Pulmonary Tuberculosis Clinical Features and Radiology
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Direct answer
Pulmonary tuberculosis is a Mycobacterium tuberculosis infection of the lung, either primary, seen in children and non-immune contacts, or post-primary, arising in adults when a latent focus reactivates. Radiology separates the two: primary disease shows a Ghon complex, a focus with a draining hilar node, while post-primary disease favours upper lobe apical and posterior consolidation, cavitation and fibrosis. Microscopy, culture or molecular testing confirms the diagnosis, with radiology supporting it.
What you must remember
- Ghon complex: a subpleural caseating focus with a draining hilar or mediastinal node, which usually heals and calcifies; the healed lesion is called a Ranke complex.
- Simon focus: an apical lesion seeded during the initial bacteraemia, which reactivates decades later and underlies most post-primary cavities.
- Primary disease: middle and lower zone consolidation with hilar lymphadenopathy, common in children and HIV-positive patients, and sometimes with pleural effusion.
- Post-primary disease: upper lobe apical and posterior segment involvement, with cavitation, fibrosis and tree-in-bud nodules from bronchogenic spread.
- Cavitary pattern: a thick-walled cavity with surrounding consolidation and satellite lesions signals high bacillary load and infectivity.
- Miliary pattern: innumerable 1 to 3 millimetre nodules from haematogenous dissemination, which can be missed on early plain films.
- Diagnosis: CBNAAT, the molecular test used first-line under the National Tuberculosis Elimination Programme, detects both Mycobacterium tuberculosis and rifampicin resistance.
Reading a film in a young labourer and a child
A 28-year-old construction worker has six weeks of evening fever, night sweats, weight loss and productive cough. His chest film shows right upper lobe consolidation with a thick-walled cavity and satellite nodules.
- Confirm the bacteriology: Sputum CBNAAT is positive and sensitive to rifampicin, smear is 2-plus, and HIV testing is negative.
- Name the pattern: The diagnosis is post-primary pulmonary tuberculosis with infectious cavitary disease, because a cavity with satellite lesions signals high bacillary load and infectivity.
- Contrast the child: A 5-year-old household contact of the same family has a fortnight of fever and a right hilar node with lower zone consolidation on film.
- Name the primary pattern: The child shows a primary pattern, and the diagnosis rests on the contact history, tuberculin or interferon-gamma testing and clinical features rather than sputum, which is seldom available in children.
- Use location, not symptoms: Lesion location, not symptoms alone, distinguishes primary from post-primary disease.
- Screen the household: Because the adult's smear is positive, screening of household contacts is urgent, and the child is evaluated for primary infection rather than dismissed as an unrelated fever.
Where radiology and tests mislead
The same few confusions recur with radiology and testing.
- Trap: assuming all tuberculosis is apical. Correct: lower and middle zones are common in HIV-positive patients and children, and the classic apical picture is a clue for immunocompetent adults.
- Trap: confusing the Ghon complex with the Simon focus. Correct: the Ghon complex is the primary lesion with its node, whereas the Simon focus is the apical site of later reactivation.
- Trap: trusting a normal chest film or a negative smear in HIV. Correct: neither excludes tuberculosis in HIV, so molecular testing or culture is needed.
- Trap: assuming a febrile patient with a nodular pattern has pneumonia. Correct: in an Indian context miliary tuberculosis often presents with fever and pancytopenia, so the nodular pattern should be recognised.
Frequently asked questions
What is a Ghon complex?
A Ghon complex is the primary tuberculosis lesion, a subpleural focus of caseating granuloma together with a draining hilar or mediastinal lymph node. It often heals and calcifies, and the healed complex is called a Ranke complex.
Where are cavities typically seen in post-primary pulmonary tuberculosis?
Cavities in post-primary pulmonary tuberculosis favour the apical and posterior segments of the upper lobes, reflecting reactivation of the Simon focus. Thick-walled cavities with satellite lesions indicate a high bacillary load and marked infectivity.
Which radiological pattern suggests miliary tuberculosis?
Miliary tuberculosis shows innumerable 1 to 3 millimetre nodules spread uniformly through both lungs, reflecting haematogenous dissemination. The pattern can be missed on a plain film in early disease, so high-resolution CT is useful when suspicion is high.
Why can primary tuberculosis appear in the lower lobes?
Primary tuberculosis in children and non-immune adults commonly involves the middle and lower zones, which receive more ventilation and therefore more inhaled bacilli. Hilar lymphadenopathy with lower zone consolidation is the classic primary pattern.