The word costophrenic is a combination of two words — costo, meaning ribs, and phrenic, meaning diaphragm. An angle is usually seen where the diaphragm and the chest wall meet. This is known as the costophrenic angle and this is often seen in X-rays. Normally, the costophrenic angle measures about 30 degrees and often has a sharp point. In several disorders, blunting or increase in the size of the costophrenic angle can be observed.

Examples of disorders associated with blunting of the costophrenic angle include pleural effusion, hemothorax, and hyper-expansion of the lungs. Pleural effusion is the accumulation of fluid in the space surrounding the lungs. It is often caused by congestive heart failure, lung cancer, and lung infections such as tuberculosis and pneumonia. In pleural effusion, fluid often gathers in the lower portion of the infected lung, pushing this lung upwards. This generally results in the blunting of the costophrenic angle of the affected lung.

When blood accumulates in the space around the lungs, it is called a hemothorax. A hemothorax frequently results from direct trauma to the thorax or chest area. Hyper-expansion of the lungs is commonly seen in patients with asthma and emphysema. When the lung hyper-expands, it pushes the diaphragm downwards, which also leads to the blunting of the costophrenic angle in one or both lungs.

Patients with lung disorders are often managed by pulmonologists, or lung specialists. They often ask about their medical history, do physical exams, and request diagnostic tests like blood tests and imaging tests. The X-ray results are usually read by a radiogist, an expert in reading imaging tests. When results from the chest X-ray reveal blunting of the costophrenic angle, doctors may perform thoracentesis to evaluate the type of fluid that has gathered in the area.

A thoracentesis is a procedure performed by surgeons that involves the insertion of needle through the skin into the pleural cavity. Several fluid samples are then collected and sent to the laboratory for analysis. Treatment often depends on the results of this analysis.

When readings from the chest X-ray reveal blunting of the costophrenic angle and the cause is massive build up of fluid or blood in the pleural cavity, it is often considered an emergency situation. Surgeons may need to perform tube thoracostomy. Tube thoracostomy is a procedure in which a chest tube is inserted in the pleural cavity to drain the fluid which continue to accumulate in the affected region.