Forensic asphyxiology

Asphyxiology is the specialized field within forensic medicine that studies asphyxial deaths. Asphyxia is a condition resulting from the interference with the uptake or utilization of oxygen by the body. The main types of asphyxia are strangulation, hanging, suffocation, and drowning. Most asphyxial deaths exhibit a common triad of findings: peripheral cyanosis, visceral congestion, and petechial hemorrhages.

Asphyxial triad

• In most cases of fatal oxygen deprivation, the autopsy reveals a non-specific triad of findings:
  • Peripheral cyanosis
  • Visceral congestion
  • Petechial hemorrhages (Tardieu spots)
• While these indicate that death was likely asphyxial, they are not diagnostic of the specific mechanism (e.g., whether it was hanging or drowning).

Autopsy technique considerations

The correct sequence of an autopsy is essential for identifying true asphyxial injuries and avoiding the creation of postmortem artifacts.

• Dissection sequence
  • In suspected asphyxial deaths due to compression of the neck, dissection should follow a specific order to prevent post-mortem artifacts:
    1. Thoracic cavity and thoracic organ removal: allows blood to drain out of the large vessels of the neck into the empty thoracic cavity
    2. Cranial cavity: further decompresses the vessels at the top of the neck
    3. Neck
  • This approach allows venous blood drainage from the head and neck, facilitating a "bloodless" dissection of the neck tissues later in the procedure.
• Prinsloo-Gordon artifacts
  • If the neck is opened before the thoracic and cranial cavities, the residual venous pressure can cause postmortem extravasation of blood into the soft tissues of the neck.
  • Associated with postmortem venous congestion/hypostasis.
  • These postmortem "leaks" create the Prinsloo-Gordon artifacts, which can be mistakenly interpreted as antemortem bruising (e.g., from strangulation or hanging).

Hyoid bone fractures

• Hyoid bone fractures are common in certain types of asphyxial deaths (e.g., strangulation).
• The morphology of a hyoid bone fracture is a critical indicator of the direction and type of force applied to the neck.
• Age and ossification: Hyoid bone fractures are rare in children and young adults (< 40 years) due to the flexibility of the bone before it fully ossifies.

Overview

• Strangulation is a form of mechanical asphyxia where the constricting force is applied to the neck by a mechanism independent of the victim's body weight.
• The most common strangulation methods are:
  • Ligature strangulation
  • Manual strangulation (throttling)
  • Mugging (choke hold)
    • Compression using the forearm or the crook of the elbow
    • Often results in significant internal soft tissue damage with few external marks
  • Garroting
    • Sudden constriction of the neck from behind using a wire or cord
    • Typically results in rapid unconsciousness
  • Bansdola
    • Compression of the neck and chest using bamboo or sticks tied with a rope on both ends
    • Causes severe crushing of the larynx and extensive internal hemorrhage

In forensic practice, strangulation is almost always considered homicidal until proven otherwise!

Ligature strangulation

• Definition: strangulation involving the use of a cord, wire, or cloth to constrict the neck
• Characterisitcs
  • Ligature mark: the primary forensic indicator
    • Direction: typically transverse (horizontal)
    • Extent: encircles the entire neck
    • Location: usually below the thyroid cartilage
  • The underlying skin often shows extensive bruising and blood extravasation, as significant force is required to overcome the victim's resistance.

Manual strangulation (throttling)

• Definition: compression of the neck using the hands or fingers
• Characterisitcs
  • Injury patterns often depend on the grip
  • External findings
    • Nail marks: crescentic abrasions caused by the assailant's fingernails
    • Six-penny bruises: small, circular bruises (∼1–2 cm) produced by the pressure of the fingertips
  • Internal findings
    • Soft tissue contusion: extensive bruising of the deep neck muscles and tissues
    • Hyoid bone fracture: typically an adduction fracture of the greater horns
    • Cricoid and thyroid cartilage fracture: frequently observed due to the direct pressure applied to the larynx

Hanging is a form of ligature asphyxia where the constricting force is provided by the weight of the victim's body.

Classification of hanging

Hanging is categorized based on the position of the knot and the degree of suspension.

Based on knot position

• Typical hanging: The knot is located over the occipital bone or at the nape of the neck.
• Atypical hanging: The knot is located anywhere other than the occipital region or nape of the neck.

Based on suspension

• Complete hanging
  • The entire body is suspended, and no part of the body touches the ground.
  • The constricting force is the full weight of the body.
• Partial hanging
  • A portion of the body (e.g., knees, feet, or buttocks) remains in contact with the ground.
  • The constricting force is only a fraction of the body's weight.
  • Results in a slower death when compared to complete hanging

Autopsy findings in hanging

Neck findings

• Ligature mark
  • Dependent on the knot location, type of suspension (complete vs. partial hanging), and ligature material
  • Most commonly oblique, incomplete, and located above the thyroid cartilage
  • In partial hanging, the mark can be horizontal.
  • Ecchymoses around the ligature mark can be present.
  • Abrasions at mark edges indicate movement during hanging.
  • Petechial hemorrhages adjacent to the mark support antemortem hanging.
• Amussat sign
  • Transverse intimal tear of the common carotid artery
  • Results from the stretching and mechanical compression of the neck
  • Suggests antemortem hanging
• Hyoid bone fracture
• Hangman fracture: most common in judicial hanging
• Simon's hemorrhage
  • Hemorrhage in the anterior aspect of the intervertebral discs, most commonly in the lumbar or thoracolumbar region
  • Results from mechanical stretching and traction of the spine during the process of suspension
  • Indicative of antemortem hanging

Facial findings

• Saliva dribbling
  • Due to increased salivation before death as a consequence of salivary gland stimulation by the ligature
  • Typically occurs on the opposite side of the knot
  • Confirms antemortem hanging
• La facies sympathique
  • Eyelid opening and pupillary dilation ipsilateral to the knot site
  • Caused by cervical sympathetic chain compression
  • Indicates antemortem hanging

Forensic significance

• In most cases, hanging is a suicidal act.
• Homicidal hanging (lynching) is rare and typically involves multiple assailants or a defenseless victim.
• Accidental hanging: may occur in children during play or during sexual asphyxia (autoerotic hanging)

• Suffocation encompasses all forms of asphyxia where airflow obstruction occurs through means other than drowning or neck pressure.
• Common causes of suffocation include:
  • Airflow obstruction from the outside (e.g., smothering)
  • Airflow obstruction from the inside (e.g., choking)
  • Mechanical restriction of respiratory movements (e.g., positional asphyxia)

Smothering

• Definition: mechanical occlusion of the mouth and nostrils simultaneously, preventing air from entering the respiratory system
• Findings: If the hands are used, perioral injuries such as abrasions, bruises, and lip lacerations are frequently observed.
• Forensic significance
  • Accidental: commonly seen in infants (e.g., due to soft bedding) or during "overlaying," where an adult accidentally rolls onto an infant while sleeping
  • Homicidal: involves the intentional closure of the airway using a pillow or the hands

Choking

• Definition: mechanical obstruction of the airway by a foreign object at the level or below the larynx
• See "Foreign body aspiration" for more details.

Gagging

• Definition: the thrusting of a cloth, pad, or foreign object into the mouth, causing pharynx obstruction and leading to rapid asphyxia.

Traumatic asphyxia

• Definition: mechanical restriction of chest movements caused by a heavy weight applied to a person's chest
• Findings: masque ecchymotique, characterized by facial edema, cyanosis, subconjunctival hemorrhage, and petechiae over the face, neck, and upper chest
• Variants:
  • Burking: a homicidal method combining smothering and traumatic asphyxia (historically by sitting on the victim's chest)
  • Overlaying
    • An accidental variant, often occurring when an adult rolls onto an infant during sleep
    • It may involve smothering, chest compression, or both.

Positional asphyxia

• Definition: form of asphyxia that results from the body being held in an abnormal position that restricts the airway or chest expansion
• Variants:
  • Jackknife position: The body is folded forward at the waist, compressing the thoracic and abdominal cavities.
  • Inverted crucifixion: The victim is suspended in an upside-down position, leading to respiratory failure.

Overview

• Drowning is the respiratory impairment caused by submersion or immersion in a liquid, most commonly a body of water.
• Most deaths from drowning are accidental.
• Forensic evaluation focuses on differentiating antemortem drowning from postmortem body disposal.
• Drowning can be classified into typical drowning (wet drowning) and atypical drowning, with important forensic implications.

Typical drowning (wet drowning)

Wet drowning occurs through aspiration of water/liquid into the lungs.

Mechanism of drowning

• The mechanism and autopsy findings vary between freshwater drowning and saltwater drowning.
• Gettler test
  • Compares chloride concentrations between the right and left heart chambers to identify the type of water involved in drowning
  • Only differences ≥ 25% are considered significant
  • Interpretation:
    • Freshwater drowning: right > left (due to hemodilution)
    • Saltwater drowning: left > right (due to hemoconcentration)
  • Mainly of historical or supportive value and not definitive on its own

Freshwater drowning (hypotonic drowning)

• Mechanism: hypotonic water crosses the alveolocapillary membrane → hemodilution, hypervolemia, erythrocyte swelling, and rupture → cardiac overload and hyperkalemia from hemolysis → hypoxemia and cardiac arrhythmia
• Cause of death: typically ventricular fibrillation
• Fatal period: 4-5 minutes
• Lung autopsy findings
  • Color: pale-pink
  • Consistency: firm, emphysematous
  • Size and weight: ballooned but light

Saltwater drowning (hypertonic drowning)

• Mechanism: hypertonic water creates an osmotic gradient between the blood and water in the alveoli → fluid movement from capillaries to the alveoli through osmosis → pulmonary edema and hemoconcentration → respiratory failure and asystole
• Cause of death: typically asystole
• Fatal period: 8-12 minutes
• Lung autopsy findings
  • Color: bluish or purplish
  • Consistency: soft, jelly-like
  • Size and weight: ballooned and heavy (up to 2 kg)

Autopsy findings in antemortem drowning

• Prone body position: back upwards, head and extremities dangling downwards
• Froth in the mouth and/or nostrils
  • White or pink, fine foam over the nostrils and/or the mouth
  • Formed due to the vigorous respiratory efforts during drowning
  • Composed of air, water, surfactant, and seromucoid secretions
  • Typically copious and persistent (reforms after wiping)
  • Highly suggestive of antemortem drowning
• Cadaveric spasm
  • Hands often clenched around materials present in the water at the time of death
  • Indicates struggle and antemortem drowning
• Skin findings
  • Washerwoman's hands and feet
    • Pallor and wrinkling of the palms, soles, fingers, and toes
    • Indicates immersion, not drowning
  • Piloerection
  • Travel abrasions and lacerations on the forehead, backs of the hands, knees, and dorsum of the feet
• Lung findings
  • Emphysema aquosum
    • Occurs in conscious drowning
    • Voluminous, distended lungs
    • Containing froth
  • Paltauf spots: bright red spots of ∼ 1 cm in diameter, which occur due to capillary hemorrhage of the pleura
• Gastrointestinal findings
  • Wischnewsky spots (gastric mucosal petechial hemorrhages associated with hypothermia)
  • The stomach and the small intestine often contain water swallowed during drowning
• Diatom test
  • The identification of silica-walled algae (diatoms) in closed organs (e.g., bone marrow, brain, or spleen) indicates an intact heartbeat during submersion.
  • Indicates antemortem drowning

Atypical drowning

• Atypical drowning encompasses a group of conditions in which there is little to no water aspiration:
  • Dry drowning
    • Definition: drowning that occurs without a significant aspiration of water into the lungs
    • Mechanism: water in the larynx induces laryngospasm → acute airway obstruction → asphyxia
  • Immersion syndrome
    • Definition: the autonomic and respiratory responses caused by sudden immersion in cold water
    • Mechanism: sudden immersion into cold water → vagal stimulation → bradycardia → cardiac arrest
  • Unconscious drowning: the individual is unconscious (due to e.g., intoxication, head injury) before submersion and drowning
  • Post-immersion syndrome: the individual dies hours to days after the initial drowning event from complications (e.g., ARDS, infection)
• Forensic significance
  • Diatoms are often absent
  • No significant pulmonary edema
  • No froth in the airways
  • Often requires circumstantial evidence, witness testimony, and the exclusion of other causes of sudden death