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Respiratory System - Pathology Topics for ABMu (KMU Curriculum) Prof Exam

Note: At ABMu/Ayub Medical College (KMU-affiliated), the Respiratory Module is part of 3rd Year MBBS, covered under the "Respiratory II Module". The 2nd Professional Exam in Pakistan often spans modules from 2nd and early 3rd year. If your prof exam specifically covers respiratory pathology, here are all the topics you need:

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Pathology gets 18 lecture hours in the Respiratory II Module - the highest of all subjects. Topics are organized under two themes:

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Theme I: Cough with Sputum and Fever

1. Pneumonia

• Definition and classification of pneumonia
• Lobar pneumonia - stages, morphology, complications
• Bronchopneumonia - causes, morphology, differences from lobar
• Atypical/interstitial pneumonia - pathogens, features
• Community-acquired vs hospital-acquired (nosocomial) pneumonia

2. Tuberculosis (TB)

• Primary TB (Ghon complex) - pathogenesis and morphology
• Secondary (reactivation) TB - pathogenesis and morphology
• Military/disseminated TB
• Caseous necrosis and granuloma formation
• Complications: cavitation, spread, Pott's disease
• MDR-TB concepts

3. Lung Abscess

• Definition, etiology (aspiration, secondary to pneumonia)
• Pathogenesis and morphology

4. Pleural Effusion & Empyema

• Transudates vs exudates
• Empyema - causes, morphology

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Theme II: Wheezy Chest and Shortness of Breath

5. Atelectasis

• Definition
• Types: resorption, compression, contraction, patchy/microatelectasis

6. Acute Lung Injury (ARDS)

• Definition of ARDS (Acute Respiratory Distress Syndrome)
• Pathogenesis - diffuse alveolar damage
• Morphological features (hyaline membranes)

7. Obstructive Pulmonary Diseases (COPD)

• Emphysema: types (centriacinar, panacinar, paraseptal, irregular), pathogenesis, morphology, clinical course
• Chronic Bronchitis: definition (clinical), pathogenesis, Reid index, morphology
• Asthma: types (atopic vs non-atopic), pathogenesis (IgE-mediated, immune mechanisms), morphology, clinical course - Curschmann spirals, Charcot-Leyden crystals
• Bronchiectasis: definition, causes, morphology, pathogenesis

8. Restrictive / Diffuse Interstitial Lung Diseases (ILD)

• Definition and classification
• Usual Interstitial Pneumonia (UIP) / Idiopathic Pulmonary Fibrosis (IPF)
• Pneumoconioses:
  • Coal worker's pneumoconiosis
  • Silicosis - silica nodules, progressive massive fibrosis
  • Asbestosis - asbestos bodies, ferruginous bodies, pleural plaques, mesothelioma link
• Hypersensitivity Pneumonitis (extrinsic allergic alveolitis)
• Sarcoidosis - non-caseating granulomas, lung involvement

9. Pulmonary Vascular Disease

• Pulmonary embolism - sources, types, consequences, infarction
• Pulmonary hypertension - primary vs secondary, plexogenic arteriopathy

10. Lung Tumors

• Carcinoma of the lung - major focus:
  • Squamous cell carcinoma - location (central), keratin pearls, association with smoking
  • Adenocarcinoma - peripheral, most common in non-smokers/females, BAC pattern
  • Small cell (oat cell) carcinoma - neuroendocrine, paraneoplastic syndromes, highly malignant
  • Large cell carcinoma
• Paraneoplastic syndromes (SIADH, Cushing, PTHrP, Eaton-Lambert)
• Pancoast tumor, SVC syndrome
• Mesothelioma - asbestos link, diffuse type

11. Pleural Pathology

• Pleuritis (fibrinous, serofibrinous)
• Pleural tumors - mesothelioma

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High-Yield MCQ/SAQ Topics for Prof Exam

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Recommended Study Resources

• Robbins Basic Pathology (9th/10th edition) - Chapter on Lung
• Harsh Mohan's Textbook of Pathology - widely used in Pakistan
• KMU Respiratory II Module Study Guide - available on ayubmed.edu.pk

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Tip: Focus especially on obstructive lung diseases (COPD/asthma/bronchiectasis), pneumonia types, lung carcinoma, and TB - these are the most heavily tested topics in Pakistani medical university prof exams. Diagrams for emphysema types and pneumonia stages are frequently asked in practicals/OSCEs.

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RESPIRATORY SYSTEM - COMPLETE PATHOLOGY NOTES

ABMu (KMU) - Prof Exam

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PART 1: ATELECTASIS

Types of Atelectasis

Key Points

• Lung bases and posterior segments are vulnerable to dependent atelectasis (immobilized/postoperative patients)
• Creates ventilation-perfusion mismatch leading to hypoxemia
• Sustained atelectasis can lead to infection
• On CXR: loss of lung volume, displacement of lobar fissure, mediastinum, or diaphragm toward the involved area

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PART 2: ACUTE LUNG INJURY (ALI) AND ARDS

Causes (Triggers)

• Direct lung injury: Pneumonia, aspiration of gastric contents, near-drowning, inhaled toxins
• Indirect injury: Sepsis (most common cause), severe trauma, pancreatitis, blood transfusions, drug overdose

Pathogenesis

1. Trigger activates neutrophils and macrophages
2. Release of inflammatory mediators (IL-1, IL-8, TNF)
3. Neutrophils accumulate in pulmonary capillaries and alveoli
4. Neutrophils release proteases, oxygen free radicals, and leukotrienes
5. Endothelial and epithelial injury - increased permeability
6. Protein-rich fluid floods alveoli - hyaline membrane formation

Morphology

• Lungs are heavy, red, boggy, congested
• Diffuse alveolar damage (DAD) - key histological feature
• Hyaline membranes lining alveolar ducts (pink, acellular material)
• Alveolar edema, fibrin exudate, collapsed alveoli

• Resorption of hyaline membranes
• Proliferation of type II pneumocytes (attempting repair)
• Alveolar septa thickened by fibroblasts, collagen
• May resolve or progress to fibrosis

Clinical Features

• Onset within 72 hours of the initial insult in 85% of cases
• Bilateral ground glass opacities on CT scan
• Severe hypoxemia refractory to oxygen therapy
• Overall mortality ~40%
• Survivors may have decreased physical endurance

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PART 3: OBSTRUCTIVE PULMONARY DISEASES (COPD)

These are all characterized by increased resistance to airflow. Key comparison:

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3A. EMPHYSEMA

Types

• Destruction begins at respiratory bronchioles (central part of acinus)
• Peripheral alveoli are spared initially
• Most closely associated with smoking
• Affects upper lobes predominantly
• Mechanism: Cigarette smoke attracts neutrophils → release elastase → destroy elastic tissue (protease-antiprotease imbalance)

• Affects all parts of the acinus uniformly - from respiratory bronchiole to alveolar sac
• Associated with alpha-1 antitrypsin (AAT) deficiency (homozygous)
• Affects lower lobes predominantly
• More extensive destruction

• Destroys the distal alveoli adjacent to pleura
• Proximal acinus is spared
• Most closely associated with bulla formation and spontaneous pneumothorax (young males)
• Often found adjacent to mediastinum, interlobar fissures

• Acinus irregularly involved
• Always associated with scarring (post-inflammatory)
• Usually clinically silent

Pathogenesis - Protease-Antiprotease Imbalance

• Normal lung: Alpha-1 antitrypsin (AAT) inhibits elastase from neutrophils
• In smoking: Smoke → attracts neutrophils and macrophages → release elastase + reactive oxygen species → inactivates AAT + directly destroys elastin → air space enlargement
• In AAT deficiency: Inherited low AAT → even normal amounts of elastase cause panacinar emphysema

Morphology

• Lungs are enlarged, hyperinflated, pale
• Loss of alveolar walls, enlarged air spaces
• CXR: Barrel chest, flattened diaphragm, hyperinflation
• Bullae may be present (especially paraseptal type)

Clinical Features

• "Pink puffer" - dyspnea dominant, maintain near-normal oxygenation (hyperventilate to compensate)
• Pursed lip breathing
• Barrel chest, diminished breath sounds
• Prolonged expiration

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3B. CHRONIC BRONCHITIS

Pathogenesis

• Chronic irritation (mainly tobacco smoke, air pollutants)
• Hypersecretion of mucus by hypertrophied and hyperplastic mucous glands in bronchial wall
• Goblet cell metaplasia in bronchiolar epithelium
• Impaired mucociliary clearance → recurrent infections → further damage

Morphology

• Reid index (key exam fact): Ratio of mucous gland thickness to total wall thickness
  • Normal: ≤ 0.4
  • Chronic bronchitis: > 0.5 (mucous gland hypertrophy)
• Goblet cell hyperplasia in bronchiolar epithelium
• Chronic inflammatory infiltrate in bronchial walls
• Squamous metaplasia of epithelium

Clinical Features

• "Blue bloater" - cough + sputum + cyanosis + edema
• Cor pulmonale in severe cases
• Frequent respiratory infections (H. influenzae, S. pneumoniae)

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3C. ASTHMA

Types

• Begins in childhood
• Triggered by allergens (dust mites, pollen, animal dander)
• IgE-mediated (Type I hypersensitivity)
• Strong family history, positive skin tests
• Often associated with eczema, allergic rhinitis (atopic triad)

• Adults, triggered by respiratory infections (especially viruses), cold air, exercise, stress
• No allergen sensitization
• Serum IgE normal
• Mechanism less clear - possibly involves hyperreactivity of sensory nerve endings

• Aspirin-sensitive asthma - aspirin/NSAIDs inhibit COX → shunting to lipoxygenase pathway → excess leukotrienes → bronchospasm

• Triggered by fumes, dusts, chemicals in workplace

Pathogenesis of Atopic Asthma

1. First exposure to allergen → IgE production by B cells (sensitization)
2. IgE binds to mast cells in airways
3. Re-exposure → antigen cross-links IgE on mast cells
4. Early phase (minutes): Mast cell degranulation → histamine, leukotrienes, prostaglandins → immediate bronchospasm, mucus secretion, vascular permeability
5. Late phase (hours): Recruitment of eosinophils, neutrophils, Th2 cells → release IL-4, IL-5, IL-13 → sustained inflammation, AHR

Morphology (Autopsy findings in fatal asthma)

• Lungs overinflated, obstructed with mucus
• Mucus plugs in bronchi containing:
  • Curschmann spirals (spiral plugs of shed epithelium)
  • Charcot-Leyden crystals (eosinophil membrane protein, crystalline structures)
  • Creola bodies (clusters of shed epithelial cells)
• Bronchial wall changes:
  • Smooth muscle hypertrophy and hyperplasia
  • Goblet cell hyperplasia
  • Subepithelial fibrosis ("basement membrane thickening") - due to collagen deposition beneath epithelium
  • Eosinophilic infiltration
  • Mucous gland hyperplasia

Clinical Features

• Episodic wheeze, dyspnea, cough (typically at night/early morning)
• Prolonged expiratory phase
• Use of accessory muscles
• Status asthmaticus - prolonged, severe attack unresponsive to bronchodilators (life-threatening)

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3D. BRONCHIECTASIS

Causes

• Obstruction - tumor, foreign body, mucus plug (airway clearance impaired)
• Post-infectious - TB (most common cause in developing countries), adenovirus, measles, pertussis
• Congenital/Hereditary:
  • Cystic fibrosis (most common cause in developed countries)
  • Kartagener syndrome (immotile cilia, situs inversus, bronchiectasis)
  • Immunodeficiency (hypogammaglobulinemia)
• Allergic bronchopulmonary aspergillosis (ABPA)
• Rheumatoid arthritis, IBD

Pathogenesis - Vicious Circle

Morphology

• Affects lower lobes (gravity-dependent)
• Bronchi/bronchioles dilated up to 4x normal size
• Three types: cylindrical, varicose, saccular/cystic
• Airways filled with purulent, greenish exudate
• Histology: necrotizing ulcerating inflammation in bronchial walls, fibrosis, goblet cell hyperplasia

Clinical Features

• Chronic productive cough with copious purulent sputum (30 mL+ per day)
• Sputum has three layers on standing: frothy (top), mucoid (middle), purulent (bottom)
• Hemoptysis (sometimes massive)
• Common organisms: Haemophilus influenzae, Staphylococcus aureus, Pseudomonas aeruginosa
• CT chest: "tram-track" sign, airway dilation

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PART 4: PNEUMONIA

4A. LOBAR PNEUMONIA

Four Classic Stages (must memorize!)

Complications

• Pleuritis with pleural effusion or empyema
• Bacteremia/Septicemia
• Lung abscess (if resolution fails)
• Organization (if macrophage clearance fails → fibrous scar - "carnification")
• Pericarditis, meningitis (hematogenous spread)

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4B. BRONCHOPNEUMONIA (LOBULAR PNEUMONIA)

• Patchy consolidation affecting multiple lobules, often bilateral and basal
• Less severe, more common in extremes of age (infants, elderly), debilitated patients
• Organisms: Staphylococcus, H. influenzae, Klebsiella, E. coli, Pseudomonas
• Morphology: Multiple foci of consolidation, patchy gray-red areas 3-4 cm, centered on bronchioles
• Histology: Exudate in bronchioles and adjacent alveoli; neutrophil-rich

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4C. ATYPICAL PNEUMONIA (INTERSTITIAL PNEUMONIA)

• Diffuse, patchy, interstitial inflammation - no consolidation
• Organisms: Mycoplasma pneumoniae (most common), viruses (influenza, RSV, adenovirus), Chlamydia, Legionella
• "Walking pneumonia" - patient not as sick as CXR suggests
• Morphology: Interstitial edema, mononuclear inflammatory infiltrate, no consolidation, hyaline membranes in severe cases

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4D. LUNG ABSCESS

• Aspiration (most common) - mixed flora, anaerobes; right lower lobe more commonly affected
• Post-pneumonia (especially Staphylococcus, Klebsiella)
• Septic embolism (endocarditis)
• Bronchial obstruction (carcinoma - "obstructive abscess")
• Bacteremia with seeding

• Single or multiple cavities
• Wall: fibrotic rim; green-yellow pus
• Destruction of lung parenchyma

• Fever, cough with copious foul-smelling/blood-stained sputum
• CXR: Cavity with air-fluid level

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PART 5: TUBERCULOSIS

Primary Tuberculosis

1. Inhalation of M. tuberculosis droplets
2. Bacilli reach lower lobes (well-ventilated areas)
3. Engulfed by alveolar macrophages
4. Macrophages cannot kill bacilli → bacilli multiply inside macrophages
5. 3-8 weeks: T cell-mediated immunity activated (tuberculin positivity)
6. CD4 T cells (Th1) → activate macrophages → kill bacilli
7. Granuloma formation with caseous necrosis

• Ghon focus: 1-1.5 cm area of consolidation, usually subpleural, lower part of upper lobe or upper part of lower lobe
• Central caseous necrosis surrounded by epithelioid granuloma + Langhans giant cells
• • Hilar/mediastinal lymphadenopathy = Ghon complex (Primary complex)
• Usually heals by fibrosis and calcification (Ranke complex when calcified)

• In 95% of healthy individuals → heals (contain but does not eradicate bacilli)
• In 5% (immunocompromised, malnourished) → progressive primary TB

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Secondary (Reactivation) Tuberculosis

• High oxygen tension favors mycobacterial growth
• Poor lymphatic drainage
• Less macrophage activity

• Reactivation triggered by: immunosuppression, malnutrition, HIV, diabetes, steroids
• Pre-existing immunity → rapid, exaggerated response → more tissue destruction
• Granuloma formation with extensive caseous necrosis
• Cavitation (hallmark of secondary TB)

• Apical fibrocalcific lesion
• Cavities in upper lobe - caseous material liquefies and drains into bronchi → coughed up (infectious aerosols)
• Simon foci: small apical foci of caseous necrosis
• Satellite lesions from bronchogenic spread

• Miliary TB: Hematogenous dissemination → millet seed-sized granulomas in multiple organs (lung, liver, spleen, marrow)
• Bronchopneumonia: Spread through airways
• Pleural involvement - pleural effusion, empyema
• Pott's disease: Vertebral TB (most common site of skeletal TB)
• Laryngeal TB - through infected sputum
• Intestinal TB - swallowed sputum
• Renal TB - hematogenous

• TB: CASEATING (cheese-like central necrosis)
• Sarcoidosis: NON-CASEATING
• Organism: Acid-fast bacilli (AFB) stained by Ziehl-Neelsen (ZN) stain

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PART 6: INTERSTITIAL LUNG DISEASES (ILD) / DIFFUSE PARENCHYMAL LUNG DISEASES

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6A. IDIOPATHIC PULMONARY FIBROSIS (IPF)

• Most common and most lethal ILD
• Histological pattern: Usual Interstitial Pneumonia (UIP)
• Cause unknown
• Median survival: 3-5 years from diagnosis
• Morphology: Fibrosis is patchy, predominantly subpleural and basal
  • "Honeycombing" (fibrotic cystic spaces, 0.5-2 cm) - late feature
  • "Fibroblastic foci" - active fibrosis at disease edges
  • Temporal heterogeneity (old fibrosis + new active areas)

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6B. SARCOIDOSIS

• Non-caseating granulomas in multiple organs (lung most commonly involved)
• Young adults, more common in Black individuals
• Cause unknown - abnormal CD4 T-cell response
• Morphology: Non-caseating epithelioid granulomas with Langhans/foreign body giant cells
  • Schaumann bodies (calcium-protein inclusions in giant cells)
  • Asteroid bodies (star-shaped inclusions)
  • No caseation - key differentiator from TB
• Clinical: Bilateral hilar lymphadenopathy, skin lesions, uveitis, hypercalcemia
• Laboratory: Elevated serum ACE, hypercalcemia

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6C. PNEUMOCONIOSES (Occupational Lung Diseases)

Coal Worker's Pneumoconiosis (CWP)

• Inhalation of coal dust (carbon particles)
• Carbon engulfed by macrophages → accumulate in lung + lymphatics
• Simple CWP: Coal macules (dust-laden macrophages) + coal nodules + small amounts of collagen; upper lobe predominant; centrilobular emphysema may develop
• Complicated CWP (Progressive Massive Fibrosis, PMF):
  • Coalescence of coal nodules > 2 cm (up to 10 cm)
  • Dense collagen + black pigment
  • Progressive even after dust exposure ends
  • Pulmonary hypertension, cor pulmonale
• Does NOT increase lung cancer risk (unlike silica and asbestos)

Silicosis

• Inhalation of crystalline silica (quartz)
• Most prevalent chronic occupational disease worldwide
• Workers at risk: Sandblasters, hard-rock miners, foundry workers, stone cutters

1. Silica particles ingested by macrophages
2. Lysosomal damage → release of IL-1, TNF, free radicals, fibrogenic cytokines
3. Macrophage death → silica released → re-ingested by more macrophages → vicious cycle of inflammation and fibrosis

• Silicotic nodules: Concentrically arranged hyalinized collagen fibers in a "whorled" pattern (pathognomonic)
• Upper lobe and hilar lymph node involvement
• "Eggshell calcification" of hilar lymph nodes (calcification at periphery of lymph node)
• Progression to PMF in severe cases
• Birefringent silica particles in center of nodules (seen under polarized light)

• Slowly progressive dyspnea over decades
• Increased susceptibility to TB (silica impairs macrophage function)
• Increased lung cancer risk

Asbestosis

• Inhalation of asbestos fibers (serpentine = chrysotile; amphibole = crocidolite, amosite)
• Amphibole fibers are more carcinogenic
• Occupations: Shipbuilders, insulation workers, construction, roofing

• Asbestos bodies (Ferruginous bodies): Golden-brown, beaded, dumbbell-shaped rods - asbestos fibers coated with iron-protein (pathognomonic)
• Pulmonary fibrosis: Lower lobes + subpleural, progressive
• Pleural plaques: White, firm plaques on parietal pleura (calcified) - most common manifestation, by themselves not fibrosis
• Pleural effusions
• Mesothelioma (malignant, strongly associated - most are due to asbestos)

1. Asbestosis (pulmonary fibrosis)
2. Mesothelioma (pleural malignancy)
3. Bronchogenic carcinoma (especially with smoking - synergistic effect!)
4. Pleural plaques, pleural effusions

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PART 7: PULMONARY VASCULAR DISEASE

7A. PULMONARY THROMBOEMBOLISM (PE)

• Massive PE: Occludes > 60% of pulmonary circulation → sudden death, acute cor pulmonale
• Submassive PE: Occludes segmental arteries → right heart strain
• Small/Microemboli: Peripheral small arteries → often silent; repeated episodes → pulmonary hypertension

• Sudden death (massive, saddle embolus at bifurcation)
• Pulmonary infarction (12-15% of PEs) - wedge-shaped, hemorrhagic, base at pleura; only if circulation already compromised
• Pulmonary hypertension (repeated small emboli)
• Often no infarction because dual blood supply (bronchial + pulmonary arteries)

• Wedge-shaped hemorrhagic area, apex toward hilum, base at pleura
• Initially red-brown (hemorrhagic); later, if patient survives, fibrous scar

1. Venous stasis (immobility, heart failure)
2. Hypercoagulability (cancer, oral contraceptives, pregnancy)
3. Endothelial injury (surgery, trauma)

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7B. PULMONARY HYPERTENSION

• No identifiable cause
• Mutation in BMPR2 gene (familial cases)
• Most common in women aged 20-40 years
• Rapidly fatal - 2-5 years

• Left heart disease (most common cause worldwide)
• Chronic lung disease (COPD, IPF)
• Chronic thromboembolic disease
• Connective tissue diseases (scleroderma)

• Medial hypertrophy of pulmonary arteries
• Intimal fibrosis
• Plexiform lesions (pathognomonic of advanced/severe pulmonary hypertension) - complex tufts of cells within small arteries

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PART 8: LUNG TUMORS

8A. CARCINOMA OF THE LUNG

• Leading cause of cancer deaths in both men and women (Western countries)
• Peak incidence: 50s-60s
• >50% have distant metastases at diagnosis
• Overall 5-year survival: ~20%
• Strongest risk factor: Cigarette smoking (20-25x increased risk)

Molecular Pathogenesis

• KRAS mutation - common in adenocarcinoma (smoking-associated)
• EGFR mutation - adenocarcinoma, especially in never-smokers, Asians, women
• ALK rearrangement - young, never-smokers
• p53, RB mutations - especially in small cell
• Squamous cell: mutations in p53, CDKN2A, SOX2 amplification

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Four Major Histological Types

1. Adenocarcinoma - Most Common Overall

• Location: Peripheral, subpleural
• Most common in: Women, non-smokers, young patients (<45 years), and currently most common overall in many countries
• Microscopically: Glandular structures, acinar, papillary, micropapillary, solid, or lepidic patterns
• Lepidic growth: Tumor cells grow along existing alveolar walls without destruction (low-grade type, formerly "bronchioloalveolar carcinoma/BAC")
• Mucin production (mucin stains positive)
• EGFR/KRAS/ALK mutations most common here - target for therapy
• Can arise from Clara cells or type II pneumocytes

2. Squamous Cell Carcinoma

• Location: Central, near hilum (arises from main/lobar bronchi)
• Most closely associated with smoking (along with small cell)
• Microscopically: Keratin pearls, intercellular bridges, squamous differentiation
• Often preceded by squamous metaplasia → dysplasia → carcinoma in situ → invasive
• Histochemistry: Positive for cytokeratin 5/6, p63
• Cavitation common (central necrosis)
• Paraneoplastic: PTHrP → hypercalcemia (most common paraneoplastic syndrome)

3. Small Cell Carcinoma (SCLC)

• Location: Central (hilar)
• Strongest association with smoking
• Most aggressive - virtually always metastasized at diagnosis
• Arises from neuroendocrine cells (Kulchitsky cells)
• Microscopically: Small cells with scant cytoplasm, "oat-like" nuclei, salt-and-pepper chromatin, no nucleoli, nuclear molding
• IHC: Positive for synaptophysin, chromogranin, NSE, CD56 (neuroendocrine markers)
• NOT treated surgically - chemotherapy + radiation
• Paraneoplastic syndromes (most common of all lung cancers to cause them):
  • SIADH → hyponatremia (ADH-like peptide)
  • Cushing syndrome → ACTH production
  • Eaton-Lambert myasthenic syndrome (proximal muscle weakness - autoantibodies against voltage-gated Ca²⁺ channels)

4. Large Cell Carcinoma

• Location: Peripheral
• Diagnosis of exclusion - undifferentiated, cannot classify as above
• Large cells with prominent nucleoli, no squamous/glandular/neuroendocrine differentiation
• Very poor prognosis

Key Comparison Table

Special Presentations

• Pancoast tumor: Apex of lung → invades brachial plexus, cervical sympathetics → Horner's syndrome (ptosis, miosis, anhidrosis) + arm pain
• SVC syndrome: Central tumor compresses SVC → facial swelling, arm swelling, venous distension of neck
• Hoarseness: Left recurrent laryngeal nerve compression
• Phrenic nerve palsy: Elevated hemidiaphragm

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PART 9: PLEURAL LESIONS

9A. PLEURAL EFFUSION & PLEURITIS

9B. MALIGNANT MESOTHELIOMA

• Rare, highly aggressive malignancy of pleural mesothelial cells
• Strongly associated with asbestos exposure (especially amphibole/crocidolite fibers)
• Latent period: 20-50 years after exposure
• Diffuse mesothelioma - spreads along pleural surface, encasing the lung ("rind-like")
• Morphology: Biphasic pattern - epithelioid cells + sarcomatoid cells
  • Epithelioid type - better prognosis
  • Mesothelial cells form tubular/papillary structures
• IHC: Positive for calretinin, WT-1, D2-40, CK5/6 (distinguishes from adenocarcinoma which is CEA, TTF-1 positive)
• Prognosis: Very poor, median survival < 1 year

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PART 10: GRANULOMATOUS LUNG DISEASES

Sarcoidosis

Hypersensitivity Pneumonitis (Extrinsic Allergic Alveolitis)

• Immunologically-mediated (mixed Type III + Type IV)
• Triggered by repeated inhalation of organic dusts (antigens)
• Examples:
  • Farmer's lung - Thermophilic actinomycetes in moldy hay
  • Bird fancier's lung - Avian proteins
  • Air conditioner lung - Thermophilic bacteria in humid air
• Morphology: Interstitial inflammation, non-caseating granulomas, organizing pneumonia
• Clinical: Fever, dyspnea, cough 4-8 hours after exposure; resolves with antigen avoidance

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QUICK SUMMARY: KEY EXAM FACTS

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What's Covered (10 Complete Topics)

1. Atelectasis - All 5 types with mechanisms
2. ARDS - Pathogenesis, acute vs healing phase morphology, hyaline membranes
3. Obstructive Lung Diseases - Full table comparison + detailed individual topics:
   • Emphysema (all 4 types, protease-antiprotease mechanism)
   • Chronic Bronchitis (Reid index, blue bloater)
   • Asthma (all types, IgE mechanism, Curschmann spirals, Charcot-Leyden crystals, subepithelial fibrosis)
   • Bronchiectasis (vicious circle, causes including cystic fibrosis, Kartagener)
4. Pneumonia - Lobar (4 stages with table), Bronchopneumonia, Atypical, Lung Abscess
5. Tuberculosis - Primary (Ghon complex), Secondary (reactivation, cavitation, complications), Miliary TB
6. Interstitial Lung Diseases - IPF/UIP, Sarcoidosis, Pneumoconioses (Coal, Silicosis, Asbestosis with all key associations)
7. Pulmonary Vascular Disease - PE (causes, types, infarction) + Pulmonary Hypertension (plexiform lesions)
8. Lung Tumors - All 4 carcinoma types with full comparison table, paraneoplastic syndromes, Pancoast tumor, SVC syndrome
9. Pleural Lesions - Effusion types, Mesothelioma (asbestos link, IHC markers)
10. Granulomatous Diseases - Sarcoidosis, Hypersensitivity pneumonitis