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Ghon's Complex — Full Details for MD Examination (15 Marks)

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1. DEFINITION

1. Ghon focus — a 1–1.5 cm area of gray-white caseous consolidation in the lung parenchyma
2. Regional lymph node involvement — caseous necrosis of the draining hilar/tracheobronchial lymph nodes, connected to the Ghon focus by a lymphangitic streak

The combination of the parenchymal lung lesion + draining lymph node involvement = Ghon complex (also called the Primary complex or Ranke complex when calcified).

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2. CAUSATIVE ORGANISM

• Mycobacterium tuberculosis (primary pathogen)
• Rarely: M. bovis (from unpasteurized milk) — produces a similar primary complex in the intestine (mesenteric lymph node + intestinal Ghon focus) or tonsil

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3. SITE OF THE GHON FOCUS

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4. PATHOGENESIS — HOW GHON'S COMPLEX FORMS

Stage 1: Initial Infection (Days 1–3)

• Inhaled bacilli (droplet nuclei, 1–5 µm) reach alveoli
• Engulfed by alveolar macrophages, but mycobacteria resist killing by:
  • Inhibiting phagolysosome fusion
  • Scavenging reactive oxygen intermediates
  • Producing lipoarabinomannan (LAM)
• Bacteria multiply within macrophages → macrophage death → local inflammatory exudate

Stage 2: Early Bacillemia (Weeks 1–3)

• Bacilli (free or within phagocytes) drain via lymphatics to regional hilar lymph nodes
• Hematogenous seeding of distant organs (bones, kidneys, meninges, liver, spleen) — clinically silent at this stage
• No cell-mediated immunity yet → no effective killing

Stage 3: Sensitization & Cell-Mediated Immunity (Weeks 3–8)

• Mycobacterial antigens processed by dendritic cells → presented to CD4+ T cells in draining lymph nodes
• IL-12 (from macrophages) drives differentiation into Th1 subset
• Th1 cells secrete IFN-γ → activates macrophages → release:
  • TNF (monocyte recruitment)
  • iNOS → nitric oxide (bactericidal)
  • Antimicrobial peptides (defensins)
• Activated macrophages differentiate into epithelioid histiocytes → fuse to form Langhans giant cells → form granulomas

Stage 4: Granuloma Formation & Caseous Necrosis

• Classic caseating granuloma = central caseous necrosis surrounded by:
  • Epithelioid macrophages
  • Langhans giant cells (nuclei arranged in horseshoe/ring pattern)
  • Peripheral rim of CD4+ lymphocytes
  • Fibroblastic capsule
• In the lung → Ghon focus; in lymph nodes → caseating lymphadenopathy

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5. GROSS MORPHOLOGY

• Ghon focus: 1–1.5 cm, gray-white, firm, subpleural consolidation; center undergoes caseous necrosis (cheese-like, amorphous, acellular material)
• Lymph node: Enlarged hilar/tracheobronchial nodes with caseous necrosis
• Lymphangitic streak: Visible inflammatory track connecting focus to lymph node

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6. HISTOLOGY

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7. FATE OF GHON'S COMPLEX (Most Important for Exams)

A. HEALING / RESOLUTION (Most Common — 95%)

• Granulomas undergo progressive fibrosis
• Followed by dystrophic calcification (calcium deposits in the caseous necrotic material)
• The calcified lesion is visible on chest X-ray as a calcified mid-lung nodule ± calcified hilar nodes
• When calcification of both the Ghon focus and hilar nodes is visible radiographically → called the Ranke complex
• Bacilli may remain viable (dormant) within the fibrocalcific lesion for decades → latent TB
• Tuberculin skin test (Mantoux) / IGRA converts to positive (indicating sensitization)

Goldman-Cecil Medicine (p. 3251): "The Ghon complex may leave a calcified Ghon lesion in the mid-lung fields or calcified hilar nodes; when found together this is referred to as the Ranke complex."

B. LATENT TUBERCULOSIS INFECTION (LTBI)

• Organisms remain dormant; immune system keeps them in check
• No symptoms, non-infectious
• Positive Mantoux / IGRA
• May reactivate decades later if immunity wanes (secondary/post-primary TB)
• Risk factors for reactivation: HIV, malnutrition, diabetes, immunosuppressive drugs (especially anti-TNF agents), renal failure, malignancy

C. PROGRESSIVE PRIMARY TUBERCULOSIS (~5%)

• Children (immature immunity)
• Elderly
• HIV-positive (especially CD4 < 200 cells/µL)
• Severely malnourished
• Other immunocompromised states

• No granuloma formation (absent or poorly formed)
• Macrophages contain massive numbers of bacilli
• Resembles acute bacterial lobar pneumonia — lobe consolidation + hilar lymphadenopathy + pleural effusion
• Enlarged lymph nodes can cause bronchial compression → lobar/segmental collapse (epecially middle/upper lobe)
• May progress to miliary TB or TB meningitis

D. REACTIVATION / SECONDARY (POST-PRIMARY) TB

• Dormant bacilli in the Ghon focus or seeded organs reactivate months to years later
• Typically involves the apical segments of upper lobes (high O₂ tension)
• Features: cavitation, fibrosis, bronchogenic spread
• Regional lymph node involvement is less prominent than in primary TB (because pre-existing hypersensitivity mounts rapid response)
• Presents with: cough, hemoptysis, weight loss, night sweats, low-grade fever

E. HEMATOGENOUS DISSEMINATION → MILIARY TB

• During the first few weeks of primary infection, hematogenous spread seeds distant organs
• In 95%, this is controlled; in others (immunocompromised), leads to:
  • Miliary TB: 2-mm yellow-white foci scattered throughout lungs, liver, spleen (resembling millet seeds)
  • TB meningitis
  • TB of bones (Pott's disease — vertebral TB), joints, kidneys, adrenals, etc.
• Can occur from progressive primary TB or secondary TB

F. ENDOGENOUS REINFECTION / LYMPH NODE COMPLICATIONS

• Caseous lymph nodes may rupture into bronchus → endobronchial TB
• Rupture into adjacent structures → sinus formation
• Epituberculosis (in children): enlarged hilar nodes compress adjacent bronchus → lobar collapse/consolidation

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8. SUMMARY TABLE — FATE OF GHON'S COMPLEX

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9. RADIOLOGICAL FEATURES

A transient pleural effusion may develop in primary TB (Goldman-Cecil, p. 3251).

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10. IMMUNOLOGICAL SIGNIFICANCE

• The Ghon complex represents the intersection of innate and adaptive immunity in TB
• Tuberculin skin test (Mantoux) converts to positive 3–8 weeks after primary infection — marks the development of CMI
• False-negative Mantoux may occur in: active TB disease, HIV, malnutrition, sarcoidosis, viral infections, Hodgkin lymphoma, immunosuppression
• False-positive Mantoux: prior BCG vaccination, atypical mycobacteria
• IFN-γ release assays (IGRAs): more specific; not affected by BCG; preferred in BCG-vaccinated populations

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11. DIFFERENCES: PRIMARY vs. SECONDARY TB

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12. KEY EPONYMOUS TERMS (Frequently Asked)

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KEY POINTS FOR EXAM

1. Ghon complex = Ghon focus + regional lymph node caseous necrosis
2. Location: lower part of upper lobe or upper part of lower lobe, subpleural
3. Fate in 95%: fibrosis → calcification → Ranke complex (latent TB)
4. Fate in 5%: progressive primary TB (children, immunocompromised, HIV)
5. Histology: caseating granuloma with epithelioid macrophages, Langhans giant cells, lymphocytes
6. Immunocompromised → no granulomas, sheets of macrophages loaded with bacilli
7. Hematogenous seeding during primary infection → Simon foci (apical) → later reactivation
8. Mantoux converts positive 3–8 weeks after primary infection
9. Miliary TB = uncontrolled hematogenous dissemination
10. Ghon complex is the sine qua non of primary TB — distinguishes it from secondary TB

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• Robbins, Cotran & Kumar Pathologic Basis of Disease (10th ed.), pp. 352–356
• Robbins & Kumar Basic Pathology (11th ed.), pp. 474–478
• Goldman-Cecil Medicine, pp. 3250–3252