Forensic Pathology - Science of Death

what is meant by the mechanism of death

altered physiology where disease or injury causes death

what is meant by the manner of death

• determined by implications superimposed on biological causes and mechanisms of death

• example include - homocide, suicide, accidental and natural death

what is post mortem hypostasis

• liver mortis

• skin discolouration from gravitational blood pooling in veins

what factors affect rigor mortis

• enviromental factors

• muscular activity before death

what is cadaveric spasms

• instantaneous rigor mortis

• muscular rigidity at the movement of death

• affects a specific group of muscles

what are the three terms used for what happens to the body before and after death

• post mortem

• perimortem

• antemortem

what is a somatic death

the end of vital life functions

what is cellular death

no metabolic activity with the death of cells and tissues

what is brain death

brain damage that causes no response to stimuli

what are some post mortem changes to the eye

• loss of light reflex

• unreactive pupils

• decrease in eyeball tension (softer inner eye minutes after death)

what is rigor mortis

• progressive stiffening of the muscle of the body

• starts in the smaller muscles and spreads down the body

• starts early on

• late onset if lack of muscle before death

what factors affect rigor mortis

• environmental temperature

• degree of muscular activity before death

• develops early and passes fast in death from infections

how many hours after death does the body feel warm and flaccid

less than 3 hours

how many hours after death does the body feel warm and stiff

3-8 hours

how many hours after death does the body feel cool and stiff

8-36 hours

how many hours after death does the body feel cold and flaccid

more than 36 hours

what is algor mortis

• cooling of the body

• measures the core temperature

what is the body cooling

• physical process

• normally a temperature plateau followed by linear cooling

what is putrifaction

• begins when death occurs

• first changes affect the lower abdomen and green discolouration

what are the orders of change for putrifaction

• first sign is green discolouration

• skin marbling

• skin slippage

• skin blisters form

• gas formation begins

  • puging of urine, faeces and bodily fluids

what is mummification

• dehydration of desiccation of the tissue

• body shrivels and is converted into leathery mass of skin

• internal organs decomposed but present

what is adipocere

• crumbly white wax substances

• accumulates on parts on the body containing fat

• production of chemical reaction in which fat reacts with water and hydrogen in presence of bacterial enzymes breaking down fatty acids

what is skeletonisation

• loss of soft tissue

• based on environmental conditions and presence of insects and animals

what insects are present during the fresh stage of decomposition

• blow flies and fresh flies

• eggs are laid around the natural openings and wounds

what insects are present during the bloating stage of decomposition

• blow flies continue to feed

• maggots continue to feed

• rove beetles feed on fly and larve eggs

what insects are present during the decay stage of decmposition

• masses of maggots still feeding externally and internally

  • beetles are now attracted to the corpse

what insects are present during the post decay stage of decomposition

• masses of maggots still feeding externally and internally

• beetles are now attracted to the corpse

what insects are present in the dry stage of decomposition

• skin and bone left

• insects that are able to digest keratin become attracted

what is the meaning of apshyxia

derives from the greek meaning → absence of pulsation

in forensics → the interference with oxygenation from environmental to cellular level

what are examples of asphyxia

• absence or reduction of the oxygen tension in the atmosphere

• obstruction of the external respiratory passage

• blockage of internal respiratory movements

• disease of the lungs → reduction of gas exhange

• reduction in heart function

• reduced ability of blood to transport O²

• inability of tissue to utilise O²

what is mechanical asphyxia

the broad term that is used to cover wide range of different asphyxial situations where external pressure on the chest, neck or other areas of the body that make respiration difficulty

what are the classic signs of asphyxia

• petechial haemorrhages

• congestion and odema

• cyanosis

what is a petechial haemorrhage

a small pin point collection that may disappear with lengthening post mortem intervals

what is the size of a petechial haemorrhage

1-2mm

what is the cause of a petechial haemorrhage

the rupture of the thin walled venules, especially in the lax tissue

what is congestion and odema

the result of obstructed venous return

what happens when the neck is compressed

the face, lips and tongue will become swollen and reddened (caused by hypoxia) and froth may emerge from the mouth and nostrils

what is cyanois

the normal pink colour of the oxygenated skin may change to a blue colour when the oxygen is lacking

what leads to the bluish colour of cyanosis

the constriction of the neck that traps blood in the veins with decreased oxygenated haemoglobin

what is suffocation

the broad term that encompasses the different types of asphyxia and refers to death cause by a reduction of o² in the respired atmosphere and in physical replacement of o² by other gases such as CO² or CO

what is smothering

mechanical death from occlusion of the mouth and nose

how does death occur by smothering

by occluding substances pressing down on the facial orifices or by passive weight of the head pressing down

what is the overlaying of infants

a form of mechanical asphyxia → often accidental smothering by rolling over it in bed

what is the cause of death in overlying of infants

the infants airway is obstructed, the thorax and abdomen are compressed and neck circulation impaired with autopsy finds usually negative

what is plastic bag suffocation

a common form of suicide but can also occur in homocide or accidental

→ it is rapid and leaves no visible signs

→ petechial haemorrhage not seen

what is the method of death in plastic bag suffocation

involves the creation of a local hypoxic environment within the plastic bag securely fastened around the neck

what is choking

blockage of internal airways

what is the method of death in choking

• occurs between the pharynx and bifurcation of trachea

• death can result from pure hypoxia from occlusion of airway from congestion and cyanosis from neurogenic cardiac arrest

what is traumatic asphyxia

referring to the mechanical fixation of the chest with restricted respiratory movement preventing inspiration

what are the conditions for traumatic asphyxia

• chest compressed by an object so expansion is prevented

• collapse of an excavation or other industrial accidents

• crushing in crowds

• trapping between vehicles

what are the four mechanisms of death by fatal pressure

1. airway occlusion

2. occlusion of the neck veins

3. compression of carotid arteries

4. nerve effects

what is airway occlusion

the direct compression of the larynx or trachea - the closure of the the pharynx by the root of the tongue

what is occlusion of the neck veins

responsible for the classic signs of congestion, cyanosis, swelling and petechia above the line of constriction

what are nerve effects

pressure put on the baroreceptors → vagal nerve stimulation → this will lead to heart stoppage

a blow to the larynx → death occurs in seconds → no signs of asphyxia

what is hanging

it involves the compression of the neck structure by a ligature being placed around it so the neck is constricted with the help of all or a part of the body weightwhat

what is strangulation

involves the compression of the neck sutures by a force such as manual squeezing or application ligature

are hanging and strangulation different

YES

what is manual strangulation

• common method in homicide

• most often associated with power and size of assailant

• most commonly seen in domestic homicides

• most common in sex related homicides

how is the hyoid bone involved in asphyxia

fractured

what is ligature strangulation

• the ligature may consist of a variety of objects

• u shaped ligature or multiple turns

• geometry and position of mark is important in interpreting fatal events

• in strangulation ligature marks tend to encircle the neck horizontally and at a lower level

what are the signs of asphyxia in ligature strangulation

• pale skin below and swollen haemorrhagic skin

• petechie on face and eye

• bleeding from ear to nose

h

how can arm locks and mugging lead to asphyxia

• throttling pressure from an arm held around the throat and the pressure is exerted either on the front or on larynx or sides of the neck

• sometimes the hyoid and thyroid horns are fractured when pressed backwards against spinal column

what is judicial hanging

• body drops for some distance before the neck is caught by a taut rope

• mechanical disruption of neck sutures

• fracture of the cervical spine

• stretching and tearing of the spinal chord

  • immediate loss of consciousness and rapid death

can the position of a hanging mark vary on the neck

yes

what is the position of the hanging mark (top)

the usual position with a fixed noose and a high suspension point

what is the position of the hanging mark (middle)

if the slipknot is used the tightness deeply impressed in the loop tends to find the smallest circumference of the neck

what is the position of the hanging mark (bottom)

if the suspension point is low the subject may lean away and the mark can be horizontal

what is an autoerotic death

sexual asphyxia

what is the WHO 2020 definition for interpersonal violence

violence which occurs between individuals and covers cases of child abuse, domestic abuse and acquaintance or stranger violence

what is intimate partner violence (as defined by the CPS)

describes the nature of violence including psychological, physical, sexual, financial and emotional abuse

what is interpersonal violence

when a person uses power and control over another

what are the categories of interpersonal violence

• physical

• sexual, emotional threats or actions

• economic control

• isolation or coercive behaviour

what are the categories for defining interpersonal violence

• clinical

• forensic

• archaeological

what is a periorbital haemotoma

what are black eyes

what forensic roles are important to interpersonal and fire deaths

• clinical forensic physician/clinical pathologist

• forensic pathologist

what is a clinical physician

• examines physical injuries

• generally occurs in a hospital

• violent causes with legal implications

what is a clinical pathologist

they work to determine the cause of death and manner of death as well as giving closure for cases that happen within the hospital

issue death certificate

what is the forensic pathologist

when a death seems to be non natural they determine the cause and manner of death and issuing a death certificate (with legal implication)

what are the categories for fire deaths

• accidental

• suicide

• criminal

how can fire deaths be criminal

• arson

• concealment of homicide

• insurance fraud

what are the aims of an autopsy in a fire death

• establish a positive identity

• was the deceased alive at the time of the fire

• determine the cause of death

• any contributory factors

• preventing escape

• time of death

other identification factors

• visual

• circumstantial

• radiographs

• dental and DNA

what can cause deaths in a fire

• neurogenic shock

• thermal injury

• inhalation of smoke and fire gases

• delayed death

• fire caused death and injuries

what are the types of burns that can be present

• flame burns

• contact burns

• radiant burns

• scalding burns

• chemical burns

what is coagulation necrosis

prevents the further penetration of acid into the next layer down into the skin and acid burns don’t go all they way into the body

what is liquefaction necrosis

• tissues are liquefied when they come into contact with chemicals

• destroys most the tissue including the adipose tissue

• alkaline burns more severe than acid

what is necrosis

tissue that dies

why are tissues are taken

tissues are taken to be tested for toxicology and other analysis for definitive cause and manner of death

what tissue is taken

• liver (main tissue)

• larynx and throat tissue for smoke inhalation

• stomach contents

what is the burn scale

1-4th degree

what are first degree burns

erythema, odema and pain

what is second degree burn

blisters and pain

what is a third degree burn

full thickness and sensation loss

what is 4th degree burns

they cause charring and incineration

what is the rule of nines

the percentage of the total body surface area that is covered by burns

what is taken into account for the probability of survival

• age of individual

• percentage of total body surface

• children can survive extensive burns

how can you tell between antemortem and postmortem burns

• the differentiation is usually impossible

• gross - red flare and blistering

• microscopic - vital reaction

what can a heat fracture also be known as

skull fractures

what is shown in charred bodies

• internal organs are well preserved

• splits in skin and muscle (often running parallel)

• pugilistic pose