Is pleurisy visible on a computed tomography (CT) scan?

Pleurisy Visibility on CT Scans

Yes, pleurisy is visible on CT scans, appearing as pleural thickening with enhancement of both parietal and visceral pleural surfaces, often with a characteristic "split pleura sign" in cases of exudative effusions. 1

CT Imaging Features of Pleurisy

CT scanning can effectively visualize pleural inflammation (pleurisy) with several characteristic findings:

• Pleural thickening: Seen in 86-100% of empyemas and 56% of exudative parapneumonic effusions 1
• Pleural enhancement: With contrast-enhanced CT studies, both parietal and visceral pleural surfaces show enhancement 1
• Split pleura sign: Enhancing pleural tissue visible on both visceral and parietal pleural surfaces, indicating inflammation and exudation 1
• Increased attenuation of extrapleural fat: Inflammatory changes extend to adjacent tissues 1

Differentiating Features Based on Etiology

Different causes of pleurisy have distinguishing CT features:

Infectious Pleurisy (Parapneumonic/Empyema)

• Lentiform configuration of pleural fluid
• Visceral pleural thickening ("split pleura sign")
• Hypertrophy of extrapleural fat (>2 mm)
• Increased density of extrapleural fat
• Adjacent pulmonary consolidation 1

Tuberculous Pleurisy

• Regular pleural thickening often >1 cm
• Pleural effusion (present in 98.5% of cases)
• Hilar and mediastinal lymphadenopathy (in 39% of cases)
• May mimic malignancy with circumferential pleural thickening 1, 2

Non-infectious Inflammatory Pleurisy

• Mild smooth thickening of parietal pleura
• Not typically involving the mediastinum
• May develop pleuroparenchymal bands and folded lung in chronic cases 1

Malignant Pleural Disease vs. Benign Pleurisy

• Multiple pleural nodules and nodular pleural thickening are almost exclusively seen in malignant pleural disease 3
• Circumferential pleural thickening with nodularity involving the mediastinal surface suggests malignancy rather than benign pleurisy 1

Clinical Applications and Limitations

While CT is valuable for visualizing pleurisy, it has some limitations:

• CT cannot always reliably identify the stage of pleural effusion 1
• Septations within loculated effusions are better visualized with ultrasound than CT 1
• The absence of pleural thickening on CT suggests a simple parapneumonic effusion rather than complicated pleurisy 1
• Poor sensitivity (0.20-0.48) of CT features for distinguishing specific etiologies necessitates diagnostic thoracentesis for definitive diagnosis 1

Imaging Algorithm for Suspected Pleurisy

1. Initial imaging: Chest radiography to detect pleural effusion
2. Ultrasound: Confirm presence of fluid, assess for septations, guide thoracentesis
3. CT scan: Reserved for:
   • Diagnostic difficulties
   • Differentiating empyema from lung abscess
   • Cases failing to respond to initial management
   • Suspected malignancy
   • Immunocompromised patients
   • Pre-surgical planning 1, 4

Important Caveats

• Contrast-enhanced CT is preferred for evaluating pleurisy as it better demonstrates pleural enhancement 1
• Malignancy can co-exist with pleural infection in approximately 5% of cases, requiring follow-up imaging for up to 2 years if there are ongoing symptoms 1
• CT findings alone cannot definitively distinguish between all causes of pleurisy; pleural fluid analysis remains the most reliable diagnostic test 1
• In children, ultrasound is preferred over CT to avoid radiation exposure 1

Remember that while CT is excellent for visualizing pleural pathology, the definitive diagnosis of the underlying cause of pleurisy typically requires pleural fluid sampling and analysis.