Diagnostic Clues for Pneumoperitoneum in Premature Infants Through Ultrasonography: Two Newborn Cases


Pneumoperitoneum (PP) is a life-threatening condition that requires urgent intervention depending on etiology. Besides traditional methods for detecting free air in the abdominal cavity, abdominal ultrasonography may be an alternative tool for diagnosing intestinal injuries. We report two premature infants with PP diagnosed through bedside abdominal ultrasonography (BAUS). The first case was an extremely low-birth weight infant with PP due to necrotizing enterocolitis. The second case was 35 gestational-aged premature infants who had sudden abdominal distension. Abdominal ultrasonography use is trending in follow-up, especially in intensive care units and emergency departments. It is important to perform BAUS serially as a part of point-of-care ultrasonography application and consider with the physical examination in high-risk infants.


Pneumoperitoneum (PP) is defined as air leaks into the peritoneal cavity that often requires urgent surgical intervention. It is important to rule out a perforated viscus. There are sporadic reported cases of PP whose underlying cause remains uncertain.[1,2] Necrotizing enterocolitis (NEC) and spontaneous intestinal perforation (SIP) are the most common diagnoses in preterm babies with PP.[3]

Diagnosis of PP is usually based on characteristic plain abdominal X-ray findings abdominal radiograph (AR). Furthermore, bedside abdominal ultrasonography (BAUS) should be used for diagnosis, which is recommended to improve diagnostic accuracy.[4] High-resolution (8-15 Hz) linear transducers are typically recommended in the premies to determine PP, abdominal wall thickness, or pneumatosis intestinalis.[5] Color Doppler ultrasonography is often used to evaluate gut viability and intestinal mural perfusion.[6] BAUS is recommended to be performed in two stages. First, the superior mesenteric artery, portal venous gas, free fluid, or free air should be evaluated, and then the intestinal loops should be assessed. The abdomen is divided into four quadrants, and each quadrant is scanned in the transverse and sagittal planes.[7] Although it may take time to learn the application, BAUS, which can be performed quickly at the bedside, may be useful in diagnosing PP. It is crucial to perform BAUS at specific intervals and to pay close attention to typical BAUS images in the clinical course for patients with intestinal injuries. Herein, we report two premature babies with PP diagnosed by routine BAUS implementation.


Case 1

A 24 gestational week, 570 g preterm infant was born to a P1G1 mother by cesarean section for maternal hypertension. The antenatal steroid was not performed. Apgar scores were 5 and 6 at the 1st and 5th min, respectively. She was intubated and administered surfactant for respiratory distress. Anthropometric measurements were normal. An umbilical arterial catheter and umbilical venous catheter were inserted, and ampicillin and gentamycin were started. On day 3, she developed bilious gastric aspirate, abdominal distension, erythema, and tenderness. Routine evaluation with BAUS as a part of fellow training revealed abdominal free air with a strong linear echo as a pathognomonic peritoneal stripe sign [Figure 1] that was not previously present. Other signs of intestinal injury including, free fluid between loops, absent peristalsis, and thinning of the intestinal wall were also noted, despite the low sensitivity but high specificity to suggest NEC. An abdominal X-ray showed PP. Bedside peritoneal drainage using a Penrose drain was performed, and the stool leaked. Antibiotics were revised. However, she died due to septic shock on her 4th day of life.

Figure 1: 
Abdominal free air with a strong linear echo on liver region via BAUS. BAUS – Bedside abdominal ultrasonography

Case 2

A male infant was born at the 35th week of gestation after a twin pregnancy. He has a VACTERL phenotype with anal atresia, tracheoesophageal fistula, esophageal atresia, penile atresia, and limb anomalies. He was intubated for respiratory distress syndrome. Apgar scores were 5 and 7 at the 1st and 5th min, respectively. His birth weight was 1900 g (−1.54 standard deviation [SD]), height was 41 cm (−2,18 SD), and head circumference was 32 cm (0,29 SD). Ampicillin and gentamicin were started. On the 2nd day of life, he suddenly had abdominal distention and BAUS revealed PP. A diffuse A-line pattern with enhanced peritoneal stripes was seen, and the gas obscured the liver [Figure 2]. PP was also confirmed with an abdominal X-ray. Urgent exploratory laparotomy showed perforation in the stomach fundus region and duodenal atresia was diagnosed. Gastrostomy, duodenal atresia repair, and ileostomy were performed. Active bleeding developed around the ostomy after the procedure. The patient remained hypotensive and hypoxic despite hemodynamic and ventilatory support. On the postnatal 3rd day, the infant died due to multiorgan dysfunction.

Figure 2: 
Peritoneal stripe sign; reverberation artifacts are seen like lung A-lines


In this report, we describe two cases, in which PP was suspected based on clinical deterioration and confirmed by AR, as well as BAUS. PP is a rare condition that often requires urgent intervention. It is important to differentiate SIP from NEC, whereas SIP does not have signs of pneumatosis intestinalis or portal venous gas with PP on AR. Although plain AR is the gold standard choice of imaging tool for the diagnosis of NEC or SIP, BAUS is more sensitive for evaluating gut injury and provides more detail.[8] In addition, BAUS provides more valuable information than AR in evaluating intra-abdominal free fluid and intestinal viability that may require surgery and especially in evaluating the prognosis of NEC in premature infants.[9–11] Researchers found that BAUS is superior to AR for predicting the prognosis of NEC.[12] A study conducted by Cuna et al. showed that bowel ultrasound may be useful for the early identification of high-risk infants with NEC and that free air, absent peristalsis, complex ascites, and focal fluid collection are strongly associated with poor outcomes.[13]

Recently, BAUS has become a trending imaging modality for diagnosing and monitoring the disease progression of NEC and is widely used for other abdominal pathologies in neonates and pediatric patients.[13,14] It offers a number of advantages, including nonionization, real-time and serial evaluations, portability, and noninvasiveness. The limitations are the high skill set required and that no formal guidelines exist for neonatology training. It is critical that BAUS practitioners in the neonatal intensive care unit are supported by the radiology department and the providers.

Ultrasound images of the PP are very typical for diagnosis. PP demonstrates some sonographic signs through BAUS. Gas above the liver gives a bright reflection, called the peritoneal stripe sign when the patient is in a supine position. The liver image will be obscured by the gas, and a similar image as lung A-line-like reverberation artifacts are visible.[15] Respiration has no impact on intra-abdominal free air image obtained through BAUS. The free air should push away from the liver when the probe is gently compressed toward the abdomen. The gas should return after releasing the probe, making the reverberation artifact more apparent. In our cases, infants had a high risk for gut injury. BAUS is routinely used for infants with a high risk of NEC or abdominal pathology in our unit. PP was identified earlier during clinical progress, and urgent interpretation was performed. A bright reflection, a peritoneal stripe sign, was seen on BAUS, and the gas obscured the liver image [Video 1]. When the probe was gently pressed onto the abdomen, the free air pressed away from the liver, and then the release of the probe caused prominent reverberation artifacts [Video 2].


Diagnosis and follow-up of intra-abdominal incidents can be performed quickly, cheaply, and reliably with BAUS. Training programs and formal guidelines for the implementation of BAUS should be developed for neonatology practice.

Ethics approval and consent to participate

The parents of the patients provided written informed consent to participate in this study.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the parents have given their consent for their images and other clinical information to be reported in the journal. The parents understand that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1. He TZ, Xu C, Ji Y, Sun XY, Liu M. Idiopathic neonatal pneumoperitoneum with favorable outcome:A case report and review. World J Gastroenterol 2015;21:6417–21.
2. Sammut A, Soares Oliveira M, Jackson C, Sortica da Costa C. Pneumoperitoneum in a neonate weighing less than 500 g. What do we really know about it?. BMJ Case Rep 2018;2018:r–224398.