Pediatrics · Year 3 · from Pediatrics
Case 2: Pyloric Stenosis
Patient Demographics
- Age: 5-week-old male
- Sex: Male
Chief Complaint
"My baby vomits after every feed and isn't gaining weight."
History of Present Illness
A 5-week-old first-born male presents with progressive non-bilious vomiting that started 1 week ago and has worsened over the past few days. Initially, he spit up small amounts after feeds, but now he vomits "everything he eats" - parents describe the vomiting as "shooting across the room" (projectile). The vomiting occurs 15-30 minutes after feeds. He is bottle-fed with standard formula and appears hungry immediately after vomiting, eagerly trying to feed again. Parents note decreased wet diapers (3 per day, down from 6-8). Last bowel movement was 2 days ago. Birth weight was 3.4 kg at term; he gained appropriately until 2 weeks ago. Family history notable for father who had "stomach surgery" as an infant.
Growth Parameters
- Birth weight: 3.4 kg (50th percentile)
- Current weight: 3.6 kg (10th percentile - below expected)
- Length: 53 cm (35th percentile)
- Expected weight at 5 weeks: ~4.3 kg
Physical Examination
- General: Alert, hungry-appearing infant, thin with visible rib outlines
- Vital signs: T 36.8C, HR 165, RR 40, BP 75/50
- HEENT: Sunken anterior fontanelle, dry mucous membranes, sunken eyes
- Cardiovascular: Tachycardia
- Abdomen:
- Scaphoid
- Visible gastric peristaltic waves moving left to right (seen during feeding)
- Firm, mobile, olive-shaped mass palpable in right upper quadrant/epigastrium (palpable pylorus)
- No distension
- Skin: Decreased skin turgor, dry
- Neurologic: Alert, good suck
Workup
- Abdominal ultrasound:
- Pyloric muscle thickness: 5 mm (abnormal >3 mm)
- Pyloric channel length: 18 mm (abnormal >14 mm)
- Target sign with elongated pyloric channel
- Basic metabolic panel:
- Na 133 mEq/L (low)
- K 3.0 mEq/L (low)
- Cl 88 mEq/L (low)
- HCO3 32 mEq/L (elevated)
- BUN 28 mg/dL (elevated)
- Cr 0.5 mg/dL
- Blood gas: pH 7.52, pCO2 48, HCO3 34 (hypochloremic, hypokalemic metabolic alkalosis with respiratory compensation)
Diagnosis
Hypertrophic pyloric stenosis with dehydration and hypochloremic, hypokalemic metabolic alkalosis
Clinical Reasoning
The classic presentation of pyloric stenosis includes: first-born male, age 3-6 weeks, progressive non-bilious projectile vomiting, hungry after vomiting, palpable "olive" mass, visible peristaltic waves, and failure to thrive. The metabolic abnormalities result from loss of gastric HCl in vomitus - the kidney retains H+ in exchange for K+, leading to the classic "paradoxical aciduria" and the characteristic hypochloremic, hypokalemic metabolic alkalosis. Ultrasound criteria (muscle >3 mm, length >14 mm) confirm the diagnosis.
Management
- NPO and IV fluids:
- Initial: NS 20 mL/kg bolus
- Maintenance: D5 + 0.45% NS with 20 mEq/L KCl at 1.5x maintenance
- Correct electrolyte abnormalities:
- Goal: Cl >100 mEq/L, K >3.5 mEq/L, HCO3 <26 mEq/L before surgery
- May take 24-48 hours of fluid resuscitation
- Surgical consultation:
- Pyloromyotomy (Ramstedt procedure) - definitive treatment
- Laparoscopic or open approach
- Surgery is NOT emergent - stabilize patient first
- Preoperative management:
- NGT only if persistently vomiting
- Serial electrolytes every 6-12 hours
- Postoperative:
- Resume feeds 4-6 hours after surgery
- Advance as tolerated
- Some postoperative emesis is common and self-limited
- Prognosis: Excellent, cure rate essentially 100%
Clinical Image
Image Description: Ultrasound image demonstrating hypertrophic pyloric stenosis with elongated, thickened pyloric muscle and the characteristic "target sign."
Source: Radiopaedia URL: https://radiopaedia.org/cases/pyloric-stenosis-ultrasound License: CC BY-NC-SA 3.0