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People who interpret medical images look for abnormal visual information in a scan of a patient that can help point them toward the presence of a medical problem. The football sign is one of these, and it represents the presence of air inside the chest in places it shouldn't be. Most often found in young children, the football sign is only recognizable in x-rays, as the scan can pick up the football-shaped area of the body where a dark patch of air is visible in contrast to the lighter colored areas of tissue.
The football sign is so named because of its distinctive American football shape. This has an oval appearance as opposed to a spherical soccer football. Air is less dense than cells, so it appears darker and more translucent than cells under an X-ray, which are more opaque. It is a possible symptom of a condition called pneumoperitoneum, which simply means that the patient has abnormal collections of air inside his or her abdomen.
Small children have smaller abdomens than adults, which may make a football sign more obvious in these cases than in adults, whose larger abdomens may dissipate the free air more thoroughly. In addition, pneumoperitoneum is more likely to occur in babies than in older people. Even though the football sign is a distinctive sign of pneumoperitoneum, it is not present in all cases, and is rarely seen in adults with the condition.
Pneumoperitoneum arises most often when a patient has damage to the organs that lets air into the abdominal space. In healthy people, the abdominal space is airtight and acts as a storage and protection space for organs. Normally, air moves though the digestive system and escapes either as gas or as burps from the mouth.
It is only when the stomach or intestine develops a hole somewhere that the air makes its way into the abdomen. The air responds to gravitational forces, and it only forms a bubble in the shape of a football when the patient is lying down. If the patient was standing up, the air tends to collect under the diaphragm in a different shape.
Gastric perforation, which is a hole in the stomach, is a possible cause of the football sign. Necrotizing enterocolitis, which is an infection that rots the intestine, is another possibility. Hirschsprung disease, which is a congenital nerve deficiency of the intestine, can also cause the football sign, along with other diseases that can cause the intestine to become blocked. In addition to disease causes, a patient can also develop air bubbles in the abdomen from artificial ventilation, where a machine pumps air into the patient's lungs.