Pyloric Stenosis Exam Findings
The classic exam finding is a palpable olive-shaped mass in the right upper quadrant, though this is absent in 50% or more of cases, making its absence insufficient to rule out the diagnosis. 1, 2
Physical Examination Findings
Palpable Pyloric Mass ("Olive")
- An olive-shaped, firm muscular tumor in the right upper quadrant is pathognomonic when present 3
- However, clinicians fail to detect this mass in 11-51% of confirmed cases 4
- Recent data shows the palpable olive is absent in approximately 50% of patients, with this percentage increasing over time as imaging is utilized earlier 2, 5
- Physical examination should be performed by an experienced examiner, ideally after gastric decompression, as a distended stomach can obscure the pyloric mass 1
Visible Gastric Peristalsis
- Vigorous gastric peristaltic waves may be visible after feeding, moving from left to right across the upper abdomen 2, 3
- This finding reflects gastric outlet obstruction and increased gastric contractions attempting to overcome the stenosis 3
Clinical Presentation Features
- Projectile vomiting is the hallmark symptom but is absent in one-third of patients 2
- Vomiting is typically non-bilious 5
- Mean age at diagnosis is approximately 40 days (range 37-43 days) 2, 5
- Male predominance of approximately 81-86% 2, 5
- Dehydration may be present, though less common with earlier diagnosis 5
Laboratory Findings
Metabolic Derangements (Less Common with Early Diagnosis)
- Classic hypochloremic, hypokalemic metabolic alkalosis is present in only a minority of cases when diagnosed early 2
- Bicarbonate >28 mEq/L found in only 20% of patients 2
- pH >7.45 present in only 25% of patients 2
- Hypochloremia noted in approximately one-third of cases 2
- Elevated serum urea and creatinine may indicate dehydration 5
Critical Clinical Pitfall
The absence of a palpable mass does not exclude pyloric stenosis, and ultrasound should be performed when clinical suspicion remains high 1. The declining frequency of palpable masses (now absent in ~50% of cases) is likely due to declining clinical examination skills and earlier utilization of imaging studies rather than an actual change in disease presentation 2, 5. This earlier diagnosis prevents progression to the severe metabolic derangements historically considered "classic" for this condition 5.
Diagnostic Approach When Exam is Non-Diagnostic
- Ultrasound is the imaging modality of choice and should be the initial imaging procedure 6, 7, 3
- Ultrasound has 100% sensitivity and specificity when performed properly 7
- Upper GI series is reserved for cases where ultrasound findings are equivocal or negative despite strong clinical suspicion 6
- Definitive diagnosis should be performed by a pediatric radiologist 6