Teaching Case

A 15-day-old male neonate, premature (born at 24 weeks of gestation) and with a history of hyaline membrane disease, was transferred from another hospital to our emergency department with 1-day abdominal distension and signs of sepsis.

An anteroposterior supine abdominal radiograph (Figure 1) reveals a large, vertically oriented, oval-shaped radiolucent area in the central part of the abdomen, outlined by the parietal peritoneum along the abdominal wall. The falciform ligament is distinctly visualised and well-demarcated. The scrotal sacs are distended by a radiolucent image.

First described by Dr Roscoe E. Miller in the 1960s, the football sign has been widely used in paediatric radiology. This sign is identified on supine abdominal radiographs and appears as a large, oval, radiolucent area shaped like an American football, representing a massive pneumoperitoneum that distends the peritoneal cavity. In the supine position, the free air accumulates anterior to the abdominal organs, creating a distinct interface with the parietal peritoneum, which results in a football-shaped outline. The long axis of this “football” is oriented cephalocaudally, from the diaphragm to the pelvic floor [1,2].

The pneumoperitoneum can outline the falciform ligament, appearing as a faint linear opacity running longitudinally in the right upper abdomen. Similarly, it may outline the median umbilical ligament or the medial and lateral umbilical ligaments. Like the falciform ligament, these anterior abdominal wall structures may appear as subtle vertical linear opacities in the midline of the lower abdomen. Visualisation of these structures further supports the diagnosis of pneumoperitoneum and they are often described as part of this radiologic sign, interpreting them as resembling the seams or laces of an American football [1,2].

This sign is most commonly observed in neonates. In adults, however, it is exceptionally rare. Lin et al. reported the first clear image of this sign in an adult, and to our knowledge, remains unique in the literature. A small to moderate amount of pneumoperitoneum may be insufficient to produce the football sign in adults, but the same volume can represent a substantial amount of free air in a small infant [1,3].

In our case, the pneumoperitoneum was secondary to necrotising enterocolitis complicated with ileal perforation (stage IIIb) and underwent a successful surgical intervention. There is even the presence of air within the scrotum, a condition known as pneumoscrotum. This is due to the patency of the processus vaginalis. Air from the pneumoperitoneum can travel into the scrotal sac through this embryologic defect, which is very common in infants, occurring in approximately 60% of them [4].

In conclusion, the football sign observed on supine abdominal radiography is indicative of substantial pneumoperitoneum, being virtually diagnostic of gastrointestinal perforation, and no additional imaging is required [1].

Written informed patient’s family consent for publication has been obtained.