DOI: 10.1148/radiol.2311011290
(Radiology 2004;231:81-82.)
© RSNA, 2004
The Football Sign1
John W. Rampton, MD
1 From the Division of Diagnostic Radiology, Department of Radiology, Duke University Health System, Durham, NC. Received July 27, 2001; revision requested September 24; final revision received November 29, 2002; accepted December 20. Address correspondence to the author, 1047 Saint Gregory St, Cincinnati, OH 45202 (e-mail: john.rampton@cchmc.org).
Index terms: Abdomen, anatomy, 791.11, 791.92 • Pneumoperitoneum, 791.71 • Signs in Imaging
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APPEARANCE
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The football sign, which is seen on supine abdominal radiographs, refers to a large oval radiolucency in the shape of an American football (1). 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.
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EXPLANATION
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The oval radiolucency seen in the football sign (Figure) 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 (Figure). 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 (1,2). 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 (3,4).
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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.
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DISCUSSION
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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 (5). 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. Most of the published accounts of this sign are found in the pediatric radiology or pediatric surgery literature. Overall, the football sign is present in only 2% of adults with radiographically evident pneumoperitoneum (6); the incidence of the football sign in infants with radiographically evident pneumoperitoneum is not available in the published literature.
Although the source of pneumoperitoneum may vary, the football sign is most frequently encountered in infants with spontaneous or iatrogenic gastric perforation (1,7,8). 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 (1,9). Other causes of pneumoperitoneum in neonates include necrotizing enterocolitis, bowel obstruction (ie, malrotation with midgut volvulus, Hirschsprung disease, meconium ileus, or atresia), and sources of inflammation such as gastric or duodenal ulcers (1,2,7,10). Mechanical ventilation causing barotrauma and extraventilatory air can extend beneath the diaphragm, resulting in pneumoperitoneum without gastrointestinal perforation (5,9,11).
Until the early 1960s, pneumoperitoneum in infants was commonly confirmed with an upright radiograph depicting free air collection under the diaphragm. It was during this time that Roscoe E. Miller, MD, often cited as being the first to describe the football sign on supine abdominal radiographs (12), stated:
A new roentgen sign has been found on supine films by which the characteristic pneumoperitoneum may be recognized, namely, a huge oval shadow outlining the periphery of the peritoneal cavity. In the presence of a significant amount of fluid, this shadow appears as a large bubble of gas centrally located in the abdomen, divided in its cephalad portion, along its central longitudinal axis, by a narrow streak which represents the falciform ligament. Occasionally, the caudal half is divided by a similar streak, representing the urachus (the plica umbilicus media). The oval shadow produced by the air-filled dome of the distended abdomen has been likened in appearance to an American football. (1)
In this passage, the football appearance is directly attributed only to the configuration of the pneumoperitoneum. The identification of the falciform ligament and urachus are mentioned as other features of pneumoperitoneum, without specific reference to football laces or seams. While there is consensus that massive pneumoperitoneum resembles a football (2,5,6,10,13), authors subsequent to Miller have attributed these other features of pneumoperitoneum to the football sign. The falciform ligament has been described as a component of the football sign with no further clarification (14), as representing the football laces (3), or as representing the football seam, with the median or medial umbilical folds composing the caudal portion of the seam (15). Some references seem to imply that these findings are central components to the football sign (3,4). One report has cited Miller’s article, but the radiographic appearance of pneumoperitoneum outlining the falciform ligament was renamed in this report as the "falciform ligament sign" (16). For these reasons, it is not clear that any feature other than the ovoid air collection can be said to represent a portion of a football (and thus the football sign).
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.
In summary, 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.
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ACKNOWLEDGMENTS
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The author thanks Don Frush, MD, for his role as mentor and friend.
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FOOTNOTES
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A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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REFERENCES
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- Miller RE. Perforated viscus in infants: a new roentgen sign. Radiology 1960; 74:65-67.
- Buonomo C, Taylor GA, Share JC, Kirks DR. Gastrointestinal tract. In: Kirks DR, eds. Practical pediatric imaging: diagnostic radiology of infants and children. 3rd ed. Philadelphia, Pa: Lippincott-Raven, 1998; 890-893.
- Cho KC, Baker SR. Extraluminal air diagnosis and significance. Radiol Clin North Am 1994; 32:829-843.[Medline]
- Ebel KD, Blickman H, Willich E, Richter E, eds. Differential diagnosis in pediatric radiology New York, NY: Thieme, 1999; 289-290.
- Rice RP, Thompson WM, Gedaudas RK. The diagnosis and significance of extraluminal gas in the abdomen. Radiol Clin North Am 1982; 20:819-837.[Medline]
- Levine MS, Scheiner JD, Rubesin SE, Laufer I, Herlinger H. Diagnosis of pneumoperitoneum on supine abdominal radiographs. AJR Am J Roentgenol 1991; 156:731-735.[Abstract/Free Full Text]
- Pochaczevsky R, Bryk D. New roentgenographic signs of neonatal gastric perforation. Radiology 1972; 102:145-147.[Medline]
- Parrish RA, Sherman RT, Wilson H. Spontaneous rupture of the gastro-enteric tract in the newborn. Ann Surg 1964; 159:244-251.[Medline]
- Swischuk LE. The abdomen. In: Swischuk LE, eds. Emergency imaging of the acutely ill or injured child. 4th ed. Philadelphia, Pa: Lippincott, Williams & Wilkins, 2000; 146-289.
- McAlister WH, Kronemer KA. Emergency gastrointestinal radiology of the newborn. Radiol Clin North Am 1996; 34:819-844.[Medline]
- Zerella J, McCullough J. Pneumoperitoneum in infants without gastrointestinal perforation. Surgery 1981; 89:163-167.[Medline]
- Mulligan ME. Classic radiologic signs: an atlas and history New York, NY: Parthenon, 1996.
- Weiner CI, Diaconis JN, Dennis JM. The "Inverted V": a new sign of pneumoperitoneum. Radiology 1973; 107:47-48.[Medline]
- Cohen BE, Berman W. Radiological case of the month: rupture of the stomach in the newborn infant. Am J Dis Child 1970; 119:257-258.[Medline]
- Miller JA. The "football sign" in neonatal perforated viscus. Am J Dis Child 1961; 102:311-312.
- Richardson WR. Diagnosing surgical emergencies on the day of birth. Am J Dis Child 1961; 102:134-150.[Medline]
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