Postmortem Changes

Pathology - Lec 10 - Exam 1

postmortem

after death

antemortem

before death

perimortem

around death

autopsy

self-examination

necropsy

death examination

postmortem examination (necropsy/autopsy)

exam of the animal after death

What is the goal of postmortem examination?

determine the cause of death/ the extent of disease

Postmortem examination involves the careful process of

dissection, observation, interpretation, & documentation

What is the importance of postmortem examination?

• scientific knowledge (physio/ anatomy, etc)

• education of students

• confirmation of clincial dx

• public heath, legal cases, etc

autolysis

decomposition of cells that takes place after somatic death

T/F: Autolysis is the breakdown of the body by endogenous substances/ enzymes.

true

putrefaction

decomposition of organic matter by bacterial or fungal digestion

postmortem predication/ scavenging 

animals feed on bodies after death

decomposition

process by which dead organic substances are broken down into simpler organic or inorganic matter

Postmorerm degeneration is the result of what?

autolysis and putrefaction

T/F: Postmortem degeneration is evidence of actual lesions.

FALSE

What is the important distinction to make regarding postmortem degeneration?

differentiate antemortem cell death from postmortem cell degeneration

What are some examples of postmortem degeneration?

• livor mortis/ hypostatic congestion

• postmortem clots

• rigor mortis

• autolysis & putrefaction

livor mortis/ hypostatic congestion

gravitational pooling of blood on the dependent (down) side of the carcass

What type of animals would you be able to physically see livor mortis?

skin of pale-skinned, sparsely haired animals (pigs)

When does livor mortis begin? What happens when you palpate the carcass?

0.5 - 2 hours after death

blanches on palpation

When does livor mortis become permanent?

once the blood clots → static or “fixed” after 8-12 hours

T/F: Pooled blood will remain on the original down side.

TRUE

What are the 3 main characteristics of a postmortem clot?

1. smooth shiny surface

2. lack of lamination

3. lack of attachment to endothelial surface of vessel

How is a “black currant clot” formed?

blood (RBC) settle at the bottom → buffy coat of leukocytes → clotted serum at top

What species would you expect to find a black currant clot in? Why?

horses → high sedimentation rate

What causes an increased sedimentation rate?

inflammation

What causes a decreased sedimentation rate?

• anticoagulant rodenticide toxicity

• hereditary coagulopathies

What do “chicken fat clots” look like?

yellow fatty appearance

rigor mortis

generalized contraction of skeletal muscle

T/F: Rigor mortis only affects certain muscles.

FALSE - affects all skeletal muscles

T/F: Smaller muscles are more visible due to rigor mortis.

TRUE

When does rigor mortis start?

1-6 hours after death → can persist for 2+ days

Rigor mortis occurs because muscle relaxation requires what?

ATP

T/F: Intracellular glycogen can provide some postmortem ATP.

TRUE

T/F: Once glycogen stores are depleted, rigor can be reversed by multiple pathways.

FALSE - only reversible via autolysis post depletion

T/F: Rigor mortis requires the complete breakdown of proteins, not just cross-bridges.

TRUE

What 3 things can accelerate rigor mortis?

1. antemortem exertion

2. seizures

3. antemortem hyperthermia

T/F: Autolysis is only caused by endogenous substances/ enzymes.

FALSE - also by aseptic chemical processes

What 2 things contribute to putrefaction?

1. postmortem bacilli

2. fermentation

Putrefaction implies the presence of what?

severe softening and gas in the tissue

Putrefaction may suggest what in regards to examination?

samples are not too suitable for microscopic examination

T/F: It is difficult to determine the postmortem interval.

TRUE

Why is it difficult to determine the postmortem interval?

• highly variable

• limited data in animals → lack of validation

• lack of supporting evidence in animals → no last social media post

What factors can cause increased autolysis?

• long interval between death & necropsy

• high ambient temp

• large body size

• heavy hair or wool coat

• continued fermentation in GI tract (equine/ ruminants)

• antemortem hyperthermia

• antemortem bacterial infection

What factors can cause reduced autolysis?

• short interval between death and necropsy

• rapid cooling of carcass postmortem (lower ambient temp, refrigeration)

• thin animal (reduced fat & muscle)

• high levels of tissue antibiotics

When does autolysis develop in the rumen or intestine? Why?

within 20 mins

exposure to bacteria & digestive enzymes (sloughing of mucosa, pH of rumen drops)

What tissues are quick to autolyze?

brain & spinal cord

What is a handling artifact to rule out when examining nervous tissue?

dark neurons

T/F: Skeletal muscle retains the ability to contract after somatic death.

TRUE

What are 3 examples of postmortem changes?

1. bloating of carcass

2. rectal &/or vaginal prolapse

3. tissue softening, discoloration, & gas bubbles present (putrefaction)

What causes postmortem gas production?

gut bacteria

What is the result of postmortem gas production/ gaseous distension?

bloated appearance → rupture of GI tract or carcass (or diaphragm) → displacement of abdominal viscera → eversion of rectal mucosa through anus (vagina, phimosis, protrusion of tongue)

What causes emphysema in the tissues postmortem?

bacteria traveling to various tissues

What is the gross appearance of autolysis?

• usually diffuse

• pallor

• tissue soft & pulpy, gas filled

• friable (tears easily)

• oozes reddish fluid

• strong odor (hydrogen sulfide, methyl mercaptan)

What is the microscopic appearance of autolysis?

• tissues pale staining

• no inflammatory rx

• cadaver bacilli

• erythrocytes not preserved

• loss of tissue pattern

• cells released from basement membrane

What are other possible histological artifacts?

• water

• frozen prior to fixation

• traction artifacts

hemoglobin imbibition

reddish discoloration of tissue by hemoglobin from lysed erythrocytes

Where will you normally see hemoglobin imbibition?

intima & endocardium, surrounding tissues

bile imbibition

greenish discoloration from leakage of bile through wall of the gallbladder or bile ducts

pseudomelanosis

blue-green to black discoloration of tissues by iron sulfide deposits

T/F: Pseudomelanosis deposits are actually melanin.

FALSE - not actually melanin

What reaction causes pseudomelanosis?

rx of hydrogen sulfide from putrefactive bacteria with iron in hemoglobin

What does pseudomelanosis signify?

severe autolysis

Why do you see pallor?

postmortem pressure on organs can force blood out of tissues → “pale imprints” (rib imprints)

T/F: Pallor can be caused by postemortem bacterial proliferation in the liver.

TRUE - must differentiate from antemortem necrosis

lens artifact

chilling or partial freezing of the carcass can make the lens opaque and white

T/F: Lens artifact will not revert back to normal transparency upon warming.

FALSE - but may not after freezing

T/F: Peristalsis continues to occur postmortem.

TRUE

What does postmortem peristalsis cause?

• traps blood in ridges

• mimics intussusception

perimortem findings

changes associated with the process of dying

Agonal breathing is a perimortem finding. This can cause what?

interstitial edema, tracheal foam

Perimortem hemorrhages are typically seen where?

epicardial & endocardial tissue

What are the artifacts associated with barbituate overdose (euthanasia)?

• splenic congestion

• pulmonary congestion & edema

• discoloration of blood

• coagulation of endocardium

What may be seen with electrocution?

petechial hemorrhages

What are the artifacts of resuscitation?

• fractured ribs

• cutaneous hemorrhage

• hemorrhage around injection sites (laceration of heart w/ intracardiac injection)

• collapse of lungs if animal was on 100% oxygen (or anesthetic gas)