How to Interpret a Chest X-Ray:(Almost) everything a med student needs to

know

Dr Eric HeffernanSt Vincent’s University Hospital

Outline

• Introduction• Normal CXR- technical aspects• Normal Anatomy• Approach to Interpretation• Patterns of Abnormality

Introduction

• The CXR is the most commonly performed imaging procedure in general Radiology departments

• Comprises 30 – 50% of studies• One of the most difficult films to interpret– For Radiologists– For you… on-call… at night… on your own!

Technical Aspects

The Normal CXR

• Standard CXR is taken:– PA – minimal magnification of the heart– Patient standing– Full inspiration

• In ill patients, the CXR is usually taken:– AP – magnifies cardiac shadow– Often supine – diaphragms higher, lung volumes

lower, pathology often obscured

PA

AP

Effect of projection on apparent heart size

X-ray tube

PA

AP

Effect of projection on apparent heart size

X-ray tube

The Lateral CXR

• Purpose:– To pinpoint location of a lesion seen on PA– To identify lesions hidden behind the heart on PA

• Left lateral = left side of patient is against digital plate = standard lateral projection

• Right lateral = performed to assess a lesion in the right lung (decreases magnification of lesion)

The Lateral CXR

• In practice, lateral radiographs are not routinely performed any more so you will rarely have to interpret one

• We occasionally request one ourselves when reporting a PA chest radiograph, to clarify an apparent abnormality rather than going straight to CT

• When there is a definite abnormality on a PA radiograph that requires further investigation, we tend to go directly to CT nowadays

Additional CXR Views

• Lordotic– Direction of x-ray beam relative to patient is angled

upwards at 45 degrees– This projects clavicles above lung apices– Useful if suspect an apical mass but is obscured by

clavicle– Also useful if suspect an apparent apical lesion is

actually in a rib or clavicle• Decubitus– To confirm the presence of fluid suspected on upright

film (e.g. subpulmonic effusion)

Subpulmonic effusion on decubitus film• The PA film shows an apparently elevated right diaphragm• On the decubitus view, the effusion flows up along the side of the lung

Expiratory CXR

• Makes a pneumothorax appear relatively larger than on an inspiratory film

• PTx may only visible on expiration film• When you see the word ‘expiration’ on a CXR you

are almost certainly looking for a pneumothorax (especially in an exam!)

• Expiratory film is also useful in kids when looking for air trapping due to an obstructing foreign body – lung on obstructed side remains expanded

Inspiration - 500mls air in pleural space,2500mls in lung= 17% pneumothorax

Expiration - 500mls air inpleural space,1500mls in lung= 25% pneumothorax• Pleural line displaced further inferiorly

Pneumothorax on inspiration

Same patient on expiration – Pleural line is pushed lower and there is now evidence of tension

Densities Displayed on CXR

• Air

• Fat

• Water/soft tissue

• Calcium

• Bone

• Metal

Black

White

Normal CXR Anatomy

Normal PA CXR

Assessing for Rotation

Spinous process should be equidistant from medial ends of both clavicles

Trachea

Left main bronchus

Right main bronchus

Carinal Angle (40-75 degrees)

Right pulmonary artery

Left pulmonary artery

Aortic Arch

Descending Aorta

Aortopulmonary Window

Right Heart Border = Right atrium

Left Heart Border = Left Ventricle

Left Atrium

Cardiothoracic Ratio (<50%)

Anterior Ribs - full inspiration

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2

3

4

5

6

Gastric air bubble

Normal lateral CXR

Trachea

Scapulae

2 hemidiaphragms

Gastric air bubble

Aortic Arch

Left pulmonary artery

Left upper lobe bronchus

Right pulmonary artery

Left atrium

Left ventricle

IVC

Oblique Fissures

Fissures

Horizontal

Thoracic Vertebrae getting darker inferiorly(if the lower vertebrae appear denser, it suggests pathology in a lower lobe e.g. consolidation)

Interpreting the CXR

Rule #1 – Don’t panic!

Rule #1 – Don’t panic!

Before you start…

1. Check patient label – name, DOB, gender2. Orientation– R or L marker (?dextrocardia)– PA or AP (if not labeled, assume PA)– Inspiratory or expiratory (if not labeled = insp)– Erect or supine (again, if not labeled assume erect)– Rotated? (clavicles relative to spinous process!)

Rotated ED film

One lung field appears whiter,Difficult to assess cardiac silhouette

Same patient, better centred CXR

Traumatic diaphragmatic hernia

Don’t get caught out by markers!

Same image shown the correct way around – Patient had Kartagener’s Syndrome with situs inversus

Before you start…

3. Adequate exposure?– Should just about be able to see thoracic

vertebrae through heart• Can’t see them at all? – underexposed, everything too

white• Vertebrae and disk spaces very clear? – overexposed,

everything too dark• In over- and under-exposed CXRs, lung pathology is

easily obscured• This is less of a problem now that we have digital

radiography and automatic exposure control

Before you start…

4. Adequate inspiration?– Count ribs – choose one of these methods• 9 or 10 ribs posteriorly• 6 ribs anteriorly (I prefer this one)

– If inspiration is suboptimal, basal lung pathology may be obscured

Interpretation of Findings

ABCDEs

Interpretation of Findings

A – airwayB – breasts and bonesC – cardiovascularD – diaphragmE – examine the lungss – soft tissues

Airway

• Trachea, carina and main bronchi

Airway

• Trachea– Central?• Can be pulled by

– lobar collapse– fibrosis (e.g. old TB)– lobectomy

• Can be pushed by – mediastinal mass– tension pneumothorax– large pleural effusion

Airway

• Trachea– Narrowed?• Retrosternal goitre, other mediastinal masses

• Carina– Splayed?• Normal carinal angle is ~60 degrees (range 40-75)• Angle increased by subcarinal lymphadenopathy, left

atrial enlargement

Airway

• Bronchi– Narrowed?– Elevated or depressed?• Lobar collapse, lobectomy, fibrosis

Retrosternal goitre

Goitre

Trachea

Goitre on CT

Splayed carina due to left atrial enlargement (cardiomyopathy)

Breasts

• Mastectomy?– Makes underlying lung look relatively dark– Look for:• Lung mets• Pleural effusion• Interstitial disease (lymphangiitis)• Lymphadenopathy• Bone mets

Right mastectomy – arrow pointing at left breast shadowNote how relatively lucent the right lung appears.

Left mastectomyBeware of remaining nipple mimicking a nodule!

Right mastectomy - rib met and pathological fracture left humerus

Bones

• Destructive lesions – metastases• Erosion by adjacent tumour, e.g. Pancoast• Rib fractures– Sensitivity of CXR is less than 20%– However, when you see one look carefully for

pneumothorax, haemothorax, lung contusion• Shoulder dislocation

Rib met

Pancoast tumour – eroding second rib

Dislocated humeral head

Forequarter amputation – left clavicle and scapula missing

Cardiovascular system

• Heart size <50% of cardiothoracic ration on PA film

• Generalize cardiomegaly or specific chamber?• Valve replacement?• Sternotomy wires?• Pacemaker? – check for complications if

recently inserted (pneumothorax)

Left atrial enlargement in mitral stenosis - double right heart border, splayed carina

Sternotomy wires and aortic valve replacement

Cardiovascular

• Abnormal calcifications– Valves– Coronary arteries– Old infarct– Atrial myxoma– Previous pericarditis e.g. old TB

Cardiovascular

• Thoracic aorta – aneurysm?

• Aortopulmonary window – nodes?

• Hila - ?enlarged – nodes or vessels

Ascending thoracic aortic aneurysm

Cardiovascular

• Pulmonary vasculature– Generalized increase in vascular markings• Left to right shunt

– Focal or unilateral decrease in lung markings• Westermark’s sign (PE)

– Large central pulmonary arteries with sudden tapering• Pulmonary hypertension, e.g. chronic lung disease, PPH

Cardiovascular

• Pulmonary vasculature– Increased size of upper lobe pulmonary veins in

CCF – subtle early CXR sign• Finally, look BEHIND the heart– Lung nodule/mass– Hiatus hernia– Oesophageal dilatation (tumour, achalasia)

Upper lobe venous diversion- patient with mitral stenosis

Left atrial enlargement

Kerley B lines

Magnified Kerley B lines in same patient

Large hiatus hernia

Diaphragms

• Right higher than left by no more than 2.5 cm• Larger difference, or L higher than R– Phrenic nerve palsy e.g. tumour, surgery– Volume loss in lung e.g. lobar collapse, lobectomy,

pneumonectomy– Diaphragmatic hernia– Subpulmonic effusion

Diaphragms

• Depressed, flattened diaphragms– Hyperinflation (asthma, COPD, cystic fibrosis)

• GAS BELOW DIAPHRAGM (erect film)– Need to be sitting up for at least 20 minutes

• NO gas below diaphragm (no gastric air bubble)– Sign of achalasia

• Costophrenic angles - blunted?– pleural effusion

Pneumoperitoneum

Achalasia - no gastric air bubble

Same patient – Barium swallow

Examine the Lungs

• Are the lungs equal in density?• One lung too dark– Rotation– Mastectomy– Pneumothorax– Large bulla– PE

Left lung slightly dark-small pneumothorax

Examine the Lungs

• Are the lungs equal in density?• One lung too white– Solitary breast– Pleural effusion– Pleural mass (mesothelioma, mets)– Lobar collapse– Consolidation– Pulmonary mass

Large effusion with mediastinal shift

Effusion with absent meniscus - hydropneumothorax

Examine the Lungs

• Are the lungs equal in density?• Both lungs too dark– Overexposed film – check if vertebral bodies too

clearly seen– COPD• Count ribs (8 or more anteriorly)• Flattened diaphragms• Bullae

Emphysema • Flattened diaphragms• Too many ribs

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1

Examine the Lungs

• Are the lungs equal in density?• Both lungs too white– Underexposed film– Pulmonary oedema– Pulmonary fibrosis (what zones??)– Miliary shadowing – TB, mets

Pulmonary oedema - cardiomegaly

Examine the Lungs

• Are the hemithoraces equal in volume?– Increased volume• Tension pneumothorax• Large effusion• Expanded lobe (e.g. Klebsiella pneumonia)

Examine the Lungs

• Are the hemithoraces equal in volume?– Decreased volume• Lobar collapse• Lobectomy, pneumonectomy• Fibrothorax (restrictive, thickened pleura secondary to

old TB or empyema)• Diaphragmatic paralysis or rupture

Tension pneumothorax

Soft Tissues

• Surgical emphysema – neck and chest– Trauma– Surgery– Chest drain– Asthma

• When you see surgical emphysema, search very carefully for a pneumothorax and/or pneumomediastinum

Surgical emphysema – pneumothorax (arrow)

Patterns of Abnormality on CXR

CXR Patterns

• Having identified that the lungs are abnormal, you now need to decide what the problem is

• Which of the following patterns does the abnormality fit into?– Alveolar consolidation– Interstitial lung disease– Atelectasis (collapse)– Nodules and masses– Cavities and cysts– Calcification/ossification

Alveolar Consolidation

• Signs– May be localized or diffuse– Homogeneous, amorphous increased density– Ill-defined margins– Air bronchograms– No volume loss

Air bronchograms in left lower lobe and lingular pneumonia

Alveolar Consolidation

• Causes– Water (oedema)– Pus (pneumonia)– Blood (contusion, vasculitis, Goodpasture’s,

anticoagulation)– Chronic infiltrative lung disease (BOOP, alveolar

proteinosis, eosinophilic pneumonias)– Neoplasm (adenocarcinoma)– Aspiration (gastric contents, near-drowning)

Alveolar Consolidation

• Which lobe is involved?• Look for absent silhouette:– Right hemidiaphragm = RLL– Right heart border = RML– Left hemidiaphragm = LLL– Left heart border = lingula (of LUL)– None – could be upper lobes or apical segments of

lower lobes

RUL (above horizontal fissure) and lingular (obscuring left heart border) pneumonia

Horizontal fissure

RLL pneumonia LLL pneumonia (apical segment)

Small effusion(meniscus sign)

LLL pneumonia obscuring left hemidiaphragm

Interstitial Lung Disease

• Signs– Opacities• Linear (reticular – fine or coarse)• Nodular• Mixed (reticulonodular)

– Septal lines e.g. Kerley B– Honeycombing

Interstitial Lung Disease

• Examples– Reticular pattern• Fibrotic lung diseases

– UIP/CFA/IPF– Collagen vascular disease– Asbestosis

Interstitial Lung Disease

• Examples– Nodular pattern• Silicosis• Coal workers’ pneumoconiosis• Sarcoidosis• Miliary TB

Fine reticular pattern - Idiopathic pulmonary fibrosis

Nodular pattern - miliary TB

Atelectasis

• Signs– Opacification of a lobe– Volume loss• Displacement of fissures• Elevated hemidiaphragm• Mediastinal displacement• Tracheal displacement• Compensatory hyperinflation of opposite lung

Atelectasis

• Right upper lobe atelectasis– Collapses superiorly and medially– Wedge shaped opacity in right upper zone– Horizontal fissure displaced upwards– Oblique fissure displaced anteriorly on lateral CXR

Atelectasis

• Left upper lobe atelectasis– ‘veil’-like opacity in left hemithorax– Often obliterates left heart border silhouette (as

lingula is in LUL)– Elevated left hilum– Oblique fissure displaced anteriorly

LUL collapse - trachea displaced to leftleft hilum elevatedleft hemidiaphragm elevated

Atelectasis

• Right middle lobe atelectasis– Collapses medially obliterating right heart border– On lateral, see wedge-shaped opacity anteriorly– Pulls horizontal fissure downwards

RML collapse

Atelectasis

• Lower lobe atelectasis– Similar appearance on both sides– Obliterates normal silhouette of hemidiaphragm– On lateral CXR, see triangular density posteriorly

with increasing opacity of lower thoracic vertebrae

LLL collapse – ‘sail’ sign

LLL collapse – lateral

Nodules and Masses

• Nodule is <3cm, mass is >/= 3cm• Solitary or multiple?• Solitary – long differential diagnosis e.g.– Bronchogenic ca, granuloma, hamartoma, met

• Multiple – also long ddx– Mets, granulomas, rheumatoid nodules,

sarcoidosis

Bronchogenic carcinoma - background COPD and thoracic aortic aneurysm

Cannonball metastases

Cavities and Cysts

• Cyst = thin wall (< 3mm)– Fluid or air-filled, or both (air/fluid level)

• Cavity = thicker wall (> 3mm)– Always contain air +/- air/fluid level– Usually in an area of consolidation, a mass or a

nodule

Cavities or Cysts

• Types– Congenital

• Bronchogenic cyst• Cystic adenomatoid malformation

– Acquired• Infection – abscess, TB, fungal, septic infarct• Rheumatoid nodules• Wegener’s• Neoplasms - primary (SCC), mets• Bullae• Bronchiectasis

Cavitating pneumonia

Calcification and Ossification

• Nodules– TB, histoplasmosis, mets from osteosarcoma

• Diffuse– Alveolar microlithiasis– Silicosis– End-stage mitral stenosis– Healed infections – miliary TB, chickenpox

Multiple very dense lung masses – Metastatic osteosarcoma

Final Comments

• Before diving into a CXR, take a step back and look at the age/gender, any labels on the image (L/R, erect, AP, expiration), technical quality

• If you remember your ABCDEs you’re unlikely to miss any findings

svuhradiology.ie

Dr Eric HeffernanSt Vincent’s University Hospital