Thrombosis, Emboli, and Infarction

Post mortem clots: attached to vessel wall?

no!

Post mortem clots: appearance

shiny and wet

Post mortem clots: structure within vessel

forms perfect cast of vessel lumina

Ante mortem clots: attached to vessel wall?

yes!

Ante mortem clots: appearance

dull, dry, and laminated

Ante mortem clots: structure within vessel

tail of clot extends downstream

Ante mortem clots are called...

thrombi

Thrombosis

the formation of a blood clot (thrombi), attached to a vessel wall during life

What is a thrombus made out of? (3)

-fibrin

-platelets

-other elements of the blood

What vessels does thrombosis usually occur?

usually in veins, but more serious in arteries

Why do thrombi usually form in veins?

vein have low pressure and low blood flow, so a clot is more likely to form

Virchow's Triad of Thrombosis

describes the three major factors that promote thrombus (blood clot) formation

Three components of Virchow's Triad of Thrombosis:

1.) Endothelial injury

2.) Abnormal blood flow

3.) Hypercoagulability

Endothelial injury

Damage to the vessel lining exposes pro-clotting substances and activates platelets

Endothelial injury is the _______ cause of most thrombi

primary

Pathogenesis of endothelial injury

1.) damage to the endothelial cells occurs and subendothelial collagen is exposed

2.) subendothelial collagen releases platelet-activating factor (PAF)

3.) Platelets adhere to the damaged vessel wall

4.) Platelets become activated and aggregate, recruiting and activating additional platelets

5.) coagulation cascade is activated simultaneously

6.) A platelet-fibrin thrombus forms

7.) Fibrin-platelet clot releases additional thromboplastin to recruit more platelets

8.) Circulating erythrocytes and leukocytes become entrapped in the fibrin

meshwork, parallel to the direction of blood flow

Four causes for endothelial injury/damage

1.) inflammation of the vessel wall

2.) deposition of mineral

3.) physical trauma

4.) parasite migration

Abnormal blood flow

Stasis or turbulence disrupts normal blood flow and promotes clot formation

Stasis

slow flow rate that causes accumulation of activated clotting factors and platelets with endothelium

What vessel type is stasis most common in?

veins

Turbulence

disruption in laminar blood flow; mixes blood (interaction w/ coagulation factors) and physically injures the endothelium

Where does turbulence typically occur?

where vessels branch, narrow, or sites of venous/lymphatic valves

Normal blood flows by the process of...

axial plasmatic streaming

axial plasmatic streaming

normal blood flow where the fluid component of plasma (containing anticoagulants) flows close to the vessel walls, and the cellular portions flows down the center

Hypercoagulability

An increased tendency of the blood to clot due to changes in coagulation factors

Hypercoagulability involves a ________ in prothrombotic factors and _______ in inhibitory factors

increase; decrease

Examples of things that can increase coagulation factors

-inflammation

-stress

-neoplasia

-surgery

-renal disease

What is the most common cause of hypercoagulability?

inflammation

Which of Virchow's Triad of Thrombosis is most important? Why?

Endothelial injury; damage to the endothelium exposes procoagulant substances (like collagen and tissue factor), causing platelet adhesion/activation and activation of the coagulation cascade, which directly promotes thrombus formation

**also can affect the other two factors of Virchow's Triad

Six descriptive words for thrombi:

1.) mural

2.) vegetative

3.) occlusive

4.) obturating

5.) saddle

6.) septic

mural

walls of a vessel; a thrombus attached to a large vessel or endocardium of heart chambers by a very wide base

vegetative

on heart, thrombus located on great vessel valves

Valvular (Vegetative) Endocarditis

Infection and inflammation of a heart valve that causes formation of friable thrombotic vegetations on the heart valves

Vegetations

septic thrombi with very high numbers of bacteria

Pathogenesis of Valvular (Vegetative) Endocarditis

1.) Valve endocardium is injured, exposing the underlying tissue

2.) A platelet-fibrin mesh covers the damaged surface

3.) The mesh becomes colonized by bacteria (or rarely fungi)

4.) Plaque fragments may break off, sending septic emboli to capillaries in other organs

occlusive

vascular obstruction

obturating

tail extends in the direction of blood flow and partially occludes vessel

saddle

thrombus at the bifurcation of vessels

septic

thrombus that involves an infectious agent

Verminous thrombi

thrombus due to parasites or their fragments within cores of thrombi (such as heartworm)

Venous vs arterial thrombi:

venous thrombi are the most _______ site of thrombus formation

arterial thrombi are the most _______ site of thrombus formation

common

serious

Venous vs arterial thrombi:

venous thrombi are ________ occlusive

arterial thrombi are ________ occlusive

fully

partially

Venous vs arterial thrombi:

venous thrombi ________ yield infarction

arterial thrombi ________ yield infarction

seldom

often

infarction

complete obstruction of blood flow so that the tissue dies

Ischemia

reduced blood flow to tissue

Venous vs arterial thrombi:

venous thrombi have ________ RBCs

arterial thrombi have ________ RBCs

many ("red")

few ("white")

Venous vs arterial thrombi:

venous thrombi _________ have lamination

arterial thrombi ___________ have lamination

won't

will

Will venous or arterial thrombi readily embolize?

venous

Do venous or arterial thrombi have "Lines of Zahn"?

arterial

"Lines of Zahn"

Laminations- alternating layers platelets, fibrin, RBC's, and Leukocytes

Three outcomes of thrombus formation:

1.) resolution

2.) organization/recanalization

3.) embolism

thrombus resolution

involves small thrombi; thrombi are removed from the vessel wall via thrombolysis

organization

involves larger thrombi; thrombi are removed through phagocytosis and form a scar on the vessel wall

recanalization

new vascular channels are formed within the thrombus to resume blood flow; organized by fibroblasts

embolism

aka thromboembolism; parts of a thrombus dislodge and form obstruction at distant location

Embolus

Detached intravascular solid/liquid/gaseous mass that is carried by blood to a distant site

Emboli often occlude ________ vessels

small

When emboli occlude small vessels, what can this lead to?

complete obstruction and ischemic necrosis (infarction)

Emboli usually originate from _________, but may have other origins

thrombi

examples of other things that can form emboli

-bacteria

-cartilage

-neoplasm

-parasites

Infarcts

A localized area of ischemic necrosis from blockage or occlusion of arterial supply or venous drainage

What type of necrosis is most common with infarcts?

coagulative necrosis

Are infarcts most common in arteries or veins?

arteries

What type of organs are infarcts most common in?

those with limited collateral blood supply (such as the brain or kidney)

Two mechanisms that produce infarcts

1.) obstruction

2.) compression

obstruction

something that blocks the flow of blood from inside the vessel (such as thrombi, emboli)

compression

something that blocks the flow of blood from outside the vessel (such as mases, torsion, tourniquets)

arterial obstruction

usually secondary to emboli; blood supply is interrupted

For an arterial infarct, blood can't enter or leave?

blood can't enter!

gross appearance of arterial obstruction

pale

venous obstruction

caused by blockage of veins leading away from an organ

For a venous infarct, blood can't enter or leave?

blood can't leave!

gross appearance of venous obstruction

dark red/black

Disseminated intravascular coagulation (DIC): Syndrome

widespread endothelial injury resulting in platelets adhering and activation of the coagulation cascade at numerous sites and activation fibrinolytic system (dissolves clots as form)

Causes of DIC

Complication of sepsis, endotoxemia, neoplasia, burns, heat stroke, shock, and endotheliotropic viral infections

Gross appearance of DIC

-numerous petechiae

-poor blood clotting

-systemic microthrombosis

Venous thrombi are characterized by?

A Few RBC's (white)

B Laminated

C Readily embolize

D Often yield infarction

C Readily embolize

Thrombi are caused by which of the following?

A Intact endothelium

B Hypercoagulability

C Normal blood flow

D Axial plasmatic streaming of blood

B Hypercoagulability

A species and tissue specific manifestation of DIC that causes generalized renal cortical necrosis in the horse is called?

A Axial plasmatic streaming

B Vegetative endocarditis

C Schwartzman Reaction

D Lines of Zahn

C Schwartzman Reaction

Which type of thrombus is

represented in this image?

What type of emboli is most

likely associated with it?

Thrombus: Vegetative

Emboli: bacterial

Which process is going on after

formation of this thrombus?

A. Recanalization

B. Organization and fibrosis

C. Little to no resolution

D. Complete resolution

C. Little to no resolution

What pathology is associated with the local

wedge-shaped area of necrosis in this kidney?

A. Infarction

B. Ischemic necrosis

C. Emboli

D. Coagulative necrosis

E. All of above

E. All of above

Which type of thrombus is

represented in this image?

What would be the likely

outcome of this thrombus?

Saddle thrombus

Emboli forms

In which tissue/organs occlusion of nearly any sized vessel typically results in infarction of the dependent tissue?

A. Liver

B. Gastrointestinal tract

C. kidney, and spleen

D. Skeletal muscle

C. kidney, and spleen

Which abnormal altered blood flow is usually associated with a

venous infarction?

A. Hyperemia

B. Congestion

C. Edema

D. Ascites

E. B and D

B. Congestion

Which type of thrombus is represented in this image?

A. Mural

B. Vegetative

C. Saddle

D. Verminous Thrombi

A. Mural

Which pathologic process is associated with this disease?

What type of emboli is most likely associated with it?

Endothelial injury and hypercoagulability

Parasitic or verminous emboli

In what species a generalized renal cortical necrosis can be an organ-specific manifestation of (DIC)?

A. Horses and Rabbits

B. Ruminants

C. Canine

D. Feline

A. Horses and Rabbits

Which abnormal altered blood flow can cause this gross morphology?

Congestion and right sided heart failures (Nutmeg liver)

Which abnormal altered blood flow can cause this gross morphology?

A. Ascites, congestion

B. Edema, congestion

C. Edema, hyperemia

D. A and B

A. Ascites, congestion