What is the significance of finding blunting of the costophrenic (costo-diaphragmatic) angle on a chest X-ray (X-ray)?

From the Guidelines

Blunting of the costophrenic angle on a chest X-ray is a significant finding that often indicates the presence of a small pleural effusion, which requires further evaluation to determine the underlying cause. This finding is crucial because it can be an early sign of various conditions, including heart failure, pneumonia, malignancy, pulmonary embolism, or inflammatory disorders. Normally, the costophrenic angles appear sharp and well-defined on X-ray; when fluid accumulates in the pleural space, these angles become rounded or "blunted." Even small amounts of pleural fluid (approximately 200-300 mL) can cause visible blunting, making this a sensitive indicator of early or mild effusions, as noted in the BTS guidelines for the investigation of a unilateral pleural effusion in adults 1. When this finding is observed, additional imaging such as lateral chest X-rays, ultrasound, or CT scans may be warranted for confirmation and better characterization of the effusion, as suggested by the European Respiratory Journal's statement on benign pleural effusions in adults 1. The clinical context is crucial in interpreting this finding, as the management approach depends entirely on identifying and treating the underlying cause rather than the effusion itself, which is merely a symptom of another process. Some key points to consider when evaluating blunting of the costophrenic angle include:

• The amount of pleural fluid that can cause visible blunting, which is approximately 200-300 mL, as mentioned in the BTS guidelines 1
• The potential underlying causes of the pleural effusion, such as heart failure, pneumonia, malignancy, pulmonary embolism, or inflammatory disorders
• The importance of additional imaging, such as lateral chest X-rays, ultrasound, or CT scans, to confirm and characterize the effusion, as suggested by the European Respiratory Journal's statement 1
• The clinical context and the need to identify and treat the underlying cause of the effusion, rather than just the effusion itself. It is also worth noting that the diagnosis of diffuse pleural thickening, which can be associated with blunting of the costophrenic angle, is often made using CT scans, and the newly revised ILO classification recognizes pleural thickening as diffuse "only in the presence of and in continuity with, an obliterated costophrenic angle" 1. Overall, blunting of the costophrenic angle is an important finding that requires further evaluation and consideration of the underlying cause, and the use of additional imaging and clinical context is crucial in making an accurate diagnosis and developing an effective management plan, as supported by the most recent and highest quality study 1.

From the Research

Importance of Finding Blunting of the Costophrenic Angle on Chest X-Ray

• The blunting of the costophrenic angle on a chest X-ray is an important finding that can indicate the presence of pleural effusion 2, 3, 4.
• Pleural effusion is an excessive accumulation of fluid in the pleural space, which can be caused by various disorders, including lung or pleura disorders, or systemic disorders 5.
• The diagnostic evaluation of pleural effusion includes chemical and microbiological studies, as well as cytological analysis, which can provide further information about the etiology of the disease process 5.
• A blunted costophrenic angle without pleural effusion can be an indicator of prior pleural disease, and its diagnostic accuracy for complete pleural symphysis is significant 6.
• The evaluation of the costophrenic angle can be an efficient, simple, and convenient screening tool for predicting complete pleural symphysis, with moderate sensitivity and high specificity, accuracy, and positive likelihood ratio 6.

Key Findings

• A computerized method for delineating the costophrenic angles in digital posteroanterior chest radiographs can detect abnormal blunting of the costophrenic angle 2.
• The use of thoracic ultrasound, computed tomography, magnetic resonance imaging, and positron emission tomography can play important roles in further investigation of pleural disease, but appropriate modality selection is critical 4.
• A blunted costophrenic angle can predict complete pleural symphysis with high specificity, accuracy, and positive likelihood ratio, making it a valuable screening tool 6.