The Football Sign

American Football with laces and seams.

The football sign, which is seen on supine abdominal radiographs, refers to a large oval radiolucency in the shape of an American football. The long axis of the “football” runs cephalocaudad, and the blunted ends are defined by the diaphragm and pelvic floor. A well-defined and vertically oriented linear opacity may be identified within the cephalic portion of the radiolucency, overlying the right upper abdomen. An additional, well-defined and vertically oriented linear opacity may be seen within the caudal portion of the radiolucency, overlying the midline of the lower abdomen.  

The oval radiolucency seen in the football sign represents massive pneumoperitoneum, which distends the peritoneal cavity. In the supine position, free air collects anterior to the abdominal viscera, producing a sharp interface with the parietal peritoneum and thereby creating the football outline. The pneumoperitoneum may outline the falciform ligament, which is seen as a faint linear opacity situated longitudinally within the right upper abdomen.

 

Also, the massive pneumoperitoneum may outline the median umbilical ligament, which comprises the urachal vestige, or may outline the medial and lateral umbilical ligaments, which comprise the umbilical arteries and inferior epigastric vessels, respectively. Similar to the appearance of the falciform ligament, these anterior abdominal body wall structures may be visualized as faint longitudinal linear opacities in the midline of the lower abdomen. Some authors describe these anterior abdominal wall structures as necessary components of the football sign; they represent the seams or laces of an American football.

Anteroposterior supine abdominal radiograph shows the football sign in a neonate with rectal perforation secondary to traumatic placement of a rectal tube. Pneumoperitoneum is seen as a large oval radiolucency demarcated by the parietal peritoneum of the abdominal wall (curved arrows). The falciform ligament (straight arrows) is outlined by air.                       

  

Conditions that result in a degree of pneumoperitoneum sufficient to create the football sign occur most commonly in infants. Massive pneumoperitoneum is much less common in adults and older children. In part, this may relate to the improved ability of older patients to communicate their abdominal symptoms, which leads to earlier intervention. A small-to-moderate volume of pneumoperitoneum in an adult may be inadequate to produce the football sign, but this may represent a relatively large amount of free air in a small infant.

Although the source of pneumoperitoneum may vary, the football sign is most frequently encountered in infants with spontaneous or iatrogenic gastric perforation. In many cases of perforated small bowel or perforating appendicitis, there is little to no pneumoperitoneum identified, which is likely because of the localized inflammatory process surrounding the perforation.

Other causes of pneumoperitoneum in neonates include necrotizing enterocolitis, bowel obstruction (i.e. malrotation with midgut volvulus, Hirschsprung disease, meconium ileus, or atresia), and sources of inflammation such as gastric or duodenal ulcers. Mechanical ventilation causing barotrauma and extra-ventilatory air can extend beneath the diaphragm, resulting in pneumoperitoneum without gastrointestinal perforation.

In most cases, the football sign in infants is DIAGNOSTIC of gastrointestinal perforation, and NO further imaging is necessary. With smaller quantities of extraluminal air, the football sign may be absent, and other features, such as air on both sides of the bowel wall or localized radiolucency, may be seen. Either left lateral decubital or cross-table lateral views are standard in assessment for pneumoperitoneum.

The football sign, seen at supine abdominal radiography, refers to a large oval radiolucency that represents a large amount of pneumoperitoneum in the shape of an American football. The ovoid appearance is the acknowledged hallmark of the football sign. Ancillary findings, including visualization of the falciform ligament or the umbilical ligaments, are also confirmatory of pneumoperitoneum and have been variously included in descriptions of this sign.