© 2021, Gupta R
Received Day: 03 Month: 09 Year: 2020
Accepted Day: 25 Month: 11 Year: 2020
J Neonatal Surg. 2021; 10: 6.
DOI: 10.47338/jns.v10.930
Spontaneous pneumoperitoneum: Discerning from radiological imaging
Rahul Gupta Department of Paediatric Surgery, SMS Medical College, Jaipur, Rajasthan, India
[corresp] Dr. Rahul Gupta, Assistant Professor, Department of Paediatric Surgery, SMS Medical College, Jaipur, Rajasthan India E-mail: meetsurgeon007@gmail.com
Abstract

Background: Pneumoperitoneum without any gastrointestinal (GI) perforation or peritonitis is entitled spontaneous pneumoperitoneum. We aimed to describe a radiological perspective in spontaneous pneumoperitoneum.

Methods: This case series presented data of 4 cases of spontaneous pneumoperitoneum managed at our institution.

Results: There were 85 patients with a provisional diagnosis of necrotizing enterocolitis (NEC) and/or pneumoperitoneum. Out of these, there were 4 patients with the final diagnosis of spontaneous pneumoperitoneum; three males and 1 female. At presentation, respiratory distress was seen in 3. It was preceded by mechanical ventilation in 3 patients. All 4 had soft abdominal distension, absence of features suggestive of peritonitis, and the presence of free air with an absence of air-fluid level in peritoneal cavity on erect abdominal radiographs. The Rigler sign was present in 3 patients. Abdominocentesis followed by abdominal drain placement was performed in 2 patients. Laparotomy was performed in 1 patient which could not point to any pathology (negative). An unfavorable outcome was seen in one patient with associated esophageal atresia. No patient had any evidence (either ultrasound/radiological or on laparotomy) of leakage of contents from the GI tract.

Conclusions: In infants, especially preterm neonates, presenting with soft abdominal distension with abrupt onset of pneumoperitoneum, without clinical features of peritonitis and preceded by mechanical ventilation, diagnosis of spontaneous pneumoperitoneum should be considered.

Keywords: Mechanical ventilation, Neonate, Rigler sign, Spontaneous pneumoperitoneum.

INTRODUCTION

Pneumoperitoneum in neonates is classically due to gastrointestinal (GI) perforation.[1] In contrast, pneumoperitoneum without any GI perforation or peritonitis is entitled spontaneous pneumoperitoneum.[1], [2] These neonates may improve primarily with conservative management or may require abdominocentesis and/or abdominal drain placement.[3] The author managed 4 cases of spontaneous pneumoperitoneum and is sharing his experience along with a review of radiological findings pertinent to spontaneous pneumoperitoneum.

METHODS

This study was performed from October 2018 to February 2020. The data of 4 cases of spontaneous pneumoperitoneum were analyzed and special emphasis was put on radiological findings that can differentiate spontaneous from pathological pneumoperitoneum.

All patients were admitted to the intensive care unit. Enteral feeds were stopped and nasogastric tube placement was performed. Intravenous fluids and parenteral nutrition were initiated in all patients along with broad-spectrum antibiotics. Baseline blood investigations including complete blood counts, serum electrolytes, CRP, renal, and liver functions were performed. Abdominal Radiographs, both erect (AP) and supine views were performed, initially 12 hourly for the first 48 hours and then 24 hourly after 48 hours. Additional views including the lateral decubitus view were performed, when required. Ultrasound with color Doppler was performed to evaluate the GI pathology i.e. perforation/gangrenous bowel/ischemia and associated malformations.

Patients with or without pneumoperitoneum with clinical, laboratory signs and ultrasonography suggestive of perforation or peritonitis were optimized, subjected to exploratory laparotomy, and managed separately. Patients with pneumoperitoneum and without clinical signs suggestive of peritonitis were managed on the lines of spontaneous pneumoperitoneum. All patients were closely observed for the development of signs suggestive of peritonitis. Conservative management was contemplated; abdominocentesis followed by abdominal drain placement was considered in these patients.

RESULTS

Clinical records revealed 85 pediatric patients with a provisional diagnosis of either necrotizing enterocolitis (NEC) and/or pneumoperitoneum due to gastrointestinal (GI) perforation. Out of these, 73 manifested with pneumoperitoneum including 4 patients with spontaneous pneumoperitoneum.

Of these 4 cases, 3 were males and 1 female, and the age of presentation ranged from 1 day to 4 months. Three patients were born preterm. Three patients presented with respiratory distress. One had major malformation i.e. esophageal atresia (EA) Vogt type 3b with retroperitoneal cystic swelling. Presentation of spontaneous pneumoperitoneum was preceded by mechanical ventilation in 3 patients. Two patients were hemodynamically stable at presentation, while poor general condition with hemodynamic instability was present in the other two. Abdominal examination revealed soft distension in all 4 patients. Signs of peritonitis were absent in all the patients. Table 1 showed the clinical profile of these patients.

Pneumoperitoneum with air under both the domes of the diaphragm was seen in all 4 patients on erect abdominal radiographs (Fig. 1)(Fig. 2)(Fig. 3)(Fig. 4). There was an absence of free fluid in the peritoneal cavity evident by the absence of air-fluid level in the peritoneal (abdominal) cavity i.e. outside bowel loops in all the patients. Dilated small bowel loops were seen in 3 out of 4 patients. Rigler sign or double-wall sign was present in 3 patients. Radiographic evidence of pneumothorax (simultaneously present with pneumoperitoneum) was seen in 1 patient (Fig. 4). Pneumoscrotum was appreciated in 2 patients (Fig. 3)(Fig. 4).

C-reactive protein (CRP) was done in 2 patients and was raised in both. In the other two, CRP could not be performed due to resource limitations. Ultrasound was performed in all except in a patient with EA. Ultrasound examination didn’t suggest any perforation or visceral pathology, apart from the presence of pneumoperitoneum in all 3 patients.

Initial conservative management then abdominocentesis followed by abdominal drain placement was performed under ultrasound guidance in 2 patients; these two had favorable outcomes. Laparotomy was performed in 1 patient after initial conservative management for 24 hours. This decision was taken because of raised CRP (117mg/L) levels in addition to the diagnostic dilemma in management. It was negative for any perforation and the outcome was favorable. Due to the long-gap EA, esophagostomy and gastrostomy were performed, following transfixation and ligation of trachea-esophageal fistula in one patient. Laparotomy revealed free air but the etiology of which could not be identified. This patient had an unfavorable outcome purported to be due to associated cardiac anomalies and severe sepsis. No patient had any evidence of leakage of GI contents, either radiological or on insertion of abdominal drain/laparotomy. No patient had a recurrence of the pneumoperitoneum in follow up (3 months to 1 year) and doing well.

DISCUSSION

Pneumoperitoneum in a neonate is classically due to GI perforation and necrotizing enterocolitis (NEC).[3], [4] Pneumoperitoneum is usually diagnosed by an erect abdominal radiograph showing free air under the domes of the diaphragm. In the neonates the other radiographic signs include, (a) rounded or oval lucency over the upper abdomen in the supine position, (b) increased lucency i.e. triangular or a semilunar collection of air anterior to the abdominal viscera or above the liver in lateral decubitus position, (c) large volume of free air may give rise to the football sign, where the air outlines the whole of the peritoneal cavity and under the surface of the diaphragm, (d) the lacing of the football i.e. outlining of falciparum ligament of the liver against the radiolucency of free abdominal air on supine view [4], [5], [6] (e) Rigler sign or double-wall sign is free gas on both sides of the bowel wall,[4], [5] (f) pneumoscrotum has been explained due to presence of patent processus vaginalis and passage of air from the peritoneal cavity into the scrotum.[3], [5], [6]

The clinical findings in pneumoperitoneum secondary to NEC or neonatal GI perforation include features of peritonitis, tense abdominal distension, palpable, distended bowel loops, shiny red induration of abdominal wall, tenderness, muscle stiffness, guarding, shifting dullness, and absent (decreased) bowel sounds.[3], [7] Besides, systemic features of sepsis, like fever and toxemia are present (Table 2). These features are insidious in onset and progressive in nature and categorized as surgical pneumoperitoneum and an urgent laparotomy is mandatory to improve the outcome.[1], [3], [4]

In patients with NEC or other GI pathologies, the presence of significant intraperitoneal fluid in the abdominal cavity on radiographs is seen as gas-filled loops of bowel which float centrally in the abdomen.[5] Ultrasound is a more specific investigation for the diagnosis of intraperitoneal fluid.[5] Ultrasound with color Doppler can access bowel wall thickness, echogenicity, peristalsis, perfusion, and bowel viability.[4]

Visualization of pneumatosis intestinalis on radiographs and/or on ultrasound with underlying clinical features is suggestive of NEC. A linear or crescent type is more specific than a bubbly or foamy gas pattern.[5] Demonstration of fixed bowel loop sign and portal venous gas is diagnostic of NEC. The presence of a large air-fluid level in the peritoneal cavity with ground-glass opacity in the lower abdomen along with an absence of gas-filled dilated bowel loops is highly suggestive of pneumoperitoneum due to hollow viscus perforation.[5]

Pneumoperitoneum in a pediatric patient especially premature neonate with soft abdominal distension, without clinical features suggestive of perforation peritonitis/ NEC (as described above) and preceded by mechanical ventilation and is known as non-surgical, asymptomatic, benign, misleading, medical, idiopathic, or spontaneous pneumoperitoneum. It is also occasionally called CPAP (Continuous Positive Airway Pressure) belly syndrome.[1], [2], [3], [4], [5] The condition is rare in clinical practice.[1], [2], [3], [4], [5] In our study, it was seen in 5.48% (4) patients out of 73 cases of pneumoperitoneum. In addition to lack of definite causes (NEC, gut perforation, etc.), there is usually the absence of systemic features like fever and toxemia, though these features could be due to the presence of associated malformations as seen in 50% of patients in our study (Table 2).

In case of spontaneous pneumoperitoneum, the onset is abrupt usually following mechanical ventilation.[1], [2], [3] The pathogenesis of spontaneous pneumoperitoneum is an air-leak from the lungs as shown in the flowchart (Fig. 5). This is more common with high and prolonged airway pressure during mechanical ventilation or CPAP. In our study, the condition was preceded by mechanical ventilation in 75% (3), while it was 55.56% in our previous study.[3] The presence of pneumothorax (as seen in one of our cases) or pneumomediastinum immediately before or simultaneously with pneumoperitoneum is an indicator of spontaneous pneumoperitoneum.[3], [10]

Before labeling a patient with spontaneous pneumoperitoneum, other causes like NEC, spontaneous intestinal perforation (SIP), gastric perforation, and perforations as a complication of neonatal intestinal obstruction should be ruled out. A comprehensive clinical evaluation with frequent abdominal examination for ruling out peritonitis, laboratory workup for ruling out sepsis, radiological evaluation for the presence of pneumonitis, pneumothorax (or pneumomediastinum), and abdominal ultrasonography should be performed.

Management comprises of stabilization of the patient, nil per oral along with close surveillance for signs suggestive of peritonitis and/or systemic signs.[1], [3] Conservative management is contemplated and may be successful in 33.33% of patients.[3] Abdominocentesis followed by abdominal drain placement (continuous evaluation of the peritoneal contents) is diagnostic and therapeutic (relieving respiratory embarrassment due to splinting of the diaphragm). It also confirms the presence of free air and rules out leakage of GI contents.[3] Abdominocentesis or abdominal taping has been therapeutic in other studies.[7] Unnecessary laparotomy could be avoided in 50% of patients in our study. Complete resolution of pneumoperitoneum may take 2 to 10 days, which was a similar finding (2 to 5 days) in our study.[3]The algorithm for the management of spontaneous pneumoperitoneum is explained in (Fig. 6)

CONCLUSION

Spontaneous pneumoperitoneum is a rare entity in patients admitted with a provisional diagnosis of pneumoperitoneum in the neonatal period and/or NEC with pneumoperitoneum. In preterm neonates having major congenital malformations presenting with soft abdominal distension with abrupt onset of pneumoperitoneum without clinical features of peritonitis and preceded by mechanical ventilation, the diagnosis of spontaneous pneumoperitoneum should be considered. An unnecessary laparotomy that increases morbidity and mortality can be avoided in patients of spontaneous pneumoperitoneum with a high index of suspicion.


Figures

Figure 1 

Abdominal radiographs (erect) (A) showing pneumoperitoneum with gas under the diaphragm (red arrows), Rigler sign (white arrows) and outlining of falciparum ligament (black arrow); supine image (B) showing Rigler sign (white arrows); erect image (C) showing resolution of pneumoperitoneum after abdominal drain placemen.



Figure 2 

Abdominal radiographs (erect) (A) showing gas under the diaphragm (red arrows), Rigler sign (white arrow); supine image (B) showing pneumoperitoneum (red arrows), outlining of falciparum ligament (black arrow); erect image (C) showing resolution of pneumoperitoneum (blue arrow) with abdominal drain in-situ.



Figure 3 

Abdominal radiographs (erect) (A) showing gas under the diaphragm (red arrow), Rigler sign (white arrows); supine image (B) showing pneumoperitoneum (red arrow) and pneumoscrotum (yellow arrow).



Figure 4 

Abdominal radiographs (erect) (A) showing gas under the diaphragm, absence of gas-filled bowel loops, endotracheal tube in-situ, and features of pneumonitis; supine image (B) also showing pneumothorax (red arrow). Pneumoscrotum (yellow arrow) is appreciable in both images (A and B).



Figure 5 

A flow chart to explain the pathogenesis of spontaneous pneumoperitoneum in pediatric patients.



Figure 6 

Algorithm for the pneumoperitoneum.



Tables
[TableWrap ID: t1] Table 1 

Clinical details, investigations undertaken, management details, and outcomes of patients with spontaneous pneumoperitoneum.


Patient data Case 1 Case 2 Case 3 Case 4
Sex Male Female Male Male
Age 10 days 34 days 4 months 1 day
Maturity Preterm Term Preterm Preterm
Weight 1800g 2300g 1500g 2100g
Clinical presentation Respiratory distress (48 Hours)FeverIncreasing Abdominal distensionBilious vomiting Sudden Abdominal distensionBilious nasogastric tube aspirate Respiratory Tract infection Sudden Abdominal distensionNon-Bilious nasogastric tube aspirate FrothingDrooling of salivaRespiratory distressAbdominal distension
Fever Afebrile Afebrile Afebrile Afebrile
Associated illness or malformations Discolored skin patch (nevus) on the left ear Nil Inguinal hernia EA type 3b (long gap)Cardiac murmurRetroperitoneal cystic swelling
Meconium passed Within 24 hours Within 24 hours Within 24 hours Within 24 hours
Mechanical ventilationBefore the presentation Yes No YesCPAP YesHigh flow oxygenAMBU support
General Condition Poor Respiratory distressMild dehydration Stable Stable PoorRespiratory distressVentilatory support
Abdominal examination Soft Moderate Distension Soft Distension Soft, but MarkedDistension Soft Distension
Pneumoperitoneum Present (both domes, right > left) Present (both domes) Present(both domes, right > left) Present (both domes)
Large Air-fluid level in peritoneal cavity outside bowel loops Absent Absent Absent Absent
Dilated small bowel loops Present Present Present Absent
Multiple Air-fluid levels Absent Absent Absent Absent
Rigler sign Present Figure 1 Present Figure 2 Present Figure 3 Absent Figure 4
Pneumothorax Absent Absent Absent Present
Pneumoscrotum Absent Absent Present Present
Pneumonitis Present Nil Present Present
CRPOther Investigations Not donePlatelets 42,000/mm3 Positive (42mg/L)Platelets 71,000/mm3TLC 23,100/mm3 Positive (117mg/L)Hypoproteinemia TLC 13,500/mm3 Not done
Ultrasound abdomen Dilated bowel loopsPneumoperitoneum Dilated bowel loopsPneumoperitoneum Dilated bowel loopsPneumoperitoneum Not done
Provisional Diagnosis NEC NEC NECPerforation peritonitis EA type 3bSpontaneousPneumoperitoneum
Procedures performed Abdominal drain placement only (Diagnostic & therapeutic) Abdominal drain placement only (Diagnostic & therapeutic) LaparotomyNo evidence of any intra-abdominal pathology Primary repair of EA failed; chest tube EsophagostomyGastrostomyNo evidence of perforationAbdominal drain placement
Content of peritoneal cavity Air-only Air-only Air-only Air-only
Pneumoperitoneum to disappear 2 days 4 days 5th day postoperatively -
Postoperative Ultrasound abdomen Minimal free fluidNormal bowel loops No air bubbles Fluid-filled dilated bowel loopsSlight air bubbles noted in the interlobar fissure of the liverBowel wall edema present Not done (as laparotomy was performed) Not done (Postoperative mortality)
Oral feeds 4th day 3rd day 3rd day -
Discharge 5th day 4th day 7th day Mortality
Outcome Favorable Favorable Favorable Unfavorable
Cause of Unfavourable outcome - - - Sepsis, Cardiac anomalies

[TableWrap ID: t2] Table 2 

Differences between spontaneous pneumoperitoneum and pneumoperitoneum due to bowel perforation (surgical pneumoperitoneum)


Clinical Laboratory &Radiological Characteristics Specific Characteristics Surgical pneumoperitoneum Spontaneous pneumoperitoneum
Clinical Characters Age group All Neonates (Newborn) especially with prematurity, LBW
Abdominal distension Present Present ( Sudden Abdominal distension at admission or later)
Pain Present Absent
Onset Gradually progressive Sudden onset
Prior history of respiratory distress Usually Absent Usually present RDS, pneumonia (tachypnea)
Preceded by mechanical ventilation Absent Present (CPAP, Pressure support)
Associated malformations Absent Usually present
General Condition Unstable Usually stable
Toxaemia (systemic signs) Present Absent
Abdominal Examination Abdominal wall Shiny, red, oedematous, induration Normal
Abdominal Swelling orPalpable distended bowel loops Usually Present Absent
Distension Tense distension Soft distension with relaxed abdominal wall
Tenderness (Peritonitis) Present Non-tender
Rebound TendernessMuscle Guarding Present Absent
Shifting dullness Present Absent
Bowel sounds AbsentDecreased Normal
Cardiovascular Examination Cardiovascular instability Usually Present Usually Absent
Abdominal Radiographs Large Air-fluid level in peritoneal (abdominal) cavity outside bowel loops (erect) Present Absent
Dilated small bowel loops Usually Absent Usually Present
Multiple Air-fluid levels in small intestinal loops (erect) May be Present Usually Absent
Ground glass opacity in the lower abdomen (erect) Present Absent
Rigler sign May or may not be Present Usually Present
Chest Radiographs Pneumothorax Absent May be Present (immediately before, simultaneously, or after the resolution of Pneumoperitoneum)
Pneumomediastinum Absent May be Present
Pneumonitis Absent May be Present
Ultrasound abdomen with Colour Doppler Free fluid Echogenic Minimal
Ischemic bowel (decreased perfusion) Present Absent
Signs suggestive of NEC on previous radiological imaging films (Ultrasound abdomen and/or Radiographs) Portal venous gas Present Absent
Pneumatosis Intestinalis Present Absent
Fixed bowel loops Present Absent
Laboratory findings CRP Positive (Markedly Raised) Usually mildly raised
Thrombocytopenia Usually Present Usually Absent
Polymorpholeucocytosis Usually Present Usually Absent
Abdominocentesis and /or Abdominal drain placement Contents of the peritoneal cavity Air and gastrointestinal fluid Air-onlyMinimal clear fluid
Management Surgical procedure Laparotomy Conservative


Notes

n1Conflicts of interest. None

n2Source of Support: Nil

n3Author contributions: Author(s) declared to fulfill authorship criteria as devised by ICMJE and approved the final version. Authorship declaration form, submitted by the author(s), is available with the editorial office.

n4Consent to Publication: Author(s) declared taking informed written consent for the publication of clinical photographs/material (if any used), from the legal guardian of the patient with an understanding that every effort will be made to conceal the identity of the patient, however it cannot be guaranteed.

Acknowledgments

None


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