What is the recommended further workup for persistent blunting of the costophrenic (costophrenic angle) angle?

Workup for Persistent Blunting of Costophrenic Angle

For persistent blunting of the costophrenic angle, a contrast-enhanced CT scan of the chest extending to the level of L3 is the recommended initial diagnostic step, followed by ultrasound-guided pleural aspiration if fluid is present. 1, 2

Initial Imaging Evaluation

CT Scan Protocol

• Contrast-enhanced CT scan of the chest is the primary diagnostic tool 1, 2
  • Use multidetector CT scanner (at least 16-detector row)
  • Scan should extend caudally to level L3 to ensure complete coverage of posterior costophrenic angles
  • Use intravenous contrast (55-100 mL at 2-3 mL/s injection rate) when not contraindicated
  • Time acquisition at 60 seconds post-contrast with consideration of delayed imaging at 2-4 minutes
  • Reconstruct images in three planes: axial (1-2 mm), sagittal and coronal (1-3 mm)
  • Use both lung and soft-tissue kernels in reconstruction

Ultrasound Evaluation

• Chest ultrasound is highly valuable for further characterization 1, 2, 3
  • Superior to CT for visualizing fibrinous septations
  • Excellent for differentiating between pleural fluid and pleural thickening
  • Higher sensitivity (100%) than CT (54%) for detecting small pleural abnormalities in the costophrenic angle 3
  • Particularly useful for guiding diagnostic thoracentesis

Diagnostic Algorithm

1. Review CT findings for specific features:

   • Pleural thickening >1 cm (specificity 88% for malignancy)
   • Nodular pleural thickening (specificity 94% for malignancy)
   • Mediastinal pleural involvement (specificity 94% for malignancy)
   • Circumferential pleural thickening (specificity 100% for malignancy)
   • Chest wall invasion or diaphragmatic involvement 1, 2

2. If fluid is present:

   • Perform ultrasound-guided thoracentesis 1, 2
   • Send fluid for comprehensive analysis:
     • Cell count with differential
     • Total protein, LDH, glucose, pH
     • Cytology (first specimen yields diagnosis in 65% of malignant cases) 1
     • Consider immunocytochemistry to distinguish benign from malignant mesothelial cells 1

3. If no fluid or insufficient diagnostic yield from thoracentesis:

   • Consider image-guided pleural biopsy
   • For persistent diagnostic uncertainty, consider medical thoracoscopy, especially if:
     • Nodular lesions affecting the costal pleura are identified on ultrasound
     • Malignancy is suspected but not confirmed by less invasive means 3

Special Considerations

Asbestos Exposure

• If history of asbestos exposure, consider benign asbestos pleural effusion (BAPE) 1
• Look for concomitant signs of asbestos exposure:
  • Pleural plaques
  • Diffuse pleural thickening
  • Asbestosis
  • Folded lung/rounded atelectasis 1
• BAPE is a diagnosis of exclusion requiring:
  • Exclusion of malignancy through thorough workup
  • Monitoring for at least 24 months without development of malignant features 1

Complete Pleural Symphysis

• A blunted costophrenic angle with a measured angle <51° without pleural effusion has high specificity (96.1%) for complete pleural symphysis 4
• This finding may indicate prior pleural disease and should be noted for potential surgical implications

Pitfalls to Avoid

• Do not rely solely on plain radiographs - they have moderate sensitivity (67%) and specificity (70%) for pleural effusions 5
• Do not scan after complete drainage of fluid - pleural abnormalities are better visualized before drainage 2
• Do not overlook the need for multiplanar reconstruction - essential for assessing the full extent of pleural involvement 2
• Do not perform thoracentesis without ultrasound guidance - increases risk of pneumothorax and unsuccessful sampling 2
• Do not rely on a single cytology specimen - if first specimen is negative but suspicion remains, obtain additional specimens (second specimen adds 27% diagnostic yield) 1

By following this systematic approach to the workup of persistent blunting of the costophrenic angle, you can efficiently reach a diagnosis while minimizing procedural complications and avoiding diagnostic delays.