Post-mortem Changes

Overview

Post-mortem changes (PMC) constitute the natural progression of the body’s decomposition after death, beginning at the cellular level.

• Factors that affect post-mortem changes
  • Temperature – a hot and humid climate hastens PMC
  • Season – cold weather slows the onset of PMC
  • Geographical location
  • Fat content – increased fat content hastens PMC
  • Infection – sepsis hastens PMC
  • Injuries – open injuries hasten PMC as they provide an entry for putrefactive bacteria
  • Presence of clothing – inadequately dressed bodies have a slower onset of PMC. Heavily dressed bodies are warmer hence decomposition is faster.

Classification

• Post-mortem changes can be divided into
  • Immediate changes – These are the signs and indications of death since they occur as soon as one dies. Related to somatic death which is the irreversible cessation of vital functions. Helps in diagnosing death
  • Early changes – Associated with cell death
  • Late changes – Occurs after a while and involves disintegration of the body.

Postmortem changes

Early changes

Algor mortis

Refers to post-mortem cooling and is translated from Latin as, ’cold death’. The descendent’s body temperature steadily changes to the ambient temperature as heat is lost via radiation, convection and conduction (only in cases where ambient temperature is below body temperature). External factors heavily influence this process.

• Factors affecting cooling
  • Position – faster on a colder surface such a cold floor as opposed to a carpet
  • Posture – faster in an outstretched position than a fetal position
  • Body fat – more body fat means slower cooling
  • Clothing – heavily dressed bodies will cool slower
  • Movement of air – windy conditions will cause faster cooling
• Forensic importance
  • Determines post-mortem interval (PMI – the time between when someone dies and when they are examined)

Rigor mortis

Refers to post mortem stiffening/rigidity. Immediately after death there is usually a period characterised by muscular flaccidity. This is followed by partial or complete rigidity but with the onset of putrefaction, the rigidity wears off and secondary relaxation sets in.

It occurs due to depletion of ATP in muscles leading to actin and myosin becoming linked causing muscle stiffening. Rigor is initiated when the ATP concentration falls to 85 per cent of normal, and the rigidity of the muscle is at maximum when the level declines to 15 per cent.

It develops in all muscles at the same time but it is first noticed in small muscles in the eye, jaw and lastly in the limbs.

Time ranges are as follows:

• Factors affecting rigor mortis
  • Environmental temperature – the colder it is the slower the onset and vice versa
  • Physical activity shortly before death – excessive activity depletes the body’s store of ATP and glucose hastening rigor
  • Severe convulsions – depletes ATP at a faster rate
  • High body temperature – depletes ATP faster
• Forensic importance of rigor mortis
  • Together with temperature of the body, the following can be used to estimate post-mortem interval (time of death):
  – if the body feels warm and is flaccid, it has been dead less than 3 hours. – if the body feels warm and is stiff, it has been dead from 3 to 8 hours. – if the body feels cold and is stiff, it has been dead from 8 to 36 hours. – if the body feels cold and is flaccid, it has been dead more than 36 hours.
  • If the position of the body does not obey gravity, it means the body has been interfered with.
  • Rigor mortis of the dartos muscle and muscle fibers of the seminal vesicles and prostate leads to emission of seminal fluid which can be confused as antemortem sexual activity.

Livor mortis

Also known as lividity or hypostasis. This is the discolouration( bluish red, purple colour) of the dependent areas of the body due to accumulation of blood within capillaries due to gravity.

Once someone passes away, circulation ceases. This allows gravity to act on the stagnant blood, pulling it down to lower areas of the body.

The discolouration does not occur on parts of the body in contact with the supporting surface (contact pallor) due to compression of the vessels in this area preventing accumulation of blood.

Tight clothing can also prevent lividity from forming around an area.

As blood settles in the dependent areas, vessels may rupture due to the pressure causing minute haemorrhages known as Tardieu spots (Petechiae). It is very common in asphyxial deaths.

Timing of lividity (highly variable)

Lividity shifts to a newer dependent area when the body is moved though this can only happen before post-mortem blood clotting occurs. One can check to see if lividity is fixed by applying pressure to the area with a finger and checking to see if the skin blanches.

• Forensic importance of livor mortis
  • Note that due to its variability it is useless in estimating post-mortem interval.
  • If a body is found to have hypostasis in undependent areas then it has been moved.

Livor mortis vs Antemortem bruises

Tache noire

This is one of the ocular signs of death. A transverse reddish-brown discolouration cuts across the eye. It occurs when the eyes are not completely closed after death and the sclera is exposed to air.

Late changes

Autolysis

This is the breakdown of cells and tissues by intracellular enzymes without the involvement of microorganisms. The first external sign is the white appearance of the cornea. Organs rich with enzymes undergo autolysis faster hence the pancreas breaks down faster.

Internally the lungs and pancreas will have a doughy appearance hours after death

• Forensic importance • Estimation of post-mortem interval

Putrefaction

This is the decomposition of a dead body by microorganisms arising externally or internally. Once dead, the normal flora of an individual moves from the alimentary canal and lungs to the blood vessels and spreads all over the body as microbes from the external environment invade as well.

The usual process is variable but in average temperate climate begins at about 3 days in an unrefrigerated corpse.

• Sequence of putrefaction
  • The first external sign is greenish discoloration of the lower abdomen, particularly over the right iliac fossa where the bacteria laden caecum lies. The spread of microbes from the bowel to the abdominal wall leads to the breakdown of hemoglobin to sulphaemoglobin which causes the above staining.
  • As the bacteria spreads so does the discoloration.
  • The face and neck become red and swollen
  • Putrefactive bacteria invades the circulatory system leading to hemolysis of blood and staining of vessels walls  by sulfmethylhemoglobin causing a phenomenon known as, ‘marbling‘. (Outline of vessels seen clearly)
  • With marbling comes the formation of skin blisters which when burst leave slimy, red skin. Over hairy areas, hair sloughs off with the blisters (skin-slippage)
  • As bacteria activity increases, putrefactive gases are produced causing abdominal distention as well as swelling of the face and external genitalia ( scrotum and penis)
  • Due to increased abdominal pressure urine and feces are purged.
  • Bloody debris formed from tissue liquefaction flows from any orifice (nose, mouth, genitalia) known as post-mortem purging
  • Internally, the organs will have developed blisters and have undergone decomposition. The liver will be spongy and the brain will have liquefied.
  • After several weeks, skin color will deepen to dark green or even black as maggots start infesting the body.
  • The maggots release a proteolytic enzyme which breaks down tissue further.
• Bacteria that play a role in putrefaction
  • Clostridium perfringens
  • Bacillus species
  • Enterobacter species
  • Escherichia species
  • Fusobacterium species
  • Salmonella species
• Order of putrefaction
  • Larynx and trachea
  • Infant brain
  • Stomach and intestines
  • Spleen
  • Omentum
  • Liver
  • Adult brain
  • Heart
  • Lungs
  • Kidneys
  • Bladder
  • Pancreas
  • Diaphragm
  • Blood vessels
  • Uterus
• Factors affecting putrefaction
  • Temperature – humid climates hasten putrefaction while colder weather slows down the process
  • Clothing – clothed bodies putrefy slower as tight clothes restrict the spread of microbes. While heavily dressed bodies are warmer hastening decomposition.
  • Injury – external injuries provide an entrance for microbes to invade the body
  • Fat percentage – the greater the fat composition of a body the faster the process
• Forensic importance
  • Can be used to estimate the post-mortem interval.
  • Bloating can be confused with drowning
  • Blisters can be confused with burns
  • Post-mortem purging can be confused with trauma
  • Facial bloating with protruded eyes may be confused with neck strangulation

Adipocere formation

This is a variation of putrefaction. Hydrolysis and hydrogenation of body fat leads to the formation of whitish, firm, wax like material (grave/corpse wax) composed of oleic, stearic and palmitic acid (can also be red or green due to staining by surrounding fluids such as blood).

Usually occurs in a damp environments and in bodies immersed in water as water is a prerequisite for hydrolysis. Can start as early as 3 weeks but the more conventional timing is 3 months.

• Forensic importance
  • It allows for identification of the body as facial features and body form are well preserved
  • Injuries such as a bullet holes and stab wounds are well preserved

Maceration

This is an aseptic autolytic process that occurs intrauterine. There is enzymatic breakdown of the fetus’ tissues with epidermal desquamation and edema.

• Factors affecting the rate of maceration
  • Maternal sepsis – infection will accelerate maceration as there is increased temperatures hastening the autolytic process. Higher bacterial load increases the rate of putrefaction as well.
  • Duration of hypoxia prior to actual death
• Forensic importance
  • Used to estimate the time of death as maceration is associated with death of at least 8 hours.

Mummification

This is the dehydration of tissues instead of liquefying putrefaction. The skin hardens, leathery as it stretches over bony prominences.  The skin is discoloured (usually brown). Requires a dry and arid climate to occur preferably with moving air

Partial mummification may occur with other changes coexisting on the same body.

• Forensic importance • Can be used for identification of the body since facial features are preserved.

Skeletonization

Also known as the dry remains stage, occurs when bone exposure is extensive but the bone has yet to disintegrate. It may take several years for the remains to disintegrate. Depth of burial is also a factor, as is soil type, in determining the rate at which skeletonization proceeds.

Bone is broken down over time by physical breaking, decalcification, and dissolution due to acidic soil or water.

• Forensic importance • Estimate the post-mortem interval. The process usually begins 2 months after death with completion occurring 6 months later.