Correlation of age, sex and season with the state of human decomposition as quantified by postmortem computed tomography

The state of decomposition of a body varies considerably due to the many variables that impact the process of decay. These variations depend on environmental conditions such as temperature. Possible postmortem alterations consist of the body turning a greenish color, marbling of the skin, maggot infestation, bloating, mummification and skeletonization in the later stages [1]. Due to the large variety of postmortem changes and influencing factors, estimations of time of death are generally relatively vague and contain great variability [2]. Methods to determine the early postmortem interval (PMI) more precisely, such as thanato-chemical measurements of human cardiac troponin [3], are rarely used in practice and are mostly of academic interest [4]. Unfortunately methods to estimate the late PMI more accurately that apply a decomposition scoring system and integrate entomological data [5] suffer from shortcomings in statistical data analysis [6]. Ultimately, the complex estimation of the late postmortem interval usually still predominantly relies on the experience of the forensic pathologist [7].

In the last 20 years, postmortem computer tomography (PMCT) and postmortem magnetic resonance (PMMR) have become valuable adjuncts and even alternatives to conventional autopsy [8‐10]. PMCT is sometimes considered superior to autopsy due to its ability to detect gas inside of a body [8, 11, 12]. Gas is a common radiological finding in decedents; it is either caused by vital embolism, i.e. after open or iatrogenic trauma, or develops postmortem due to decomposition [13]. For the latter, recently a method to quantify intracorporeal gas was established, named the radiological alteration index (RAI) for PMCT [14]. The RAI is a straightforward, visual grading system that considers seven different sites in the body with different weightings, allowing for the quantification of intracorporal gas and aiding in the distinction between postmortem decomposition, versus vital air embolism [14].

A subjective perception among the forensic pathologists at the Swiss Institutes of Forensic Medicine is that there tends to be an increase in cases of advanced decomposition during summer. This is thought to be caused by both a reduced discoverability of the diseased by the relatives due to the long summer holidays (they last six weeks in Switzerland and are the longest holidays throughout the year) and generally increased temperatures. In the hot summer months, bodies decay faster due to overall high temperatures, and show a more rapid infestation with maggots. Both are well-known factors that contribute to body decomposition [15‐17].

It was furthermore shown that people with an insufficient social network, or who live alone, have an increased mortality risk if medical symptoms develop, as they lack a trusted person that would encourage medical attention [18]. Additionally, loneliness may be typical in older people with major health and mobility problems [19], which could lead to unrecognized death. In a forensic sample, this should be indicated in the autopsy data as an increased PMI and a state of advanced decomposition at detection.

The recently developed RAI allows for quantification of intracorporeal gas with a clearly defined value. Our aim was to evaluate two hypotheses by using the RAI as a proxy for the state of decomposition.

First, we examined whether there were seasonal influences on all autopsy case numbers (with decomposition gas) and the RAI.

Second, we examined whether there was a correlation between age or sex and the RAI.

The distribution of cases with an RAI > 0 per season can be seen in Table 2 (spring: 105, summer: 55, autumn: 41, winter: 81). The Kruskal–Wallis test results were not significant for all case numbers (RAI > 1) and seasons (Table 2); there was no significantly increased case number in any of the seasons. The Kruskal–Wallis test result was not significant for sex and RAI (Table 3); there was no correlation between the RAI and sex. A trend indicated that the younger age group was found with a lower RAI, suggesting a less decomposed state (RAI 31.58, error of the mean 3.71) than the older age group (RAI 41.49, error of the mean 2.89), but the Kruskal–Wallis test result was not significant (Table 3). There was a significant difference in age when comparing cases with an RAI ≥ 50 and an RAI < 50 (Table 3); bodies with an RAI ≥ 50 had a mean age of 60.86 yrs (error of the mean 1.56), while those with an RAI < 50 were slightly younger, with a mean age of 55.39 yrs (error of the mean 1.06). The Kruskal–Wallis test result was also significant when comparing the age of male cases with RAI ≥ 50 and the age of male cases with an RAI < 50 (Table 3, Fig. 2). For females, however, the test result was not significant (Table 3, Fig. 3).

The linear regression of RAI vs. age in men had a slope of 0.35, suggesting a weak positive correlation. RAI vs. age in women had a very weak correlation, with a slope of only 0.1 (see Figs. 2 and 3). Male cases aged ≥ 50 years tended to have a higher RAI, suggesting that they were found in more advanced stages of decomposition than female cases. In the female group, there was no correlation between age and the RAI / state of decomposition.

Our aim was to evaluate the correlation between seasonal influences, age and sex and the state of decomposition by using the RAI as a proxy for the extent of decomposition.

The main purpose of a forensic postmortem investigation is of the determination of the cause and manner of death and possible third-party involvement in a suspected criminal offense. It is our opinion that beyond this major primary task, important additional aspects can be derived from the collected data, such as insights into sociopolitical backgrounds and relationships.