Lung nodules and masses on chest X‑ray
A rounded opacity in the lung is one of the most important findings on a chest X-ray, because it may be the first sign of lung cancer, the leading cause of cancer death in the UK. Most nodules found on chest films turn out to be benign, but the chest X-ray cannot reliably tell the difference, and it misses many small or hidden lesions. Your job as a film reader is to notice the lesion, describe it well, check for associated signs that change urgency, rule out the common mimics, and make sure it leads to the right next test, usually CT. This page covers the definitions, the features that favour benign or malignant disease, special patterns such as Pancoast tumours and metastases, and the pitfalls.
1. Nodule or mass: definitions
The Fleischner Society glossary gives the standard definitions:
Key definitions
- Nodule: a rounded or irregular opacity, well or poorly defined, measuring up to 3 cm in diameter.
- Mass: a similar opacity larger than 3 cm.
The distinction matters because size is one of the strongest predictors of malignancy: most masses larger than 3 cm are malignant until proven otherwise. Very small nodules are often invisible on a plain film; a nodule usually needs to be somewhere around 8–10 mm before it can be seen reliably, and many nodules found on CT cannot be seen on the corresponding chest X-ray at all.
2. How to look
Nodules are missed far more often than they are misinterpreted. The classic hiding places are the review areas from the systematic approach:
- the apices, behind the clavicles and first ribs;
- the hila, where a mass blends with the vessels (see mediastinum and hila);
- behind the heart;
- below the dome of the diaphragm, where the posterior lung bases extend down;
- overlapping the ribs and the breast shadows.
Once you have found a lesion, describe it: site (zone and, if a lateral is available, lobe), size in millimetres, number, margin (smooth, lobulated, spiculated), density (soft tissue, calcified, cavitating), and associated findings. Then look for an old film. Comparison is the most useful single step.
3. Benign versus malignant features
No single feature is decisive, and CT is needed to characterise almost every new nodule. The features below shift probability.
| Favours benign | Favours malignant |
|---|---|
| Benign calcification patterns: diffuse, central, laminated (concentric), or popcorn (chondroid calcification, typical of a hamartoma) | Eccentric or stippled calcification, or no calcification |
| Stable size for 2 years on comparison films (solid nodules only) | Growth on comparison films |
| Small size, smooth well-defined margin | Size >3 cm; spiculated ("corona radiata") or lobulated margin |
| Fat within the nodule (a hamartoma; seen on CT, not on the plain film) | Thick-walled cavitation |
| Thin-walled cavity | Associated hilar or mediastinal lymphadenopathy, effusion, or bone destruction |
Key measurements: cavity wall thickness (Woodring)
For cavitating lesions, a maximum wall thickness of 4 mm or less favours a benign cause, and a wall over 15 mm favours malignancy. Between these values there is considerable overlap. Squamous cell carcinoma is the lung cancer subtype that most often cavitates; infection (abscess, TB) and granulomatosis with polyangiitis are important benign causes.
Pitfall: the two-year rule
Two years' stability is a reasonable marker of benignity for a solid nodule, but it does not apply to ground-glass or part-solid nodules, which are often slow-growing adenocarcinomas. These are usually seen only on CT, which is another reason the plain film is not adequate for follow-up.
4. How lung cancer shows on a chest X‑ray
Lung cancer does not always look like a mass. Think of it when you see:
- a nodule or mass;
- lobar collapse, especially in an adult with no obvious cause, from a central tumour obstructing a bronchus. A "reverse S" (Golden S) sign in right upper lobe collapse suggests a central mass;
- consolidation that does not resolve after treatment;
- hilar enlargement or a dense hilum;
- a pleural effusion, especially unilateral and recurrent;
- an elevated hemidiaphragm from phrenic nerve involvement;
- lytic rib lesions or other bone destruction.
A normal chest X-ray does not exclude lung cancer. Central tumours, small peripheral tumours and lesions hidden behind other structures are all missed. NICE NG12 sets out when to request an urgent chest X-ray and when to refer directly on a suspected cancer pathway; if clinical suspicion stays high despite a normal film, CT or referral is appropriate.
5. Pancoast (superior sulcus) tumours
A tumour at the lung apex can invade the chest wall, the lower brachial plexus (C8/T1), the sympathetic chain and the upper ribs and vertebrae. On the film:
- an apical mass, or asymmetric apical pleural thickening of more than about 5 mm compared with the other side;
- destruction of the posterior 1st–3rd ribs or of the adjacent vertebrae.
Clinically it may present with shoulder and arm pain, weakness of the hand, and Horner's syndrome (ptosis, miosis, anhidrosis). Apical findings are easy to dismiss as old scarring. Compare carefully with previous films and look at the ribs. MRI is often used to assess local invasion.
6. Metastases and lymphangitis
- Pulmonary metastases are typically multiple, round and of varying sizes, mainly in the periphery and the lower zones, where blood flow is greatest.
- Large, well-defined "cannonball" metastases are classically associated with renal cell carcinoma, choriocarcinoma, sarcoma and colorectal cancer.
- Cavitating metastases suggest squamous cell carcinoma (for example from the head and neck or cervix) or sarcoma.
- Lymphangitis carcinomatosa is tumour spreading through the lymphatics. It shows as reticular (net-like) shadowing, Kerley B lines and hilar lymphadenopathy, often unilateral or asymmetric. Common primaries include breast, stomach, lung, pancreas and prostate. It can look like pulmonary oedema or interstitial lung disease.
Multiple small nodules have a wide differential. Innumerable uniform nodules of 1–3 mm suggest a miliary pattern, for example miliary TB or miliary metastases.
7. Mimics
Several common things look like a nodule:
- Nipple shadows: often bilateral and symmetrical, at the expected height, with a sharp lateral edge. Repeat with nipple markers if in doubt.
- Healing rib fractures: callus forms a rounded density on the rib. Trace the rib.
- Skin lesions (moles, neurofibromas, seborrhoeic keratoses): the edge is often "too sharp", outlined by air, and the lesion may be visible on the skin.
- Bony islands and costochondral calcification.
- Vessels seen end-on, especially near the hila: a vessel seen end-on is about the same size as the vessels next to it.
- Round pneumonia (more common in children), a fluid-filled fissure (pseudotumour in heart failure), and an azygos fissure.
- True but benign lesions: granulomas (often calcified) and hamartomas.
See artefacts and mimics for more.
8. Next steps
- Any new nodule or mass needs CT, unless it is clearly a benign mimic or proven to be stable over years. The chest X-ray is not adequate to characterise a nodule.
- The British Thoracic Society (BTS) pulmonary nodule guideline manages nodules using CT: size or volume, growth over time, and risk models (the Brock model, and the Herder model after PET-CT).
- A mass with features of malignancy should go onto the local suspected lung cancer pathway (NICE NG12 and NG122).
- Report clearly, and make sure someone is responsible for acting on it. Missed follow-up of an incidental nodule is a well-recognised cause of harm.
Red flags: act now
Needs an urgent plan
- A new mass, especially >3 cm or spiculated, or with hilar enlargement, effusion or bone destruction.
- A nodule that has grown since a previous film.
- Unexplained lobar collapse or non-resolving consolidation in an adult.
- An apical mass with rib destruction, arm symptoms or Horner's syndrome.
- A mass causing superior vena cava obstruction or stridor (widened mediastinum, facial swelling): same-day senior review.
What to focus on, by role
| Role | Priorities |
|---|---|
| Medical student | The 3 cm definition, benign versus malignant features, the ways lung cancer can present, and the main mimics. In an OSCE, describe the lesion fully and say "I would compare with old films and request CT". |
| Nurse | Make sure a reported nodule or mass reaches the responsible clinician and the patient is told about follow-up. |
| Junior doctor | Never dismiss a new nodule. Look for old films, arrange CT or referral, and document who is following it up. |
| Radiographer | Optimise inspiration and exposure; nipple markers or a repeat with a different projection can resolve some mimics. |
| Advanced / FRCR | Subtle hilar and apical lesions, the BTS nodule pathway, and differentials for multiple and cavitating nodules. |
Practise on real chest X-rays →
References
- Hansell DM, et al. Fleischner Society: glossary of terms for thoracic imaging. Radiology 2008;246(3):697–722. pubs.rsna.org
- Callister MEJ, et al. British Thoracic Society guidelines for the investigation and management of pulmonary nodules. Thorax 2015. brit-thoracic.org.uk
- NICE. Suspected cancer: recognition and referral (NG12). nice.org.uk
- NICE. Lung cancer: diagnosis and management (NG122). nice.org.uk
- Woodring JH, Fried AM. Significance of wall thickness in solitary cavities of the lung: a follow-up study. AJR 1983;140:473–474.
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.