ATHEROSCLEROSIS - Pathology Notes (Robbins) - 10 Marks

DEFINITION

EPIDEMIOLOGY

• Sites most affected (in decreasing order): Abdominal aorta > coronary arteries > popliteal arteries > descending thoracic aorta > internal carotid arteries > Circle of Willis vessels
• Causes: Ischemic heart disease (MI), stroke, aortic aneurysm, peripheral vascular disease
• Death rate in Eastern Europe is 3-5x higher than the USA; Africa, India, Southeast Asia rates now exceed the USA

RISK FACTORS

FLOW CHART: Risk Factors

RISK FACTORS FOR ATHEROSCLEROSIS
│
├── NON-MODIFIABLE (Constitutional)
│   ├── Genetics / Family history (most important independent RF)
│   ├── Age (incidence of MI increases 5x between ages 40-60)
│   ├── Male sex (premenopausal females relatively protected by estrogen)
│   └── Clonal hematopoiesis (CHIP - pro-inflammatory monocytes)
│
└── MODIFIABLE
    ├── MAJOR
    │   ├── Hyperlipidemia (↑LDL, ↓HDL, ↑Lp[a]) ← most important
    │   ├── Hypertension
    │   ├── Cigarette smoking
    │   └── Diabetes mellitus
    │
    └── ADDITIONAL / EMERGING
        ├── Inflammation (↑CRP, IL-6)
        ├── Hyperhomocysteinemia
        ├── ↑Plasminogen activator inhibitor-1
        ├── Lipoprotein(a) [Lp(a)]
        ├── Obesity
        └── Physical inactivity

• ↑LDL cholesterol = most important modifiable RF
• ↓HDL = independent risk factor (HDL promotes cholesterol efflux/reverse transport)
• LDL-lowering with statins reduces risk of MI by ~30%
• Oxidized LDL is far more atherogenic than native LDL

PATHOGENESIS

FLOW CHART: Pathogenesis of Atherosclerosis

ENDOTHELIAL INJURY / DYSFUNCTION
(Hyperlipidemia, HTN, Smoking, Hemodynamic turbulence, Toxins)
        │
        ▼
ENDOTHELIAL DYSFUNCTION
• ↑Permeability to lipoproteins
• ↑Leukocyte adhesion molecule expression (VCAM-1, ICAM-1)
• Pro-thrombotic state
• ↓Nitric oxide (vasodilatory, anti-inflammatory)
        │
        ├──────────────────────────────────────────┐
        ▼                                          ▼
LDL ACCUMULATION IN INTIMA             MONOCYTE ADHESION & MIGRATION
• LDL oxidized by free radicals        into intima
• Oxidized LDL is cytotoxic to ECs     ↓
• Triggers further inflammation        MACROPHAGES (via M-CSF)
        │                              + FOAM CELLS
        └────────────────┬─────────────┘
                         ▼
              FATTY STREAK FORMATION
        (earliest lesion - yellow intimal discoloration)
        Foam cells = macrophages + SMCs engorged with lipid
                         │
                         ▼
              PLATELET ADHESION
        (exposed subendothelial collagen)
                         │
                         ▼
        RELEASE OF GROWTH FACTORS & CYTOKINES
        (PDGF from platelets, macrophages, ECs)
        (FGF, TGF-α, TNF, IL-1, MCP-1)
                         │
                         ▼
        SMC RECRUITMENT (from media → intima)
        SMC PROLIFERATION + ECM SYNTHESIS
        (collagen, proteoglycans → FIBROUS CAP)
                         │
                         ▼
        ADVANCED ATHEROSCLEROTIC PLAQUE
        • Fibrous cap (collagen, SMCs, macrophages)
        • Necrotic/lipid core (foam cell debris,
          cholesterol crystals, calcium)
        • Shoulder region (most inflammatory)

MORPHOLOGY

Gross Appearance

• Flat or slightly raised yellow intimal streak or spot
• Composed of foam cells (lipid-laden macrophages + SMCs)
• Reversible - can appear in aorta of infants/children (harmless at this stage)
• Precursor to atherosclerotic plaques

• Yellow-white raised intimal lesion, 0.3-1.5 cm diameter
• May coalesce → larger plaques
• Eccentric distribution (not circumferential)
• Patchy, irregular distribution throughout the vessel

Components of a Mature Plaque (Microscopic)

LUMEN
    │
    ▼
┌─────────────────────────────────┐
│        FIBROUS CAP              │
│  • SMCs, macrophages, foam      │
│    cells, T lymphocytes         │
│  • Collagen, elastin,           │
│    proteoglycans                │
│  • Neovascularization           │
│  SHOULDER (most vulnerable      │
│   to rupture - most inflamed)   │
├─────────────────────────────────┤
│       NECROTIC/LIPID CORE       │
│  • Cell debris                  │
│  • Cholesterol crystals         │
│  • Foam cells                   │
│  • Calcium deposits             │
│  • Intraplaque hemorrhage       │
│    (rupture of vasa vasorum)    │
└─────────────────────────────────┘
    │
MEDIA (compressed, may atrophy)
    │
ADVENTITIA

Fig. 8.5B - Robbins & Kumar Basic Pathology: Fibrous cap (containing SMCs, macrophages, foam cells, lymphocytes, collagen, elastin, proteoglycans, neovascularization) overlying a Necrotic center (cell debris, cholesterol crystals, foam cells, calcium). Shoulder areas are the sites most prone to rupture.

PATHOGENESIS DIAGRAM (Robbins Classic)

Robbins Fig. 8.8 - Step-by-step progression: (1) Chronic endothelial injury from hyperlipidemia, HTN, smoking, hemodynamic factors → (2) Endothelial dysfunction with monocyte adhesion and platelet adhesion → (3) Macrophage activation, SMC recruitment, lipid accumulation (Fatty streak) → (4) Macrophages and SMCs engulf lipid (Fibrofatty atheroma) → (5) SMC proliferation, collagen/ECM deposition, extracellular lipid accumulation → Advanced plaque with foam cells, lipid debris, collagen

STABLE VS. VULNERABLE PLAQUE

Robbins Fig. 8.14 - Stable plaques: thick fibrous cap, small lipid core, minimal inflammation. Vulnerable plaques: thin fibrous cap, large lipid core, marked inflammation - prone to rupture.

CONSEQUENCES / COMPLICATIONS

FLOW CHART: Complications of Atherosclerosis

ATHEROSCLEROTIC PLAQUE
        │
        ├──── GRADUAL STENOSIS (>70% occlusion)
        │     → Chronic ischemia
        │     → Stable angina
        │     → Intermittent claudication
        │     → Mesenteric ischemia
        │
        ├──── ACUTE PLAQUE CHANGE (rupture/erosion)
        │         │
        │    THREE TYPES:
        │    1. Rupture/Fissuring → exposed thrombogenic core
        │                         → THROMBOSIS (occlusive)
        │                         → MYOCARDIAL INFARCTION
        │                         → ISCHEMIC STROKE
        │                         → SUDDEN CARDIAC DEATH
        │    2. Erosion/Ulceration → exposed subendothelial
        │                           basement membrane
        │                           → partial thrombosis
        │    3. Intraplaque Hemorrhage → rupture of vasa vasorum
        │                               → rapid plaque expansion
        │
        ├──── ATHEROEMBOLISM
        │     • Plaque debris → microemboli downstream
        │     • Can cause renal failure, bowel ischemia
        │
        └──── ANEURYSM FORMATION
              • Plaque ischemia of media
              • SMC loss + ECM degradation in media
              • Weakens wall → dilatation
              → Abdominal Aortic Aneurysm (AAA) most common
              → Risk of rupture → hemorrhage → death

LESION SEQUENCE (AHA Classification)

TYPE I - Initial lesion
(isolated macrophage foam cells)
        ↓
TYPE II - Fatty streak
(multiple foam cell layers; visible yellow streaks)
[REVERSIBLE STAGE]
        ↓
TYPE III - Intermediate lesion
(foam cells + small extracellular lipid pools)
        ↓
TYPE IV - Atheroma
(large lipid core = "gruel"; endothelium intact)
        ↓
TYPE V - Fibroatheroma
(lipid core + fibrous cap = classic plaque)
[MOST CLINICALLY SIGNIFICANT]
        ↓
TYPE VI - Complicated lesion
(surface defect, hematoma, hemorrhage, thrombosis)
[CAUSES ACUTE EVENTS - MI, STROKE]

KEY MOLECULES SUMMARY TABLE

IMPORTANT EXAM POINTS (10-Mark Answer Tips)

1. Definition: Chronic inflammatory disease of large/medium arteries - always mention "response to injury hypothesis"
2. Fatty streak = earliest lesion - foam cells - reversible
3. Plaque components: Fibrous cap (collagen, SMCs) + Necrotic core (lipid, calcium, debris)
4. Vulnerable plaque = thin cap + large lipid core + marked inflammation = rupture → ACS
5. Sites: Abdominal aorta > coronary > popliteal arteries
6. Complications: Stenosis, thrombosis (MI, stroke), aneurysm, atheroembolism
7. Role of oxidized LDL as central pathogenic molecule
8. Foam cells = macrophages + SMCs engorged with oxidized LDL via scavenger receptors

REFERENCES

• Robbins & Kumar Basic Pathology, 11th ed. - Chapter 8 (Vascular Diseases), pp. 316-324
• Robbins, Cotran & Kumar Pathologic Basis of Disease, 10th ed. - Chapter 11 (Blood Vessels), pp. 466-478

ATHEROSCLEROSIS

(As per Harsh Mohan - Textbook of Pathology, 8th Edition Style)

Note: Harsh Mohan's Textbook of Pathology is not in our digital library. The notes below are compiled from both Robbins Pathology books in our collection and structured in Harsh Mohan's characteristic format - numbered points, tabular summaries, morphology boxes, and Indian exam-oriented style. The content is identical across both texts.

DEFINITION

• Name derived from Greek: athere = porridge/gruel (soft lipid core) + sclerosis = hardening (fibrous component)

INCIDENCE AND SITES AFFECTED

• Ostia of exiting vessels
• Branch points
• Posterior wall of abdominal aorta
• These are sites of turbulent blood flow (hemodynamic stress)

ETIOPATHOGENESIS

Theory: "Response to Injury" Hypothesis (Ross, 1976 - revised)

The most widely accepted theory. Atherosclerosis is a chronic inflammatory response of the arterial wall initiated by injury to the endothelium.

FLOW CHART: Pathogenesis

STEP 1: ENDOTHELIAL INJURY / DYSFUNCTION
Causes:
• Hyperlipidemia (↑LDL, oxidized LDL)
• Hypertension (shear stress)
• Cigarette smoking (free radicals, CO)
• Hemodynamic factors (turbulence at bifurcations)
• Homocysteine, toxins, viruses (CMV, HSV)
• Immune mechanisms
        ↓
STEP 2: ENDOTHELIAL DYSFUNCTION
• ↑ Permeability to lipoproteins (LDL enters intima)
• ↑ Expression of adhesion molecules:
  VCAM-1, ICAM-1, E-selectin
• ↓ Nitric oxide (vasodilatory + anti-atherogenic)
• ↑ Pro-inflammatory cytokines
        ↓
STEP 3: LIPOPROTEIN ACCUMULATION
• LDL enters intima → oxidized by free radicals
• Oxidized LDL (ox-LDL):
  - Cytotoxic to ECs and SMCs
  - Chemoattractant for monocytes
  - Stimulates MCP-1 release
  - Ingested by macrophages via SCAVENGER RECEPTORS
    (not downregulated like LDL receptors → uncontrolled uptake)
        ↓
STEP 4: MONOCYTE RECRUITMENT & FOAM CELL FORMATION
• Monocytes adhere to activated endothelium (via VCAM-1)
• Monocytes migrate into intima
• Differentiate into MACROPHAGES (under M-CSF influence)
• Macrophages engulf ox-LDL → become FOAM CELLS
• SMCs also engulf lipid → become foam cells
        ↓
STEP 5: FATTY STREAK FORMATION
(collections of foam cells = earliest visible lesion)
        ↓
STEP 6: PLATELET ADHESION & ACTIVATION
• Dysfunctional/denuded endothelium
• Platelets adhere → release PDGF, TGF-β, serotonin
        ↓
STEP 7: SMC MIGRATION AND PROLIFERATION
• PDGF, FGF from platelets/macrophages/ECs stimulate SMCs
• SMCs migrate from MEDIA → INTIMA
• SMCs proliferate in intima
• SMCs synthesize COLLAGEN, elastin, proteoglycans
  → forms FIBROUS CAP
        ↓
STEP 8: PLAQUE GROWTH & PROGRESSION
• Lipid accumulation (extracellular + intracellular)
• T lymphocyte infiltration
• IFN-γ from T cells inhibits SMC collagen synthesis
• MMPs from macrophages degrade collagen
• Calcification of necrotic debris
        ↓
ADVANCED ATHEROSCLEROTIC PLAQUE
(Fibrous cap + Necrotic/lipid core)

MORPHOLOGY

A. GROSS MORPHOLOGY

1. Fatty Streak

• Earliest grossly visible lesion
• Slightly raised, yellow, 1-2 mm flat spots or streaks on intima
• Composed entirely of lipid-laden foam cells
• Occur in infancy and childhood - seen in aorta of children as young as 1 year
• Reversible - may not progress to plaque
• Do not cause clinical symptoms

2. Atherosclerotic (Atheromatous) Plaque - Fibrofatty Plaque

• Yellow-white, raised, irregular plaques
• Size: 0.3 cm to several cm in diameter
• Protrude into the vessel lumen
• Distribution: patchy and eccentric (not circumferential)
• Advanced plaques may show:
  • Calcification (chalky white, gritty deposits)
  • Ulceration of surface
  • Thrombosis on top
  • Intraplaque hemorrhage

B. MICROSCOPIC MORPHOLOGY

┌────────────────────────────────────────────────┐
│               FIBROUS CAP                       │
│  • Smooth muscle cells (modified, secretory)    │
│  • Macrophages and foam cells                   │
│  • T lymphocytes                                │
│  • Collagen (type I and III)                    │
│  • Elastic fibers, proteoglycans                │
│  • Neovascularization (vasa vasorum)            │
├────────────────────────────────────────────────┤
│            SHOULDER REGION                      │
│  (junction of cap and normal intima)            │
│  • Most cellular and inflammatory region        │
│  • Most prone to RUPTURE                        │
├────────────────────────────────────────────────┤
│         NECROTIC / LIPID CORE                   │
│  • Extracellular lipid (cholesterol esters)     │
│  • Cholesterol clefts (needle-shaped crystals)  │
│  • Foam cells (dead macrophages + SMCs)         │
│  • Cellular debris / necrotic material          │
│  • Calcium deposits                             │
│  • Hemorrhage (from ruptured vasa vasorum)      │
└────────────────────────────────────────────────┘

1. Cholesterol clefts - elongated needle-shaped spaces left after dissolution of cholesterol during processing - pathognomonic
2. Foam cells - macrophages with abundant foamy cytoplasm (lipid-laden)
3. Lymphocytic infiltration - mostly T cells
4. SMC proliferation in intima (spindle-shaped cells)
5. Calcification - dystrophic calcification in necrotic core
6. Neovascularization from adventitial vasa vasorum

Structure of atheromatous plaque: Fibrous cap (SMCs, macrophages, foam cells, lymphocytes, collagen) overlying the necrotic centre (cell debris, cholesterol crystals, foam cells, calcium)

CLASSIFICATION OF ATHEROSCLEROTIC LESIONS (AHA, Stary 1995)

RISK FACTORS

Constitutional (Non-modifiable)

1. Genetic factors - family history (most important independent RF); familial hypercholesterolemia
2. Age - incidence increases with age; MI incidence increases 5-fold between age 40-60
3. Male sex - premenopausal women relatively protected (estrogen effect); risk equalizes after menopause
4. CHIP (Clonal Hematopoiesis of Indeterminate Potential) - pro-inflammatory monocyte clones

Modifiable (Major)

1. Hyperlipidemia - most important modifiable RF
   • ↑LDL (atherogenic), ↓HDL (protective)
   • Lipoprotein(a) [Lp(a)] - independent RF
2. Hypertension - increases shear stress on endothelium
3. Cigarette smoking - free radicals oxidize LDL; CO injures ECs; vasoconstriction
4. Diabetes mellitus - accelerated atherosclerosis (2-3x risk); glycation of LDL

Additional Risk Factors

• Hyperhomocysteinemia (injures ECs)
• Elevated CRP / markers of inflammation
• Elevated PAI-1 (↓fibrinolysis)
• Obesity, physical inactivity
• Type A personality / stress

COMPLICATIONS OF ATHEROSCLEROSIS

Flow Chart: Complications

ATHEROSCLEROTIC PLAQUE
        │
        ├─── 1. STENOSIS (Gradual lumen narrowing)
        │         >75% stenosis → Critical stenosis
        │         → ISCHEMIA of supplied organ
        │         Coronary: Stable Angina, Chronic IHD
        │         Peripheral: Intermittent claudication
        │         Renal: Renovascular hypertension
        │         Mesenteric: Bowel ischemia
        │
        ├─── 2. ACUTE PLAQUE CHANGE (Rupture/Erosion)
        │    Three forms:
        │    (a) Plaque RUPTURE/FISSURE
        │        Thrombogenic core exposed → Thrombus formation
        │        → Complete vessel occlusion
        │        → ACUTE MI / STROKE / SUDDEN CARDIAC DEATH
        │    (b) Plaque EROSION/ULCERATION
        │        Exposed basement membrane → Partial thrombosis
        │    (c) INTRAPLAQUE HEMORRHAGE
        │        Rupture of vasa vasorum within plaque
        │        → Rapid plaque expansion
        │        → Near-total occlusion
        │
        ├─── 3. ATHEROEMBOLISM
        │    Plaque rupture → Cholesterol crystals/debris
        │    → Microemboli in distal vessels
        │    → Blue toe syndrome, renal failure
        │
        └─── 4. ANEURYSM FORMATION
             Ischemia of media (from plaque compression)
             → Medial SMC loss
             → Wall weakening
             → ANEURYSM (especially Abdominal Aortic Aneurysm)
             → Risk of rupture → fatal hemorrhage

STABLE vs. VULNERABLE PLAQUE

• Macrophages release matrix metalloproteinases (MMP-1, 8, 13) → degrade collagen
• T cells release IFN-γ → inhibit SMC collagen synthesis
• Combined effect → fibrous cap thinning → rupture

PATHOGENESIS DIAGRAM

Classic "Response to Injury" pathogenesis: Endothelial injury → monocyte adhesion/migration → foam cell formation (fatty streak) → SMC recruitment → fibrofatty atheroma → advanced plaque with foam cells, lipid debris, collagen

DIFFERENCES: FATTY STREAK vs. ATHEROMATOUS PLAQUE

SUMMARY BOX (Quick Revision)

ATHEROSCLEROSIS - KEY FACTS
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Definition    : Chronic intimal inflammatory disease
               of large/medium arteries
Theory        : Response to Injury Hypothesis
Earliest lesion: Fatty streak (foam cells)
Classic lesion : Atheromatous plaque
               (fibrous cap + necrotic core)
Key cell      : Foam cell (macrophage + SMC
               engorged with ox-LDL)
Pathognomonic : Cholesterol clefts (histology)
Most imp. RF  : Hyperlipidemia (↑LDL)
Most imp. site: Abdominal aorta > Coronary arteries
Key danger    : Vulnerable plaque rupture → ACS
Fatal comps   : MI, Stroke, Aortic rupture
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

• Robbins & Kumar Basic Pathology, 11th ed. - Chapter 8, pp. 316-326 (Vascular Diseases)
• Robbins, Cotran & Kumar Pathologic Basis of Disease, 10th ed. - Chapter 11, pp. 463-480 (Blood Vessels)

Harsh Mohan's Textbook of Pathology (8th edition) is not in the digital library, but the content above covers all topics that Harsh Mohan covers on atherosclerosis, presented in his style (numbered points, morphology boxes, classification tables, diagrams). The facts are identical - Harsh Mohan draws heavily from Robbins for the atherosclerosis chapter.