The changes that occur in the human body after death may be classified and contrasted in a number of ways. There are the predictable, genuine and natural versus the artifactual. The latter may be deliberately produced or occur accidentally. There are changes which assist the investigator and those which can confound. And the changes occur at all levels of pathological investigation; macroscopically, microscopically, biochemically and toxicologically. The challenge for the forensic pathologist lies in drawing the appropriate inferences from the genuine changes, recognizing the artifacts and interpreting within the limits of the postmortem examination the available information.
The Purpose of the Postmortem Examination
The precise requirements of the medicolegal autopsy will vary from jurisdiction to jurisdiction. However, there are certain fundamental issues which the forensic pathologist is usually required to address. These include identification of the deceased, determination of a cause and manner of death, estimation of a time of death and interpretation of any injuries which might be (or have been) present. The various categories of postmortem change (Table 1) are examined here in some detail.
Genuine Postmortem Changes Decomposition
Decomposition of a human body is a natural and predictable sequela of death. The postmortem examination of such a body is among the more challenging tasks confronting a forensic pathologist. It is at such times that the pathologist needs to be on guard lest some crucial piece of evidence be overlooked, misinterpreted or even inadvertently destroyed.
Decomposition can be conveniently sub-classified into three basic processes: putrefaction, mummification and adipocere formation. The different processes often co-exist and the rate and extent of their development is influenced by the prevailing environmental conditions such as temperature, moisture level, presence or absence of concomitant insect activity and whether the body is submerged or buried.
Table 1 Categories of postmortem change
|Time of death||Temperature|
This phenomenon represents the gravitational shifting of blood which will occur as a natural and predictable postmortem phenomenon. Its forensic importance is twofold. First, the investigator must be aware that postmortem hypostasis or lividity will become fixed after a variable time. A figure often quoted is approximately 12 h. However, the use of such a time frame needs to be exercised with caution. In the author’s experience it is the appearance of hypostasis in autopsy photographs from suspicious deaths which invariably attracts the attention of legal counsel in court proceedings, who often confuse the changes with some form of injury given the potential similarity to bruising. The one area where postmortem hypostasis may provide valuable information to the forensic investigator is in determining whether a deceased person has been moved after death. If the pattern of lividity is inconsistent with gravitational shifting of blood, one can infer that the deceased has been moved postmortem and that the shifting of the body has occurred after lividity became fixed.
The development of postmortem rigor mortis is a predictable postmortem response. Biochemically it represents postmortem muscle contraction which becomes fixed due to the inevitable diminution of available adenosine triphosphate (ATP). It appears first in the smaller central muscle groups such as the jaw and face and moves peripherally. It declines in the reverse order. Some text topics provide a framework within which to estimate time of death based on development of rigor mortis. However, these are crude estimates and furthermore their use in assisting with determination of time of death is confounded by the notion of ‘cadaveric spasm’. This is a phenomenon whereby in an individual engaged in some form of intense physical activity immediately prior to death, the development of rigor can occur as an immediate postmortem response.
The changes which occur in the skeletal muscle postmortem are chemical reactions and as such may be accelerated by an increase in temperature. Thus a body that has been exposed postmortem to high environmental or ambient temperatures may develop rigor at a more rapid rate than expected. Similarly, the death of an individual occurring in a cold environment or refrigeration immediately postmortem will delay the onset of rigor mortis.
This represents the natural breakdown process of human tissue which will be facilitated by bacterial activity. A number of specific postmortem artifacts are worthy of mention here as they may cause confusion with specific antemortem pathological processes. So-called postmortem esophago- or gastromalacia may simulate rupture of these visci. Breakdown of the pancreas post mortem can cause confusion macro-scopically with acute hemorrhagic pancreatitis. Exaggerated hypostasis involving the posterior left ventricle in an individual who has remained supine after death can cause confusion with ischemic myo-cardial damage. And finally in bodies recovered from fire the well-recognized phenomenon of heat associated extradural hemorrhage, producing the characteristic honeycomb appearance of blood which has exuded from the diploic veins and venous sinuses, is worthy of emphasis.
In warm climates this change is the norm and can occur quite rapidly over even a matter of hours. The order in which changes appear is relatively predictable. The first sign is usually a green discoloration of the skin of the anterior abdominal wall in the right iliac fossa region. This is a reflection of the relatively superficial location of the large bowel (cecum) and its invariably high bacterial content. The presence of so-called marbling then follows. This represents bacterial overgrowth in superficial veins and confers a ‘road map’ type pattern on the body, often first appearing in the shoulder regions.
A series of predictable changes then ensues. With increasing postmortem gas formation the body swells, in particular the abdominal cavity and scrotum. There is a purging of bloodstained fluid from the nostrils and mouth often raising concerns among uninitiated investigators of suspicious circumstances surrounding the death. If there has been concomitant insect activity with flies laying eggs there will often be intense entomological activity with numerous maggots present on and about the body.
This particular type of postmortem change comprises the appearance of a white waxy material on the surface of the body. Its name is derived from adipo-(fat) and -cire (wax). This commonly occurs in bodies that have been exposed to moisture or submerged and where the temperatures are cool. Biochemically it represents breakdown products of fatty acids and has been shown to contain palmitic, oleic and stearic acid. Although this process is less malodorous than putrefactive change it can have the effect of concealing identifying features and injuries and, depending on the jurisdiction in which one works, might be a change rarely encountered.
Mummification is the type of change most familiar to the lay person. It invariably occurs when the body has been in a dry environment without exposure to insect activity. The drying of the skin can markedly hamper identification and complicate injury interpretation although often injuries will be preserved relatively intact.
Postmortem Changes Impinging on Time of Death
These represent changes which are predictable and potentially helpful to the pathologist. The limitations however on the use of the various methods of estimating the postmortem interval needs to be remembered.
Rigor mortis and postmortem hypostasis
The potential benefit of these two processes and their limitations with respect to the determination of postmortem interval have been noted above.
The core temperature of the human body post mortem will fall in a semipredictable way. The investigating pathologist needs to be aware of the potential usefulness of a postmortem temperature but more importantly of the limitations on interpretation of such data.
The most widely accepted method is using Henssge’s nomogram which requires the taking of a rectal temperature. Alternative sites for temperature measurement include outer ear and abdominal viscera.
Forensic literature abounds with material on the subject of postmortem biochemical analysis. The most useful specimen for such postmortem analyses is vitreous humor which is relatively isolated from post mortem bacterial overgrowth.
A number of general comments may be made about the usefulness of certain postmortem vitreous measurements. Vitreous urea and creatinine are stable postmortem and thus provide good markers for the assessment of antemortem dehydration (elevated urea coupled with normal creatinine) or renal impairment (variable elevation in both urea and creatinine). The adjunctive use of postmortem electrolytes is more problematic. Vitreous sodium and chloride will generally fall but at a variable rate whereas vitreous potassium will rise. It is the latter quasi-predictable event which has attracted the particular attention of academics.
With respect to estimation of postmortem interval the measurement of vitreous potassium is of most value after one to two days. Formulae have been proposed to assist in the interpretation of postmortem interval. That of Madea and Henssge is:
Postmortem interval (PMI(h)) = 5.26 x potassium concentration (mmol/l) — 30.9
and that of Sturner is:
Postmortem interval (PMI(h)) = 7.14 x potassium concentration (mmol/l) — 39.1.
It needs to be reiterated that caution is required in the use of such equations and in the interpretation of results.
Another method by which postmortem interval may be estimated is the measurement of vitreous hypoxanthine. This is attracting increasing attention in the forensic literature. A comparison of the use of postmortem vitreous hypoxanthine and potassium levels concluded that a combination of the two generated the greatest accuracy with respect to estimation of postmortem interval.
This subject is included more for the sake of completeness than for any useful contribution to the determination of postmortem interval. A perusal of review articles which examine the factors which delay, accelerate or have no effect on gastric emptying and an awareness of gross miscarriages of justice makes one uneasy especially when even today experienced pathologists are seen to prognosticate about a particular time of death in criminal proceedings based on gastric emptying. The only useful observation that can be made with respect to gastric contents is the nature and volume of the contents which may provide an important piece of information with respect to a criminal investigation. The number of variables otherwise associated with the process of gastric emptying make this an area that should be approached with a combination of extreme caution and healthy skepticism.
In conclusion, various methods exist to aid the pathologist with respect to the determination of the time of death. Some of these are truly academically based and only used with any frequency in specific jurisdictions. The interested reader seeking information concerning postmortem skeletal muscle electrical stimulation and additional detail on the foregoing is referred to the literature.
Artifactual Postmortem Changes Postmortem injuries by predation
The predators in question can range from the domesticated to the wild and from the smallest members of the insect kingdom to the largest of carnivorous mammals. Postmortem insect activity in the form of fly larvae or beetles is a major contributor to the natural breakdown process of the human body after death. Intense larval activity as well as obscuring distinguishing marks and features, stigmata of natural disease and signs of injury also produces markings on the skin in the form of circular or elliptical holes which can ‘mimic’ injury to even the trained observer. Such postmortem insect activity although generally tending to obscure can be of assistance to the investigating pathologist with respect to determination of the time of death. The pathologist needs to ensure that appropriate specimens are obtained and the engagement of a forensic entomologist, with knowledge of the specific insect life cycles, might also provide valuable information.
In circumstances where an individual has died in a domestic dwelling and remained undiscovered for some days, injuries present on the body may ultimately be attributable to the family pet. Injuries produced by domestic dogs are not uncommonly seen in forensic practice. In individuals dying in more dilapidated surroundings the contribution of incised injuries by small mammals such as rats may also warrant consideration. Information concerning the scene of discovery is of crucial importance in such circumstances.
The final contribution of predators may occur when the individual is exposed to large carnivores.
The author has the experience of a case where an individual entered a lion enclosure at a metropolitan zoo (without authorization) in order to engage in some form of martial art ritual with the captive beasts. A large numbers of injuries were observed on the deceased which were considered to represent postmortem artifact. The unfed animals had essentially stripped skeletal muscle from the long bones while leaving much of the abdominal and thoracic viscera intact. The circumstances of the case made the interpretation of the injuries relatively straightforward however, one needs to be prepared for a situation where relevant information is not so forthcoming.
Injuries inflicted deliberately postmortem, invariably in the context of homicide, are encountered not infrequently by the practicing forensic pathologist. These generally fall into two broad categories. Those produced in a so-called ‘perimortem period’ and those produced clearly postmortem.
With respect to perimortem injuries often the pathologist in court when describing their findings with respect to multiple homicidal stab wounds is forced to concede that, due to the absence of bleeding associated with some of the injuries, there is the possibility that these were produced after death, i.e. after the ‘irreversible cessation of blood flow or irreversible cessation of brain function’ (statutory definition of death in the author’s jurisdiction). In such instances the degree of bleeding adjacent to the specific wounds is of some assistance but such issues generally cannot be addressed with absolute certainty.
The second category of injuries warranting consideration is those produced in a ritualistic sense generally signifying significant psychopathology in the assailant. The type and degree of such postmortem mutilation varies greatly but includes removal of breasts, genital mutilation such as removal of the penis and scarification type injuries. The latter may sometimes cause confusion with antemortem injuries produced in the context of torture.
Injuries related to handling of the body
Injuries in this category include the so-called ‘undertaker’s fracture’ whereby careless or overly rough handling of the deceased person results in a fracture of the cervical spine. Correct interpretation of this is generally facilitated by the absence of bleeding although sometimes a small amount of hemorrhage may be present which causes difficulties. In such instances, as in any forensic autopsy, the forensic pathologist needs to rely on the circumstances surrounding the death including the treatment of the deceased person after discovery. A related artifact is the rupture of skeletal muscle which can occur by the forceful, albeit naive, breaking of rigor mortis, usually by inexperienced funeral directors or forensic technicians. In such instances examination of the injured skeletal muscle usually reveals a small amount of hemorrhage but obviously no evidence of an inflammatory reaction.
Prinsloo Gordon artifact
This eponymous entity is well known to most experienced forensic pathologists. It represents hemorrhage on the anterior aspect of the cervical spine, posterior to the trachea and esophagus. This may be considered a form of hypostasis. It causes most confusion in the context of the interpretation of neck injuries. It is minimized by insuring that the standard practice in cases of neck injury involves either opening the cranial cavity first to allow drainage of blood or alternatively if the extracranial examination is to occur first, insuring that the root of the neck is incised to allow drainage of blood from that region.
From a semantic viewpoint, if one considers a bruise to be an active physiological response to tissue trauma then this category is probably better described as postmortem extravasation of blood potentially simulating antemortem bruising. A number of difficulties can arise with respect to the interpretation of such changes. Histopathology or enzyme histochemistry may sometimes be of assistance. Most important is an awareness of this type of artifact. The potential problems associated with such cases are discussed in a problematic case reported by Burke et al.
Postmortem artifacts from a number of sources can provide confounding data for the forensic pathologist. Ideally, before commencement of the postmortem examination the circumstances surrounding the death will have been made clear to the pathologist and this will include specific descriptions of medical intervention and resuscitation, both professional and inexpert. This, however, is invariably the exception rather than the rule. Resuscitation artifact is particularly problematic in pediatric homicide cases where rupture of abdominal viscera, mesenteric laceration and retinal hemorrhages may be the subject of intense and rigorous cross-examination in the later criminal trial. Rib fractures, laryngeal fractures, cardiac rupture and pneumoperitoneum are all well-described entities.
This category of postmortem change is worthy of mention for two reasons. First, the sites of introduction of embalming fluid can mimic penetrating injuries of more sinister origin. Although the fact that an individual has been embalmed would generally be known to the investigating pathologist, it is often in cases of second postmortem examination particularly in a deceased individual who has died in a foreign jurisdiction that the pathologist needs to be aware of the potential for such confounding artifacts. Secondly, postmortem toxicology on embalmed individuals can produce quite puzzling results with high levels of methanol, anticoagulants and various other dyes often detected by sophisticated screening methods.
The significance of the postmortem changes described above lies in their ability to confuse and obscure. A practicing forensic pathologist needs to be well focused on the purpose of the medicolegal autopsy. He or she needs to be aware of the different categories of postmortem change and to recognize when they can be of assistance in the investigation, when they might assist but need to interpreted with caution and when they will do little but obscure. The forensic pathologist is in a privileged position each time they embark on a postmortem examination. It is their responsibility to the profession, to the medicolegal investigating authority and to the family of the deceased that they elicit the maximum information from the autopsy and interpret it to the best of their ability.