What does a chest computed tomography (CT) scan show?

What Does a Chest CT Show?

A chest CT scan provides detailed cross-sectional imaging of the lungs, airways, mediastinum, pleura, chest wall, and cardiovascular structures, allowing for superior detection and characterization of pulmonary nodules, masses, airway abnormalities, interstitial lung disease, pleural effusions, mediastinal pathology, and vascular abnormalities that are often not visible on chest radiography. 1, 2, 3

Anatomic Structures Visualized

Pulmonary Parenchyma

• Nodules and masses: CT detects pulmonary nodules with high sensitivity, characterizing their size, location, shape, margins (spiculated, smooth, lobulated), and attenuation (solid vs subsolid) 1
• Morphologic features suggesting malignancy include spiculated margins (likelihood ratio 5.5), pleural retraction (LR 1.9), vessel sign (LR 1.7), and thick irregular cavitation 1
• Benign patterns include diffuse, central, laminated, or popcorn calcification, and the combination of round shape, smooth margins, and low attenuation predicts benignity with 100% accuracy 1

Airways and Bronchi

• Bronchiectasis: CT is the reference standard for noninvasive diagnosis, showing irreversible abnormal bronchial dilatation 2
• Bronchial wall thickening: Detected in 10-62% of patients with chronic cough, significantly associated with cough symptoms in COPD 2
• Tracheal stenosis: CT demonstrates degree of stenosis, extraluminal involvement, and extension to adjacent structures with high correlation to bronchoscopy findings 4
• Dynamic airway collapse: Expiratory CT imaging reveals tracheomalacia and excessive dynamic airway collapse 4

Mediastinum and Lymph Nodes

• Lymphadenopathy: CT identifies unsuspected mediastinal and hilar adenopathy, particularly when IV contrast is used to distinguish nodes from vessels 1, 5
• Mediastinal masses: CT can sometimes provide definitive diagnosis not obtainable by conventional radiography 6

Pleura and Chest Wall

• Pleural effusions: CT accurately detects and characterizes effusions, distinguishing simple from complex collections 3, 7
• Empyema: CT findings include split pleura sign, pleural thickening, loculation, and extrapleural fat stranding 3
• Pleural thickening and masses: CT differentiates benign from malignant pleural disease, especially with IV contrast 7

Interstitial Lung Disease

• Ground-glass opacities: CT detects subtle parenchymal abnormalities missed on chest radiography 2
• Fibrotic patterns: High-resolution CT is essential for diagnosing idiopathic pulmonary fibrosis and other interstitial pneumonias 8
• Centrilobular nodules and bronchiolectasis: Associated with chronic rhinosinusitis and cough 2

Vascular Structures

• Pulmonary metastases: CT provides superior spatial localization for detecting small pulmonary nodules compared to chest radiography (sensitivity 28% for radiography vs much higher for CT) 5
• Pulmonary embolism: CT angiography is the primary modality for diagnosis 9

Clinical Applications

Pneumonia and Complications

• Extent of disease: CT demonstrates overall disease extent providing prognostic information 10, 3
• Necrotizing pneumonia and abscess: CT detects these complications long before visible on chest radiography 10, 3
• Parapneumonic effusion: CT determines extent, degree of loculations, and guides drainage procedures 3

Chronic Cough Evaluation

• Abnormalities in 36% of patients with negative chest radiographs, most commonly bronchiectasis (12%) and bronchial wall thickening (10%) 2
• Interstitial lung patterns: Identified in 5% of patients with chronic cough 2

Lung Cancer Screening and Staging

• Low-dose CT: Used for lung cancer screening with structured reporting systems like LungRADS 11
• Incidental findings: Detected in 41-94% of baseline screening scans, though most are not clinically significant 11

COPD Assessment

• Emphysema quantification: CT estimates degree and distribution of emphysema 12
• Bronchial wall thickening and gas trapping: Correlates with lung function abnormalities 12
• Comorbidity detection: Identifies lung cancer, interstitial lung disease, pulmonary hypertension, coronary calcifications 12

Technical Considerations

Contrast Enhancement

• With IV contrast: Improves detection of mediastinal adenopathy, distinguishes nodes from vessels, increases conspicuity of empyema and pleural complications, and aids in characterizing soft tissue extension 3, 5, 4
• Without contrast: Adequate for most pulmonary parenchymal evaluation, nodule detection, and airway assessment 1, 4

Image Acquisition

• Thin-section imaging: Requires slice thickness ≤1.5 mm to avoid partial volume averaging that obscures airway anatomy and lesions 4
• Adequate breath-holding: Essential at inspiration to prevent motion artifact and false impression of bronchiectasis 4
• Dynamic expiratory imaging: Low-dose volumetric CT (40-80 mA) comparable to standard techniques for assessing tracheal collapse 4

Common Pitfalls

• Chest radiography limitations: Normal in 49 of 166 confirmed respiratory infections on CT, particularly missing ground-glass opacities, bronchial wall thickening, centrilobular nodules, and small consolidations 2
• Positive predictive value of chest radiography: Only 27% when compared with CT for pulmonary opacities 2
• Central lesions: May be missed by ultrasound due to intervening aerated lung 3