What are the causes of abdominal distension in neonates?

Causes of Abdominal Distension in Neonates

Abdominal distension in neonates is most commonly caused by congenital malformations (44.6% in preterm, 61.8% in term infants), with necrotizing enterocolitis being the leading single diagnosis in preterm neonates (34.4%) and congenital megacolon (Hirschsprung disease) being the most common in term neonates (33.8%). 1, 2

Age-Specific Etiologic Patterns

Preterm Neonates

• Sepsis is the leading single disease cause (35.4%), followed by congenital megacolon (13.8%) 1
• Necrotizing enterocolitis (NEC) accounts for 34.4% of cases when analyzed as the primary diagnosis 2
• The three essential components for NEC include: substrate for bacterial growth (feedings), infectious agent (usually bacterial), and bowel damage from vascular compromise 3
• NEC presents with increased apnea/bradycardia episodes, followed by abdominal distension, bloody stools, and bilious emesis 3

Term Neonates

• Congenital megacolon (Hirschsprung disease) is the leading cause (33.8%) 1
• Other congenital malformations include anal atresia, malrotation, intestinal atresia, intestinal duplication, and posterior urethral valves 1
• Sepsis remains the second most common cause (21.3%) 1

Anatomic Causes by Location

Proximal Obstructions

• Duodenal atresia presents with bilious vomiting within the first 2 days of life and the classic "double bubble" sign on radiographs 4
• Results from failure of recanalization of the primitive gut lumen during embryologic development 4
• Meconium passage is typically absent or abnormal at birth 4

Distal Obstructions

• Ileal atresia, meconium ileus, meconium plug syndrome, and Hirschsprung disease present with multiple dilated loops and absent or decreased distal gas 5
• Contrast enema is the diagnostic procedure of choice for suspected distal obstruction, as it differentiates between functional abnormalities, surgical pathologies, and conditions requiring therapeutic enema 6
• Microcolon may be visualized due to lack of contents moving through the bowel 5

Functional and Acquired Causes

Necrotizing Enterocolitis

• POCUS can detect free fluid, bowel wall thickness, pneumatosis intestinalis, portal venous gas, and vascular perfusion 3
• Ultrasound outperforms conventional radiography for detecting pneumatosis intestinalis or portal venous gas 3
• Survival rate is close to 95% unless NEC involves the entire bowel (occurs ~25% of the time with 40-90% mortality) 3

Other Considerations

• Intussusception is extremely rare in premature neonates but should be considered when NEC is suspected, as clinical features overlap significantly 7
• Ileo-colic intussusception with Meckel's diverticulum as a lead point has been reported in premature neonates 7

Clinical Presentation Patterns

Associated Symptoms

• Vomiting is the major associated symptom, occurring in 64.0% of term newborns and 44.6% of preterm newborns 1
• Vomiting is the common symptom across all age groups with abdominal distension 2

Physical Examination Findings

• Hypoactive bowel sounds are the major accompanying sign in neonates and infants 2
• Abdominal tenderness becomes more prominent in children over 1 year old 2

Radiographic Patterns

• Bowel distention with air-fluid level is most pronounced in preterm neonates (47.7%) 1
• Bowel distention without fluid level is more common in term neonates (57.3%) 1
• Plain abdominal radiographs should be the first imaging study, as they demonstrate dilated bowel loops, air-fluid levels, and presence or absence of distal gas 5

Critical Diagnostic Pitfalls

Multiple Concurrent Causes

• More than one major cause for distension is found in one-third of cases 8
• Diagnostic difficulties are encountered in 31% of cases, with diagnoses occasionally revised multiple times as investigations proceed 8

Unreliable Signs

• Neuhauser's sign of "bubbly" meconium is unreliable, being found in meconium ileus, ileal atresia, Hirschsprung's disease, and necrotizing enterocolitis 8
• Concomitant small-bowel atresia should be suspected in all cases of meconium ileus 8
• Intestinal malrotation should be considered in association with duodenal and intestinal atresias 8

Distinguishing NEC from Intussusception

• High index of suspicion is required, as intussusception can mimic NEC in premature neonates 7
• Subtle clinical and radiological features must be carefully evaluated to avoid delays in diagnosis 7

Focal vs. Diffuse Distension

• Asymmetrically distended bowel is not usually caused by NEC (only 9/31 cases in one series) 9
• Distended bowel in the lower abdomen or left upper quadrant is often caused by air trapping in normal but redundant rectosigmoid (11 cases) or distal transverse colon (3 cases) 9
• Sequential supine and prone filming helps distinguish normal from pathologic dilated loops 9

Diagnostic Algorithm

Initial Imaging

• Plain abdominal radiographs first for all suspected bowel obstruction 5
• For proximal obstructions with classic findings (double bubble), additional ultrasound is not supported by evidence 5

Suspected Distal Obstruction

• Contrast enema is the diagnostic procedure of choice, not ultrasound 6
• Ultrasound has no role in evaluating neonates with suspected distal obstruction 6

Suspected Malrotation/Volvulus

• Upper GI series remains the reference standard 5

Role of POCUS

• Helpful for detecting free intra-abdominal fluid when sudden clinical deterioration and hypotension occur 3
• May assess bowel peristalsis, though insufficient data correlate this with feeding tolerance 3
• Can detect obstructive uropathy and guide peritoneal drainage 3

Treatment Outcomes

• Etiological and symptomatic treatment is effective in 86.2% of premature cases and 88.2% of term cases 1
• Nonoperative management of NEC is successful ~70% of the time 3
• Peritoneal drainage may be used instead of immediate operation in very low birth weight neonates with bowel perforation 3