Interstitial lung disease on chest X‑ray

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Advanced

Interstitial lung disease (ILD) is a large group of conditions that inflame or scar the lung's supporting framework, the interstitium, rather than filling the air spaces. They include idiopathic pulmonary fibrosis (IPF), connective tissue disease, drug reactions, occupational lung disease and sarcoidosis. The chest X-ray is often the first test to show them, but it is relatively insensitive and non-specific. Its value lies in recognising an interstitial pattern, describing its distribution and the lung volumes, suggesting a sensible differential, and prompting high-resolution CT (HRCT), which is the key imaging test. This page teaches a structured description of an interstitial film.

1. How to look: pattern, zone, volume

After the usual systematic review, answer four questions:

1. What is the pattern? Reticular, nodular, reticulonodular, honeycombing, or ground glass.
2. Where is it? Upper or lower zones, central or peripheral, symmetrical or not.
3. What are the lung volumes? Small, normal or large.
4. What else is there? Hilar nodes, pleural plaques or effusions, cardiac enlargement, dilated oesophagus, bone or joint changes, or devices.

Then compare with previous films. A slowly progressive pattern over years points to fibrosis; a pattern that appears and clears within days points to oedema or infection.

2. The patterns

Pattern	What it looks like	Typical meaning
Reticular	A net-like network of fine or coarse lines	Thickened interstitium: fibrosis, oedema, lymphangitis
Nodular	Many small, round, well-defined opacities	Sarcoid, pneumoconiosis, miliary infection or metastases
Reticulonodular	A mixture of lines and nodules	Many ILDs; the dominant component guides the differential
Honeycombing	Clustered cystic spaces, roughly 3–10 mm, with thick walls, at the lung periphery and bases	End-stage fibrosis
Ground glass	A hazy increase in density through which vessels are still visible	Active inflammation, oedema or infection; far better seen on CT

Use these terms as defined in the Fleischner Society glossary, so that your description means the same thing to the next reader.

3. Lung volumes

Fibrosis stiffens and shrinks the lungs, so most fibrotic ILDs show reduced lung volumes: high hemidiaphragms and crowded markings. Judge this against inspiration on previous films, because poor effort mimics it (see RIPE).

Some conditions preserve or even increase lung volume despite interstitial change:

• lymphangioleiomyomatosis (LAM) and Langerhans cell histiocytosis (LCH), which are cystic diseases;
• sarcoidosis;
• combined emphysema and fibrosis, where the volume lost to fibrosis is offset by emphysema. See COPD and airways disease.

4. Upper versus lower zone

Distribution is the most useful clue on a plain film. Two classic memory aids:

Memory aids are a starting point, not a diagnosis. Many conditions overlap, and drug-induced disease in particular can appear anywhere.

5. Idiopathic pulmonary fibrosis

IPF is the most common idiopathic fibrosing ILD, typically in people over about 60, with progressive breathlessness, dry cough and fine "Velcro-like" basal crackles. Its imaging pattern is usual interstitial pneumonia (UIP). On the chest X-ray:

• peripheral, basal reticular shadowing, often first seen at the costophrenic angles;
• a "shaggy" or indistinct heart border and hemidiaphragms;
• small lung volumes;
• honeycombing and traction bronchiectasis in advanced disease, which are better shown on HRCT.

HRCT is the definitive imaging test, and the diagnosis is made by a multidisciplinary team (NICE CG163; BTS ILD guidance).

6. Other conditions to know

• Sarcoidosis: bilateral hilar lymphadenopathy, then perihilar and upper-zone nodular and reticular change, and finally upper-zone fibrosis with hilar retraction. The Scadding stages (0–IV) are covered in mediastinum and hila.
• Asbestos-related disease: pleural plaques (often calcified, with a "holly-leaf" outline when seen face-on, and along the diaphragm) are a marker of exposure, not of fibrosis. Asbestosis itself is lower-zone fibrosis, sometimes giving a "shaggy heart" border.
• Silicosis and coal-worker's pneumoconiosis: small upper-zone nodules, eggshell nodal calcification, and progressive massive fibrosis, with large upper-zone masses that migrate towards the hila. Silicosis increases the risk of TB.
• Connective tissue disease: look for clues outside the lungs, such as a dilated oesophagus (scleroderma) or erosive shoulder joints (rheumatoid arthritis). See rheumatoid and inflammatory arthritis.
• Lymphangitis carcinomatosa: reticular shadowing with septal lines and hilar nodes, often asymmetric. See nodules and masses.
• Hypersensitivity pneumonitis (extrinsic allergic alveolitis): an immune reaction to inhaled organic antigens, such as bird proteins or mouldy hay ("farmer's lung"). Acute disease may show fine nodular or ground-glass change, or a normal film; chronic disease causes fibrosis that often favours the upper and mid zones. The exposure history is the key to the diagnosis.
• Drug-induced lung disease: amiodarone, methotrexate, nitrofurantoin and bleomycin are classic causes. The pattern varies, from patchy consolidation to fibrosis, so always check the drug chart when a new interstitial pattern appears.

7. Pitfalls and mimics

• Pulmonary oedema is the most common "interstitial" pattern on a chest film. Look for cardiomegaly, upper lobe venous diversion, effusions and rapid change.
• Poor inspiration crowds basal vessels and mimics basal reticulation.
• Overlying soft tissue (breast tissue, obesity) creates a false basal haze.
• A normal chest X-ray does not exclude ILD. Early disease can be invisible on the plain film; in an older series, around one in ten patients with biopsy-proven diffuse lung disease had a normal film. If symptoms, crackles or lung function suggest ILD, request HRCT.
• Atypical infection (for example PCP or viral pneumonia) can look interstitial. The clinical context and time course separate them.

8. Next steps

• HRCT is the imaging test for suspected ILD, and is needed to characterise a pattern seen on a chest X-ray.
• Lung function testing, including gas transfer, and specialist respiratory referral; the diagnosis is made in an ILD multidisciplinary meeting.
• Take a careful occupational, drug and exposure history; the film can suggest the questions.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	Describe the pattern, zone and volume; know CHARTS and BADAS; know that HRCT is the next test.
Nurse	Recognise the breathless patient with known ILD who is deteriorating, and the importance of oxygen prescription and monitoring.
Junior doctor	Exclude oedema and infection first, take an exposure and drug history, and refer for HRCT and respiratory review.
Radiographer	Good inspiration is critical; a poor breath mimics basal fibrosis.
Advanced / FRCR	Cystic lung diseases, volume clues, pleural and extrapulmonary signs, and correlation with HRCT patterns.

Practise on real chest X-rays →

References

1. Hansell DM, et al. Fleischner Society: glossary of terms for thoracic imaging. Radiology 2008;246(3):697–722. pubs.rsna.org
2. NICE. Idiopathic pulmonary fibrosis in adults: diagnosis and management (CG163). nice.org.uk
3. British Thoracic Society. Interstitial lung disease guidance. brit-thoracic.org.uk
4. Radiopaedia. Pulmonary sarcoidosis. radiopaedia.org
5. Epler GR, et al. Normal chest roentgenograms in chronic diffuse infiltrative lung disease. N Engl J Med 1978;298:934–939.

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.