Postmortem changes constitute the natural progression of the body’s decomposition after death, beginning at the cellular level. The process involves complex cellular and biological phenomena. The changes that commence immediately after death continue to occur over a prolonged period at different rates for different organs. The onset and extent of these changes are affected by multiple intrinsic and extrinsic factors. The rates are not precise and differ from one geographical region to another, and also differ in the same geographical region from one season to another. An understanding of the postmortem changes is essential for the estimation of the postmortem interval (PMI) or time since death, one of the primary objectives of the forensic autopsy. The timings of the appearance of the various postmortem changes mentioned in this brief overview of postmortem changes are only guidelines pertaining to tropical climates unless otherwise specified and should never be considered as absolute.
FACTORS AFFECTING POSTMORTEM CHANGES
The rate of postmortem changes is either accelerated or decelerated by various intrinsic and extrinsic factors. Intrinsic factors involving the subject that affect postmortem changes primarily include body mass and the surface area of the body. Extrinsic factors that affect postmortem changes primarily include the subject’s clothing and insulation, the environment of the death scene, and storage of the body after death. These factors either accelerate or decelerate the onset and extent of postmortem changes. Some of the factors that accelerate the rate of postmortem changes include a high-fat content of the subject, sepsis or underlying infection as the direct or contributing cause of death, and the presence of open wounds. Some of the factors that decelerate the rate of postmortem changes include freezing ambient temperatures, scantily dressed or naked subject, and storage of the body in a cold chamber shortly after death.
BROAD CLASSIFICATION OF POSTMORTEM CHANGES
Postmortem changes are classified based on their order of appearance into immediate, early and late postmortem changes.
Immediate Postmortem Changes
"Immediate postmortem changes" or "rapid changes after death" relate to the cessation of bodily functions including the respiratory, circulatory, and nervous systems. These changes are specifically the "signs of death" or "indications of death." In brief, death is considered to have occurred when the vital functions of the body have irreversibly ceased.
Respiration completely stops after death resulting in loss of respiratory movements and breathing sounds. The feather test and mirror test are a couple of traditional tests used to confirm this. However, these tests are quite unreliable. Circulatory stoppage results in a loss of pulse, which can also be confirmed by a flat electrocardiogram (ECG) in a hospital setting. The absence of respiratory and cardiac sounds on auscultation over a period of 5 minutes indicates a sign of death as advocated by expert clinicians. The finding of the break-up of the columns of blood in the retinal blood vessels (retinal vascular segmentation) on ophthalmoscopy confirms stoppage of circulation and is one of the earliest indications of death. Cessation of nervous system functions results in the loss of sensory and motor functions and reflexes. The muscles begin to become flaccid with lose of tone. Pupils also dilate as a result of this. In a hospital setting, a flat electroencephalogram (EEG) is confirmatory of loss of electrical activity in the brain.
Early Postmortem Changes
Three early postmortem changes that occur while the body is still in the fresh stage, before the breakdown of soft tissues, namely algor mortis, livor mortis, and rigor mortis are of forensic significance.
The eye changes that occur during the early postmortem period include corneal turbidity/opacity and tache noire formation. The intraocular tension progressively falls to nil in about 2 hours after death, although this is disputable.
Algor mortis is the postmortem cooling of body temperature until it equalizes the temperature of the surrounding environment. The rate of cooling lags initially, then becomes linear before slowing down again as it approaches the ambient temperature, giving a sigmoid-shaped curve when graphically represented. The ambient temperature is a critical factor that affects the rate of postmortem cooling of the body. Postmortem cooling of the body continues for about 6 hours after death, and the rate of cooling is primarily dependent on the difference in body temperature at the time of death and the temperature of its surroundings. The rate of cooling will hasten in a body immersed in water, naked body, and a thin body. The rate of cooling will be slower in a well-clothed body and an obese body. A prudent forensic pathologist will not estimate the time since death based on the single criterion of algor mortis as the rate of postmortem cooling of the body is affected by multiple variables.
Livor mortis, also known as postmortem hypostasis or postmortem lividity, is a passive process of blood accumulating within the blood vessels in the dependent parts of the body as a result of gravity, causing a discoloration of the skin that varies from pink to dark purplish. It begins to be apparent about an hour after death, is well formed in about 3 to 4 hours after death, and gets fixed in about 6 to 8 hours after death. However, it is worth noting that the timing of livor mortis is highly variable. Hemolysis leads to fixation of lividity. Once fixed, lividity does not shift its distribution when the position of the body changes. The dermal manifestation of postmortem lividity may be absent in the severely anemic or in those who have died of severe hemorrhage. It may not be apparent in the dark-skinned.
Livor mortis should be differentiated from a contusion or bruise, which occurs as a result of blood vessel rupture from blunt force impact and exsanguination of blood into the surrounding tissues.
Rigor mortis (postmortem rigidity) is the stiffening of the muscles of the corpse due to depletion of adenosine triphosphate (ATP) after death with the subsequent build-up of lactate in muscle tissue, resulting in an inability to release the actin-myosin bond. This postmortem muscle change appreciated grossly follows the initial phase of primary flaccidity of muscles and is itself followed by the secondary flaccidity of muscles that coincides with the beginning of putrefactive changes. The process of rigor mortis uniformly involves all muscles of the body. However, it is first apparent generally in smaller muscles such as the jaw and the eyelids due to a quicker depletion of ATP relative to larger muscles in the trunk and limbs. Rigor mortis occurs in both voluntary and involuntary muscles including the cardiac muscle. It is first evident in the facial muscles at 1 to 4 hours after death. The gelling of the muscle proteins is apparent as muscle stiffening in about 6 hours after death in the rest of the muscles and is complete in about 12 hours after death. This rigidity of the muscles lasts for about another 12 hours or so. The body then returns to a flaccid state after the enzymatic breakdown of the binding sites of actin and myosin. The rate at which rigor mortis passes off will be rapid in a hot environment as the onset of putrefaction is hastened in such an environment. Cold temperatures lengthen the duration of rigor.
In brief, postmortem changes in the muscles include:
Rigor mortis of the arrector pili muscle attached to the base of a hair follicle is also responsible for the phenomenon of cutis anserina (cutis anserine), otherwise known as postmortem goosebumps. Rigor mortis needs to be distinguished from cadaveric spasm/instantaneous rigor, which is an immediate contraction of a small group of muscles at the instance of death, seen in scenarios of violent death like in the case of drowning.
Late Postmortem Changes
Two mechanisms are involved in decomposition: autolysis and putrefaction. Although decomposition begins soon after death in the form of autolysis, the macroscopic changes brought about by decomposition become apparent much later when putrefaction occurs.
Autolysis is a process that occurs due to leakage of hydrolytic cellular enzymes from cells after death. The changes that occur in this process are mainly on a microscopic rather than a macroscopic level. Internally, autolytic changes are most prominent in the pancreas and other organs with a high concentration of cellular enzymes. In comparison, the prostate and the non-gravid uterus take a longer duration of time to decompose.
The leakage of cellular contents also leads to a suitable environment for microbes such as bacteria, fungi, and protozoa, normally present in the human microbiota, to grow and degrade surrounding tissues, which is known as the process of putrefaction.
Unlike autolytic changes, putrefactive changes are visible on a macroscopic level as discoloration of skin or bloating of body parts such as the face, abdomen, breast, and scrotum. It can appear in various forms such as putrefactive fluids and putrefactive gases.
STAGES OF DECOMPOSITION
There are five stages of decomposition, namely fresh, bloated, active decay, advanced decay, and skeletal stage. These stages may occur simultaneously in different parts of the same corpse, and it may be difficult for a forensic pathologist to label the state of the corpse with a single stage.
The fresh stage is the immediate period following death in which autolysis occurs. Algor mortis, livor mortis, and rigor mortis are apparent in this stage.
The earliest external sign of putrefaction is the greenish discoloration of the skin of the anterior abdominal wall in the right iliac fossa region. In this region of the abdomen, the caecum, loaded with semi-solid intestinal content and commensal gut bacteria lies quite superficial. This greenish discoloration of the skin results from the formation of sulfhemoglobin facilitated by the commensal intestinal bacteria that invade the tissues after death. This skin discoloration in the right iliac fossa region appears in about 18 hours after death. In temperate climates, this greening may first appear 2 to 3 days after death. The ambient temperature affects the speed of onset of putrefaction and its rate of progression.
The blowflies (Calliphoridae) and flesh flies (Sarcophagidae) are often the first insects to be attracted to a dead body. In brief, the invasion of the body by flies and the life cycle of flies (oviposition, hatching of eggs, feeding activity of larvae or maggots, the transformation of maggots to adult flies) coincide primarily with the bloated and decay stages of decomposition. The flies may even be attracted to a dead body towards the end of the fresh stage.
In the bloated stage, body parts, including organs and soft tissues swell due to the accumulation of putrefactive gases or other decompositional products from the putrefaction process. It usually starts in the abdomen and then slowly affects other parts including the face, breasts, and genitals. Also during this stage, skin changes occur such as blisters and slippage. Skin slippage at the extremities is known as degloving. Moreover, the phenomenon of marbling is also present during this stage, where blood vessels are visible on the skin as greenish-black streaks and eventually results in skin discoloration ranging from green to black. These postmortem changes are apparent in about 24 to 48 hours after death.
Active decay is a stage where putrefaction accelerates after bloating. Postmortem purging where putrefactive body fluids are forced out of body orifices is observed during this stage of decay. The detachment of hair or hair sloughing and black discoloration of ruptured skin are observed.
Advanced decay, also called black putrefaction or late decay is a stage where bones begin to get exposed, and the body assumes a "caved in" appearance. Degradation-resistant tissue such as hair (although already sloughed) and cartilage are spared up to this stage.
Skeletal stage, also called dry remains stage or skeletonization, begins when bone exposure is extensive, but the bone is yet to breakdown. Remaining dried skin, cartilage, and tendons are minimal in this stage. Decomposition significantly slows down at this stage, and it takes years or decades for the skeletal remains to disintegrate.
The literature also reports differential decomposition involving mummification or adipocere formation.
Mummification results from tissue desiccation and is a phenomenon that occurs when the corpse is in an environment that is hot and dry. The skin of the corpse becomes dark, dry and appears leathery in appearance. Overall the body appears parched; this preserves the corpse for a longer period. It can occur to the corpse as a whole, or in localized areas such as the extremities or the tongue.
Adipocere is yellowish to gray like colored waxy substance that can preserve the corpse as a whole or some parts of it. Adipocere formation in the buccal pad of fat will retain the outline of the cheeks. Unlike mummification, the process of adipocere formation occurs in corpses in environments that are high in moisture. Anaerobic conditions, such as a flooded burial or submersion in water facilitate adipocere formation. The process primarily involves hydrolysis and hydrogenation of body fats to fatty acids and soaps and the formation of adipocere. Although adipocere formation is reported to have occurred as early as about 3 weeks after death, in most cases, it becomes apparent only months after death.
Although early and late postmortem changes are heralded as definite signs of death in traditional textbooks, in practical reality, they are not criteria in considering the diagnosis of death. Nevertheless, the immediate postmortem changes are clinically significant in diagnosing death. In the context of the diagnosis of death, the condition known as suspended animation or apparent death should also merit consideration. Suspended animation is a condition where the person appears to be dead due to the fact that the vital conditions are at such a low pitch as to be minimum compatible with life. This condition may occur in a person fished out of water or hypothermia. In such situations, doctors erroneously declaring a patient dead is a huge embarrassment. Nonetheless, the literature contains reports of cases of wrongful declaration of death.
The early and late postmortem changes are significant from a forensic perspective in primarily estimating the time since death or PMI.
Post-mortem interval (PMI) is the time that has passed since the death of a person until found, is an essential tool in forensic investigations as providing an estimated time since death, is pivotal in judicial cases and can even either incriminate or acquit a suspect.
Understanding the appearance and progression of the postmortem changes is essential in estimating the PMI. The earlier a corpse is found, the more accurate the PMI estimation is likely to be. Once a corpse undergoes putrefaction, PMI can only be provided as a rough range as many variables affect the rate of these changes. Estimation of PMI should not be based solely upon a single postmortem change, and instead, all the postmortem changes should be considered collectively in forming an opinion of the time since death. A sensible forensic pathologist will never provide an assessment of the specific "time of death," but will only provide a range of estimation of the "time since death."
Secondly, a doctor should also be aware of the postmortem changes to avoid misinterpretation of these findings as signs of physical violence or unnatural death. It is not uncommon for the emotionally charged legal heirs of the deceased or members of the lay public to wrongly interpret postmortem lividity for a contusion, especially in instances where death is not witnessed by them, despite assertions from a forensic pathologist.
Incorrect opinions from a misinterpretation of postmortem changes for traumatic injuries during the postmortem examination may mislead the investigation in the wrong direction leading to unnecessary inquiries that may even end up in the miscarriage of justice.
Two specific reasons for a doctor to know the progress of postmortem changes include:
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