From the Guidelines
The costophrenic angles become blunted when as little as 50 ml of pleural fluid accumulates, which can be detected on a lateral chest radiograph. This is because the lateral view is more sensitive to small amounts of fluid, allowing for earlier detection of pleural effusions 1.
Key Points to Consider
- The amount of fluid required to blunt the costophrenic angles is significantly less than what is typically visible on a standard chest X-ray, which requires around 200 ml of fluid 1.
- The lateral chest radiograph is more sensitive to small amounts of fluid, making it a valuable tool in the early detection of pleural effusions.
- Blunting of the costophrenic angles can be caused by various conditions, including pleural effusion, hemothorax, empyema, and heart failure.
- Further evaluation with ultrasound or CT scan may be necessary to confirm the presence of fluid and determine its cause, as treatment will depend on the underlying etiology.
Diagnostic Considerations
- Plain chest radiography, including PA and lateral views, should be performed in the assessment of suspected pleural effusion 1.
- Lateral decubitus films can be useful in differentiating between pleural thickening and free fluid, as free fluid will gravitate to the most dependent part of the chest wall 1.
- In the intensive care setting, supine chest radiographs may underestimate the volume of pleural fluid, and other signs such as the loss of the sharp silhouette of the ipsilateral hemidiaphragm and thickening of the minor fissure should be looked for 1.
From the Research
Costophrenic Angle Blunting
The costophrenic angles are blunted in the following conditions:
- Pleural effusion due to pulmonary embolism, which is usually small and occupies less than one third of the hemithorax in 90% of cases 2
- Prior pleural disease, as indicated by a blunted costophrenic angle without pleural effusion 3
- Complete pleural symphysis from adhesions, which can be predicted by a blunted costophrenic angle with moderate sensitivity and high specificity, accuracy, and positive likelihood ratio 3
- Pleural effusions in cardiovascular disease, such as left-sided CHF, which can cause unilateral right-sided or bilateral pleural effusions of similar size 4
Quantification of Pleural Effusion
The quantity of pleural effusion required to produce blunting of the lateral costophrenic angle on an erect posteroanterior radiograph is estimated to be between 175-525 ml 5
- Small to medium-sized effusions are typical in patients with uncomplicated CHF 4
- Larger effusions can cause more noticeable increases in density on supine radiographs, with classical findings of increased density over the entire hemithorax and apical capping seen in large effusions 5
Diagnostic Considerations
Diagnostic thoracentesis is not always required for evaluation of pleural effusions in patients with CHF, but is indicated when atypical features are present or other diagnoses are under consideration 4