STEP 1 — MCQs (NO answers here)

MCQ 1 — Four Main Fates

After a thrombus forms, over days to weeks it may undergo all of the following EXCEPT:

a. Propagation

b. Embolization

c. Dissolution

d. Organization and recanalization

e. Calcification as the only possible fate

MCQ 2 — Propagation

Propagation of a thrombus means:

a. It breaks off and travels as an embolus

b. It enlarges by adding more platelets and fibrin

c. It is completely lysed by plasmin

d. It turns into a tumor

e. It becomes sterile and acellular

MCQ 3 — Consequence of Propagation

Propagation increases the risk of:

a. Vascular occlusion or embolization

b. Dissolution

c. Hemorrhage only

d. Myocardial regeneration

e. Complete immunity to further thrombosis

MCQ 4 — Embolization

Embolization is best defined as:

a. Organization of the thrombus with capillary ingrowth

b. Detachment and transport of part or all of the thrombus in the circulation

c. Lysis by t-PA

d. Conversion to scar tissue

e. Formation of lines of Zahn

MCQ 5 — Dissolution and Thrombus Age

Dissolution by fibrinolysis is MOST effective when the thrombus is:

a. Newly formed

b. Weeks old and fully organized

c. Completely calcified

d. Already incorporated into the vessel wall

e. Infected

MCQ 6 — Resistance of Older Thrombi

Older thrombi are more resistant to plasmin-induced lysis mainly because:

a. They lose all fibrin

b. Extensive fibrin polymerization makes them resistant

c. They contain only platelets

d. They are located in veins only

e. They become avascular

MCQ 7 — Clinical Relevance of Fibrinolytics

Therapeutic fibrinolytic agents (e.g., t-PA in acute coronary thrombosis) are generally most effective when:

a. Given days after thrombus formation

b. Given within a few hours of thrombus formation

c. Given only after organization and recanalization

d. Given only in chronic thrombi

e. Age of thrombus does not matter

MCQ 8 — Organization and Recanalization

Organization and recanalization involve:

a. Only dissolution of fibrin by plasmin

b. Ingrowth of endothelial cells, smooth muscle cells, fibroblasts, and formation of capillary channels

c. Purely mechanical fragmentation

d. Replacement of thrombus by fat

e. Formation of aneurysm without tissue ingrowth

MCQ 9 — End Result of Complete Organization/Recanalization

With time, organization and recanalization can:

a. Convert a thrombus into a vascularized mass of connective tissue incorporated into the vessel wall

b. Fully restore the lumen without any residual tissue

c. Always cause necrosis of the vessel

d. Always cause rupture of the vessel

e. Prevent any future blood flow through the vessel

MCQ 10 — Enzymatic Digestion and Infection

If the center of a thrombus is enzymatically digested and then seeded by bacteria, an important possible consequence is:

a. Formation of atherosclerotic plaque

b. Formation of a mycotic aneurysm

c. Development of Libman-Sacks endocarditis

d. Immediate complete dissolution of thrombus

e. Purely benign scar formation

STEP 2 — ANSWERS + SHORT EXPLANATIONS

MCQ 1 — e

Main fates: propagation, embolization, dissolution, organization and recanalization.

Calcification can occur but is not one of the four primary textbook fates listed here.

MCQ 2 — b

Propagation = thrombus enlarges by accretion of more platelets and fibrin.

MCQ 3 — a

Propagation → bigger thrombus → higher chance of occlusion or embolization.

MCQ 4 — b

Embolization = part/all of the thrombus dislodges and is carried elsewhere in vasculature.

MCQ 5 — a

Newly formed thrombi are most susceptible to fibrinolytic dissolution.

MCQ 6 — b

Over time, extensive fibrin polymerization makes thrombi resistant to plasmin-mediated lysis.

MCQ 7 — b

Clinical fibrinolytics (e.g., t-PA) are generally effective only if given within a few hours of thrombus formation.

MCQ 8 — b

Organization and recanalization: ingrowth of endothelium, smooth muscle, fibroblasts, and formation of capillary channels.

MCQ 9 — a

Further recanalization can convert the thrombus into a vascularized connective tissue mass that becomes incorporated into the remodeled vessel wall.

MCQ 10 — b

Enzymatic central digestion + bacterial seeding → infection → weakening of wall → mycotic aneurysm.

STEP 3 — HIGH-YIELD NOTES (EXAM-READY)

1. Big Picture: Four Main Fates of a Thrombus

If the patient survives the initial thrombotic event, the thrombus can follow one or several paths over days–weeks:

1. Propagation
2. Embolization
3. Dissolution
4. Organization and recanalization

These are not mutually exclusive; a single thrombus can partially propagate, embolize, and the remainder organize.

2. Propagation

• Definition:
• Thrombus enlarges by continued deposition of platelets and fibrin.
• Consequences:
• Increased risk of vascular occlusion (ischemia/infarction).
• Larger, more unstable tail segment → higher risk of embolization.

3. Embolization

• Definition:
• Part or all of the thrombus is dislodged and travels through the circulation as an embolus.
• Outcome depends on:
• Site of origin (venous vs arterial).
• Size of embolus.
• Destination (e.g., pulmonary arteries for venous thrombi, systemic circulation for left-sided or arterial thrombi).

4. Dissolution (Fibrinolysis)

• Mechanism:
• Activation of fibrinolytic pathways, especially plasmin, can break down fibrin.
• New thrombi:
• Loosely cross-linked fibrin → relatively susceptible to lysis.
• Can undergo rapid shrinkage or complete dissolution.
• Older thrombi:
• Extensive fibrin polymerization → fibrin network becomes more resistant to plasmin.
• Lysis by natural or therapeutic fibrinolytics becomes ineffective.
• Clinical relevance:
• Fibrinolytic drugs (e.g., t-PA in acute coronary thrombosis) must be given within a few hours of thrombus formation to work well.
• Late administration → thrombus is too organized and resistant.

5. Organization and Recanalization

Organization

• Older thrombi undergo organization:
• Endothelial cells, smooth muscle cells, and fibroblasts grow into the thrombus.
• The thrombus is gradually replaced by granulation tissue and eventually fibrous connective tissue.

Recanalization

• Within organized thrombi:
• New capillary channels form along the length of the thrombus.
• These channels can partially restore blood flow through or around the thrombus.
• Long-term outcome:
• The organized thrombus can be transformed into a vascularized fibrous mass.
• This may be incorporated into the vessel wall, contributing to remodeling and sometimes luminal narrowing.

6. Enzymatic Digestion and Mycotic Aneurysm

• Sometimes, instead of smooth organization:
• The center of a thrombus undergoes enzymatic digestion, helped by lysosomal enzymes from trapped leukocytes.
• If this is accompanied by bacterial seeding:
• The partially digested thrombus becomes an ideal culture medium.
• Infection can weaken the vessel wall.
• Result: formation of a mycotic aneurysm (infective aneurysm) – an important and dangerous complication.