learning objectivespeople.upei.ca/smartinson/circ_5-thrombosis_embolism... · 2018. 10. 11. ·...

Learning Objectives

• Discuss the mechanisms that lead to thrombosis (Virchow’s triad).

• List the possible outcomes of thrombosis.

• Identify and classify thrombi (arterial vs venous, etc) based on location and gross/microscopic features.

• Describe the causes and consequences of embolism.

• What materials may form emboli?

• Which is most common?

• Describe the pathogenesis of ischemia and infarction.

THROMBOSIS, EMBOLISM AND INFARCTION

Circulatory Disturbances 5: Thrombosis, Embolism, Infarction

Shannon Martinson, Feb 2018 http://people.upei.ca/smartinson/ VPM 1520 General Pathology

• Inappropriate activation of hemostasis resulting in formation of a solid mass (thrombus) within the blood vessels or heart

Thrombosis

• Aggregate of platelets, fibrin, RBCs/WBCs within the lumen of blood vessels or heart • Can lead to vascular obstruction and embolism

Thrombus

(pl. Thrombi)

THROMBOSIS

Image: Zachary and McGavin PBVD

Often adheres to BV wall

THROMBOSIS

Abnormal blood flow

Hyper- coagulability

Endothelial injury

Pathogenesis of Thrombosis Virchow’s Triad

THROMBOSIS

Alterations in blood flow

• Turbulence

• Endothelial injury / activation

• Stasis

• No dilution of clotting factors

• Build-up of thrombi

Endothelial injury

• Dominant influence

• Causes thrombosis on own

Hypercoagulability

• Prothrombotic factors

• Inhibitory factors

THROMBOSIS

Pathogenesis of Thrombosis Virchow’s Triad

Location of thrombi in cardiovascular system: Cardiac chambers

Left atrial thrombus Left ventricular thrombus

THROMBOSIS

Valvular endocarditis

THROMBOSIS

Location of thrombi in cardiovascular system: Cardiac valves

Caudal abdominal aortic thrombus

THROMBOSIS

Location of thrombi in cardiovascular system: Blood vessels

• Usually form at sites of endothelial injury and/or turbulence

Images: Zachary and McGavin PBVD

THROMBOSIS

Location of thrombi in cardiovascular system: Arterial thrombi

• Grow towards from the heart (retrograde)

THROMBOSIS


• Often pale and meatier than venous thrombi


• Grow towards from the heart (retrograde)

THROMBOSIS


• Often pale and meatier than venous thrombi


• May have lines of Zahn = alternating lines of RBCs and fibrin


THROMBOSIS

Location of thrombi in cardiovascular system:

• Grow towards the heart (anterograde)

Venous thrombi

THROMBOSIS

Location of thrombi in cardiovascular system:

• Usually form in slow flow regions (stasis)

• Contain numerous RBCs → gelatinous and red

• Often occlusive

Venous thrombi

Image: Zachary PBVD, 2017

• Grow towards the heart (anterograde)

Image: Zachary PBVD, 2017 Can be difficult to differentiate from a postmortem blood clot

• Can refer to a thrombus or a post-mortem blood clot Blood clot

Postmortem blood clots are not associated with pathologic change and are not attached to the wall


THROMBOSIS

• Gelatinous yellow post-mortem clot

• Due to sedimentation of RBCs Chicken fat clot

THROMBOSIS

Lysis (resolution)

Outcome of Thrombi

Image: Robbin and Cotran, PBD, 2005

THROMBOSIS

THROMBOSIS

Outcome of Thrombi


Organization / Recanalization

Image: Zachary PBVD 2017

THROMBOSIS

Outcome of Thrombi

Organization / Recanalization

Image: Zachary PBVD 2017

Propagation


THROMBOSIS

Outcome of Thrombi


THROMBOSIS

Outcome of Thrombi

Embolization

• Passage through the circulation of any material capable of lodging in a blood vessel thereby obstructing the lumen Embolism

• Detached intravascular material carried via blood to a distant site from its origin

• Can be solid, liquid or gaseous

Embolus

(Pl. Emboli)

• Occlusion of a blood vessel by an embolus that has broken away from a thrombus

• Travels until it gets stuck Thromboembolism

• The piece(s) of thrombotic material transported in the bloodstream to another site

Thromboembolus (Pl. Thromboemboli)

EMBOLISM

Thromboembolism

Images: Modifed from Zachary and McGavin PBVD

EMBOLISM


Thromboembolism

EMBOLISM

Parasites - nematodes • Dirofilaria immitis


Other forms of embolism

EMBOLISM

Parasites – nematode larvae • Ascarid spp

• Strongylus vulgaris


EMBOLISM

Fat (bone marrow) emboli • Can occur with bone fractures,

prolonged surgery, and osteomyelitis

www.pathologystudent.com/wp-content/uploads/2012/12/800px-Bone_marrow_embolus.jpg


EMBOLISM

• Tumor cells • Foreign material emboli • Amniotic fluid


EMBOLISM

Tumour emboli

Some bacteria and viruses can cause localized or widespread endothelial damage, thrombosis, +/- thromboembolism

INFECTIOUS CAUSES OF THROMBOSIS / THROMBOEMBOLISM

Images: Zachary and McGavin PBVD

INFECTIOUS CAUSES OF THROMBOSIS / THROMBOEMBOLISM

Some bacteria and viruses can cause localized or widespread endothelial damage, thrombosis, +/- thromboembolism

• An area of ischemic necrosis resulting from occlusion of either arterial supply or venous drainage Infarct

• Most often due to: thrombosis, embolism, or vascular occlusion from twisting of a vessel • Pulmonary, intestinal and renal infarction are most common in animals

INFARCTION

Factors that influence the development / characteristics of an infarct

1. Nature of the vascular supply

2. Rate of development of occlusion

3. Vulnerability of the affected tissue to hypoxia

4. Oxygen content of blood at time of infarction

INFARCTION

• Often wedge-shaped

• Early – ill defined and red

• Later – may become more pale

Infarct - Gross appearance


INFARCTION

• Contain blood • Acute infarcts – with damaged

vessels and hemorrhage

INFARCTION

Infarct - Gross appearance Red Infarct


INFARCTION




Red Infarct

• Venous infarcts

INFARCTION




Red Infarct

• Venous infarcts

• Organs with dual blood supply

INFARCTION


• Lack of blood • Usually arterial occlusion in

solid organs • Often have a red zone at the

periphery

Pale Infarct

Ischemic (coagulative) necrosis of affected tissue

INFARCTION

Infarct - Histopathology

• Scar tissue replaces the parenchyma • Parenchymal loss + Fibrous tissue contraction = Depression / Indentation of the surface

INFARCTION

Infarct - Repair

• Mostly from a septic (bacterial infected) thromboembolus • Occasionally a necrotic tissue seeded by opportunistic bacteria

INFARCTION

Septic Infarct

• Complete venous obstruction leads to venous infarction • Often due to twisting of vessels (eg intestinal volvulus) → shock / death • Occasionally obstruction of portal vein or vena cava (eg thrombosis or tumour)

INFARCTION

Venous Obstruction/Infarction

Acute blockage of portal venous system

INFARCTION

With volvulus the venous outflow is obstructed while arterial flow is maintained →→ Shock and intestinal infarction


Etiology in dogs: • Severe heartworm infection • Tumour invasion

INFARCTION


Blockage of the caudal vena cava

Image: Dr C Legge

Etiology in ruminants: • Rupture of hepatic abscesses into the

caudal vena cava

INFARCTION

Outcome • Acute – sudden death • Chronic – possible collateral

circulation from azygous vein


Blockage of the caudal vena cava

Many possible causes: • Pneumonia • Parasites (eg. Heartworm) • Hypercoagulability

• Nephrotic syndrome • Hyperadrenocorticism • Exogenous steroids

• Liver abscess rupture into the vena cava • Thromboembolism to lung

INFARCTION

Pulmonary Arterial Thrombosis / Thromboembolism (PTE)

Result may depend on the size of the artery blocked: • If small vessel or

incomplete → subclinical • If complete and large

artery → death • May cause pulmonary

infarction

INFARCTION

Pulmonary Arterial Thrombosis / Thromboembolism (PTE)

learning objectivespeople.upei.ca/smartinson/circ_5-thrombosis_embolism... · 2018. 10. 11. ·...

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