[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Radiology](https://durgical.com/en/radiology/) › [Chest](https://durgical.com/en/radiology/areas/chest/) › Interstitial patterns: lines, nodules and honeycombing

# Interstitial patterns: lines, nodules and honeycombing

- Finding

When the lung's thin supporting tissue thickens, the X-ray shows a net of fine lines, many tiny dots or, at the end, small cysts like a honeycomb.

Updated Nov 13, 2026

## Key points

- Interstitial = lines and small nodules; air space = fluffy shadows with air bronchograms.
- Kerley B lines = thickened septa, most often oedema.
- Honeycombing at the bases = end-stage fibrosis (think idiopathic pulmonary fibrosis).
- Upper zone (CHARTS) vs lower zone (IPF, connective tissue disease, asbestosis).
- The X-ray can be normal: HRCT is the study for interstitial disease.

## What it is

The interstitium is the lung's supporting framework: the walls between alveoli, the septa between lobules and the sheath around bronchi and vessels. When it thickens with fluid, cells or scar, the chest X-ray shows an interstitial pattern instead of the fluffy, merging shadows of air-space disease. The pattern may be reticular (a net of fine lines), nodular (many small, well-defined dots), or both (reticulonodular). Short horizontal lines at the lung bases reaching the pleura (Kerley B lines) are thickened interlobular septa, most often from oedema. In advanced fibrosis the lungs shrink and small cystic spaces cluster under the pleura (honeycombing). Where the pattern lies (upper or lower zones), whether volumes are reduced and how it changes over time narrow the differential, but the X-ray is insensitive: it can be normal in early interstitial lung disease, and high-resolution CT is the study that characterises it.

## What it looks like

- Reticular: a fine to coarse net of lines; coarse lines with small volumes suggest fibrosis.
- Nodular: many small, well-defined dots; uniform tiny nodules (millet-seed size) throughout both lungs are the miliary pattern.
- Kerley B lines: short horizontal lines at the lateral lung bases touching the pleura (thickened septa).
- Honeycombing: clustered small cysts with thick walls, at the bases and periphery; a sign of end-stage fibrosis.
- Fibrosis pulls structures: small lungs, raised hemidiaphragms, blurred heart border; oedema keeps volumes normal.

## Why it looks that way

- Septa contain veins and lymphatics, so fluid (heart failure) or tumour in the lymphatics thickens them into lines.
- Granulomas and blood-borne seeding make small nodules; scar shortens and distorts the lung, giving coarse lines and cysts.

## Differential and pitfalls

- Lower-zone, peripheral reticulation with small lungs: idiopathic pulmonary fibrosis, connective tissue disease, asbestosis, some drugs.
- Upper-zone pattern: sarcoidosis, silicosis and coal-worker pneumoconiosis, tuberculosis, chronic hypersensitivity pneumonitis.
- Miliary nodules with fever: miliary tuberculosis until proven otherwise; also fungi and metastases.
- Pitfall: interstitial oedema mimics fibrosis; look for a large heart, upper-lobe vessel diversion and effusions, and repeat after treatment.
- Pitfall: a poor inspiration or a rotated, under-exposed film crowds the basal markings and creates a false pattern.
- Pitfall: a normal X-ray does not exclude interstitial lung disease in a patient with dyspnoea and crackles.

## Next step

- Compare with older films: a pattern that has been stable for years means something different from one that appeared in weeks.
- Suspected interstitial lung disease: request high-resolution CT of the chest and pulmonary function tests (spirometry and diffusing capacity).
- Suspected oedema: treat the heart failure, request an echocardiogram and repeat the film; persistent lines need CT.
- Miliary pattern or upper-zone disease with fever or weight loss: sputum for tuberculosis and airborne isolation while it is excluded.
- Fibrotic pattern confirmed: refer to pulmonology for multidisciplinary discussion (pulmonologist, radiologist, pathologist).

## Memory aid

Upper-zone pattern, CHARTS: Coal-worker pneumoconiosis, Histiocytosis (Langerhans cell), Ankylosing spondylitis, Radiation, Tuberculosis, Silicosis and Sarcoidosis.

## Test yourself

Think of the answer, then tap the question to see it.

## What are Kerley B lines and what do they most often mean?

Short horizontal lines at the lateral lung bases reaching the pleura; they are thickened interlobular septa, most often from interstitial oedema.

## What does honeycombing look like on the chest X-ray?

Clusters of small cystic spaces with thick walls at the lung bases and periphery, usually with small lung volumes: end-stage fibrosis.

## Which study characterises interstitial lung disease when the X-ray is abnormal or normal but suspicion is high?

High-resolution CT of the chest, together with pulmonary function tests.

## A febrile patient has countless tiny uniform nodules in both lungs. What must you think of first?

Miliary tuberculosis: send sputum, isolate the patient and work it up; fungi and metastases are the other causes.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/radiology/interstitial-patterns-lines-nodules-and-honeycombing/)

## Connections

## Related 5

- [High-resolution CT patterns: ground glass, crazy paving, tree-in-bud](https://durgical.com/en/radiology/high-resolution-ct-patterns-ground-glass-crazy-paving-tree-in-bud/)
- [Cardiomegaly and pulmonary oedema on the chest X-ray](https://durgical.com/en/radiology/cardiomegaly-and-pulmonary-oedema-on-the-chest-x-ray/)
- [Reading a chest X-ray step by step](https://durgical.com/en/radiology/reading-a-chest-x-ray-step-by-step/)
- [A nodule or a mass on the chest X-ray](https://durgical.com/en/radiology/a-nodule-or-a-mass-on-the-chest-x-ray/)
- [Cavities and air-fluid levels in the lung](https://durgical.com/en/radiology/cavities-and-air-fluid-levels-in-the-lung/)

## Related conditions 6

- [Interstitial lung disease](https://durgical.com/en/conditions/interstitial-lung-disease/)
- [Sarcoidosis](https://durgical.com/en/conditions/sarcoidosis/)
- [Hypersensitivity pneumonitis](https://durgical.com/en/conditions/hypersensitivity-pneumonitis/)
- [Pneumoconioses (silicosis, asbestosis, coal workers' pneumoconiosis)](https://durgical.com/en/conditions/pneumoconioses/)
- [Pulmonary tuberculosis](https://durgical.com/en/conditions/pulmonary-tuberculosis/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)

[← All of radiology](https://durgical.com/en/radiology/)

Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Sources: [Interstitial Lung Disease](https://www.ncbi.nlm.nih.gov/books/NBK541084/) (StatPearls (NCBI Bookshelf), 2026); [Idiopathic Pulmonary Fibrosis](https://www.ncbi.nlm.nih.gov/books/NBK448162/) (StatPearls (NCBI Bookshelf), 2024); [Chest and Mediastinal Imaging](https://www.ncbi.nlm.nih.gov/books/NBK559145/) (StatPearls (NCBI Bookshelf), 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/radiology/interstitial-patterns-lines-nodules-and-honeycombing/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/radiology/interstitial-patterns-lines-nodules-and-honeycombing/