Observation and identification of metabolites emerging during postmortem decomposition of brain tissue by means of in situ¹H‐magnetic resonance spectroscopy

Abstract

One of the most important and most difficult tasks of a forensic investigation is the estimation of the time span passed between death and recovery of the body, in particular if a body remained undiscovered for more than 2 days. Under these circumstances, the common indicators for the estimation of the postmortem interval (PMI), i.e., rigor mortis, livor mortis, and the body's core temperature, will have reached steady state in most cases.Since the early 1970s various chemical methods have been developed in order to ameliorate and extend PMI estimation, e.g., using blood and serum (1), cerebrospinal fluid (2), vitreous humor (3,4), skeletal muscle (5), and liver (6). Brain tissue remained largely excluded from these investigations, despite the fact that interindividual differences in tissue composition are very small and that the skull represents a natural barrier against external factors. Daldrup (7, and Refs. therein) proposed a formula for the time of death for PMIs of up to 20 days using the changes in the concentration of amino acids that occur during brain decomposition. The limited success of these methods might also be a consequence of the time-consuming and labor-intensive chemical analysis required.Proton magnetic resonance spectroscopy ( 1 H-MRS) has been used to study brain autolysis (8 -11); however, not in situations that are relevant for forensic sciences. Most examinations dealt with the influence of the conditions and the time span between autopsy or surgical removal of tissue samples and the moment of chemical analysis. These studies covered time ranges of up to 195 hr for "sterile" test tube conditions (11), up to 24 hr postmortem (8,10) for autopsied, nonsterile samples at room temperature, and up to 120 hr at a storage temperature of 4°C (8). Short-term changes were investigated in dog brain in situ up to 24 hr in the clinically relevant case of global ischemia (9).The later phase of brain decomposition is governed by bacterial growth (12), resembling the situation in an abscess in vivo. 1 H-MRS has been found valuable to distinguish between abscess and other cystic lesions, in particular tumors (13)(14)(15).The eventual goal of the present investigation is an estimation of PMI up to 3 weeks, based on changes in the concentration of brain metabolites determined by 1 H-MRS in situ and quantitative analysis of the spectra by the program LC Model (16). In a first step, a sheep model was used to study brain decomposition longitudinally. The metabolite patterns obtained in this model were compared with selected human cases to investigate if the chosen model is qualitatively representative for human bodies. Metabolites that are not present in vivo are identified and included in the basis set for LC Model to check the assignments in situ. In particular, free trimethylammonium (fTMA, not to be confused with TMA compounds that occur in brain in vivo), propionic acid (Prop), butyrate (But), and iso-butyrate (iBut) were found postmortem in both sheep and human brain tissue. Following a characterization...

Forensic Application of Postmortem Diffusion-Weighted and Diffusion Tensor MR Imaging of the Human Brain in Situ

“…A single asterisk indicates P Ͻ .05; double asterisks, P Ͻ .005; and triple asterisks, P Ͻ .001. objective methods are hardly developed. 33,34 A significant difference of ADC Tc was found mainly in the GM between the group with PMIs Յ1 day and that with PMIs of Ͼ2 days. This is in agreement with previous studies that investigated the effect of PMI in tissue samples of animal brain fixed at different time points after death.…”

Essentials of forensic post-mortem MR imaging in adults

“…the time of death) represents a perpetual challenge to forensic investigators. 55 Ith et al [55][56][57] investigated the potential of MR spectroscopy to determine the post-mortem interval based on the changing profile of brain metabolites during decomposition in a sheep model. Although fascinating, this approach is still limited to the realm of research because of the complexity of MR spectroscopy and the significant logistical challenges related to using MR spectroscopy on a routine basis in forensic death investigations.…”

Correlating Quantitative MR Imaging with Histopathology in X-Linked Adrenoleukodystrophy

“…We did not obtain MRS after death because spectra are known to change rapidly due to postmortem decay, 27 obviating the possibility of directly correlating metabolites with histopathologic parameters. However, in the 2 patients with X-ALD in whom we were able to perform a postmortem examination, histopathology confirmed active demyelination and inflammation in the edge of the lesion and almost complete loss of axons and myelin with dense gliosis in the center of the lesion.…”