Pulmonary Tuberculosis Radiology

Tuberculosis remains one of the most heavily examined topics in NEET PG Radiology, because its imaging spectrum is wide, age-dependent, and overlaps with malignancy and other infections. This note organises the radiological appearances of primary and post-primary TB, the named lesions (Ghon, Ranke, Assmann, Simon), HRCT signs, and the high-yield differentials.

Definition & Why Radiology Matters

Pulmonary tuberculosis is infection of the lung parenchyma by Mycobacterium tuberculosis. Imaging is central because (a) chest radiograph remains the first-line screening tool, (b) the pattern reliably predicts whether disease is primary (first exposure, usually paediatric) or post-primary/reactivation (adult), and (c) certain patterns (cavitation, miliary, tree-in-bud) directly imply active, potentially infectious disease. The single most consistently tested fact is the anatomical distribution difference between the two forms.

High-yield: Primary TB favours the lower and middle zones with lymphadenopathy; post-primary (reactivation) TB favours the apical and posterior segments of the upper lobes and the superior segment of the lower lobe, with cavitation and without prominent nodes.

Classification: Primary vs Post-Primary

The classic Ranke division underlies almost every TB radiology question.

Feature	Primary TB	Post-primary (reactivation) TB
Typical age	Children, immunocompromised	Adolescents & adults
Zone predilection	Lower & middle lobes, any zone	Apical/posterior upper lobe, superior segment lower lobe
Lymphadenopathy	Hallmark — hilar/right paratracheal	Usually absent
Cavitation	Uncommon	Common
Pleural effusion	Common (esp. adolescents)	Less common
Consolidation	Homogeneous, lobar/segmental	Patchy, fibronodular
Healing pattern	Ranke complex, Ghon focus	Fibrosis, traction, upper-lobe volume loss
Infectivity	Lower	Higher (open cavities shed bacilli)

High-yield: A right paratracheal + right hilar nodal mass with lower-lobe consolidation in a child = primary TB until proven otherwise. Nodes are typically unilateral and right-sided.

Named Lesions & Eponyms (exam goldmine)

• Ghon focus — the initial subpleural parenchymal granuloma of primary infection, usually in the mid/lower zone (well-aerated regions receiving most inhaled bacilli).
• Ghon complex — Ghon focus + draining lymphadenitis (hilar/mediastinal nodes).
• Ranke complex — the healed, calcified Ghon complex: calcified parenchymal nodule + calcified hilar node. Indicates old, healed primary TB.
• Simon focus — apical nodular focus seeded haematogenously during primary infection; the future site of reactivation.
• Assmann focus (infraclavicular infiltrate) — early subapical reactivation infiltrate.
• Rasmussen aneurysm — pseudoaneurysm of a pulmonary artery branch within a TB cavity; classic cause of life-threatening haemoptysis.
• Puttuti / tuberculoma — rounded granuloma, often with central or laminated calcification and satellite nodules.

High-yield: Ranke complex = healed/calcified; Ghon complex = active/recent. This distinction is a repeated one-liner MCQ.

Mnemonic — "GRASS" for primary-TB eponyms: Ghon focus, Ranke (healed), Assmann (reactivation infiltrate), Simon focus (apex seeding), Satellite nodules (tuberculoma).

Radiographic Spectrum

Primary TB

1. Parenchymal consolidation — dense, homogeneous, segmental/lobar; any lobe but lower-zone predominance. Often resolves slowly.
2. Lymphadenopathy — most reliable sign in children; right paratracheal and hilar; nodes may show low-attenuation centres with rim enhancement on CT (caseation).
3. Pleural effusion — usually unilateral, from subpleural focus rupture; common in adolescents.
4. Miliary spread — haematogenous dissemination (see below).
5. Healing — Ghon focus → calcified nodule; complex → Ranke.

Post-Primary TB

1. Patchy/confluent consolidation in apical-posterior segments.
2. Cavitation — thick or thin-walled; the radiological marker of activity and infectivity.
3. Fibrocavitary disease — fibrosis, upper-lobe volume loss, hilar elevation, tracheal deviation, compensatory lower-lobe hyperinflation.
4. Bronchogenic spread — endobronchial seeding producing ill-defined acinar nodules distant from the cavity.
5. Tuberculoma — rounded mass, calcification, satellite lesions.

High-yield: Upper-lobe cavitation with fibrosis and apical volume loss in an adult is the textbook post-primary picture. Elevation of hila and tracheal/mediastinal shift toward the diseased side indicate fibrotic volume loss.

Miliary Tuberculosis

Haematogenous dissemination producing innumerable 1–3 mm nodules uniformly distributed throughout both lungs ("millet seeds").

• Distribution is random (uniform, non-gravitational) — contrasts with the gravitational lower-zone predominance of some other miliary mimics.
• Chest radiograph may be normal early; HRCT is more sensitive and detects nodules before they are visible on plain film.
• Associated with immunosuppression, infancy, and HIV.

Pattern	Nodule distribution	Classic causes
Miliary (random)	Uniform, both lungs, random to secondary lobule	TB, fungal, metastases (haematogenous)
Centrilobular / tree-in-bud	Spares pleura/fissures, branching	Endobronchial TB, infections, aspiration
Perilymphatic	Along fissures, bronchovascular bundles, subpleural	Sarcoidosis, silicosis, lymphangitic carcinomatosis

High-yield: Random uniform micronodules = miliary; tree-in-bud = endobronchial (active) spread; perilymphatic = sarcoid/silicosis. Distinguishing these three nodule distributions is one of the most frequently tested HRCT concepts.

HRCT Findings

HRCT is the most sensitive tool for detecting early, subtle, and active disease.

• Tree-in-bud pattern — branching centrilobular nodules resembling a budding tree; represents bronchiolar impaction by caseous material and is the CT hallmark of active endobronchial spread. Highly suggestive of active TB (though not specific — also seen in other infective bronchiolitides).
• Centrilobular nodules — peribronchiolar inflammation.
• Consolidation — lobular or segmental.
• Cavitation — air-containing lucency within a nodule/consolidation.
• Lymphadenopathy with central low attenuation + rim enhancement — caseating nodes; nearly characteristic of TB (also seen in fungal disease, some metastases).
• Miliary nodules — random distribution.
• Sequelae — bronchiectasis (traction, upper lobe), fibrosis, calcified nodes, broncholithiasis.

Approach to "active vs inactive" on imaging: Tree-in-bud / centrilobular nodules → cavitation → consolidation → low-density rim-enhancing nodes → ACTIVE. Calcification (Ranke, calcified nodes) → fibrosis → traction bronchiectasis → stable over serial films → INACTIVE/HEALED.

High-yield: Tree-in-bud = active disease. A NEET PG favourite. The presence of cavitation also strongly implies activity and infectivity.

Complications & Sequelae

• Cavitation with secondary infection.
• Aspergilloma (mycetoma) — a fungus ball colonising a healed cavity; produces the air-crescent sign and is mobile on prone/supine films. A classic cause of recurrent haemoptysis in healed TB.
• Rasmussen aneurysm — pulmonary artery pseudoaneurysm in a cavity → massive haemoptysis.
• Bronchiectasis — traction (upper-lobe) and post-obstructive.
• Fibrothorax & pleural calcification — after tuberculous empyema.
• Empyema necessitans — empyema tracking through the chest wall to a subcutaneous collection (TB is a classic cause).
• Broncholithiasis — a calcified node erodes into a bronchus.
• Fibrosing mediastinitis; bronchopleural fistula.
• Cor pulmonale from extensive destroyed lung.

High-yield: Air-crescent sign + mobile intracavitary mass = aspergilloma in an old TB cavity. Haemoptysis in a treated TB patient → think aspergilloma or Rasmussen aneurysm.

Diagnosis & Investigation of Choice

Imaging suggests TB; microbiological confirmation is mandatory.

1. Chest radiograph → screening / first-line imaging.
2. HRCT → most sensitive for early, miliary, and activity assessment; characterises nodes.
3. Sputum for AFB / smear microscopy → simple, but low sensitivity.
4. CBNAAT / GeneXpert MTB-RIF (NAAT) → investigation of choice under the National TB Elimination Programme (NTEP) — rapid, detects M. tuberculosis DNA and rifampicin resistance simultaneously.
5. Culture (LJ medium / liquid MGIT) → gold standard for confirmation and drug-susceptibility, but slow.

High-yield: Under NTEP, CBNAAT (GeneXpert) is the preferred initial diagnostic test for presumptive TB; it gives rifampicin-resistance status in ~2 hours. Culture remains the gold standard.

Management / Drug of Choice (brief, for integration)

• First-line regimen (NTEP, daily fixed-dose): HRZE — isoniazid (H), rifampicin (R), pyrazinamide (Z), ethambutol (E) for the intensive phase (2 months), followed by HRE for the continuation phase (4 months).
• Rifampicin is the single most important sterilising drug; isoniazid is bactericidal against rapidly dividing bacilli.
• Drug-resistant TB → regimens guided by drug-susceptibility testing (newer oral BPaLM-type regimens for MDR/RR-TB).
• Radiological resolution lags behind clinical/microbiological cure — fibrosis and calcification persist.

Key Differentials

Mimic	Distinguishing radiological clue
Bronchogenic carcinoma	Spiculated mass, eccentric thick-walled cavity, no satellite nodules, mediastinal nodes without rim enhancement
Sarcoidosis	Symmetric bilateral hilar + right paratracheal nodes, perilymphatic nodules, upper-zone fibrosis
Fungal infection (histoplasmosis, etc.)	Calcified nodes/splenic calcification; overlaps strongly with TB
Non-tuberculous mycobacteria (MAC)	"Lady Windermere" — middle lobe/lingula bronchiectasis + tree-in-bud in elderly women
Pneumonia (bacterial)	Acute, lobar, rapidly responds to antibiotics; no upper-lobe predilection
Pneumoconiosis (silicosis)	Upper-zone perilymphatic nodules, eggshell calcification of nodes, occupational history
Lymphangitic carcinomatosis	Perilymphatic, septal thickening, known primary

High-yield: Symmetric bilateral hilar lymphadenopathy → sarcoidosis; unilateral right-sided hilar/paratracheal nodes → primary TB. Eggshell node calcification → silicosis/sarcoid (not typical of TB, where nodes show central low density + rim enhancement).

TB vs Sarcoidosis Lymphadenopathy

Feature	TB nodes	Sarcoid nodes
Symmetry	Asymmetric, often unilateral right	Symmetric, bilateral
CT density	Central low attenuation, rim enhancement	Homogeneous
Calcification	Dense calcification when healed	Eggshell (also silicosis)
Parenchyma	Consolidation/cavitation	Perilymphatic nodules, fibrosis

Recently asked / exam angle

• Ghon vs Ranke complex — active vs healed/calcified (recurring single-line MCQ).
• Tree-in-bud pattern — meaning (endobronchial spread) and that it indicates active disease; HRCT image-based question.
• Site of reactivation TB — apical/posterior segments of upper lobe and superior segment of lower lobe; "best aerated, highest O₂ tension favours aerobic M. tuberculosis."
• Air-crescent sign / mobile intracavitary mass — aspergilloma in old TB cavity; cause of haemoptysis.
• Rasmussen aneurysm — definition and association with cavitary TB haemoptysis.
• Random vs perilymphatic vs centrilobular nodule distribution — match miliary TB to random.
• Investigation of choice under NTEP — CBNAAT/GeneXpert; culture as gold standard.
• Lymphadenopathy: unilateral (TB) vs bilateral symmetric (sarcoid) — image differentiation.
• Rim-enhancing low-attenuation nodes on contrast CT — caseating TB nodes.
• Simon focus — apical seeding during primary infection, the future reactivation site.

Rapid revision

1. Primary TB → lower/mid zones + lymphadenopathy; reactivation TB → apical-posterior upper lobe + cavitation.
2. Ghon focus = parenchymal granuloma; Ghon complex = focus + node; Ranke complex = calcified (healed) complex.
3. Simon focus = apical haematogenous seeding → site of future reactivation.
4. Primary TB nodes are typically unilateral, right paratracheal/hilar; sarcoid nodes are bilateral symmetric.
5. Tree-in-bud on HRCT = active endobronchial spread.
6. Miliary TB = random uniform 1–3 mm nodules; HRCT more sensitive than CXR.
7. Caseating TB nodes on CT = central low attenuation + rim enhancement.
8. Air-crescent sign + mobile mass = aspergilloma in a healed cavity → haemoptysis.
9. Rasmussen aneurysm = pulmonary artery pseudoaneurysm in a TB cavity → massive haemoptysis.
10. CBNAAT/GeneXpert = investigation of choice (NTEP); culture (MGIT/LJ) = gold standard.
11. First-line regimen: 2HRZE + 4HRE; rifampicin = key sterilising drug.
12. Eggshell calcification of nodes → silicosis/sarcoid, NOT typical TB; reactivation favours upper lobes due to high O₂ tension.