Pyloric Stenosis
The most likely diagnosis is hypertrophic pyloric stenosis (HPS), which classically presents with forceful, projectile non-bilious vomiting in a neonate with a palpable epigastric mass ("olive"), along with decreased urine output from dehydration and decreased stool output from reduced gastric emptying. 1, 2, 3
Clinical Presentation and Diagnosis
Forceful projectile vomiting in a neonate with epigastric swelling strongly suggests HPS, which typically presents between 2-8 weeks of age (though can occur earlier) with progressive non-bilious vomiting that becomes increasingly forceful. 2, 3
Key Clinical Features Supporting HPS:
- Epigastric fullness/swelling represents the classic palpable "olive" mass in the right upper quadrant, which is pathognomonic for HPS when present 2
- Decreased urine output results from progressive dehydration due to persistent vomiting and inability to retain fluids 2, 4
- Decreased stool output occurs because minimal gastric contents pass through the obstructed pylorus into the intestines 5
- The vomiting is characteristically non-bilious because the obstruction is proximal to the ampulla of Vater 3, 5
Immediate Diagnostic Approach
Ultrasound of the abdomen is the imaging modality of choice for suspected HPS, with high sensitivity and specificity for detecting the thickened pyloric muscle. 2, 3
Diagnostic criteria on ultrasound:
- Pyloric muscle thickness >3-4 mm
- Pyloric channel length >15-17 mm
- Target sign on transverse view 2
Plain abdominal radiograph may show a distended stomach with minimal distal bowel gas, but ultrasound provides definitive diagnosis. 6, 7
Critical Differential Considerations
Rule Out Surgical Emergencies First:
If vomiting becomes bilious at any point, this represents a surgical emergency requiring immediate evaluation for malrotation with midgut volvulus, which can cause intestinal necrosis within hours. 1, 3, 4
- Malrotation with volvulus accounts for 20% of bilious vomiting cases in the first 72 hours of life and requires urgent upper GI series if suspected 3
- Duodenal atresia presents with bilious vomiting (if obstruction is infra-ampullary) and "double bubble" sign on radiograph, with epigastric distention 6, 3, 5
- Necrotizing enterocolitis (NEC) can present with abdominal distention, vomiting, and decreased output, though more common in premature infants 6, 8
Immediate Management Priorities
Resuscitation and Stabilization:
- Assess and correct dehydration immediately with IV fluid resuscitation, as HPS typically causes hypochloremic, hypokalemic metabolic alkalosis from persistent vomiting 2, 4
- Insert nasogastric tube for gastric decompression to prevent aspiration and provide comfort 4
- Check serum electrolytes (sodium, potassium, chloride, bicarbonate) and correct abnormalities before surgery 4, 7
- NPO (nothing by mouth) until surgical evaluation is complete 4
Surgical Consultation:
Immediate pediatric surgery consultation is mandatory once HPS is confirmed or strongly suspected, as pyloromyotomy is the definitive treatment. 2, 4
Common Pitfalls to Avoid
- Do not dismiss non-bilious vomiting as benign reflux when it is forceful/projectile and associated with poor weight gain or dehydration 2, 3
- Do not delay imaging if clinical suspicion is high—the "olive" mass is palpable in only 60-80% of cases 2
- Do not proceed to surgery without correcting electrolyte abnormalities, particularly the metabolic alkalosis, as this increases anesthetic risk 4
- Always reassess for bilious vomiting, as this changes the diagnosis to a more urgent surgical emergency like malrotation 1, 3, 4
Alternative Diagnosis if HPS is Excluded
If ultrasound is negative for HPS and vomiting remains non-bilious:
- Gastroesophageal reflux is the most common cause of non-bilious vomiting in infants, but typically not forceful/projectile 3
- Viral gastroenteritis causes vomiting with watery diarrhea, most common in children under 2 years 3
- Consider metabolic disorders or increased intracranial pressure if other red flags are present 4, 7