A pneumoperitoneum most commonly develops secondary to perforation of the GI tract (spontaneous, secondary from underlying GI disease, or traumatic), from the chest (respiratory causes: air leak with or without mechanical ventilation), or from no known cause (no respiratory or GI cause found), or a normal immediate postoperative finding. In a neonate, unless the infant is on high ventilator settings and has an air leak the cause is GI perforation until proven otherwise. Some classify pneumoperitoneum into medical (nonsurgical) versus surgical.
Pneumoperitoneum associated with GI perforation
Spontaneous perforation. (No demonstrable cause: no obvious gastrointestinal disease, no evidence of trauma or obstruction.) This is the second most common cause of GI perforation in neonates (most common is due to NEC). Proposed etiologies include local ischemia in the perinatal period (from asphyxia or shock) or from noncommunication of right and left gastroepiploic arteries, trauma during pregnancy or delivery, sepsis, prematurity, excessive gastric acidity, lack of intestinal cajal cells (gastric perforation), maternal use of steroids or cocaine, or congenital defects in the muscular wall of the stomach. Spontaneous perforation occurs most commonly in the terminal ileum in premature infants (spontaneous intestinal perforation [SIP]) or in the stomach (preterm and term infants); rarely occurs elsewhere in the GI tract.
Spontaneous gastric perforation. Occurs most commonly between the 2nd and 7th days of life in both full-term and preterm infants. It is more common in males and African American babies. Infants present with sudden abdominal distension, respiratory distress, vomiting, lethargy, and a massive pneumoperitoneum. Perinatal stress, prematurity, and postnatal steroid use are risk factors. Many of these infants have sepsis.
Spontaneous intestinal perforation (SIP). Occurs primarily in the terminal ileum (rarely in the jejunum and colon) in infants under 28 weeks' gestational age (GA), with low birthweight <1500 g (2–3%) and <1000 g (5%). Median age of presentation is 7 days, and it is more common in males. Prematurity and early steroid therapies are risk factors. Early postnatal exposure of indomethacin combined with steroids increases the risk of SIP. SIP is frequently associated with systemic candidiasis or coagulase-negative Staphylococcus. It does not have the clinical signs that NEC has (see Chapter 131).
Spontaneous colonic perforations. These can occur but are very rare. They are more common in preterm infants and very difficult to diagnose. Signs include significant abdominal and scrotal distension, vomiting, cyanosis, respiratory distress, and tachypnea. Most infants have a massive pneumoperitoneum.
Other perforations. Isolated perforations can occur elsewhere in the intestine, including the appendix, cecum, and Meckel diverticulum.
Medications associated with spontaneous perforation include indomethacin and steroids. A meta-analysis of the effect of early treatment (<96 hours) with high doses of steroids for chronic lung disease showed an increased risk of spontaneous GI perforation. Gastro-duodenal perforation has been associated with steroid therapy. Combined therapy (early postnatal indomethacin and glucocorticoids) increases the risk of SIP.
Other causes. Following exchange transfusion, perforation of small and large intestine can occur. Embolic phenomenon secondary to umbilical artery catheter can also contribute to perforation.
Secondary perforations. These are caused by an underlying disease: obstruction in the gastrointestinal tract or secondary to a gastrointestinal disease process.
NEC is the most common cause of secondary perforation. Mortality is high (>60%). Conflicting data exist on whether indomethacin increases the risk of NEC with intestinal perforation. The most common affected areas are the terminal ileum and ascending colon, although any part of the GI tract may be involved. Perforation occurs most commonly in the terminal ileum (ileocecal) region.
Gastrointestinal obstruction. Causes increasing intraluminal pressure and the perforation occurs proximal to the obstruction. It can occur anywhere in the gastrointestinal tract. Causes include any gastrointestinal atresia (esophageal atresia with tracheoesophageal [TE] fistula, duodenal/pylorus atresia, small/large intestine or anal atresia, and others), meconium ileus/plug, duplication cyst, small left colon syndrome, obstructive bands, Hirschsprung disease, and anorectal malformations (imperforate anus, incarcerated hernia, and others). Bowel perforation occurs in ∽3–4% of infants with Hirschsprung disease.
Gastritis or peptic ulcer disease. Perforation can be the initial presentation of ulcer disease. Perforations of the stomach (most common), duodenum, pylorus, or esophagus can occur.
Other rare causes. Malrotation with midgut volvulus, omphalocele, ruptured appendix, gastroschisis, mesenteric thrombosis, perforated Meckel diverticulum, idiopathic gastric necrosis, and pneumatosis cystoides intestinalis.
Traumatic perforations. An iatrogenic pneumoperitoneum caused by an intervention. Most gastric perforations are secondary to naso-/orogastric (NG/OG) placement or vigorous bag-and-mask/positive pressure ventilation.
Normal transient finding following laparotomy or laparoscopy.
Nasogastric tube trauma. Most gastric perforations are along the greater curvature due to trauma by vigorous NG/OG tube placement. Use of soft silastic feeding tubes may reduce this risk. An NG in an unusual position on x-ray (eg, right upper quadrant) indicates a possible perforation.
Intubation trauma. During an intubation, the endotracheal tube (ETT) can be inadvertently placed in the esophagus and then through the posterior wall of the stomach. If the ETT on chest x-ray (CXR) is seen more distally than expected, consider intubation trauma.
Bag-and-mask/positive pressure ventilation. Traumatic gastric perforation can occur from vigorous bag-and-mask ventilation or be due to positive pressure ventilation.
Neonatal rectal perforations of the sigmoid colon or rectum can be caused by a rectal thermometer or rectal tubes. Because of the shape of the neonatal rectum, when a rectal thermometer is placed to a depth of 2 cm, it impinges on the anterior wall. Insert a rectal thermometer <2 cm. An attempt to push it any further may result in perforation. Enema-induced perforations occur in the anterior wall of the rectum or rectosigmoid.
Improperly performed suprapubic bladder aspiration or paracentesis can perforate a hollow organ.
Umbilical vein catheterization can cause perforation of Meckel diverticulum.
Aerophagia (swallowing air) secondary to prolonged crying may cause gastric perforation. (There is a case report on an infant who had a circumcision with prolonged crying that may have caused a gastric rupture.)
Pneumoperitoneum associated with a respiratory disorder (eg, pulmonary interstitial emphysema [PIE], pneumomediastinum, or pneumothorax). A pulmonary air leak, with or without mechanical ventilation, can extend below the diaphragm resulting in a pneumoperitoneum. It can be secondary to barotrauma in ventilated neonates with severe respiratory disease. A thoracic leak can dissect transdiaphragmatically to the abdomen. An infant can have a pneumoperitoneum from thoracic air dissection without a pneumothorax or pneumomediastinum. Possibly an undetectable pulmonary rupture can occur with dissection into the peritoneal cavity. If there is a posterior pneumomediastinum, an air leak is probably the cause of the pneumoperitoneum.
Benign neonatal pneumoperitoneum with no known cause. There is no evidence of GI or respiratory pathology. Pulmonary rupture with a thoracic leak may not be apparent.
Pseudopneumoperitoneum. Occurs when there is a subphrenic lucency with no free intraperitoneal air. It can be from a subphrenic fat pad, linear atelectasis, abnormal subphrenic shape, subphrenic abscess, or Chilaiditi syndrome (interposition of a portion of the colon between the liver and diaphragm), which can present with respiratory distress. Gas can be seen between the liver and hemidiaphragm. This is gas-filled transverse colon. X-ray shadows can also cause a (false) radiographic pneumoperitoneum. A mimicked pneumoperitoneum includes a case report of transplacental passage of a nonionic contrast agent that resulted in opacification of the fetal bowel that mimicked a pneumoperitoneum.