The autopsy and histopathologic examination are traditional and classic approaches in forensic pathology. In recent years, with the tremendous progresses of computer technology and medical imaging technology, the developed post-mortem computer tomography, post-mortem magnetic resonance imaging and other new methods provide non-invasive, intuitive, high-precision examining methods and research tools for the forensic pathology. As a result, the reconstruction of the injury as well as the analysis of injury mechanism has been essentially achieved. Such methods have become popular in the research field of forensic science and related work has also been carried out in China. This paper reviews the development and application of abovementioned post-mortem forensic imaging methods in China based on the relevant literature.

Papilledema as a Diagnostic Sign of Cerebral Edema on Postmortem Magnetic Resonance Imaging

The purpose of this study was to investigate papilledema (PA) as a diagnostic criterion for the presence of antemortem or agonal cerebral edema despite normal postmortem brain swelling on postmortem magnetic resonance imaging (PMMR) in comparison with conventional autopsy.One hundred subjects with head PMMR and autopsy were included in this study. The sensitivities, spec icities, positive predictive values (PPVs), negative predictive values (NPVs), and accuracies were calculated in terms of the PA, PMMR, and cerebral edema on autopsy. Spearman r tests were used to analyze the linear correlations of PA and the radiological and autoptic determination of cerebral edema.In autopsy, the sensitivity regarding the presence of PA and cerebral edema was 66.2% (PPV, 70.5%), and specificity was 48.6% (NPV, 28.3%), with an overall accuracy of 60%. On PMMR, the sensitivity was 86.6% (PPV, 95%). The specificity was 90.9% (NPV, 34%), with an overall accuracy of 88%. The Spearman correlation revealed a statistically significant result (P < 0.001), which indicated a strong linear correlation of the presence of PA and cerebral edema with the autopsy results and the PMMR results.The presence of PA may aid in the diagnoses of cerebral edema despite normal postmortem brain swelling based on PMMR.

Evaluation of post-mortem lateral cerebral ventricle changes using sequential scans during post-mortem computed tomography

In the present study, we evaluated post-mortem lateral cerebral ventricle (LCV) changes using computed tomography (CT). Subsequent periodical CT scans termed “sequential scans” were obtained for three cadavers. The first scan was performed immediately after the body was transferred from the emergency room to the institute of legal medicine. Sequential scans were obtained and evaluated for 24 h at maximum. The time of death had been determined in the emergency room. The sequential scans enabled us to observe periodical post-mortem changes in CT images. The series of continuous LCV images obtained up to 24 h (two cases)/16 h (1 case) after death was evaluated. The average Hounsfield units (HU) within the LCVs progressively increased, and LCV volume progressively decreased over time. The HU in the cerebrospinal fluid (CSF) increased at an individual rate proportional to the post-mortem interval (PMI). Thus, an early longitudinal radiodensity change in the CSF could be potential indicator of post-mortem interval (PMI). Sequential imaging scans reveal post-mortem changes in the CSF space which may reflect post-mortem brain alterations. Further studies are needed to evaluate the proposed CSF change markers in correlation with other validated PMI indicators.