The Urachus—An Aid to the Diagnosis of Pneumoperitoneum

Abstract

Two findings diagnostic of pneumoperitoneum, which may be seen on roentgenograms taken in the supine position, have previously been described: (a) the visible outer surface of bowel loops (5) and (b) a visible falciform ligament (4). Another finding, the urachus conspicuously outlined by free air, made the diagnosis of pneumoperitoneum possible in the case reported below. Miller (2) noted that the urachus was occasionally visible on supine roentgenograms of infants with pneumoperitoneum, but no such adult case was found in our review of the literature. A 75-year-old female was admitted to St. Anthony's Hospital eight hours after the sudden onset of epigastric pain. Shortly prior to admission nausea and vomiting had occurred. There was no previous history of abdominal distress, weight loss, change of bowel habit, hematemesis, or melena. The patient had been taking cortisone for chronic arthritis. She had no history of genitourinary abnormality. Physical examination disclosed moderate abdominal distension. The umbilicus was in normal position. Tympany was elicited upon percussion of the abdomen. Bowel sounds were infrequent and high-pitched. Upper abdominal tenderness was present, without rebound. A complete blood count and urinalysis were normal. The blood urea nitrogen was 48 mg per 100 ml. A “fiat film” of the abdomen showed a sharply defined triangular midline longitudinal soft-tissue shadow overlying the pelvis, not typical of bowel pattern or of any shadow normally seen (Fig. 1). The possibility that this was urachus was considered. The outer wall of one loop of small bowel was questionably visualized, but the falciform ligament could not be seen. An additional roentgenogram obtained in erect position confirmed a large pneumoperitoneum (Fig. 2). The patient was noted to have a protuberant lower abdomen, and it was apparently for this reason that air had selectively collected in the lower abdomen in the supine position. At celiotomy, moderate amounts of gas were released as the parietal peritoneum was incised. Bile-stained fluid was aspirated. A small perforation of the anterior wall of the duodenal bulb was identified and repaired. The exploration of the abdomen revealed a deep midline fold anteriorly in its lower part, lined by parietal peritoneum. Its appearance was in keeping with a prominent but normal urachal remnant. The bladder was in normal position. The postoperative course was uneventful. Embryology and Anatomy The cloaca originates from the caudal end of the primitive intestine with eventual differentiation into intestine and urinary bladder (3). The allantoic stalk develops as an endodermal diverticulum from the cloaca, without functional significance except that it accompanies the umbilical arteries which bring the maternal and fetal circulation into communication.