Forensic neuropathology in the past decade: a scoping literature review

Abstract

While there has been notable research activity in the field of clinical neuropathology over the recent years, forensic approaches have been less frequent. This scoping literature review explored original research on forensic neuropathology over the past decade (January 1, 2010, until February 12, 2022) using the MEDLINE database. The aims were to (1) analyze the volume of research on the topic, (2) describe meta-level attributes and sample characteristics, and (3) summarize key research themes and methods. Of 5053 initial hits, 2864 fell within the target timeframe, and 122 were included in the review. Only 3–17 articles were published per year globally. Most articles originated from the Europe (39.3%) and Asia (36.1%) and were published in forensic journals (57.4%). A median sample included 57 subjects aged between 16 and 80 years. The most common research theme was traumatic intracranial injury (24.6%), followed by anatomy (12.3%) and substance abuse (11.5%). Key methods included immunotechniques (31.1%) and macroscopic observation (21.3%). Although a number of novel findings were reported, most were of preliminary nature and will require further validation. In order to reach breakthroughs and validate novel tools for routine use, more research input is urged from researchers across the world. It would be necessary to ensure appropriate sample sizes and make use of control groups.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12024-023-00672-9.

Introduction

Neurological diseases [1] and trauma to the central nervous system (CNS) [2] are common causes of death globally. A comprehensive postmortem examination of the CNS often requires particular expertise and sophisticated tissue processing techniques [3, 4]. Neuropathological expertise is therefore of high value in both clinical [5] and forensic pathology [3]. While there has been notable research activity in the field of clinical neuropathology over the recent years [6–15], forensic approaches appear less frequent [16–20]. However, the role of CNS remains important in the medico-legal practice [21–24], as CNS-related findings may have pivotal significance in cause-of-death investigation [3] and legal proceedings [25, 26].

Literature reviews aid in the efficient utilization of current knowledge. Systematic approaches are needed to summarize and disseminate research findings and identify gaps in the existing literature [27]. However, to the best of the authors’ knowledge, there are no broad-scoped overviews summarizing literature on forensic neuropathology, at least from the past decade. This scoping literature review explored literature on forensic neuropathology from January 1, 2010, until February 12, 2022. The aims were to (1) analyze the volume of research on the topic, (2) describe meta-level attributes and sample characteristics, and (3) summarize key research themes and methods.

Materials and methods

Research questions

Scoping reviews are exploited to determine the scope and volume of literature on a given topic and to identify key concepts [28, 29]. In contrast to systematic reviews, scoping reviews are particularly useful when the research question is broad and the body of literature has not been comprehensively reviewed before. We conducted a MEDLINE-based scoping review to explore scientific literature on forensic neuropathology published over the past decade.

The following research questions were formulated in accordance with the general aims of the study:

1. Volume of research

   1. What is the volume of original research on forensic neuropathology per year?
2. Meta-level attributes and sample characteristics

   1. Which journals publish studies on forensic neuropathology in terms of subspecialty and impact?
   2. What is the geographical distribution of publications?
   3. What kind of samples are used in terms of size and age distribution?
3. Research themes and methods

   1. What are the key concepts, i.e., main research themes and methodological approaches in forensic neuropathology?
   2. Are there knowledge gaps?

This review did not aim to summarize or classify particular findings of the studies; however, these are addressed in the supplementary material.

Search strategy, inclusion, and exclusion criteria

The search strategy was developed by the first author (P.O.) and reviewed by the last author of the paper (A.S.). Table 1 presents the specific search terms used in MEDLINE. Figure 1 is a flowchart demonstrating the article selection process with exclusions.

Table 1.

Search query in MEDLINE

#	Search term
1	(neuro*[Title/Abstract] OR nervous*[Title/Abstract] OR brain*[Title/Abstract] OR spine*[Title/Abstract] OR spinal*[Title/Abstract] OR cerebr*[Title/Abstract] OR cerebel*[Title/Abstract] OR intracran*[Title/Abstract] OR intracerebr*[Title/Abstract] OR subarachn*[Title/Abstract] OR subdur*[Title/Abstract] OR epidur*[Title/Abstract])
2	(forensic*[Title/Abstract] OR "medico-legal"[Title/Abstract] OR medicolegal[Title/Abstract] OR "medico legal"[Title/Abstract] OR "legal medicine"[Title/Abstract])
3	#1 AND #2

Fig. 1.

Flowchart demonstrating the article selection process with exclusions

We aimed to find peer-reviewed, original articles that addressed a neuropathological method or finding related to a medico-legal or forensic question in a human sample. A neuropathological method was defined as a macroscopic, microscopic, or other laboratory technique used to examine a tissue sample obtained from the CNS or intracranial structures including vasculature. We focused on English-language articles that were published and indexed in MEDLINE between January 1, 2010, and the database search date. Short communications, retrospective summaries of autopsy findings, and other similar publication types were included if they were original articles based on authentic human samples. Studies that solely focused on postmortem imaging, analysis of body fluids, human identification, or skull fractures without the use of neuropathological methods were excluded.

The search was conducted in the MEDLINE database February 12, 2022. First, P.O. screened all hits on the basis of titles, abstracts, and full texts, if necessary. Each hit was assigned with a rationale for inclusion or exclusion to be later validated by A.S.

Data extraction and synthesis

Data extraction was performed with the help of an Excel spreadsheet. Table 2 presents the variables collected in the data extraction process. The spreadsheet was a priori planned by P.O. and reviewed by A.S.; an internal pilot was carried out in the beginning of data collection (20 hits from the year 2010). Data extraction was performed on the basis of full texts and potential supplementary material of the articles. While P.O. was primarily responsible for extracting the data, the spreadsheet was reviewed and commented by A.S. A formal risk of bias assessment was not performed, as it is not customary in scoping reviews [28], and was not considered necessary in relation to the present research questions.

Table 2.

Variables used in the data extraction spreadsheet

Variable	Details
Meta-level attributes
Name of the first author	-
Year of publication	-
Digital object identifier (DOI)	-
Name of journal	-
Journal area	Categorized as follows: clinical, forensic, pathology, and other
Journal impact factor	Most recent impact factor (2020), collected from Journal Citation Reports, Clarivate Analytics, April 17, 2022
Location	Refers primarily to the country where the study was conducted, and secondarily to the authors’ main affiliation. Initially collected at the country level, then aggregated to the continent level
Sample characteristics
Sample size	Total sample size, comprising both cases and controls, if applicable
Use of control group	-
Age range	Minimum and maximum ages of the total sample, comprising both cases and controls, if applicable. Further categorized as follows: adults only (refers to subjects aged ≥ 18 years), minors only, both, not stated
Research themes and methods
Primary theme	Refers to the main research theme that was focused on. Categorized as follows: anatomy, asphyxia and hypoxia, brain edema, brain tissue identification, drowning, hypothermia and hyperthermia, laboratory methods and quality, neurodegeneration, postmortem interval, substance abuse, sudden unexpected death in epilepsy, sudden unexpected death in infancy and childhood, suicide, traumatic intracranial injury, several primary themes, and other
Primary method	Refers to the main method applied in the study. Categorized as follows: conventional measurements (e.g., weight), genetic techniques, histology and conventional staining, immunotechniques, macroscopic observation, several primary methods, and other
Aims and findings
Aims	Aims of the study. Quoted from the source article
Main findings or conclusions	Quoted from the source article

Data synthesis was conducted in accordance with the predefined research questions. The distributions of publication year, journal characteristics, geographical location, sample characteristics, primary research theme, and methodological approach were tabulated using frequencies with percentages or medians with interquartile ranges, as appropriate. In addition to these summary statistics, a supplementary table containing the extracted data of individual studies was constructed.

Results

Literature search

Of 5053 initial hits, 2864 fell within the target timeframe, and 122 were finally included in the review [30–151], corresponding to 4.3% of hits within timeframe (Fig. 1). Most exclusions were due to wrong context (e.g., forensic psychiatry) or article type (i.e., not original article). Individual summaries of the 122 included articles, together with aims and main findings, are presented in Supplementary Table 1.

Meta-level attributes

Table 3 shows the annual distribution of publications over the review period; 3 to 17 articles were published per year globally. Table 4 is a bibliographic and geographic summary of the studies. Forensic journals were the most common publication channel (57.4%), followed by clinical journals (e.g., general medicine, neurology, or pediatric journals; 23.0%), and pathology journals (8.2%). Median impact factor was 2.3, while 11.5% of studies were published in journals without an Impact Factor. As for geographical distribution, Europe (39.3%) and Asia (36.1%) were the two most common study regions.

Table 3.

Annual number of included articles over the review period

Year	Number of articles
2010	6
2011	3
2012	14
2013	6
2014	5
2015	8
2016	10
2017	17
2018	15
2019	13
2020	10
2021	11
2022 (until February 12)	4
Total	122

Table 4.

Bibliographic and geographic summary of the studies (n = 122)

	%	N
Journal area
Forensic	57.4	70
Clinical	23.0	28
Pathology	8.2	10
Other	11.5	14
Journal impact
Impact factor in 2020 (median with IQR)	2.3 (1.6–2.7)
No impact factor in 2020	11.5	14
Location of studya
Europe	39.3	48
Asia	36.1	44
Americas	18.0	22
Australia and New Zealand	4.9	6
Africa	1.6	2

IQR Interquartile range

^aLocation refers primarily to the location where the study was conducted, and secondarily to the authors’ main affiliation

Sample characteristics

Table 5 is a summary of sample characteristics. A median sample included 57 subjects (interquartile range 29–101; full range 4–1222), which included both cases and controls, if applicable. Control groups were utilized in less than half of the studies (43.4%). Medians of minimum and maximum ages were 16 and 80 years, respectively. A total of 30.3% of studies were based on adult-only samples, another 30.3% had both adults and minors, and 12.3% were based on minors. Subject ages were not stated in over a quarter of the studies (27.0%).

Table 5.

Sample characteristics of the studies (n = 122)

	%	N
Sample sizea
Number of subjects (median with IQR)	57 (29–101)
Number of subjects not stated	1.6	2
Control group used	43.4	53
Age of subjectsb
Adults only	30.3	37
Minors only	12.3	15
Both	30.3	37
Not stated	27.0	33
Age rangec
Minimum age (median with IQR)	16 (0–20)
Minimum age not stated	26.2	32
Maximum age (median with IQR)	80 (56–91)
Maximum age not stated	27.0	33

IQR interquartile range

^aTotal sample size, comprising both cases and controls, if applicable

^bAdults refer to subjects aged ≥ 18 years; minors refer to those aged < 18 years

^cMinimum and maximum ages of the total sample, comprising both cases and controls, if applicable

Research themes and methods

Lists of research themes and methodological approaches are presented in Table 6. Individual summaries of the articles, together with aims and main findings, are presented in Supplementary Table 1.

Table 6.

Research themes and methods of the studies (n = 122)

	%	N
Primary themea
Traumatic intracranial injury	24.6	30
Anatomy	12.3	15
Substance abuse	11.5	14
Laboratory methods and quality	7.4	9
Sudden unexpected death in infancy and childhood	6.6	8
Neurodegeneration	4.9	6
Suicide	4.1	5
Hypothermia and hyperthermia	3.3	4
Postmortem interval	3.3	4
Asphyxia and hypoxia	2.5	3
Brain edema	2.5	3
Brain tissue identification	2.5	3
Drowning	1.6	2
Sudden unexpected death in epilepsy	1.6	2
Other	9.8	12
Several primary themes	1.6	2
Primary methodb
Immunotechniques	31.1	38
Macroscopic observation	21.3	26
Genetic techniques	13.9	17
Conventional measurements (e.g. weight)	9.8	12
Histology and conventional staining	5.7	7
Other	3.3	4
Several primary methods	14.8	18

^aPrimary theme refers to the main research theme that was focused on

^bPrimary method applied in the study

The most common research theme was traumatic intracranial injury (24.6%), which comprised focal and diffuse traumatic brain injuries [30, 31, 39, 43, 54, 55, 64, 83, 85, 86, 94, 106, 107, 115, 116, 120, 123, 130, 132, 139, 150] and traumatic intracranial hemorrhages [30, 47, 54, 57, 58, 65, 83, 87, 99, 113, 114, 130, 141, 150]. Studies often used immunotechniques to identify traumatic changes and estimate the age of injury [39, 85–87, 94, 106, 107, 115, 120, 132, 139]. While some studies described macroscopic injury patterns and combinations in accident and assault scenarios [30, 47, 65, 99, 114, 116, 130, 141], others used conventional histology [57, 58, 113] or several methods [31, 43, 54, 55, 64, 83, 150] to address varying research questions.

The second most common entity was anatomy (12.3%). While most studies described the anatomical variants of vasculature [41, 68, 75, 105, 126, 127, 135] and other intracranial structures [44, 73, 74, 151], some aimed to generate reference values for brain weight in various populations [69, 98, 102, 125]. The main techniques were macroscopic observation, conventional histology, and weight measurement. Moreover, one study evaluated the biomechanical properties of the dura mater [151].

Substance abuse was the primary entity in 11.5% of the studies. Both chronic and acute abuse were represented. The selection of substances included alcohols [38, 52, 82], opioids [38, 100, 109, 117–119], stimulants [38, 53, 81, 136, 147], and other or multiple substances [48, 50, 117, 118]. Immunotechniques [38, 48, 50, 117, 118, 147], genetic techniques [81], or the two together [119, 136] were often utilized to identify brain damage and distinguish substance abuse from other causes of death. Some studies primarily reported macroscopic observations [52, 53, 82, 109] or brain weight [100] among substance abusers.

Laboratory methods were the main focus in 7.4% of the studies [45, 67, 70, 72, 97, 111, 133, 138, 148]. The studies showed notable heterogeneity, addressing technical aspects of, e.g., formalin pigment deposition [45], immunohistochemistry [133], DNA extraction [67], and freezing preparation of putrefied brain tissue [97].

Sudden unexpected deaths in infancy and childhood were addressed in 6.6% of the studies [33, 40, 51, 61, 66, 79, 84, 91]. Immunotechniques [33, 40, 79], genetic techniques [51], conventional histology [91], and brain weight measurement [61] were used to uncover underlying mechanisms and identify brain tissue markers in these cases. Moreover, one study suggested an optimal neuropathologic examination protocol for these deaths in a medico-legal setting [66].

Other research themes were rarely addressed (< 5% each). Neurodegenerative diseases in medico-legal settings were approached using immunotechniques [128, 143, 144], image analysis [129], or a combination of several methods [104, 112]. As for suicide, immunotechniques [32, 89], genetic techniques [62, 88], and brain weight measurement [146] were applied to identify factors that differentiate suicide victims from controls. Brain tissue markers of hypothermia and hyperthermia were studied by means of immunotechniques [78, 140, 145] and genetic techniques [60]. Studies that aimed to improve the estimation of postmortem interval were mainly based on immunotechniques [42, 92] and genetic techniques [134]. Asphyxia and brain hypoxia [35, 77, 108], brain edema [36, 37, 96], brain tissue identification [95, 121, 122], drowning [34, 71], and sudden unexpected death in epilepsy [63, 149] were addressed in two to three individual studies each.

One article studied the markers of traumatic brain injury and mechanical asphyxiation using genetic techniques [49], while another focused on the potential markers of hypothermia, hyperthermia, and intoxication using immunotechniques and genetic techniques [59]. Finally, the following entities had one study each: sudden unexplained nocturnal death syndrome [46], pediatric subdural hemosiderin deposits [56], iron in fetal and infant leptomeninges [80], DNA identification based on brain tissue swab [76], zinc in brain tissue [90], intracranial aneurysms and dissections [101], age estimation [103], electrocution [124], insulin homicide [131], fire fatalities [137], phosphine poisoning [93], and carbon monoxide poisoning [142].

Discussion

Main findings

This scoping review identified 122 original articles on forensic neuropathology from the years 2010–2022. Only 3–17 articles were published per year globally. Most articles originated from the Europe and Asia and were published in forensic journals. A median sample included 57 subjects aged between 16 and 80 years. The most common research theme was traumatic intracranial injury, followed by anatomy and substance abuse. Main methods included immunotechniques and macroscopic observation. To the best of the authors’ knowledge, this is the first scoping review to systematically explore literature on forensic neuropathology over the past decade.

Meta-level considerations

The annual volume of research output was relatively low, which may indicate rather mild research activity in the field globally. It is obvious that breakthroughs will require consistent scientific effort and active involvement of forensic pathologists in research projects. Clinical neuropathology may have outpowered the forensic branch, possibly due to stronger translational potential and active interplay with clinicians [6–15]. Neuropathology is an interdisciplinary field, touching upon neighboring fields such as neurology, neurosurgery, psychiatry, legal medicine, and general pathology. Forensic neuropathology is aligned in the midway between clinical and forensic pathology, often requiring particular expertise from a general forensic pathologist [22]. Interdisciplinary cooperation may thus be the key to increasing research activity in the field.

Articles were widely distributed between journals of various disciplines, which underlines the intersectoral nature of the field. In general, articles were published in international, field-specific journals with a median impact factor of 2.3. However, it is noteworthy that over a tenth of the articles were published in journals with no impact factor whatsoever; anatomic reports appeared to be overrepresented in this subgroup. As for geographical distribution, the vast majority of articles were from European and Asian researchers. Notably, articles from American groups were less common, and only two African articles were published over the entire review period. In order to expedite the development and implementation of forensic neuropathology globally, research input is needed from medico-legal units across the world. Unfortunately, achieving this objective may prove difficult due to resource- and policy-related barriers. It would be important to ensure sufficient personnel resources, methodological expertise, access to research funding, and comprehensible research permit policies for medico-legal data.

Sample-related considerations

Sample sizes were moderate, with a median of 57 subjects; this included both cases and potential controls. Two articles appeared to lack a clear indication of sample size. Despite the relatively small sample sizes, statistical power calculations were rarely presented. In quantitative studies, power calculations guide sample collection and corroborate the statistical approach [152]. Of note is also the fact that over a half of the studies did not have a control group, which implies that most articles were descriptive in nature. A comparative design is a prerequisite for many scientifically relevant conclusions [153].

Age ranges were generally wide, which increased the generalizability of findings across age groups. However, taking into account the moderate sample sizes, the level of heterogeneity within samples may significantly increase with widening age spans. Over a quarter of studies appeared to lack a clear statement of the minimum and maximum ages of the sample; some reported standard deviations and interquartile ranges instead.

Research themes, methods, and future directions

Traumatic intracranial injury was the most common research theme. Research activity around the topic is easy to comprehend as traumatic brain injury and intracranial hemorrhages are complex and deadly entities that often present themselves to a forensic pathologist [2, 21]. As neuropathology may have a pivotal role in a cause-of-death investigation [3] or legal proceedings [25, 26], novel tools are needed to identify traumatic changes and estimate the age of injury. However, significant breakthroughs are yet to come.

Alongside traumatic intracranial injury, the top-three research themes included anatomy and substance abuse. Somewhat surprisingly, macroscopic and microscopic anatomy of intracranial structures were among the most popular research themes. Many of these studies reported important findings for neurosurgeons, for example, but appeared to make a minor contribution to the field of forensic neuropathology. Substance abuse, which indeed is a central medico-legal entity [154], was approached from a variety of perspectives method- and substance-wise. However, more research input will be needed to identify substance-specific markers in brain tissue and differentiate substance abuse and intoxication from other causes of death.

Neurodegenerative diseases were addressed in a handful of studies. In spite of the vast research activity in clinical neuropathology, studies in medico-legal samples are also important, as neurodegenerative diseases appear to increase the risk of unnatural deaths [155]. Providing medico-legal units with diagnostic methods that have been validated in medico-legal samples will be of utmost importance. As for sudden unexplained deaths among infants and children, studies have kept chasing potential mechanisms and biomarkers, but again, significant breakthroughs are yet to come.

Although suicide is a major and diverse entity in forensic pathology [156], only a few studies addressed the topic. Considering the obscurity behind predisposing and underlying factors, there should be a lot to achieve mechanism- and prevention-wise. Medico-legal samples may have significant translational potential in this regard. Moreover, only a few studies addressed asphyxia, drowning, hypothermia, hyperthermia, sudden unexpected death in epilepsy, and estimation of postmortem interval. Higher research activity should be directed toward these themes in order to improve postmortem diagnostics.

Immunotechniques, i.e., immunohistochemistry and immunoblotting, were commonly applied to detect potential changes in brain tissue. Genetic techniques were exploited in various approaches such as brain tissue identification and gene expression analysis. A minority of studies used conventional histology as the main method. Although a number of novel findings were reported, most were of preliminary nature and will require further validation. Macroscopic observation of intracranial structures was a common method, but the studies often merely described injury patterns or anatomic variations. The crude measurement of brain weight was also used in some studies, but these often had null findings.

Limitations of the review

This scoping review had several limitations that should be considered. First, the scope of the literature search was notably broad, and conventional search terms were covered. However, articles that used specific or uncommon terminology may have been omitted. A large number of initial hits were obtained and manually evaluated, which may have reduced the risk of omitting in-scope articles. Second, as the review focused on original articles, emerging research themes may not have been fully covered. Moreover, there is a large body of research that may not be captured in this review even though it is relevant to forensic neuropathologists (e.g., CNS infections and emerging concepts in neurodegenerative diseases). Future reviews are expected to cover these aspects. Finally, as the aim was to explore and summarize original research in the field, there were no particular restrictions on scientific rigor, and no formal bias assessment was performed.

Conclusion

This scoping literature review explored original research on forensic neuropathology over the years 2010–2022. A total of 122 original articles were eventually included in the synthesis. Traumatic intracranial injury was the most common research theme, immunotechniques being the most commonly applied method. Only 3–17 articles were published per year globally. Although a number of novel findings were reported, most were of preliminary nature and will require further validation. In order to reach breakthroughs and validate novel tools for routine use, more research input is urged in forensic neuropathology from researchers across the world. Interdisciplinary cooperation may be the key to increasing research activity in the field. Researchers should ensure appropriate sample sizes and make use of comparative designs whenever possible.

Key points

1. Knowledge of diseases and trauma related to the central nervous system has high value in forensic pathology

2. This scoping review explored literature on forensic neuropathology from 2010 to 2022

3. A total of 122 original articles were included, corresponding to 3–17 publications per year globally

4. 4.The most common research theme was traumatic intracranial injury (24.6%), followed by anatomy (12.3%) and substance abuse (11.5%). Key methods included immunotechniques (31.1%) and macroscopic observation (21.3%)

5. To reach breakthroughs and validate tools for routine practice, more research input is needed from researchers across the world

Supplementary Information

Below is the link to the electronic supplementary material.

Author contribution

Conceptualization and methodology: PO and AS. Formal analysis and investigation: PO and AS. Writing—original draft preparation: PO, AH, and AS. Writing—review and editing: PO, AH, and AS. All authors read and approved the final manuscript.

Funding

Open Access funding provided by University of Helsinki including Helsinki University Central Hospital.

Availability of data and material

This is a review of published literature. The dataset generated and analysed during the study is presented in Supplementary Table 1.

Code availability

Not applicable.

Declarations

Ethics approval

Not applicable.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.