Radiodiagnosis
Chest Imaging
Chest imaging for MBBS and NEET-PG: reading the chest radiograph, silhouette and air bronchogram signs, effusion, collapse, pneumothorax and tuberculosis, mapped to NMC codes RD1.
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Chest Imaging
Chest imaging for MBBS and NEET-PG: reading the chest radiograph, silhouette and air bronchogram signs, effusion, collapse, pneumothorax and tuberculosis, mapped to NMC codes RD1.
This chapter teaches a systematic approach to the chest radiograph and the role of CT in thoracic disease. It covers the silhouette and air bronchogram signs, the patterns of consolidation, collapse, effusion and pneumothorax, the radiology of tuberculosis and cardiac failure, and when to move from plain film to cross-sectional imaging.
High-yield: Chest Imaging
- The posteroanterior erect chest radiograph is the standard view; adequacy is judged by inspiration, penetration and rotation before interpretation.
- A silhouette sign is the loss of a normal border when adjacent lung is opacified, and it helps localise disease, for example right middle lobe consolidation obscuring the right heart border.
- An air bronchogram, air-filled bronchi seen against opacified lung, indicates airspace disease such as consolidation.
- Pleural effusion causes blunting of the costophrenic angle, and a meniscus is seen on an erect film once about 200 to 300 millilitres has collected.
- A tension pneumothorax shows an absent lung marking, a deep sulcus and mediastinal shift away from the affected side, and is a clinical emergency treated before imaging.
- Lobar collapse shifts the fissures, hilum and mediastinum towards the collapsed lobe and raises the hemidiaphragm.
- The batwing or perihilar pattern of pulmonary oedema, with Kerley B lines and upper lobe diversion, points to cardiac failure.
- Miliary tuberculosis produces innumerable tiny nodules of uniform size distributed throughout both lungs.
- Primary tuberculosis often shows the Ghon focus with hilar lymphadenopathy, while post-primary disease favours the upper lobes with cavitation.
- A cavity with an air-fluid level suggests a lung abscess, while a rounded mass within a cavity may be an aspergilloma that moves with position.
- CT is the modality of choice for characterising a solitary pulmonary nodule, staging lung cancer and detecting pulmonary embolism with CT pulmonary angiography.
- High-resolution CT is the best modality for interstitial lung disease, showing reticulation, honeycombing and ground-glass change.
- A widened mediastinum after trauma raises the suspicion of aortic injury and needs CT angiography.
- Free gas under the diaphragm on an erect chest film indicates a perforated abdominal viscus.
Classic chest radiograph signs
- **Silhouette sign:** Loss of a border by adjacent opacified lung; localises the affected lobe.
- **Air bronchogram:** Air-filled bronchi against opaque lung; indicates airspace consolidation.
- **Pleural effusion:** Costophrenic angle blunting with a meniscus on the erect film.
- **Collapse:** Fissures, hilum and mediastinum pulled towards the collapsed lobe.
NMC competencies in this chapter
- **RD1.5:** Radiological investigation and interpretation in common internal medicine conditions
- **RD1.6:** Radiological investigation and interpretation in common surgical conditions
Frequently Asked Questions
What is the silhouette sign?
It is the loss of a normally visible border when the adjacent lung becomes opaque. For example, loss of the right heart border indicates right middle lobe disease, which helps localise the pathology on a plain film.
How is a pleural effusion seen on a chest radiograph?
On an erect film it blunts the costophrenic angle and forms a concave upper meniscus. Around 200 to 300 millilitres of fluid must accumulate before it becomes visible on a standard posteroanterior view.
When is CT preferred over a chest radiograph?
CT is used to characterise a solitary pulmonary nodule, stage lung cancer, assess interstitial lung disease with high-resolution technique, and diagnose pulmonary embolism with CT pulmonary angiography.
What does miliary tuberculosis look like?
It produces countless tiny nodules of uniform size spread evenly through both lung fields, reflecting haematogenous dissemination, and is a classic pattern examiners ask about.
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