Chest X-Ray Interpretation
A board-focused, systematic walkthrough of chest X-ray interpretation for Step 2 CK: the RIPE quality check and ABCDE read, classic buzzword findings mapped to diagnoses, and vignette-driven next-best-step decisions for CHF, tension pneumothorax, and perforated viscus.
Read every film the same way
A chest radiograph is only as good as your system — read every film identically so you never miss the finding you weren't looking for. First confirm technical quality with RIPE: Rotation (medial clavicle heads equidistant from the spinous processes), Inspiration (9–10 posterior ribs; fewer suggests poor effort or restriction), Penetration (vertebrae faintly visible behind the heart), Exposure/patient details.
Know the projection. A PA film is upright with the back to the tube — the heart sits near the detector, so cardiac size is accurate (cardiothoracic ratio >0.5 = cardiomegaly). A portable AP film magnifies the heart and mediastinum, so you cannot reliably call cardiomegaly or a widened mediastinum on AP. Then read structures in order (ABCDE) instead of jumping to the obvious lesion. The board trap is anchoring on a lung nodule while missing free air under the diaphragm or a tension pneumothorax at the edge of the film.
- Air bronchograms = alveolar/airspace filling → lobar pneumonia (also edema, hemorrhage)
- Silhouette sign localizes disease: lost right heart border = RML; lost left heart border = lingula; lost hemidiaphragm = lower lobe
- Kerley B lines + cephalization + cardiomegaly + effusions = cardiogenic pulmonary edema
- Batwing/perihilar airspace opacity = cardiogenic pulmonary edema / volume overload (central pattern; ARDS is typically peripheral and patchy)
- Blunted costophrenic angle + meniscus = pleural effusion (~200 mL needed on upright PA; ~50 mL on lateral)
- Visceral pleural line with absent peripheral markings = pneumothorax; deep sulcus sign = pneumothorax on a supine film
- Free air under the diaphragm (upright film) = perforated viscus
- Widened mediastinum after trauma or tearing chest pain = aortic injury/dissection
- Upper-lobe cavitation = reactivation TB; miliary micronodules = disseminated TB/fungal
- Bilateral hilar adenopathy = sarcoidosis
RIPE checks image quality; ABCDE reads the film in order:
- A — Airway: trachea midline (pulled toward collapse, pushed away by tension pneumothorax or a large effusion); carina, main bronchi
- B — Breathing: lung fields top-to-bottom, compare left vs right; pleura and costophrenic angles
- C — Circulation: heart size (CT ratio <0.5 on PA), mediastinal contour, aortic knob
- D — Diaphragm: both hemidiaphragms (right normally higher), costophrenic angles, and air under the diaphragm
- E — Everything else: bones (rib fractures, lytic lesions), soft tissue, and devices — ET tube tip 3–5 cm above the carina (neck neutral), NG tube tip below the diaphragm in the stomach, central-line tip at the cavoatrial junction
Classic sign → diagnosis
| CXR finding | Classic diagnosis |
|---|---|
| Air bronchograms + lobar consolidation | Bacterial (pneumococcal) pneumonia |
| Kerley B lines, cephalization, cardiomegaly | Cardiogenic pulmonary edema / CHF |
| Blunted costophrenic angle, meniscus | Pleural effusion |
| Deep sulcus sign (supine film) | Pneumothorax |
| Free air under diaphragm (upright film) | Perforated viscus |
| Widened mediastinum after trauma | Traumatic aortic injury / dissection |
| Boot-shaped heart | Tetralogy of Fallot |
| Egg-on-a-string mediastinum | Transposition of the great arteries |
| Water-bottle heart | Large pericardial effusion |
| Bilateral hilar adenopathy | Sarcoidosis |
| Upper-lobe cavitary lesion | Reactivation tuberculosis |
| Cannonball metastases | RCC, choriocarcinoma |
Vignette: A 76-year-old man with a prior MI has 3 days of worsening dyspnea, orthopnea (now sleeping on 3 pillows), and paroxysmal nocturnal dyspnea. Exam: bibasilar crackles, an S3, and JVD. CXR shows cardiomegaly, upper-lobe vascular redistribution (cephalization), Kerley B lines, and small bilateral pleural effusions.
Diagnosis: Acute decompensated heart failure with cardiogenic pulmonary edema.
Next best step: IV loop diuretic (furosemide) for preload reduction, supplemental O2, and sit the patient upright; add nitrates for afterload if hypertensive. Send a BNP and get an echocardiogram to confirm and assess ejection fraction. Kerley B lines are fluid-distended interlobular septa — the interstitial phase that precedes frank alveolar (batwing) edema.
Vignette: A 24-year-old man arrives after a motorcycle crash with sudden severe dyspnea. BP 82/50, HR 130. Exam: absent breath sounds and hyperresonance on the right, distended neck veins, and the trachea deviated to the left.
Diagnosis: Tension pneumothorax — air trapped under pressure shifts the mediastinum away and kinks venous return, producing obstructive shock.
Next best step: Immediate needle decompression (large-bore angiocatheter — 5th intercostal space anterior axillary line per current ATLS, or 2nd space midclavicular line), then tube thoracostomy. Do NOT wait for a CXR — tension pneumothorax is a clinical diagnosis and imaging first can be fatal. Contrast with a simple pneumothorax (stable vitals, no mediastinal shift), where you confirm on an upright CXR before placing a chest tube.
Vignette: A 60-year-old man with chronic NSAID use develops sudden severe epigastric pain that becomes diffuse, with a rigid, board-like abdomen. Upright CXR shows a thin crescent of free air under the right hemidiaphragm.
Diagnosis: Perforated viscus — perforated peptic ulcer causing pneumoperitoneum.
Next best step: NPO, IV fluids, broad-spectrum antibiotics, IV PPI, and an urgent surgical consult for exploratory laparotomy. If the upright film is nondiagnostic but suspicion is high, a left lateral decubitus film (free air rises over the liver edge) or CT abdomen detects smaller volumes of free air. Pitfall: free air is reliably seen only on an upright film taken after the patient has been sitting up for several minutes — a supine portable film can miss it entirely.
Differentiating the white/black hemithorax
| Feature | Pneumothorax | Pleural effusion | Consolidation |
|---|---|---|---|
| Density | Lucent (black), no lung markings | Opaque (white), dependent | Opaque (white), lobar |
| Key sign | Visceral pleural line; deep sulcus (supine) | Blunted CP angle, meniscus | Air bronchograms |
| Mediastinal shift | Away (if tension) | Away (if large) | Toward (if collapse) |
| Breath sounds | Decreased, hyperresonant | Decreased, dull, ↓ fremitus | Bronchial, dull, ↑ fremitus |
| First step | Decompress (tension) / O2 | Thoracentesis if large or symptomatic | Antibiotics for pneumonia |
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