Clinical skills15 min read·19 April 2026

UKMLA Chest X-ray Interpretation: Systematic Guide

A UKMLA chest x-ray masterclass — systematic ABCDE and RIPE approach, normal landmarks, lobar pneumonia and the silhouette sign, bronchopneumonia and aspiration, pulmonary oedema ABCDE radiology, simple vs tension pneumothorax with BTS 2023 conservative management, pleural effusion and Light's criteria, ARDS Berlin criteria, collapsed lobe patterns (Golden S and Luftsichel signs), TB radiology, lung cancer with Fleischner nodule follow-up and 2WW, mediastinal widening and the 4 Ts, NG/ETT/CVC safety checks, and 10 exam-pattern CXRs.

A plain chest X-ray is the most frequently ordered imaging investigation in UK hospitals and the single most-tested radiograph in the UKMLA. It will appear in respiratory stems, cardiology stems, trauma stems, paediatrics, post-operative safety, and critical-care stems. Candidates who approach every CXR with a consistent 60–90-second framework convert the investigation from a recognition lottery into a reliable source of marks.

This pillar teaches the systematic approach, ten high-frequency patterns, and the line-and-tube safety checks that appear in every ward round. Read it once, rehearse each pattern, and commit to the same reading order every time — exam and ward.

1. Why CXR interpretation is a UKMLA must-have

The GMC content map embeds CXR interpretation across at least 30 presentations. Expect to see a CXR in:

Breathlessness stems — PE, pulmonary oedema, pneumonia, pneumothorax.
Cough stems — CAP, TB, lung cancer, bronchiectasis.
Chest pain stems — pneumothorax, aortic dissection (widened mediastinum), pneumonia.
Trauma stems — rib fractures, flail chest, haemothorax, pneumothorax.
Post-op safety — NG tube placement, ETT position, CVC tip.
Paediatrics — bronchiolitis, croup (though AP neck more useful), foreign body.

The AKT rewards speed × systematic accuracy. Pattern-recognition alone produces false positives (e.g., mistaking a skin fold for pneumothorax, confusing RLL consolidation for cardiomegaly). The answer is a consistent algorithm.

Pair this pillar with our UKMLA Respiratory Masterclass for clinical integration and the UKMLA ABG Interpretation Algorithm for correlation with hypoxia.

2. ABCDE systematic approach to CXR

Every CXR is read in the same order, every time. Hospitals use variations of the ABCDE or DRSABCDE schemes. This is the version used across UK medical schools:

Details — patient name, date, time, projection (PA vs AP), rotation, inspiration.
RIPE — Rotation, Inspiration, Projection, Exposure check.
Airway — trachea central, carina visible, bronchi symmetric.
Breathing — lung fields (zones, vessels, costophrenic angles, pneumothorax, oedema, mass).
Circulation — heart size (cardiothoracic ratio), mediastinum, hila, aortic arch.
Diaphragm and bones — hemidiaphragm levels, subdiaphragmatic air, ribs, clavicles, spine.
Everything else — soft tissues, lines, tubes, pacemakers, breast shadows, surgical clips.

Key technical checks — RIPE:

Rotation — medial clavicle heads equidistant from spinous processes.
Inspiration — 5–7 anterior ribs or 9 posterior ribs visible above the diaphragm.
Projection — PA (preferred; posteroanterior — heart size accurate) vs AP (supine; heart magnified by ~15%). Marked on film.
Exposure — thoracic vertebrae just visible behind heart shadow. Over-exposed → lung detail lost. Under-exposed → small lesions missed.

An AP supine film from a critically-ill patient will exaggerate cardiac silhouette and widen the mediastinum. Do not call "cardiomegaly" on an AP film unless the ratio is dramatic.

3. Normal landmarks and anatomy

Know the normal before calling the abnormal.

Airway:

Trachea midline, narrowing at carina (T4–T5 vertebral level).
Right main bronchus more vertical than left (aspiration predilection for right lower lobe).

Lung fields:

Each lung divided into three zones (upper, mid, lower) for reporting — avoids lobe confusion on AP.
Normal vascular markings taper to periphery; absent peripheral markings = pneumothorax, bullae, or oligaemia.

Heart:

Cardiothoracic ratio (CTR) — heart width ≤50% of internal thoracic diameter (PA film).
Right heart border = right atrium; left heart border = left ventricle + left atrial appendage.
Aortic knuckle, left pulmonary artery, left atrial appendage, left ventricle — from top to bottom on left border.

Hila:

Left hilum should be equal to or slightly higher than right.
Both hila symmetric in size and density.
Raised/enlarged hilum suggests mass, lymphadenopathy, or elevation (lobar collapse).

Diaphragm:

Right hemidiaphragm usually 1–2.5 cm higher than left (liver).
Subdiaphragmatic free air = perforation.

Bones:

Count ribs, clavicles intact, scapulae symmetric, no vertebral collapse.

4. Lobar pneumonia — silhouette sign

Lobar consolidation — dense, well-demarcated opacity confined to a single lobe, often with air bronchograms (visible bronchi through opaque lobe).

Silhouette sign — loss of a normal anatomic border indicates that the lobe adjacent to that border is consolidated:

Right heart border loss → right middle lobe consolidation.
Left heart border loss → lingula consolidation.
Hemidiaphragm loss → lower lobe consolidation (right lower or left lower).
Aortic knuckle loss → left upper lobe consolidation.

Clinical integration: pneumonia diagnosis on CXR + clinical context (fever, sputum, CRP) → treat per CURB-65 and NICE NG138. Management and antibiotic choice in our UKMLA Respiratory Masterclass.

Follow-up: CXR at 6 weeks for all patients ≥50 with pneumonia to exclude underlying malignancy (NICE recommendation).

5. Bronchopneumonia and aspiration patterns

Bronchopneumonia — patchy, bilateral, lower-zone predominant infiltrates without lobar distribution. Commonest in elderly, immunocompromised, ICU patients.

Aspiration pneumonia — right lower lobe predilection (right main bronchus more vertical + gravity in supine). Delayed presentation → cavitation possible (necrotising → anaerobes).

Clinical features: reduced GCS, swallow dysfunction (stroke, neurological disease, dementia), post-anaesthetic, alcohol intoxication, NG misplacement.

Management: co-amoxiclav, clindamycin, or piperacillin-tazobactam per local guidance. SALT review before oral intake resumption. See our UKMLA Infectious Diseases pillar for antibiotic ladders.

6. Pulmonary oedema — batwing, Kerley B lines

Cardiogenic pulmonary oedema progresses through characteristic CXR stages (remember "ABCDE" for radiological oedema):

Alveolar oedema ("batwing" perihilar opacity).
B lines — Kerley B lines (short horizontal lines at lung bases, representing interlobular septal thickening).
Cardiomegaly (CTR >50% on PA).
Diversion of upper-lobe blood flow ("upper zone vessel prominence").
Effusions — usually bilateral, right greater than left.

Additional features: fissural fluid, peribronchial cuffing, air bronchograms (in severe oedema).

Clinical integration: with heart-failure symptoms, BNP, and echo → start loop diuretic IV, nitrate if acute + tolerating, oxygen targeted to saturations. For decompensation and shock, see our UKMLA Cardiology Masterclass and UKMLA Emergency Presentations pillar.

Trap: ARDS vs cardiogenic oedema — ARDS has patchy peripheral infiltrates, normal heart size, no effusions, often bilateral but without classic batwing. Context (sepsis, pancreatitis, transfusion) + PaO₂/FiO₂ ratio <300 = ARDS (Berlin criteria).

7. Simple vs tension pneumothorax

Simple pneumothorax:

Visible lung edge (visceral pleural line).
Absent lung markings peripheral to the line.
No mediastinal shift.
Size estimation (BTS): measure from hilum to the lung edge at the level of the hilum — ≥2 cm = large; <2 cm = small.

Tension pneumothorax — radiological signs:

Mediastinal shift away from the side of the pneumothorax.
Diaphragm depression on affected side.
Widened intercostal spaces on affected side.
Tracheal deviation away.
Do not wait for CXR — tension pneumothorax is a clinical diagnosis. Needle decompression (2nd ICS MCL or 4th/5th ICS AAL per ATLS) before imaging.

Management (BTS 2023 update — significant change from prior guidance):

Stable primary pneumothorax without significant symptoms → conservative management (observation) is acceptable, regardless of size.
Symptomatic or large primary → needle aspiration or chest drain.
Secondary pneumothorax (underlying lung disease) → lower threshold for drainage.
Recurrent → pleurodesis consideration.

Exam trap: skin folds can mimic pneumothorax — they usually extend beyond the lung field and are associated with skin texture. Look for absent peripheral vascular markings to confirm true pneumothorax.

8. Pleural effusion — meniscus, lateral decubitus

Small effusion (<300 mL):

Blunting of the costophrenic angle on PA/AP.
Lateral film more sensitive.

Larger effusion:

Meniscus sign — concave upper border of opacity against lateral chest wall.
Opacity graded by volume — as it enlarges it obscures hemidiaphragm → rises up chest.
Large effusion may push mediastinum away (massive effusion) — uncommon; think malignant.

Lateral decubitus X-ray — affected side dependent. Confirms free fluid vs loculated. Shifted layering confirms fluid.

Differentiating exudate from transudate:

Light's criteria — effusion protein:serum protein ratio >0.5 OR effusion LDH:serum LDH >0.6 OR effusion LDH >2/3 upper limit of normal serum LDH → exudate.

Exudate causes: infection (parapneumonic, empyema, TB), malignancy, PE, post-cardiac surgery, pancreatitis, RA/SLE.

Transudate causes: heart failure (commonest), cirrhosis, nephrotic syndrome, severe hypoalbuminaemia, Meigs' syndrome (ovarian fibroma).

Management: diagnostic tap for any new large effusion unless clear transudate (e.g., known HF + bilateral effusion responding to diuresis). Drain if empyema (pH <7.2 aspirate) or symptomatic.

9. ARDS — bilateral infiltrates, context

Berlin criteria (2012) for ARDS:

Acute onset (<1 week).
Bilateral infiltrates not explained by effusion, collapse, or nodules.
Not fully explained by cardiac failure or fluid overload.
PaO₂/FiO₂ ratio ≤300 mmHg on PEEP ≥5:
- Mild: 201–300.
- Moderate: 101–200.
- Severe: ≤100.

Common UK precipitants: sepsis (commonest), severe pneumonia, aspiration, trauma, pancreatitis, blood transfusion (TRALI), burns.

Radiological features:

Diffuse bilateral ground-glass + patchy consolidation.
Air bronchograms.
Usually peripheral, sparing costophrenic angles early.
Normal heart size distinguishes from cardiogenic oedema.

Management:

ICU admission.
Low tidal volume ventilation (6 mL/kg ideal body weight, plateau <30 cmH₂O).
Prone positioning ≥12 h/day if moderate-to-severe.
Conservative fluid strategy.
Neuromuscular blockade in severe cases.

10. Collapsed lobes — classic patterns per lobe

Right upper lobe collapse:

Elevated horizontal fissure.
Raised right hilum.
Opacity in right upper zone.
S sign of Golden — if mass cause (central lung cancer): reverse-S shape.

Right middle lobe collapse:

Loss of right heart border (silhouette sign).
Vague opacity in right mid zone.
Small on AP; best seen on lateral film (wedge-shape).

Right lower lobe collapse:

Loss of right hemidiaphragm outline.
Triangular opacity behind heart.
Preserved right heart border (differentiates from RML).

Left upper lobe collapse:

Opacity in left upper/mid zone.
Luftsichel sign — crescent of lucency between mediastinum and collapsed lobe.
Loss of aortic knuckle.

Left lower lobe collapse:

Triangular opacity behind heart ("sail sign").
Loss of left hemidiaphragm outline.
Preserved left heart border.

Complete lung collapse:

Opacified hemithorax.
Mediastinum pulled towards collapse (contrast with pleural effusion pushing mediastinum away).

Causes: mucus plug, aspiration, endobronchial tumour, foreign body, extrinsic compression (lymphadenopathy, vascular).

11. TB — apical infiltrates, cavitation, miliary

Primary TB (Ghon complex):

Mid-zone consolidation + ipsilateral hilar lymphadenopathy.
Often asymptomatic and calcifies (Ranke complex).

Post-primary (reactivation) TB:

Apical or upper-lobe predominance.
Cavitation — thick-walled, irregular.
Fibrosis, scarring, volume loss.
Lymphadenopathy less common than in primary.

Miliary TB:

Myriad small (1–3 mm) nodules throughout lung fields.
Described as "millet-seed" pattern.
Haematogenous dissemination.
Prognosis worse; often presents with fever of unknown origin.

Other TB patterns:

Pleural effusion — common manifestation in primary disease.
Bronchiectasis — post-inflammatory in chronic TB.

UK practice: notifiable disease, contact tracing, RIPE regimen + drug-sensitivity testing. Detail in our UKMLA Infectious Diseases pillar.

12. Lung cancer — coin lesion, hilar mass

Radiological patterns:

Solitary pulmonary nodule (coin lesion) — <3 cm. Malignancy risk rises with age, smoking, irregular margins, spiculation, size, and growth over time. Manage per Fleischner Society or BTS guidance.
Hilar mass — central lung cancer (usually squamous cell or small cell). May cause lobar collapse via endobronchial obstruction.
Mediastinal mass — small cell, lymphoma, thymoma.
Pancoast (superior sulcus) tumour — apical, may erode ribs/vertebrae; associated with Horner's syndrome, brachial plexus pain.
Cavitating mass — squamous cell carcinoma (malignant cavitation typically thick-walled, irregular) or necrotic infection.
Pleural effusion — often malignant in new presentation in elderly ex-smoker.

Red flags on CXR prompting 2-week-wait referral (NICE NG12):

Finding suggestive of lung cancer in any adult.
Unexplained pleural effusion.
Any unexplained mass in an ex-smoker >40.

Staging: CT chest/abdomen + PET-CT + biopsy (bronchoscopy or CT-guided). Treatment depends on histology (NSCLC vs SCLC) and stage.

Incidental nodule management — Fleischner/BTS guidance simplified:

<6 mm low-risk — no follow-up needed.
6–8 mm — repeat CT at 6–12 months; if stable, again at 18–24 months.
8 mm — PET-CT + biopsy.

13. Mediastinal widening — dissection, masses

Widened mediastinum = mediastinal width >8 cm on PA or >25% of chest width.

Causes:

Aortic dissection — especially with sudden-onset chest/back pain, unequal pulses, BP differential between arms. CT angiography urgent. Management: see UKMLA Cardiology Masterclass.
Aortic aneurysm — thoracic aortic aneurysm; saccular or fusiform.
Anterior mediastinal mass (four Ts) — Thymoma, Teratoma, Thyroid (retrosternal goitre), Terrible lymphoma.
Middle mediastinal mass — lymphadenopathy, bronchogenic cyst, aortic aneurysm.
Posterior mediastinal mass — neurogenic tumour (schwannoma, neurofibroma).
Lymphoma — bilateral hilar + mediastinal lymphadenopathy.
Sarcoidosis — bilateral symmetric hilar lymphadenopathy ("potato nodes").
AP film artefact — supine AP always appears wider than true PA. Re-image if stable.

Aortic dissection CXR clues:

Widened mediastinum.
Left pleural effusion.
Displacement of calcified intimal aortic wall ("calcium sign").
Depression of left main bronchus.

Caveat: a normal CXR does NOT exclude aortic dissection. CT angiography in all clinically suspected cases.

14. Line and tube positions (NG, ETT, CVC) — safety check

Nasogastric tube:

Tip below diaphragm AND on the left of the midline AND in the gastric bubble region.
Follows a gastric path (bisecting the carina, not deviating to right).
CXR is the gold standard for confirmation before feeding.
NEVER-events: misplaced NG with subsequent feeding — a National Patient Safety Agency Alert. Confirmed radiographically or with pH testing.

Endotracheal tube:

Tip 2–6 cm above carina (usually at T3–T4 level).
Too low → right main bronchus intubation → left lung atelectasis.
Too high → extubation risk, vocal cord trauma.
Check after every insertion, after repositioning, and after transfer.

Central venous catheter:

Tip in superior vena cava (at/above right atrium junction).
Not crossing into right atrium (arrhythmia, perforation risk).
Internal jugular CVC: tip in right heart border area.
Subclavian CVC: check for kinking or misdirection.
Always check for pneumothorax after subclavian or IJV insertion.

Chest drain:

Side-hole within pleural space (not subcutaneous).
Follows expected path.
No kinking.

Pacemaker:

Two leads: right atrium + right ventricle.
ICD: shock coil visible in lower portion.

Line and tube misplacement is a frequent UKMLA stem because errors cause serious harm. Know what normal looks like.

15. Ten UKMLA-exam CXR patterns

Rapid-fire recognition pairs — pattern, diagnosis, next action.

RLL consolidation + air bronchograms + silhouette of right hemidiaphragm → lobar pneumonia → treat per CURB-65.
Bilateral perihilar batwing + Kerley B + cardiomegaly + upper lobe diversion → pulmonary oedema → IV furosemide + oxygen + GTN if tolerating.
Visible lung edge + absent peripheral markings + no shift → simple pneumothorax → BTS-guided management.
Visible lung edge + mediastinal shift away + depressed diaphragm → tension pneumothorax → needle decompression before imaging.
Blunted CP angle + meniscus → pleural effusion → diagnostic tap with Light's criteria.
Apical cavitation + upper lobe fibrosis + weight loss stem → post-primary TB → AFB + notify.
Coin lesion in ex-smoker → SPN → size-based Fleischner follow-up or 2WW referral.
Widened mediastinum + tearing chest pain + BP asymmetry → aortic dissection → CT angiogram urgent.
NG tube tip appearing to deviate to right at carinal level → right main bronchus misplacement → withdraw before feeding.
ETT tip at/below carinal level in intubated patient → right main bronchus intubation → withdraw 2–3 cm.

Rehearse these until each pattern triggers the next action automatically.

Exam technique — the 60-90-second CXR read

On exam day you will not have time for a perfect reading. Compress it:

Glance — who is this, when was the film taken, rotation/inspiration/projection OK?
Trachea + heart size + mediastinum — 10 seconds.
Lung fields zone-by-zone — 20 seconds. Look for asymmetry.
Costophrenic angles + hemidiaphragms — 10 seconds.
Bones, soft tissues, lines — 10 seconds.
Commit — name the pattern, name the likely diagnosis, name the next management step.

Most SBAs test the action more than the name. "Pneumonia" is worth one mark; "IV co-amoxiclav + clarithromycin for a CURB-65 of 3" captures the whole stem.

Summary — five reflexes that win CXR SBAs

Read every CXR the same way, every time. Details → RIPE → A → B → C → D → E.
Silhouette sign localises consolidation by adjacent anatomic border loss.
Tension pneumothorax is a clinical diagnosis — needle decompression before CXR.
New pleural effusion → Light's criteria to separate exudate from transudate.
NG and ETT misplacement is a never-event. Confirm with CXR before feeding or leaving unsupervised.

Combine this pillar with the UKMLA Respiratory Masterclass for breathlessness algorithms, the UKMLA ABG Interpretation Algorithm for oxygenation correlation, the UKMLA Infectious Diseases pillar for pneumonia and TB management, and the UKMLA Emergency Presentations pillar for tension pneumothorax, aortic dissection, and ARDS recognition. CXR marks compound across specialties — drilling the systematic read pays off exam-wide.