Workup
Laboratory Studies
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Electrolytes, pH, BUN, and creatinine levels should be obtained at the same time as intravenous access in patients with pyloric stenosis.
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Hypochloremic, hypokalemic metabolic alkalosis is the classic electrolyte and acid-base imbalance of pyloric stenosis. This constellation of electrolyte abnormalities is now present in less than 50% of cases given the prompt and timely diagnosis of most infants with pyloric stenosis. However, delayed presentations, or missed cases may lead to persistent emesis. This prolonged vomiting causes progressive loss of fluids rich in hydrochloric acid, which causes the kidneys to retain hydrogen ions in favor of potassium.
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The dehydration may result in hypernatremia or hyponatremia and may result in prerenal renal failure.
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Elevated unconjugated bilirubin levels may be present.
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Imaging Studies
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If the clinical presentation is typical and an olive is felt, the diagnosis is almost certain. However formal ultrasonography is still recommended to evaluate the pylorus and confirm the diagnosis.
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Ultrasonography is the imaging modality of choice when evaluating a child for infantile hypertrophic pyloric stenosis (IHPS). [14] It is both highly sensitive (90-99%) and specific (97-100%) in the hands of a qualified sonographer. The pylorus is viewed in both longitudinal and transverse planes. The sonographic hallmark of infantile hypertrophic pyloric stenosis is the thickened pyloric muscle.
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As many infants present through the emergency department, point of care ultrasonography can be used at the bedside to help the emergency physician image the pylorus. One study by Svitiz et al, found that pediatric emergency physicians had a 100% sensitivity and specificity of identifying pyloric stenosis. [15]
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Criteria for making the diagnosis include pyloric muscle wall thickness equal to or greater than 3 mm, and pylorus length greater than 13mm. The entire pyloric diameter may range from 10-14 mm.
Point-of-care ultrasound performed by a pediatric emergency physician accurately identifying the pyloric wall thickness and length that meets criteria for pyloric stenosis diagnosis.
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Other sonographic signs associated with pyloric stenosis include the ‘antral nipple’ sign, the ‘shoulder’ sign and ‘donut’ sign.
The ‘antral nipple sign’ demonstrated by the arrow, the ‘X’ indicates the ‘shoulder sign’
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Infantile hypertrophic pyloric stenosis may be falsely diagnosed in infants who have pylorospasm. Ultrasonography also allows for observation of peristaltic activity, differentiating between pylorospasm and true infantile hypertrophic pyloric stenosis.
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Upper GI imaging (UGI) can help to confirm the diagnosis of infantile hypertrophic pyloric stenosis but is not routinely performed unless ultrasonography is nondiagnostic.
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Although rarely performed now, the upper gastrointestinal study used to be the gold standard. The "shoulder" sign is a collection of barium in the dilated prepyloric antrum and may be seen in the infant with infantile hypertrophic pyloric stenosis. The "double track" sign (ie, 2 thin tracks of barium compressed between thickened pyloric mucosa), once thought to be pathognomonic of infantile hypertrophic pyloric stenosis, has recently been identified in multiple cases of sonographically confirmed pylorospasm and is shown in the image below.
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Procedures
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Upper GI endoscopy has been used as an adjunct diagnostic tool in select cases of infantile hypertrophic pyloric stenosis when other imaging tests are inconclusive or when the infant presents with atypical clinical features.
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Media Gallery
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Point-of-care ultrasound performed by a pediatric emergency physician accurately identifying the pyloric wall thickness and length that meets criteria for pyloric stenosis diagnosis.
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The ‘antral nipple sign’ demonstrated by the arrow, the ‘X’ indicates the ‘shoulder sign’
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The ‘donut’ sign demonstrated by the arrow.
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Lateral view from an upper GI study demonstrates the double-track sign.
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