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Pulmonary Tuberculosis - Radiology PG High-Yield Answer

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CLASSIFICATION OF PULMONARY TB (Radiological Perspective)

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1. PRIMARY TUBERCULOSIS - Radiological Features

Chest X-Ray Findings

• Ghon focus: Focal parenchymal opacity, typically middle or lower lung zone (subpleural)
• Hilar/mediastinal lymphadenopathy: Ipsilateral hilar enlargement is characteristic (right > left)
• Pleural effusion: May be present on the affected side
• Combination of parenchymal opacity + lymphadenopathy = Ghon complex (or primary complex)
• Atelectasis may occur if enlarged nodes compress adjacent bronchi

CT Findings in Primary TB

• Ghon focus: Focal parenchymal opacity with ipsilateral lymphadenopathy
• CT clearly demonstrates lymph node enlargement (more sensitive than CXR)
• Central necrosis in nodes appears as low-density center with rim enhancement
• Air bronchograms visible in areas of consolidation

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2. REACTIVATION (POST-PRIMARY) TUBERCULOSIS

Classic Radiological Features - "The Upper Lobe Disease"

1. Apical and posterior segments of RIGHT upper lobe (most common)
2. Apical-posterior segment of LEFT upper lobe
3. Superior segments of lower lobes (less common)

Key rule: Anterior segments of upper lobes are rarely involved in reactivation TB - this is a classic exam point.

CXR Pattern Progression

Cavitation in Reactivation TB

• Cavities form by liquefaction necrosis and drainage into airways
• Typically thick-walled initially, thin-walled in chronic/healed state
• Air-fluid levels may be present (superimposed infection)
• Rasmussen aneurysm: Dilated vessels in cavity wall - cause of hemoptysis
• Aspergilloma (fungus ball) may colonize old cavities - "crescent sign" / air crescent sign

CT Features of Reactivation TB (HIGH YIELD)

• Tree-in-bud pattern: Centrilobular nodules with branching linear densities = bronchogenic spread (HIGHLY specific sign)
• Nodular opacities in upper lobes
• Cavities with thick or thin walls
• Air bronchograms within consolidation
• CT is superior to CXR: sensitivity 96% vs 48% for active TB
• CT better demonstrates bronchogenic spread characteristic of reactivation TB

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3. MILIARY TUBERCULOSIS (10-Mark Answer)

Definition and Pathogenesis

• The term "miliary" comes from the resemblance of lesions to millet seeds
• Results from hematogenous dissemination of M. tuberculosis
• Occurs when a tuberculous focus (primary or reactivation) erodes into a blood vessel or lymphatic, seeding the entire pulmonary vasculature simultaneously
• Grossly: 1-2 mm yellowish nodules that are granulomas on histology
• Can occur in both primary and reactivation settings; more common in immunocompromised

Classic CXR Features of Miliary TB

• CXR abnormal in 85-90% of miliary TB cases at diagnosis
• Classic miliary pattern seen in 50-90% of disseminated TB patients
• Nodules appear 2-3 weeks after hematogenous seeding (CXR may initially be normal!)

CT Features of Miliary TB

• Random distribution (not perilymphatic, not centrilobular) - this is the KEY CT pattern
• Nodules 1-3 mm, bilateral, diffuse
• Equal distribution in upper, middle, and lower zones
• Nodules are distributed randomly relative to secondary pulmonary lobule structures
• No zonal predilection - unlike reactivation TB which favors upper zones
• May see ground-glass opacity surrounding nodules ("halo sign")
• Additional findings: upper lobe opacities with/without cavitation, pleural effusion, pericardial effusion

CT Nodule Distribution Patterns - PG Exam Comparison Table

Exam Tip: Miliary TB = RANDOM distribution. This is THE classic teaching point separating it from sarcoidosis (perilymphatic) and endobronchial TB (centrilobular tree-in-bud).

Atypical Presentations (in HIV/Immunosuppression)

• CXR may appear normal early in disease
• Granuloma formation is impaired; instead of discrete nodules, may show diffuse uniform opacification
• Intrathoracic lymphadenopathy more prominent (unlike immunocompetent patients)
• Cavitation less common with advanced HIV (CD4 < 200)
• Lower lobe/diffuse opacities instead of upper lobe predominance
• Pattern may resemble lobar pneumonia (Klebsiella-like appearance)

Miliary TB - Differential Diagnosis

Organs Involved in Miliary TB (Autopsy Data)

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4. TB-RELATED COMPLICATIONS - Radiological Findings

Pleural TB

• Unilateral exudative pleural effusion (lymphocyte predominant)
• Rarely bilateral; rarely large
• Empyema necessitans - TB empyema eroding through chest wall
• Bronchopleural fistula with hydropneumothorax

Endobronchial TB

• Bronchial stenosis leading to lobar/segmental atelectasis
• Obstructive pneumonitis distal to stenosis
• Air trapping on expiratory CT

Bronchogenic Spread

• Tree-in-bud pattern on CT: centrilobular branching opacities
• Ill-defined centrilobular nodules
• Patchy consolidation in dependent portions of lung
• Sign of active, highly infectious disease

Calcified Ghon Complex / Ranke Complex

• Calcified Ghon focus + calcified ipsilateral hilar node = Ranke complex
• Indicates healed primary TB

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5. TB IN HIV - Radiological Spectrum (High-Yield Table)

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6. IMAGING MODALITY COMPARISON

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QUICK-FIRE HIGH-YIELD POINTS FOR PG EXAM

1. Primary TB: Lower/mid zone opacity + ipsilateral hilar adenopathy
2. Reactivation TB: Apical and posterior segments of RUL (most common site)
3. Anterior segment of upper lobe is spared in TB (unlike most other conditions)
4. Miliary TB: 1-3 mm nodules, bilateral, symmetric, RANDOM distribution, all zones equal
5. Tree-in-bud = bronchogenic spread = centrilobular distribution = active endobronchial TB
6. Ranke complex = calcified Ghon focus + calcified hilar node = healed primary TB
7. Rasmussen aneurysm: Dilated vessel in cavity wall - cause of massive hemoptysis
8. Aspergilloma in old TB cavity: "crescent sign" (Monod sign)
9. HIV + TB: More adenopathy, less cavitation, more lower zone/diffuse disease
10. CXR may be normal in miliary TB for first 2-3 weeks (nodules too small)
11. CT has 96% sensitivity vs 48% for CXR in active TB
12. Miliary TB = RANDOM nodule pattern (differential: sarcoid = perilymphatic)
13. 85-90% of miliary TB patients have abnormal CXR at diagnosis
14. Snowstorm appearance on CXR = miliary TB

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