Pulmonary Tuberculosis Imaging
On this page
Direct answer
Primary pulmonary tuberculosis produces a mid or lower-lobe parenchymal focus (Ghon focus) with unilateral hilar and paratracheal lymphadenopathy; healed calcified focus plus node forms the Ranke complex. Post-primary (reactivation) tuberculosis favours the apical and posterior segments of upper lobes and superior segments of lower lobes, with patchy consolidation, cavitation and fibrosis, and is typically asymmetric without significant adenopathy. Haematogenous spread produces miliary mottling — innumerable 1-3 mm nodules in a random distribution. These pattern differences drive radiological diagnosis in the Indian setting and are core NEET-PG Radiology content.
What you must remember
- Primary TB: unifocal consolidation in lower or middle lobes, prominent hilar lymphadenopathy (more prominent in children and in Indian primary disease), pleural effusion possible; lymphohaematogenous spread may follow.
- Ghon focus: initial subpleural parenchymal lesion; Ranke complex: calcified Ghon focus plus calcified hilar node.
- Post-primary TB: apical and posterior upper-lobe segments plus superior segments of lower lobes; cavitation with air-fluid levels, tree-in-bud centrilobular nodules, bronchogenic spread and upper-zone fibrosis with retraction.
- Miliary TB: innumerable uniform 1-3 mm nodules in random (haematogenous) distribution on HRCT; on radiograph, millet-seed mottling.
- Complications to recognise: aspergilloma (mobile intracavitary fungus ball with air crescent), tuberculous bronchopleural fistula, destroyed lung, pleural empyema and spine involvement (Pott disease).
- TB lymphadenitis on CT shows rim-enhancing, low-density (necrotic) nodes — the reverse of sarcoidosis.
- The chest radiograph remains the first investigation in India; sputum microscopy, cartridge-based NAAT and culture confirm, and CT defines complications such as bronchiectasis and fistulae.
Common confusion
The exam repeatedly contrasts primary with post-primary disease. Primary is a lower-lobe infection of the non-immune host with striking adenopathy, whereas post-primary reactivation concentrates in oxygen-rich apical sites with cavitation and minimal nodes. The second trap is miliary mottling versus other micronodular patterns: miliary nodules are uniform in size and randomly distributed (vessels and septa not respected), distinguishing them from the perilymphatic nodules of sarcoidosis or centrilobular tree-in-bud of endobronchial spread. Finally, a chronic upper-zone cavity may be TB, but consider squamous carcinoma and aspergilloma when the wall is thick or a fungus ball is present.
Exam-focused takeaway
Expect image-based questions on the apical cavitary pattern and one-liners on the Ghon focus, Ranke complex and miliary seeding. Chest radiograph as first-line investigation in India, CT for complications, and the characteristic necrotic rim-enhancing nodes of tubercular lymphadenitis are favourite picks. Be ready to pair post-primary location (apical and posterior segments) with underlying pathology questions.
Frequently asked questions
What is the Ranke complex?
A healed, calcified primary Ghon focus together with a calcified hilar lymph node. It indicates healed primary tuberculosis and is a classic MCQ definition.
Which segments are involved in post-primary tuberculosis?
Apical and posterior segments of the upper lobes and superior segments of the lower lobes, bilaterally asymmetric. High regional oxygen tension favours reactivation at these sites.
What does miliary mottling represent?
Innumerable 1-3 mm nodules scattered randomly throughout both lungs from haematogenous dissemination. It may appear two to six weeks after bacteraemia and calls for urgent antitubercular therapy.
How is tuberculous lymphadenitis distinguished from sarcoidosis on CT?
Tuberculous nodes show central low-density necrosis with rim enhancement and are often unilateral, whereas sarcoid nodes enhance uniformly, are bilateral and symmetrical, and may show stippled calcification when chronic.
What is an aspergilloma?
A fungus ball colonising a pre-existing tuberculous cavity, appearing as a mobile soft-tissue mass with an air crescent (Monod sign) that changes position between supine and prone imaging. Haemoptysis is the key complication.