L4 - Postmortem Changes and Non-Lesions

What do postmortem changes result from?

Autolysis

Are postmortem changes considered lesions?

No

What are decompositions?

Dead organic substances that are broken down

What are the two mechanisms of decompostion?

1. Putrefaction

2. Autolysis

What is putrefaction?

State of decomposition where microorganisms cause dissolution of tissues into gases, liquids and simpler molecules

What is autolysis?

Destruction of cells/tissues by their own enzymes (self-digestion)

What tissues die faster than others? How long do they take?

Neurons: 3-4 minutes

What is the difference between autolysis and necrosis?

Autolysis occurs in dead tissue, involves the entire body and there is no inflammation

Necrosis occurs in live tissue in local/regional areas and inflammation is present

Autolysis begins in ______ of the last heartbeat and involves physical and chemical changes that are ______ and ______.

minutes, irreversible, unavoidable

What is the general process of autolysis beginning from the last hearbeat?

Last heartbeat → Hypoxia → CO2 accumulation → Drop in tissue pH → Rupture of cytosolic lysosomes → Lysosomal enzymes enter cytosol and cause autolysis

Postmortem autolysis can mask what?

Antemortem lesions

What does autolysis look histologically?

Lack of cellular architecture and detail. Saprophytic bacteria.

What is rigor mortis?

Muscle stiffening that occurs 2-36 hours postmortem

What position does rigor mortis leave muscles?

Hyperextension

How does rigor mortis occur?

Muscles are flaccid at death. Sarcoplasmic reticulum degrades and releases calcium, which floods the sarcomere and binds actin and myosin. No ATP to disengage, so body can’t relax.

What is livor mortis?

Purple tissue discoloration postmortem due to intravascular blood pooling due to gravitational pull

What is another word for intravascular pooling?

Hypostatic congestion

How does livor mortis occur?

Hypoxic capillaries dilate, causing blood to accumulate in skin and organs

How long after death does livor mortis develop?

30 minutes to 2 hours

How long after death does livor mortis become fixed?

8-12 hours

What is algor mortis?

Body cooling postmortem to match environment

Which is faster: external cooling or internal cooling?

External cooling

What characteristics allow a body to autolyze more rapidly?

Animals with thick fur or that are hyperthermic

What is hemoglobin imbibition?

Staining of tissues by free hemoglobin, causing a red discoloration to tissues

What is bile imbibition?

Staining of tissues near the gallbladder/ducts by bile, causing yellow/green discoloration

What is pseudomelanosis?

Putrefactive bacteria rapidly diffuse through tissues and react with iron in hemoglobin to create iron sulfide, causing black discoloration to tissues

Where does pseudomelanosis mostly occur?

GIT

What makes the black discoloration associated with pseudomelanosis?

Reaction of the iron in hemoglobin with putrefactive bacteria that grows on the organ post-mortem to create iron sulfide

Does pseudomelanosis an antemortem or postmortem reaction?

Postmortem

What is melanosis?

Normal melanin pigment that causes black discoloration to tissues in dark colored animals. Typically occurs in focal or multifocal spots.

How do postmortem clots appear?

Blood is stagnant and separates. RBCs stick towards the ground while plasma and platelets remain on top. AKA “chicken fat clot”

How long after dead do postmortem clots resolve?

2 hours

What causes postmortem clots to dissolve?

Fibrinolysin is released from endothelium and prevents clots from forming

What causes an antemortem clot?

Any element of Virchow’s trid (ex. hypercoagulability, endothelial damage, turbulent blood flow)

What are the characteristics of an antemortem clot?

• Rough

• Difficult to remove (friable, falls apart, loosely adhered to endothelial wall)

• Red and uniform in color

What are the characteristics of a postmortem clot?

• Smooth and shiny

• Simple to remove

• “Chicken Fat” appearance and feel

You’re doing a necropsy on an animal and notice pink coloration to the teeth. Is this a postmortem autolysis or pathology?

Postmortem autolysis → Hemoglobin imbibition

Is this considered an antemortem or postmortem clot? Why?

Antemortem → rough, uniform red color, no separation of RBCs and plasma

Pathology or non-lesion? Why?

Non-lesion. Pseudomelanosis, which occurs in GIT and is a postmortem condition (Putrefactive bacteria = putrefaction!)

Pathology or non-lesion? Why?

Non-lesion. Hemoglobin imbibition, results from free hemoglobin, but a pathological condition

Pathology or non-lesion? Why?

Non-lesion. Livor mortis, occurs post-mortem not due to pathology.

Pathology or non-lesion? Why?

Non-lesion. Bile imbibition due to GB/duct leakage, not pathological.

Livor mortis

Bile imbibition

Hemoglobin imbibition

Antemortem clot with heartworm

Postmortem clots

Pseudomelanosis

Pseudomelanosis