Using micro-computed tomography to examine the larynx in cases of suspected strangulation—a comparison of case findings and control images

International Journal of Legal Medicine https://doi.org/10.1007/s00414-019-02194-y ORIGINAL ARTICLE Using micro-computed tomography to examine the larynx in cases of suspected strangulation—a comparison of case findings and control images Waltraud Baier 1 & Brian A. Burnett 2 & Mark Payne 3 & Jason M. Warnett 1 & Mark A. Williams 1 Received: 4 April 2019 / Accepted: 22 October 2019 # The Author(s) 2019 Abstract The examination of strangulation is one of the most challenging causes of death diagnoses encountered in forensic pathology. The injuries are often subtle and difficult to detect, especially in cases that lack superficial marks. Fractures of the laryngeal skeleton are commonly regarded as evidence of strangulation but these can be too subtle to be detected during autopsy. Micro-CT is a novel imaging technique that achieves a spatial resolution 1 μm or less which lends itself to the examination of small and delicate structures such as the larynx. However, there is little information to date regarding the appearance of the larynx at this scale, thus complicating the interpretation of the micro-CT images. This study therefore uses micro-CT to examine ten larynges from strangulation deaths and to compare them to nineteen samples from donor individuals in order to distinguish between naturally occurring features and actual trauma. It was found that there are several features which mimic damage in the donor group. Using associated case information, initial trends and patterns of different strangulation methods were established. Keywords Micro-computed tomography . Forensic Imaging . Strangulation . Larynx Introduction Strangulation is the third most common homicide method in the UK, although women are even more likely to become a victim due to intimate partner violence [1, 2]. Despite the * Waltraud Baier Brian A. Burnett Mark Payne Jason M. Warnett Mark A. Williams 1 WMG, International Manufacturing Centre, University of Warwick, Coventry CV4 7AL, UK 2 UHCW NHS Trust, Coventry CV2 2DX, UK 3 West Midlands Police, B4 6NQ, Birmingham, UK frequent occurrence of such cases, the diagnosis of strangulation in forensic pathology is still predominantly one of exclusion, in particular if there is a lack of distinctive signs such as petechial bleeding or bruising of the soft tissues of the neck. Fractures of the laryngeal cartilages or the hyoid bone are considered evidence for strangulation but they can have other causes such as sports injuries, motor vehicle accidents or falls [3]. Such fractures tend to be associated with haemorrhages, but absence thereof can make subtle injuries even more difficult to detect at the risk of potentially missing them during autopsy. In some cases, histological examination is conducted to examine fractures identified at postmortem to assess the timing of the injury in relation to time of death [4]. This process is destructive, time consuming and costly. With advances in technology, new ways of dealing with this issue have emerged with many researchers advocating the use of computed tomography (CT) to study laryngeal trauma [5, 6]. Even more recently, initial studies have explored the use of microcomputed tomography (micro-CT) to examine such cases in order to identify micro-fractures which might not be visible on medical CT or postmortem examination [7, 8]. Micro-CT has proven successful in a number of different forensic applications such as toolmark analysis [9–11], gunshot wound Int J Legal Med analysis [12, 13] and forensic entomology [14]. However, all of the existing literature on using micro-CT for laryngeal trauma analysis is based on casework; no comparative studies exist to date to the authors’ knowledge. This study aims to address this void as it draws on an unprecedented database of micro-CT scans of larynges from strangulation cases as well as from natural deaths. The injuries observed in the former group were compared with those in the latter control group of uninjured larynges from donor individuals in order to assess which features can occur in the normal population. Studies by Tsai et al. [15] and Baier et al. [16] have compared micro-CT to histology, the current gold standard for forensic injury analysis, and found the method to be reliable for injuries in bone. Method validation is becoming an increasing concern in forensic science and while micro-CT had been validated in industrial settings [17–19] where the method as such has been proven to work, it has not been systematically tested for forensic purposes. This study forms an exploratory study to inform future more structured validation studies. Materials and methods Micro-CT The overall principles of micro-CT are similar to medical CT as it uses a stack of 2D radiographs to examine the internal structure of a sample, but it allows a spatial resolution, or voxel size, of approximately 40 μm for a sample of the size of a larynx. The source and detector of a typical lab-based micro-CT machine are stationary during the scan with the sample on a rotating stage at the centre. Radiographs are acquired at every degree angle through a full 360° rotation and later reconstructed to form the 3D model of the object [20]. All samples were scanned using a Nikon 225/320 LC micro-CT scanner (Nikon Metrology, Tring, UK) and reconstructed using the system’s proprietary software CTPro. Typical scan parameters were 120 kV, 135 μA, 500-ms exposure, 24-dB gain, no filtration, creating 3141 projections, although some adjustments were made where necessary. The scan images were visually inspected in VG Studio MAX 2.2 (Volume Graphics, Heidelberg, Germany). Two groups of larynges were examined. The first consisted of ten samples from forensic strangulation cases. Only cases where strangulation had been confirmed through multiple lines of enquiry (witness statements, confessions, CCTV, forensic post-mortem) were considered in this group; no inconclusive cases were included (age range 20–68 years; male 4, female 6). The second group consisted of nineteen control samples from donor individuals with no recorded history of laryngeal trauma (age range 46–94 years; male 12, female 7). Only the thyroid cartilage and the hyoid were considered for this study. Full demographic details are provided in Appendix Tables 1 and 2. The examination criteria were determined from the control group as potentially misleading features during analysis. These were circular defects within the ossified cartilage, fragmented appearance of ossified material, incomplete fusion of the hyoid elements, abrupt angles and linear grooves within the ossified cartilage, and the presence of triticeous cartilages. Based on the literature, the presence, completeness (incomplete, complete, displaced) and location of fractures were also included as a criterion as they are frequently encountered in strangulation deaths. In order to include all possible fracture origins, they were termed discontinuities in the analysis. An (...truncated)