# Air Bronchogram

> Air bronchogram and consolidation for NEET-PG Radiology: alveolar versus interstitial patterns, the silhouette sign, air-space disease causes and their exam one-liners.

- Canonical URL: https://prepelephant.com/topics/neet-pg/radiology/air-bronchogram
- Exam / course: NEET-PG · Subject: Radiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Air Bronchogram", PrepElephant, https://prepelephant.com/topics/neet-pg/radiology/air-bronchogram

## Direct answer

An air bronchogram is an air-filled, patent bronchus rendered visible because the surrounding alveoli have been filled by fluid or exudate; it is the signature of alveolar (air-space) disease rather than interstitial disease. Consolidation is pathological air-space opacification, and because the bronchi remain open there is classically no volume loss. Its causes — lobar pneumonia, pulmonary oedema, ARDS and pulmonary haemorrhage — are separated by distribution and by the clinical setting rather than by the shadow alone.

## What you must remember

- Air bronchogram equals alveolar filling with a patent airway: pneumonic consolidation, pulmonary oedema, ARDS, pulmonary haemorrhage and alveolitis; it argues against pleural fluid and against complete collapse with absorbed air.
- The silhouette sign (Felson) localises disease: loss of the right heart border means middle lobe disease, loss of the left heart border means lingular disease, and loss of a sharp hemidiaphragm means lower lobe disease — an opacity that obliterates a border touches that structure.
- Consolidation shows no mediastinal shift or fissure displacement (no volume loss); collapse shows volume loss with fissure deviation, crowded vessels and shift of the mediastinum towards the lesion.
- Lobar pneumonia is homogeneous and confined by fissures; bronchopneumonia is patchy and multifocal; central bat-wing consolidation that spares the periphery suggests pulmonary oedema.
- Interstitial pattern is different in kind: reticular or reticulonodular opacities, Kerley B lines (short, peripheral, basal linear opacities) and ground-glass haze rather than confluent air-space shadowing.
- Cavitation within consolidation narrows the cause to tuberculosis, staphylococcal or klebsiella pneumonia, anaerobic abscess or infarct — a favourite follow-on question.
- A unilateral white-out must be interpreted with the mediastinum: shifted away suggests effusion, shifted towards suggests collapse, and central (unshifted) suggests consolidation or post-pneumonectomy with a thoracotomy clue.

## Common confusion

The classic confusion is between consolidation and collapse: both produce opacity, but only collapse loses volume, and an air bronchogram within the opacity favours consolidation with a patent bronchus. Students also overcall interstitial markings as consolidation; Kerley lines, fine reticulation and ground glass belong to the interstitial compartment, where air bronchograms are characteristically absent. Finally, an air bronchogram is not specific for infection — oedema and haemorrhage produce it too, so the vignette's temperature, orthopnoea or haemoptysis does the discriminating, not the radiograph.

## Exam-focused takeaway

NEET-PG frames this topic as three question types: the mechanism stem (air bronchogram indicates patent bronchi with alveolar filling), the silhouette stem (which lobe is involved when a named border is lost), and the white-out stem (effusion, collapse or consolidation decided by mediastinal position). Kerley B lines as a one-liner for pulmonary oedema and cavitation within consolidation as a one-liner for tuberculosis or staphylococcal pneumonia recur constantly. Learn the compartment logic — alveolar versus interstitial — as the first sorting step, and every subsequent option in these stems falls into place.

## Frequently asked questions

### What does an air bronchogram indicate?

Alveolar (air-space) filling with a patent airway — classically consolidation, and also pulmonary oedema, ARDS or haemorrhage; it is not a feature of pure interstitial disease.

### How does the silhouette sign localise a lesion?

An opacity that obliterates the border of a structure must be in contact with it: right heart border loss means middle lobe, left heart border loss means lingula, and diaphragmatic loss means lower lobe.

### How are consolidation and collapse distinguished radiographically?

By volume: consolidation preserves lung volume with no fissure or mediastinal shift, while collapse shows fissure deviation, crowding of markings and mediastinal shift towards the opaque side.

### What are Kerley B lines?

Short, horizontal, peripheral basal linear opacities representing thickened interlobular septa, classically of pulmonary oedema and also of lymphangitis carcinomatosa.

### Which consolidations cavitate?

Tuberculosis, staphylococcal and klebsiella pneumonia, anaerobic lung abscess and pulmonary infarction — cavitation within consolidation should always prompt this differential.

### How is a unilateral white-out approached?

By the mediastinum: shifted away indicates a large effusion, shifted towards indicates collapse, and an unshifted mediastinum suggests consolidation, ARDS of one lung or post-pneumonectomy change.