Pathology
MBBS Pathology — high-yield long questions and short notes from Robbins & Cotran and Harsh Mohan, covering general pathology (cell injury, inflammation, haemodynamics, immunopathology, neoplasia), haematology, and systemic pathology of the cardiovascular, respiratory, GI, hepatobiliary, renal, endocrine and other systems, written to the marks with definitions, mechanisms, morphology, classification, clinical correlation and pearls.
12chapters144questions99High-Yield
Definition
COPD is chronic, progressive, largely irreversible airflow limitation comprising chronic bronchitis and emphysema.
Chronic Bronchitis
- Clinical definition: productive cough for 3 months in 2 consecutive years
- Mucous gland hyperplasia — ↑ Reid index (>0.4)
- Goblet cell hyperplasia, squamous metaplasia, loss of cilia
- ‘Blue bloater’ — cyanosis, cor pulmonale, hypoxia
Emphysema
- Anatomical definition: permanent dilatation of airspaces distal to terminal bronchioles with destruction of walls, without fibrosis
- Centriacinar — smoking, upper lobes; panacinar — α₁-antitrypsin deficiency, lower lobes
- Protease-antiprotease imbalance
- ‘Pink puffer’ — barrel chest, pursed-lip breathing
Chronic irritation drives both mucus excess and alveolar destruction. Feature Bronchitis Emphysema Type Blue bloater Pink puffer Cough Prominent Slight Cor pulmonale Early Late Applied
- Spirometry: ↓ FEV₁/FVC ratio (<0.7)
- Smoking cessation is the only measure that slows progression
🔑KEY POINTS TO REMEMBER- COPD = chronic bronchitis (clinical) + emphysema (anatomical).
- Reid index >0.4 in bronchitis; protease-antiprotease imbalance in emphysema.
- Centriacinar from smoking; panacinar from α₁-antitrypsin deficiency.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Pneumonia is inflammation of the lung parenchyma with consolidation of alveolar spaces by inflammatory exudate.
Classification
- Anatomical — lobar, bronchopneumonia (lobular), interstitial
- Clinical — community-acquired, hospital-acquired, aspiration, in immunocompromised
- Organisms: S. pneumoniae (commonest), Klebsiella, Staphylococcus, Mycoplasma, viruses
Stages of Lobar Pneumonia
- Congestion (1–2 days) — heavy, red, vascular engorgement
- Red hepatisation (2–4 days) — liver-like; red cells, fibrin, neutrophils
- Grey hepatisation (4–6 days) — red cells lysed, grey-brown, fibrinopurulent
- Resolution (8–10 days) — enzymatic digestion, restoration of architecture
Lobar pneumonia progresses through four well-defined stages. Stage Appearance Congestion Red, heavy Red hepatisation Liver-like, red Grey hepatisation Grey-brown Applied
- Complications: lung abscess, empyema, pleurisy, septicaemia, organisation
- Resolution is usually complete in lobar pneumonia
🔑KEY POINTS TO REMEMBER- Pneumonia = alveolar consolidation; lobar, bronchopneumonia or interstitial.
- S. pneumoniae is the commonest cause.
- Four stages: congestion, red hepatisation, grey hepatisation, resolution.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Pulmonary tuberculosis is chronic granulomatous infection by Mycobacterium tuberculosis, spread by inhaled droplet nuclei.
Primary Tuberculosis
- First exposure, usually in children
- Ghon focus — subpleural lesion in the lower part of upper lobe or upper part of lower lobe
- Ghon complex = Ghon focus + draining hilar lymph nodes
- Usually heals by fibrosis and calcification
- May progress → miliary tuberculosis or progressive primary disease
Secondary (Post-Primary) Tuberculosis
- Reactivation or reinfection in a sensitised host
- Apex of upper lobe — highest oxygen tension
- Cavitation is characteristic; caseous necrosis
- Clinical: chronic cough, haemoptysis, evening fever, night sweats, weight loss
- Spread: bronchial, lymphatic, haematogenous (miliary), direct
Prior sensitisation converts a walled-off focus into destructive cavitation. Feature Primary Secondary Site Mid/lower zone Apex Age Children Adults Cavitation Rare Typical Applied
- Diagnosis: sputum AFB (ZN stain), CBNAAT, culture, chest X-ray
- Treatment: HRZE under DOTS
🔑KEY POINTS TO REMEMBER- Primary TB: Ghon complex (focus + hilar nodes) in children.
- Secondary TB: apical cavitating disease in sensitised adults.
- Caseating granuloma is the hallmark; diagnosed by AFB and CBNAAT.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Lung carcinoma (bronchogenic carcinoma) is the commonest cause of cancer death worldwide, strongly linked to cigarette smoking.
Types
- Squamous cell carcinoma — central, strongest smoking link; keratin pearls; PTH-related peptide → hypercalcaemia
- Adenocarcinoma — peripheral, commonest overall and in non-smokers and women; EGFR mutations
- Small cell carcinoma — central, highly malignant, early metastasis; neuroendocrine; SIADH and ectopic ACTH; not surgically treated
- Large cell carcinoma — undifferentiated
Clinical Features & Spread
- Cough, haemoptysis, chest pain, weight loss, recurrent pneumonia
- Pancoast tumour — apical; Horner syndrome, brachial plexus involvement
- Superior vena cava syndrome; hoarseness (recurrent laryngeal nerve)
- Metastasis: brain, bone, liver, adrenal
- Paraneoplastic syndromes are common
Chronic smoke injury drives a metaplasia-dysplasia-carcinoma sequence. Type Site Association Squamous Central Hypercalcaemia Adenocarcinoma Peripheral Non-smokers Small cell Central SIADH, ACTH Applied
- Small cell is treated by chemotherapy; non-small cell may be resectable
- EGFR/ALK testing guides targeted therapy in adenocarcinoma
🔑KEY POINTS TO REMEMBER- Squamous (central, hypercalcaemia) and small cell (central, SIADH/ACTH) are smoking-related.
- Adenocarcinoma is peripheral and commonest in non-smokers and women.
- Small cell carcinoma is not treated surgically.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Bronchial asthma is a chronic inflammatory airway disorder with reversible bronchoconstriction and airway hyper-responsiveness.
Types & Mechanism
- Extrinsic (atopic) — Type I IgE-mediated; childhood; family history; raised IgE and eosinophils
- Intrinsic (non-atopic) — adults; triggered by infection, exercise, cold, drugs, stress
- Aspirin-induced, occupational, drug-induced
- Early phase — mast cell mediators (histamine, leukotrienes) → bronchospasm
- Late phase — eosinophils and cytokines → mucosal oedema and mucus
Pathology
- Airway smooth muscle hypertrophy, thickened basement membrane
- Goblet cell hyperplasia and mucus plugging
- Eosinophilic infiltration
- Curschmann spirals (mucus casts), Charcot-Leyden crystals (eosinophil membrane protein), Creola bodies
Reversibility distinguishes asthma from COPD. Finding Significance Curschmann spirals Mucus plugs Charcot-Leyden crystals Eosinophils Basement membrane Thickened Applied
- Status asthmaticus — severe unremitting attack, may be fatal
- Treatment: inhaled β₂ agonists (reliever) and corticosteroids (controller)
🔑KEY POINTS TO REMEMBER- Asthma = chronic inflammation with reversible bronchoconstriction.
- Extrinsic (IgE, atopic) and intrinsic (non-atopic) types.
- Curschmann spirals and Charcot-Leyden crystals are characteristic.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Emphysema is permanent abnormal dilatation of airspaces distal to the terminal bronchiole with destruction of alveolar walls and no fibrosis.
Types
- Centriacinar (centrilobular) — commonest; smokers; upper lobes; respiratory bronchioles affected
- Panacinar — α₁-antitrypsin deficiency; lower lobes; whole acinus
- Paraseptal (distal acinar) — subpleural; causes spontaneous pneumothorax in young adults
- Irregular — around scars (commonest incidental type)
Pathogenesis & Features
- Protease-antiprotease imbalance — neutrophil elastase unopposed
- Oxidant-antioxidant imbalance from smoke
- Loss of elastic recoil → small airway collapse on expiration
- ‘Pink puffer’ — dyspnoea, barrel chest, pursed-lip breathing, weight loss
- Complications: bullae, pneumothorax, cor pulmonale, respiratory failure
Unopposed elastase digests the alveolar walls. Type Region Cause Centriacinar Upper lobe Smoking Panacinar Lower lobe α₁-antitrypsin Paraseptal Subpleural Pneumothorax Applied
- Chest X-ray: hyperinflation, flattened diaphragm, ↓ vascular markings
- Panacinar emphysema in a young non-smoker suggests α₁-antitrypsin deficiency
🔑KEY POINTS TO REMEMBER- Emphysema is airspace dilatation with wall destruction, no fibrosis.
- Centriacinar (smoking, upper lobe) vs panacinar (α₁-antitrypsin, lower lobe).
- Protease-antiprotease imbalance is the central mechanism.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Lobar pneumonia consolidates an entire lobe, while bronchopneumonia produces patchy consolidation centred on bronchioles.
Lobar Pneumonia
- Healthy young adults; S. pneumoniae in over 90%
- Uniform consolidation of a whole lobe
- Passes through four stages; complete resolution usual
- Bronchi relatively spared
Bronchopneumonia (lobular)
- Extremes of age, debilitated, bedridden, post-operative patients
- Multiple organisms: Staphylococcus, Klebsiella, H. influenzae, Pseudomonas
- Patchy, bilateral consolidation, especially basal and posterior
- Centred on bronchioles; no defined stages
- Often heals with fibrosis; complications commoner
Host health determines which pattern of consolidation develops. Feature Lobar Bronchopneumonia Age Young adults Extremes of age Distribution Whole lobe Patchy, bilateral Resolution Complete Often fibrosis Applied
- Bronchopneumonia is often a terminal event in chronically ill patients
- Lobar pneumonia responds well to antibiotics
🔑KEY POINTS TO REMEMBER- Lobar pneumonia: whole lobe, young adults, S. pneumoniae, four stages, resolves.
- Bronchopneumonia: patchy and bilateral, extremes of age, multiple organisms.
- Bronchopneumonia commonly heals with fibrosis.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
The Ghon complex is the characteristic lesion of primary pulmonary tuberculosis, comprising the parenchymal focus and its draining lymph nodes.
Components
- Ghon focus — 1–1.5 cm subpleural caseating granuloma
- Situated in the lower part of the upper lobe or upper part of the lower lobe (best ventilated areas)
- Lymphangitis — involved draining lymphatics
- Hilar/mediastinal lymphadenitis — caseating nodes, often larger than the focus
- Ghon focus + nodes = Ghon complex (primary complex)
Fate
- Healing by fibrosis and calcification — usual outcome (Ranke complex)
- Bacilli may remain dormant → later reactivation
- Progressive primary tuberculosis in malnourished or immunosuppressed children
- Haematogenous spread → miliary tuberculosis
- Rupture into a bronchus or pleura
The primary complex usually heals but may leave dormant bacilli. Component Detail Ghon focus Subpleural granuloma Nodes Hilar caseation Healed form Ranke complex Applied
- Calcified Ghon complex is often an incidental chest X-ray finding
- Indicates past primary infection, not active disease
🔑KEY POINTS TO REMEMBER- Ghon complex = subpleural Ghon focus + draining hilar lymph nodes.
- Occurs in primary tuberculosis, typically in children.
- Usually heals by calcification (Ranke complex) but may reactivate.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Bronchiectasis is permanent, abnormal dilatation of bronchi and bronchioles caused by destruction of their muscular and elastic walls.
Causes
- Post-infective — childhood measles, whooping cough, tuberculosis, necrotising pneumonia
- Bronchial obstruction — tumour, foreign body, mucus plug
- Cystic fibrosis — thick secretions
- Kartagener syndrome — bronchiectasis + situs inversus + sinusitis; ciliary dyskinesia
- Allergic bronchopulmonary aspergillosis, immunodeficiency
Features & Complications
- Chronic cough with copious foul-smelling purulent sputum
- Three-layered sputum on standing; haemoptysis, clubbing
- Coarse crepitations; recurrent infections
- Usually lower lobes, bilateral
- Complications: lung abscess, empyema, amyloidosis, cor pulmonale, brain abscess
A vicious cycle of infection and destruction sustains the disease. Feature Detail Sputum Copious, foul, 3 layers Sign Clubbing Investigation HRCT (signet-ring sign) Applied
- HRCT is the investigation of choice
- Management: postural drainage, physiotherapy, antibiotics
🔑KEY POINTS TO REMEMBER- Bronchiectasis = permanent bronchial dilatation from wall destruction.
- Causes: post-infective, obstruction, cystic fibrosis, Kartagener syndrome.
- Copious foul sputum with clubbing; diagnosed by HRCT.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Pulmonary embolism is occlusion of the pulmonary arterial tree by an embolus, most often a thrombus from the deep veins of the leg.
Source & Risk Factors
- Over 95% arise from deep veins of the lower limb (popliteal, femoral, iliac)
- Risk: prolonged immobilisation, surgery (especially orthopaedic), fracture, malignancy, pregnancy, oral contraceptives, cardiac failure, thrombophilia
- Virchow triad operates
Consequences
- Massive (saddle) embolus — straddles bifurcation → sudden death, acute right heart failure
- Medium embolus → haemorrhagic (red) infarct if circulation already compromised; pleuritic pain, haemoptysis
- Small recurrent emboli → pulmonary hypertension and cor pulmonale
- Most small emboli resolve without infarction (dual blood supply)
- Diagnosis: CT pulmonary angiography, D-dimer, ECG (S1Q3T3)
Embolus size determines whether the outcome is silent or fatal. Size Effect Massive Sudden death Medium Haemorrhagic infarct Small recurrent Pulmonary hypertension Applied
- Prevention: early mobilisation, heparin prophylaxis, compression stockings
- Lung infarct is red because of dual blood supply
🔑KEY POINTS TO REMEMBER- Over 95% of pulmonary emboli arise from deep leg veins.
- Saddle embolus causes sudden death; medium emboli cause haemorrhagic infarcts.
- Recurrent small emboli lead to pulmonary hypertension and cor pulmonale.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Pneumoconioses are chronic interstitial lung diseases caused by inhalation of mineral dusts, usually occupational.
Main Types
- Silicosis — silica (mining, stone cutting, sandblasting); silicotic nodules, eggshell calcification of hilar nodes; ↑↑ tuberculosis risk (silicotuberculosis)
- Coal worker’s pneumoconiosis — anthracosis → simple → progressive massive fibrosis; Caplan syndrome with rheumatoid arthritis
- Asbestosis — shipbuilding, insulation; ferruginous bodies, pleural plaques, lower lobe fibrosis; bronchogenic carcinoma and mesothelioma
- Berylliosis — non-caseating granulomas resembling sarcoidosis
Pathogenesis & Features
- Particles 1–5 μm reach alveoli and are engulfed by macrophages
- Macrophage activation → cytokines → progressive fibrosis
- Restrictive lung disease: dyspnoea, ↓ lung volumes, cor pulmonale
- Irreversible; management is preventive
Macrophages that cannot digest the dust drive relentless fibrosis. Disease Hallmark Silicosis Eggshell calcification Coal worker Progressive massive fibrosis Asbestosis Ferruginous bodies, mesothelioma Applied
- Silicosis markedly increases tuberculosis risk — screen these workers
- Prevention: dust control, ventilation, protective masks
🔑KEY POINTS TO REMEMBER- Pneumoconioses follow inhalation of dust particles 1–5 μm.
- Silicosis predisposes to tuberculosis; asbestosis to mesothelioma.
- Coal worker's disease may progress to massive fibrosis (Caplan syndrome).
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.Definition
Acute (adult) respiratory distress syndrome (ARDS) is acute diffuse alveolar damage causing refractory hypoxaemia and non-cardiogenic pulmonary oedema.
Causes & Pathogenesis
- Sepsis (commonest), severe trauma, shock, aspiration, pancreatitis, burns, transfusion, drugs, near-drowning
- Neutrophil activation → proteases and free radicals
- Endothelial and alveolar epithelial damage → ↑ permeability
- Protein-rich exudate + surfactant loss → hyaline membranes and alveolar collapse
Features & Diagnosis
- Rapid onset within 24–72 hours of the insult
- Severe dyspnoea and refractory hypoxaemia (poorly responsive to oxygen)
- Chest X-ray: bilateral diffuse infiltrates (white-out lungs)
- Normal pulmonary capillary wedge pressure — excludes cardiac failure
- Pathology: diffuse alveolar damage with hyaline membranes; later fibrosis
Alveolar-capillary barrier failure floods the alveoli with protein-rich fluid. Feature ARDS Cardiac oedema Wedge pressure Normal Raised Onset 24–72 h Variable Response to O₂ Poor Better Applied
- Management: treat the cause, lung-protective ventilation with low tidal volume and PEEP
- Mortality remains high (about 40%)
🔑KEY POINTS TO REMEMBER- ARDS = diffuse alveolar damage with hyaline membranes.
- Sepsis is the commonest cause; hypoxaemia is refractory to oxygen.
- Normal wedge pressure distinguishes it from cardiogenic oedema.
📚SOURCES: Robbins & Cotran Pathologic Basis of Disease; Textbook of Pathology (Harsh Mohan); Robbins Basic Pathology.