What are the steps for interpreting a chest radiograph and formulating a diagnosis based on radiological findings?

Systematic Approach to Chest Radiograph Interpretation

The American College of Radiology recommends a consistent, systematic approach to chest radiograph interpretation that begins with technical quality assessment, followed by sequential evaluation of airways, mediastinum, lungs, pleura, diaphragm, and bony structures, with correlation to clinical findings to formulate a diagnosis. 1

Initial Technical Assessment

Before interpreting any radiographic findings, verify the following technical parameters:

• Confirm patient identification, examination date, and image quality including proper penetration, rotation, and degree of inspiration 1
• Recognize that posteroanterior (PA) and lateral views are superior to anteroposterior (AP) portable radiographs, which have significantly lower sensitivity for detecting pneumothorax, hemothorax, lung contusions, and rib fractures 2, 1
• Note that approximately 40% of patients with "normal" portable chest radiographs may have injuries detected on CT, highlighting the limitations of AP technique 1

Systematic Anatomical Review

Airways and Mediastinum

• Trace the trachea and main bronchi from top to bottom, noting any deviation, narrowing, or mass effect 1
• Assess mediastinal width and contour for widening that might suggest aortic pathology, lymphadenopathy, or mass lesions 1
• Evaluate the aortopulmonary window and hilar regions for abnormal masses, lymphadenopathy, or vascular enlargement 2, 1
• In suspected pulmonary hypertension, measure the main pulmonary artery (>35 mm from midline to left lateral border) and right descending pulmonary artery (>15 mm in women, >16 mm in men), which have 93% sensitivity and 88% specificity for pulmonary hypertension 2

Lung Parenchyma

• Systematically examine all lung zones (upper, middle, lower) in both lungs for opacities, nodules, masses, or areas of increased lucency 1
• Recognize that chest radiography has 69-75% sensitivity for detecting pneumonia, with lower sensitivity early in disease course 2
• Be aware that chest radiography misses up to 50% of pulmonary nodules and metastases compared to CT 3
• Look for patterns suggesting interstitial lung disease, emphysema, or consolidation that may guide further workup 2

Pleura and Diaphragm

• Trace both pleural surfaces completely, looking for effusions, pneumothorax, or pleural thickening 2, 1
• Assess both PA and lateral views for parapneumonic effusions, as positioning significantly impacts detection 2
• Evaluate diaphragmatic contours bilaterally for flattening (suggesting hyperinflation), elevation, or depression 2, 1
• Note that nodular pleural thickening with volume loss may suggest malignant pleural mesothelioma, though this finding is nonspecific 2

Cardiac Silhouette

• Assess cardiac size and contour for cardiomegaly or abnormal chamber enlargement 2
• In blunt trauma, look for enlarged cardiomediastinal silhouette, abnormal cardiac contour, or pneumopericardium as indirect signs of cardiac injury 2
• Recognize that right ventricular enlargement (95% prevalence) is a common finding in pulmonary hypertension 2

Bony Structures and Soft Tissues

• Systematically examine all visible ribs, spine, shoulders, and clavicles for fractures, lytic or blastic lesions 1
• Pay particular attention to ribs 3-9 in trauma patients, as displaced fractures in this region may indicate underlying cardiac or pericardial injury 2
• Assess soft tissues for abnormal air, calcifications, masses, or asymmetry 1
• Identify and verify proper positioning of all medical devices, including endotracheal tubes, central lines, chest tubes, and cardiac devices 1, 4

Recognition of Abnormal Findings

Common Radiographic Patterns

Consolidation (pneumonia):

• Chest radiography is the reference standard for diagnosing community-acquired pneumonia when combined with clinical symptoms (cough, fever, dyspnea, pleuritic chest pain) 2
• Both PA and lateral views are essential for detecting complications like parapneumonic effusions and abscesses 2

Pulmonary hypertension:

• Enlarged main pulmonary artery (97% prevalence), enlarged right ventricle (95%), and enlarged right descending pulmonary artery (93%) are the most prevalent findings 2
• Chest radiography has 96.9% sensitivity and 99.1% specificity for moderate to severe pulmonary hypertension, but is insensitive for mild disease 2

Pleural abnormalities:

• Asymmetric nodular pleural thickening with unilateral effusion and volume loss suggests malignant pleural mesothelioma, though cross-sectional imaging is required for definitive diagnosis 2

Critical Pitfalls to Avoid

• Perceptual errors are the predominant source of missed findings on chest radiography and a leading cause of malpractice litigation 5
• Chest radiography misses approximately 80% of hemothorax cases and 50% of vertebral and rib fractures compared to CT 2
• A normal chest radiograph does not exclude significant pathology—if clinical suspicion remains high for pneumonia, pulmonary hypertension, or other conditions, pursue further imaging 2
• In elderly or immunocompromised patients, pneumonia may present without fever, making radiographic confirmation even more critical 2

Formulating a Diagnosis

Integration with Clinical Data

• Correlate radiographic findings with clinical history, physical examination, and laboratory data to narrow differential diagnoses 2, 1
• Consider epidemiologic factors (alcoholism, COPD, nursing home residence, travel history, animal exposure) that suggest specific pathogens in pneumonia 2
• Use chest radiography for risk stratification in conditions like pneumonia to predict need for hospitalization 2

When to Pursue Advanced Imaging

• Order chest CT when radiographic findings are abnormal or equivocal and require further characterization 2, 1, 3
• CT is indicated when chest radiography is normal but clinical suspicion remains high for conditions like interstitial lung disease, pulmonary embolism, or occult trauma 2, 1
• For chronic dyspnea with normal radiography, CT is the most informative imaging test for detecting parenchymal disease 2
• In suspected pulmonary hypertension with normal or equivocal radiography, proceed to transthoracic echocardiography for definitive assessment 2

Specific Clinical Scenarios

Community-acquired pneumonia:

• Obtain PA and lateral chest radiographs as initial imaging 2
• If radiography is negative but clinical suspicion is high (especially in elderly or immunocompromised patients), consider CT 2
• Use radiography to identify complications (effusions, abscesses, multilobar involvement) that affect prognosis and management 2

Suspected pulmonary hypertension:

• Begin with chest radiography to detect moderate-severe disease, but recognize its poor sensitivity for mild disease 2
• Proceed to transthoracic echocardiography with contrast for definitive diagnosis, which has 85% sensitivity and 74% specificity 2

Blunt chest trauma:

• Obtain bedside AP chest radiograph as first-line imaging in hemodynamically unstable patients 2
• Look for indirect signs of cardiac injury (hemothorax, widened mediastinum, enlarged cardiac silhouette, pneumopericardium, displaced rib fractures) 2
• Recognize that chest radiography alone has limited ability to detect traumatic cardiac injuries—proceed to echocardiography or CT if clinical suspicion exists 2