CXR Masterclass: The ABCDEF Approach for MRCP Part 1
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CXR Masterclass: The ABCDEF Approach for MRCP Part 1

TL;DR: 

For MRCP Part 1, chest X-ray (CXR) questions reward a disciplined, systematic read rather than pattern-spotting alone. The ABCDEF approach (Airway, Breathing, Cardiac, Diaphragm, Everything else, Fields/Failure) minimises missed signs, maps directly to exam stems, and improves accuracy under time pressure. This article explains the method, highlights the most tested patterns and traps, and includes a worked mini-case.


Why CXRs matter in MRCP Part 1

Chest radiographs appear regularly across respiratory medicine, cardiology, infection, and oncology. The images are chosen to test recognition of classic signs plus your ability to avoid common interpretive errors (projection, inspiration, devices). A structured approach is therefore essential.

Authoritative guidance on interpreting CXRs underpins UK postgraduate exams and aligns with how radiologists are trained to read films:


The ABCDEF approach (step-by-step)

A — Airway

Start centrally and orient yourself.

  • Tracheal position: Midline, deviated towards volume loss (collapse, fibrosis) or away from mass effect (large effusion, tension pneumothorax).

  • Carina and main bronchi: Widening may suggest left atrial enlargement or lymphadenopathy.

  • Tubes: Endotracheal tube tip should sit ~3–5 cm above the carina.

Exam tip: Right upper lobe collapse commonly causes tracheal deviation towards the affected side with a raised hilum.

B — Breathing (lungs and pleura)

Compare sides carefully, apex to base.

  • Parenchymal patterns

    • Alveolar: Fluffy opacities, air bronchograms (e.g. pneumonia).

    • Interstitial: Reticular or nodular markings (e.g. pulmonary oedema, fibrosis).

  • Pleura

    • Effusion: Blunted costophrenic angle, meniscus sign.

    • Pneumothorax: Visceral pleural line with absent peripheral lung markings.

High-yield diagnoses: Lobar consolidation, pneumothorax, pulmonary oedema, COPD hyperinflation.

C — Cardiac and mediastinum

Assess size, shape, and contours.

  • Cardiothoracic ratio (CTR): >50% suggests cardiomegaly on a PA film only.

  • Mediastinal width: Consider aortic pathology, lymphoma, or technical factors.

  • Pulmonary vessels: Upper lobe diversion suggests raised left atrial pressure.

Classic trap: Calling cardiomegaly on an AP film—heart size is exaggerated.

D — Diaphragm

A quick but important step.

  • Right hemidiaphragm normally up to 2 cm higher than left.

  • Blunted costophrenic angles indicate pleural effusion.

  • Free sub-diaphragmatic air implies perforated viscus until proven otherwise.

E — Everything else

This is where easy marks are often lost.

  • Bones: Ribs, clavicles, vertebrae (fractures, lytic lesions).

  • Soft tissues: Surgical emphysema, breast shadows.

  • Foreign bodies and devices: Pacemakers, central lines, NG tubes (tip should pass below the diaphragm into the stomach).

F — Fields / Failure (final sweep)

Finish with a global review.

  • Compare lung fields side-by-side.

  • Look for heart failure patterns: cardiomegaly, upper lobe diversion, interstitial oedema, pleural effusions.


Five most tested CXR subtopics in MRCP Part 1

  1. Collapse vs consolidation

    • Collapse: Volume loss, fissure displacement, tracheal shift towards.

    • Consolidation: Preserved volume, air bronchograms.

  2. Pulmonary oedema

    • Upper lobe diversion, Kerley B lines, perihilar “bat-wing” shadowing.

  3. Pleural effusion

    • Meniscus sign, blunted angles; large effusions push the mediastinum away.

  4. Pneumothorax

    • Peripheral pleural line with no lung markings beyond.

  5. Mediastinal masses

    • Use compartment thinking (anterior vs middle vs posterior mediastinum).

Radiopaedia offers excellent visual examples for these patterns and is widely used by UK trainees: https://radiopaedia.org


High-yield comparison table

Feature

Collapse

Consolidation

Pleural Effusion

Lung volume

Decreased

Normal

Reduced (compressed lung)

Trachea

Deviates towards

Midline

Deviates away if large

Air bronchograms

Uncommon

Common

Absent

Costophrenic angle

Sharp

Sharp

Blunted

Focused MRCP Part 1 study setup for chest X-ray and radiology revision

Mini-case (exam style)

Stem: A 72-year-old man presents with fever and productive cough. CXR shows a right mid-zone opacity with visible air bronchograms. Trachea is central. The right heart border is obscured.

Question: What is the most likely diagnosis?

Answer: Right middle lobe pneumonia.

Explanation: Air bronchograms and preserved lung volume indicate consolidation. Loss of the right heart border (silhouette sign) localises disease to the right middle lobe. Central trachea argues against lobar collapse.


Common pitfalls (exam favourites)

  • Diagnosing cardiomegaly on an AP film.

  • Missing a small apical pneumothorax.

  • Confusing collapse with consolidation by ignoring volume loss.

  • Forgetting to check lines and tubes.

  • Overcalling disease on a poorly inspired film.


Practical revision checklist

  • Use ABCDEF on every film, even if the diagnosis seems obvious.

  • Identify projection (PA vs AP) and degree of inspiration first.

  • Link CXR findings to clinical context in the stem.

  • Practise with mixed image sets rather than isolated examples.

  • Regularly review normal CXRs to recalibrate your eye.


FAQs

Is ABCDEF required for MRCP Part 1?

No single method is mandated, but a systematic approach is expected. ABCDEF is concise and exam-friendly.

How many CXR questions come up in MRCP Part 1?

Numbers vary, but CXRs recur reliably across respiratory and cardiology topics.

Do I need CT knowledge to answer CXR questions?

CT concepts help understanding, but answers are based on plain film findings shown.

Are AP films used in the exam?

Yes. Always identify projection, as AP films exaggerate heart size and reduce diagnostic confidence.


Ready to start?

Consolidate your CXR interpretation skills with exam-standard image practice. Revise this ABCDEF framework alongside timed MRCP-style questions and full-length simulations to improve speed and accuracy under pressure.👉 Practise now with free image-based questions in the Crack Medicine Qbank: https://crackmedicine.com/qbank/👉 Benchmark your progress with a full MRCP Part 1 mock test: https://crackmedicine.com/mock-tests/


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