Early Postmortem Changes

When do postmortem changes begin?

At the time of death

When do early postmortem changes become observable?

The first few hours after death

Define early postmortem changes

Cellular death combined with extrinsic and intrinsic processes

Is there a strict threshold between early - late postmortem changes?

No

How do you determine PMI estimates?

Evaluation of changes in relation to time

Why is it important to recognize postmortem changes?

Differentiate taphonomy to pathology/trauma; estimate time since death (PMI); get insight into place of death and position of the body

Algor mortis

The postmortem tendency of the body’s temperature to equilibrate with the surrounding environmental temperature, usually through cooling

Methods to calculate PMI as a function of temperature decrease:

Glaister’s equation, Henssge’s nomogram

Glaister’s equation

Time since death = (98.6 - body temperature) / T; based on the notion that a dead body is expected to “lose” temperature at a linear rate of T = 1.5 degrees F / hr

Problems with Glaister’s equation?

Doesn’t take into account intrinsic factors of the body, clothing, fluctuations in ambient temperature etc; based on a “rule of thumb”

Henssge’s nomogram

Based on a single measurement of rectal temperature; variables: rectal temperature, ambient temperature, body weight

Pros of Henssge’s nomogram?

Correction factors for environmental conditions (air currents, fluctuating temperatures etc) and clothing provided; provides a nomogram for “avoiding” mathematical equations, provides statistical validation as opposed to “rule of thumb”

Cons of Henssge’s nomogram?

Recognizes limitations of study; multitude of factors affect the rate of body temperature drop: high ambient temperatures, high or low body temperature prior to death, artificial changes of cooling conditions (heating devices, A/C units)

Factors affecting algor mortis:

Environmental conditions (temp fluctuations, humidity, air currents), clothing (type and layers), BMI (body mass and size), other intrinsic factors (age, sex, pharmaceuticals/drug toxicity), intrinsic perimortem conditions (hypothermia, fever, seizures)

Pallor mortis

Paleness of the body as the usual skin color appears lighter due to lack of capillary circulation; is obvious faster if significant blood loss before death and slower in cases and areas of pronounced congestion; little to no use in determining time since death

Livor mortis

Discoloration of the body after death due to the gravitational settling of blood as a result of cardiovascular circulation cessation; less pronounced in cases of significant blood loss before death; appears 1-2 hours after death (blanching first 8 - 12 hrs, fixed over 10 - 12)

Patterned lividity

Blanching areas or contact pallor; location can indicate body positioning, gives information on objects or surfaces in touch with the body

Tardieu spots

Spot-like hemorrhages due to the rupture of capillaries in areas of most pronounced lividity; postmortem artifact relating to increased pressure of settling blood on vessel walls

Where are tardieu spots observed?

Frequently at the lower extremities of hanging victims after prolonged suspension

Are tardeiu spots a hallmark of asphyxia?

Not if encountered in positionally acceptable areas

What is the function of hemoglobin?

Attaches to and transports O2 from the lungs to the tissues (oxygen-carrying: oxyhemoglobin, non oxygenated: deoxyhemoglobin)

Pathological forms of hemoglobin

Carboxyhemoglobin, methemoglobin, sulfhomeglobin

Carboxyhemoglobin

Byproduct of incomplete thermal reactions; displays higher affinity for high binding than O2; strong, stable compounds; lethal CO poisoning if CO-Hgb > 50% in healthy adults

Methemoglobin

Nonfunctional form in which ferrous is oxidized to ferric iron; unable to bind O2; normal levels 1 - 2%; potentially lethal >50%, lethal >70%; congenital or acquired methemoglobinemia

Sulfhemoglobin

Nonfunctional form in which ferrous is oxidized to ferric iron and binding of a sulfur atom; unable to bind O2; ingestion of sulfur-containing compounds; usually not lethal on its own

Conditions indirectly affecting hemoglobin and color of lividity

Cyanide poisoning (higher venous O2 saturation, brighter colored venous blood); low temperatures (increase solubility of O2 and binding capacity)

Color of normal lividity?

Purple

What does pink lividity indicate?

Carbon monoxide or cyanide poisoning, postmortem/antemortem low temperatures, fluoroacetate

What does brown lividity indicate?

Sodium chlorate, inorganic nitrite, aniline

What does green lividity indicate?

Hydrogen sulfide, sulfuric compounds, intrinsic formation

Factors accelerating the onset of livor mortis

Warm ambient temperatures, larger blood volume, abnormal cardiac function (antemortem blood pooling), tight-fitting clothing, confined space, body position (supine or suspended)

Factors decelerating the onset of livor mortis

Cold ambient temperatures, antemortem or perimortem blood loss, body position (not supine)

How does lividity differentiate form bruising?

Blood within vessels (no hemorrhage), purple - red, gravity-dependent areas, indistinct borders, no edema, superficial discoloration, blanching area

How does bruising differ from lividity?

Blood out of vessels (associated hemorrhage), purple - blue, anywhere, well-defined borders, associated edema, deep discoloration, non-blanching area

Rigor mortis

Postmortem muscle rigidity due to ATP depletion; first notable ~2 hours after death (hands); can be manually overcome

Timeline of rigor mortis

First notable ~2 hours after death (hands), peaks and reaches plateau after 8-12 hours, decreases after 12-15 hours, disappears after 24-36 hour; slower in the cold, faster in the heat

Nysten’s Rule

Rigidity starts immediately after death but perceptibility changes depending on muscle size - facial muscles (~2 hours), upper limbs (~2-6 hours), torso and lower limbs (~6-12 hours)

Cutis anserina

Goosebumps - arrector pili muscle (hair follicles) affected

Factors accelerating the perceptive onset of rigor mortis

High ambient temperature, fever/hyperthermia, intense muscular activity prior to death, seizures/electrocution, infection/sepsis/cancer, narcotics, age and body mass

Factors decelerating the perceptive onset of rigor mortis

Low ambient temperature, hypothermia, large muscle mass, minimal muscle activity prior to death

Pilot studies for evaluating rigor mortis: technique?

Shear wave elastography

How does shear wave elastography work?

Non-invasive medical technique that evaluates tissue rigidity using US pulses (idea that stiff tissues tend to deform less than soft tissues); US shear waves move transversely to the muscle and their velocity is detected: higher velocity in hard vs soft tissue; quantification of rigidity

Other early postmortem changes:

Corneal clouding, tache noir, postmortem drying of tissues

Corneal clouding

Change in corneal opacity increasing with progressing PMIs; degeneration of endothelial cells resulting in aqueous humor moving towards the cornea

Issues with corneal clouding?

Hinders identification of eye color, must be differentiated to senile cataracts

Tache noir

Black spot resulting from drying of the sclera; discolored band corresponding to the position of the eyelids

Postmortem drying of tissues

Expedited in increased ambient temperatures or UV radiation; tight clothing items or ligature may result in localized blanching and parchment-like drying of the skin; incision on the area will demonstrate no bruising of the surrounding tissues - superficial phenomenon related to exposure