What is the Costophrenic Angle?

The costophrenic angle is an anatomical term that describes the place where the diaphragm and chest wall meet. In most cases it is only visible, or at least is most visible, in an X-ray or other scan of the ribs and lungs. People generally have two, one on each side of the ribcage, and ideally each measures just about 30° and has a sharp point. Blunted or rounded angles are usually a sign of health problems. Radiologists and X-ray technicians in most places are specially trained to look out for problems with this angle, since these commonly indicate very serious conditions.

Most healthy humans have rib cages that angle downwards near the bottom. The ribs completely cover some organs, like the heart, but others, particularly the lungs and diaphragm, are only partially protected. In most cases half of the diaphragm hits the ribcage on each side near the bottom in such a way that it creates a sharply pointed angle known as the “costophernic” angle, so named for the root words costo, meaning “ribs,” and phrenic, meaning “diaphragm.”

There are a couple of different reasons why these angles may appear blunted or obscured on an X-ray, though fluid build-up in the lungs is one of the most common — and one of the most serious. Excessive fluid in the lungs is often considered an emergency situation, since it can inhibit breathing and can limit or cut off oxygen supply to many of the body’s vital organs. When this sort of fluid buildup is detected, surgeons may need to perform a tube thoracostomy, which is basically a procedure in which a chest tube is inserted in the pleural cavity to drain the fluid. X-ray technicians are usually trained to look for angle problems or variances that might indicate fluid buildup, since time is often very much of the essence. Prompt treatment is often life-saving.

Sometimes the angle is obscured or blunted because of degenerative conditions, too. Effusion, hemothorax, and hyper-expansion of the lungs are a few examples. Pleural effusion is the accumulation of fluid in the space surrounding the lungs, rather than in them, and often grows progressively worse slowly and with time. It is often caused by congestive heart failure, lung cancer, and lung infections like tuberculosis and pneumonia. In pleural effusion, fluid pushes the impacted lung upwards, which generally results in the blunting of the angle on that side of the body.

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, like an accident or serious injury. Hyper-expansion of the lungs is more common 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 other lung specialists. These medical experts often ask patients about their medical history, do physical exams, and request diagnostic tests like blood tests and imaging tests in order to have a baseline sense of a person’s condition and general health. It’s common for people with known lung problems to have X-ray scans somewhat regularly so that care providers can track problems and issues as they arise, rather than waiting for pain or other prompting.

When results show blunting of the costophrenic angle, doctors and nurses may perform thoracentesis to evaluate first whether fluid has gathered in the area, and if it has, what kind. A thoracentesis is a procedure 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, and the results that come back often shape future treatments.