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Article

MRI Segmentation of Cervical Muscle Volumes in Survived Strangulation: Is There an Association between Side Differences in Muscle Volume and the Handedness of the Perpetrator? A Retrospective Study

1
Department of Forensic Medicine and Imaging, Institute of Forensic Medicine, University of Zurich, 8057 Zurich, Switzerland
2
Clinical Neuroscience Center, Department of Neuroradiology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland
3
Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, 8091 Zurich, Switzerland
*
Author to whom correspondence should be addressed.
Diagnostics 2022, 12(3), 743; https://doi.org/10.3390/diagnostics12030743
Submission received: 1 March 2022 / Revised: 15 March 2022 / Accepted: 16 March 2022 / Published: 18 March 2022
(This article belongs to the Special Issue Advanced Techniques in Body Magnetic Resonance Imaging 2.0)

Abstract

:
We evaluate the potential value of magnetic resonance imaging (MRI) in the examination of survivors of manual strangulation. Our hypothesis was that trauma-induced edema of the cervical muscles might lead to a side difference in the muscle volumes, associated with the handedness of the perpetrator. In 50 individuals who survived strangulation, we performed MRI-based segmentation of the cervical muscle volumes. As a control group, the neck MRIs of 10 clinical patients without prior trauma were used. The ratio of the right to left muscle volume was calculated for each muscle group of the control and strangulation groups. Cutoff values for the assumed physiological muscle volume ratios between the right and left sides were identified from our control group. There was no significant difference among the individuals in the pathological muscle volume ratio between right-handed versus both-handed strangulation for the sternocleidomastoid, pretracheal, anterior deep, or trapezoid muscle groups. Only the posterior deep muscle group showed a statistically significant difference in the pathological muscle volume ratio for both-handed strangulations (p = 0.011). Measurement of side differences in cervical muscle volume does not allow for a conclusion concerning the probable handedness of the perpetrator.

1. Introduction

Medico-legal examination of victims in nonfatal strangulation and the subsequent assessment of the severity of the assault is a challenging task in routine forensic medicine for a number of reasons [1,2,3]. First, there is the discussion of a multifactorial spectrum that could cause potential fatalities in strangulation, which involves four main mechanisms—airway, arterial and/or venous occlusion, and/or autonomic nervous system reflex [3,4]. Second, only a few objective findings are recognized as proof of a life-threatening situation during strangulation:
External findings indicative of strangulation consist of hematoma, swelling, abrasions, and fingernail marks, among others, but these findings do not allow for a conclusive assessment of the severity of the assault [4]. In up to 50% of cases, external findings might be absent entirely [5]. In addition, although symptoms such as unconsciousness, loss of urine or feces, and optical or acoustical sensations are interpreted as a manifestation of cerebral hypoxia (and therefore of a life-threatening assault), these findings are mostly based upon anamnestic information from the victim and are rarely verifiable [3,6]. To date, petechial hemorrhages are the only objectifiable external finding indicative of a sufficient pressure and duration of strangulation that could constitute a life-threatening danger of assault [3].
In addition, medical examinations with computed tomography or laryngoscopy are only performed if there is a clinical suspicion of injuries that might require medical treatment [6]. However, internal objective findings proving a life-threatening situation, such as hyoid bone or laryngeal fractures or carotid dissections, are quite rare [7,8].
Only recently, another imaging modality, magnetic resonance imaging (MRI), has been evaluated for its benefit in the forensic examination of survivors of manual strangulation [2,3,6,8]. It could be shown, in MRI, that typical strangulation signs include subcutaneous and intramuscular hemorrhage, hemorrhage of the lymph nodes and salivary glands, and (rarely) injuries of the larynx and hyoid [2,6,8]. A radiological zone score was also developed in an attempt to help in the appropriate assessment of the severity of the strangulation assault [2]. Nevertheless, despite the recognition of additional valuable documentation of internal findings of the neck from MRI, its use in the assessment of the severity of the assault is currently still very limited [1,2,3,6,8]. Therefore, there is still an urgent need to evaluate further diagnostic possibilities that might help in the adequate medico-legal appraisal of a strangulation assault.
The aim of this study was to further evaluate the potential value of MRI in the examination of survivors of manual strangulation, which might aid in the medico-legal appraisal of such an event. Hypothesizing that trauma-induced edema of the cervical muscles might lead to side differences in the muscle volumes, we wanted to assess whether there is an association between side differences in the cervical muscle volume of the victim and the handedness of the perpetrator.

2. Materials and Methods

2.1. Study Population

We searched the forensic database of the Institute of Forensic Medicine, University of Zurich, Switzerland, from October 2011 to March 2018 for individuals who survived strangulation (n = 633). We included all patients who underwent voluntary (informed consent obtained) noncontrast MRI examination of the head and neck in addition to routine forensic examination (exclusion criteria for MRI: >72 h after the event, <16 years of age, pregnancy, and medical contraindications to MR), resulting in n = 114 patients. Of those, we only included individuals for whom the whole neck (from the mandibular angle to the 7th cervical vertebral body) was covered by the MRI examination and whose MR images showed excellent image quality without artifacts. Our final study group consisted of 50 patients (females n = 39, males n = 11; median age 28.3 years, range 16–57 years).
As a control group, the neck MRIs of 10 clinical patients without prior trauma or other pathology were used (females n = 5, males n = 5; median age 39.8, range 16–58 years). Informed consent was obtained from all patients.

2.2. Magnetic Resonance Imaging

Strangulation cases: MRI was performed at the associated MR center of the University Hospital Zurich, Switzerland, on a 3T MR system (Discovery MR750w, GE Healthcare) according to a standardized, noncontrast study protocol for the neck and head [3].
Control group: MRI, likewise, was performed at the University Hospital Zurich, Switzerland, on a 3T MR system (Achieva 3.0T TX, Philips Healthcare, Best, The Netherlands). The protocol included an axial T2 weighted (Propeller), an axial noncontrast 3D T1 weighted (magnetization-prepared rapid gradient echo, MPRAGE), and an axial diffusion-weighted (DW) (multiplex sensitivity-encoding, MUSE) sequence of the brain, as well as an axial T2 weighted (FLEX, InPhase and WATER), an axial noncontrast fat saturated T1 weighted, and a coronal T2 weighted short-tau inversion recovery (STIR) (Propeller) sequence of the cervical soft tissues.

2.3. Segmentation

Segmentation was performed on axial T2-weighted images by a master student in medicine under the supervision of a board-certified radiologist and forensic pathologist using the software platform Amira (Amira 6.1.1., Visage Imaging GmbH [European Headquarters, Berlin, Germany]). A combination of manual segmentation and interpolation was used. The segmentation range was defined from the mandibular angle (cranial) to the 7th cervical vertebral body (caudal) for the following muscle groups on each side: sternocleidomastoid muscle, pretracheal muscles (M. sternohyoideus, M. omohyoideus, M. thyrohyoideus, and M. sternothyroideus), anterior deep muscles (M. constrictor pharyngeus inferior, M. constrictor pharyngeus medius, M. constrictor pharyngeus inferior, M. palatopharyngeus, M. longus capitis, M. longus colli, and M. scalenus anterior), posterior deep muscles (M. scalenus medius, M. levator scapulae, M. longissimus cervicis, M. splenius cervicis, M. iliocostalis thoracis, M. semispinalis capitis, M. splenius capitis, M. multifidus, M. semispinalis capitis, M. semispinalis cervicis, M. spinalis cervicis, and M. scalenus posterior), and trapezoid muscle with cranial parts of the M. rhomboideus minor. A horizontal line through the transverse processes of the cervical spine and the scalene gap divided anterior and posterior deep muscles. See Figure 1 for an example.

2.4. Data Preparation and Statistics

We included females and males together to increase the statistical significance of our analysis. To adequately reflect potential side differences in the volume of the cervical muscle groups, independent of the individual anatomy, the ratio of the right to left muscle volume was calculated for each muscle group of the control and strangulation groups. We assumed the muscle volume ratios to be normally distributed within our study population. First, we derived a cutoff value for the assumed physiological muscle volume ratios between the left and right sides with the data from our control group. Therefore, the mean plus or minus the standard deviation (SD) for each muscle volume ratio was computed. The SD was used as the cutoff to define the pathological (and thus potentially forensically relevant) cases. In the strangulation mode groups with a sufficiently large case number, we conducted one-way analysis of variance (ANOVA) at a significance level of p = 0.05. The statistical analysis was performed using Microsoft® Excel for Mac v. 16, as well as the statistical software R v. 4.0.5 11.

3. Results

Table 1 shows the mean and standard deviation of the cervical muscle volume ratio (right to left) of the control group. The interval of the mean ± standard deviation was used to define the physiological range of asymmetry in the muscle volume ratio between the right and left cervical muscle groups.
For the analysis of the strangulation group, only individuals with a ratio outside of the defined physiological range were regarded, and an overview of their data is shown in Table 2.
Figure 2 shows a modified boxplot (mean ± standard deviation instead of the median, 1st and 3rd quantiles) of the muscle volume ratios of both control (white box representing mean ± standard deviation of the control group; whiskers minimum and maximum values) and individual strangulation (scattered colored points) cases.
Only three left-hand and chokehold strangulations were identified each, and consequently, no statistical assessment for these strangulation modes could be performed. Conversely, a sufficient number of cases remained only for right-handed and both-handed strangulation (10 and 13, respectively). There was no significant difference in the pathological muscle volume ratio for right-handed versus both-handed strangulations for the sternocleidomastoid, pretracheal, anterior deep, or trapezoid muscle groups. Only the posterior deep muscle group showed a statistically significant difference in the pathological muscle volume ratio for both-handed strangulations (p = 0.011).

4. Discussion

Addressing the urgent need to evaluate further diagnostic possibilities that might help in the adequate medico-legal appraisal of a strangulation assault, the aim of this study was to further evaluate the potential value of MRI in the examination process. Hypothesizing that trauma-induced edema of the cervical muscles might lead to side differences in the muscle volumes, we sought to assess whether there is an association between side differences in the cervical muscle volume ratio of the victim and the handedness of the perpetrator.
Only in one muscle group (posterior deep) was a statistically significant difference in the pathological muscle volume ratio found for both hand strangulations (p = 0.011). However, we have no comprehensive explanation for this singular result.
For left-handed and choke-hold strangulations, the number of cases was, overall, too low to allow statistical assessment.
Another limitation of this study is that the specified handedness of the perpetrator is based solely on anamnestic information from the victims. In this regard, it must be considered that a high stress level impairs the accuracy of an eyewitness testimony [9]. The anamnestic information obtained from the victim might, therefore, sometimes be incorrect.
One also has to take into consideration that the voxels from MRI data are not isotropic, which might have influenced the accuracy in the segmentation volumes.
In summary, the segmentation of cervical muscle volumes from MRI data of survivors of manual strangulation, thus far, does not add additional value in the examination of the victim and the consecutive legal appraisal of the strangulation offence.
Nevertheless, MRI of the neck remains the best modality for evaluating the soft tissue of the neck [10] and has been shown to often offer additional value in the examination and assessment of strangulation cases [1,2,3,6,8,10]. Therefore, with ongoing and future developments in MRI techniques and software, an increasing number of new forensic relevant findings might be identifiable [11].

5. Conclusions

In conclusion, our approach of measurement a side difference in cervical muscle volume does unfortunately not allow for a conclusion concerning the probable handedness of the perpetrator. Further research, especially in MRI of strangulation victims is still necessary. Furthermore, with significantly higher case numbers, training of machine learning and artificial intelligence systems could be performed in the future, which might lead to new insights into the diagnosis of specific strangulation findings and their interpretation in a medico-legal context.

Author Contributions

Conceptualization, M.M., S.F. and J.H.; methodology, S.F.; validation, M.M., L.E. and S.F.; formal analysis, S.F., A.D. and L.E.; data curation, M.M. and S.W.; writing—original draft preparation, M.M. and S.F.; writing—review and editing, S.F. and L.E.; visualization, M.M. and L.E.; supervision, L.E. and M.T.; project administration, S.F. and L.E. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Institutional Review Board approval was obtained for the publishing of case-related, forensic data (Ethics Committee of the Canton of Zurich, KEK ZH-Nr. 15-0686).

Informed Consent Statement

Informed consent was obtained from all clinical subjects involved in the study.

Data Availability Statement

Data cannot be made available due to legal restrictions.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Figure 1. Three-dimensional reconstruction of MRI muscle volume segmentations (case 41) in (a) axial, (b) right sagittal, and (c) coronal views: trapezoid muscle (“T”, right side blue, left side yellow), posterior deep muscles (“PD”, right side pink, left side green), anterior deep muscles (“AD”, right side dark yellow, left side purple), sternocleidomastoid muscle (“SCM”, right side light turquoise, left side red), and pretracheal muscles (“P”, right side dark turquoise, left side rose).
Figure 1. Three-dimensional reconstruction of MRI muscle volume segmentations (case 41) in (a) axial, (b) right sagittal, and (c) coronal views: trapezoid muscle (“T”, right side blue, left side yellow), posterior deep muscles (“PD”, right side pink, left side green), anterior deep muscles (“AD”, right side dark yellow, left side purple), sternocleidomastoid muscle (“SCM”, right side light turquoise, left side red), and pretracheal muscles (“P”, right side dark turquoise, left side rose).
Diagnostics 12 00743 g001
Figure 2. Modified boxplot (mean ± standard deviation instead of the median, 1st and 3rd quantiles) of all cases (control and strangulation), with the different muscle groups on the x-axis and the muscle volume ratio on the y-axis. The white box shows the physiological variability in asymmetry as defined by the control group (mean ± standard deviation), and the scattered colored points indicate the muscle volume ratios from all strangulation cases (yellow, both hands; orange, choke hold; green, left hand; and blue, right hand).
Figure 2. Modified boxplot (mean ± standard deviation instead of the median, 1st and 3rd quantiles) of all cases (control and strangulation), with the different muscle groups on the x-axis and the muscle volume ratio on the y-axis. The white box shows the physiological variability in asymmetry as defined by the control group (mean ± standard deviation), and the scattered colored points indicate the muscle volume ratios from all strangulation cases (yellow, both hands; orange, choke hold; green, left hand; and blue, right hand).
Diagnostics 12 00743 g002
Table 1. Ratio of muscle volumes for each muscle group (right to left side) in the control group.
Table 1. Ratio of muscle volumes for each muscle group (right to left side) in the control group.
Ratio_SternoRatio_PretrachRadio_Ant_DeepRatio_Post_DeepRatio_Trap
Mean0.970.940.980.981.22
SD0.060.090.070.060.55
Interval0.91–1.040.85–1.030.91–1.050.92–1.040.66–1.77
Table 2. All strangulation cases with the ratio of muscle volume (right to left) for each muscle group. Ratios lower than the physiological range of side asymmetry of the cervical muscle volumes are marked in orange, and ratios higher than the physiological range are marked in green. * The single cases of the “dog leash” and “not specified” strangulation modes were not investigated further.
Table 2. All strangulation cases with the ratio of muscle volume (right to left) for each muscle group. Ratios lower than the physiological range of side asymmetry of the cervical muscle volumes are marked in orange, and ratios higher than the physiological range are marked in green. * The single cases of the “dog leash” and “not specified” strangulation modes were not investigated further.
Case NrSexAgeMuscle Group RatioStrangulation Mode
SternocleidomastoidPretachealAnterior DeepPosterior DeepTrapezoid
1f340.810.871.010.930.85Right hand
2f570.960.880.971.000.78Both hands
3f341.100.630.960.990.91Left hand
4f200.931.031.041.000.75Left hand
5f161.111.181.001.110.89Both hands
6f291.150.831.010.991.18Both hands
7f291.060.980.941.001.09Right hand
8m231.061.001.041.031.08Choke hold
9f221.171.201.010.991.38Right hand
10f490.911.230.870.990.67Right hand
11m251.070.990.901.010.85Right hand
12m520.971.071.110.920.79Dog leash *
13m291.001.130.911.070.78Choke hold
14f330.880.690.921.061.34Both hands
15f200.961.051.091.070.92Both hands
16m190.910.921.111.031.56Choke hold
17m600.951.281.310.940.90Right hand
18f330.841.131.211.041.34Right hand
19f260.990.921.001.020.82Right hand
20m190.871.061.011.010.95Choke hold
21f240.961.111.091.030.77Both hands
22f280.890.921.110.991.08Right hand
23f171.050.910.921.001.14Both hands
24f251.031.000.930.960.54Right hand
25f290.910.950.941.060.66Both hands
26m181.050.951.011.020.72Choke hold
27f210.981.090.891.071.47Right hand
28f291.010.911.060.930.85Both hands
29f261.031.191.050.950.89Right hands
30f260.901.090.901.051.34Both hands
31f160.900.980.910.950.67Right hand
32f271.130.780.981.041.22Both hands
33m511.050.971.071.000.88Both hands
34f230.950.900.951.041.18Both hands
35f191.000.991.150.930.68Right hand
36m261.061.121.110.980.84Both hands
37f240.830.721.020.981.06Right hand
38f301.020.930.770.961.16Choke hold
39f201.000.860.980.941.05Right hand
40f290.871.000.851.020.90Both hands
41f291.050.840.930.990.84Left hand
42f241.081.050.940.890.60Right hand
43f180.930.761.110.930.70Right hand
44f280.900.930.971.010.81Right hand
45f261.061.091.010.980.96Both hands
46f511.051.050.911.051.81Both hands
47f241.040.890.940.931.04Not specified *
48f230.870.890.851.020.88Both hands
49f330.990.820.990.920.65Both hands
50m201.060.911.110.891.15Both hands
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MDPI and ACS Style

Marty, M.; Dobay, A.; Ebert, L.; Winklhofer, S.; Thali, M.; Heimer, J.; Franckenberg, S. MRI Segmentation of Cervical Muscle Volumes in Survived Strangulation: Is There an Association between Side Differences in Muscle Volume and the Handedness of the Perpetrator? A Retrospective Study. Diagnostics 2022, 12, 743. https://doi.org/10.3390/diagnostics12030743

AMA Style

Marty M, Dobay A, Ebert L, Winklhofer S, Thali M, Heimer J, Franckenberg S. MRI Segmentation of Cervical Muscle Volumes in Survived Strangulation: Is There an Association between Side Differences in Muscle Volume and the Handedness of the Perpetrator? A Retrospective Study. Diagnostics. 2022; 12(3):743. https://doi.org/10.3390/diagnostics12030743

Chicago/Turabian Style

Marty, Marc, Akos Dobay, Lars Ebert, Sebastian Winklhofer, Michael Thali, Jakob Heimer, and Sabine Franckenberg. 2022. "MRI Segmentation of Cervical Muscle Volumes in Survived Strangulation: Is There an Association between Side Differences in Muscle Volume and the Handedness of the Perpetrator? A Retrospective Study" Diagnostics 12, no. 3: 743. https://doi.org/10.3390/diagnostics12030743

APA Style

Marty, M., Dobay, A., Ebert, L., Winklhofer, S., Thali, M., Heimer, J., & Franckenberg, S. (2022). MRI Segmentation of Cervical Muscle Volumes in Survived Strangulation: Is There an Association between Side Differences in Muscle Volume and the Handedness of the Perpetrator? A Retrospective Study. Diagnostics, 12(3), 743. https://doi.org/10.3390/diagnostics12030743

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