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Hypertrofic Pyloric Stenosis

2-3 in 1000 infants
more common in males (males: females, 3-4:1)
4 to 6 weeks of age

projectile, non-bilious vomiting and gastric hyperperistalsis, palpable "olive" in the epigastrium

Ultrasound is the imaging gold standard

The ultrasound is performed with a 5 or 7.5 MHz linear transducer, with the child supine. Transverse images at the epigastrium will identify the pylorus to the left of the gallbladder and anteromedial to the right kidney. A distended stomach will displace and distort the pylorus and may require placement of a nasogastric tube to withdraw stomach contents. A gastric aspirate of more than 5ml is said to indicate gastric outlet obstruction. Right posterior oblique positioning and scanning from a posterior approach may aid in visualization of the pylorus

Sonographic signs of HPS, originally described in 1977 and further defined:

1. Muscle thickness (MT) greater than 3mm*
2. "Target sign": seen on transeverse images of the pylorus
3. Pyloric channel length (PL) greater than 15mm
4. Failure of the channel to open during at least 15 minutes of scanning
5. Retrograde or hyperperistaltic contractions
6. "Antral nipple sign": prolapse of redundant mucosa into the antrum creating a pseudomass
7. Ultrasonic "double track" sign: redundant mucosa in the narrowed lumen creates two mucosal outlines
8. Reversible portal venous gas
9. Nonuniform echogenicity of the pyloric muscle

*The most reliable sonographic sign is MT of greater than 3mm.

Findings on UGI include:

1. Delayed gastric emptying (if severe, this may prevent any barium from passing into the pylorus and severely limit the study)
2. "Caterpillar sign": seen best on the scout film representing the over distended stomach with exaggerated contractions
3. Cephalic orientation of the pylorus
4. "Shouldering": the filling defect at the antrum created by prolapse of the hypertrophic muscle
5. "Mushroom sign": the thickened muscle indenting the duodenal bulb
6. "Double track": redundant mucosa in the narrowed pyloric lumen will result in separation of the barium column into two channels
7. "String sign": barium passing through the narrowed channel creating a single markedly attenuated and elongated track
8. "Pyloric tit": out-pouching created by distortion of the lesser curve by the hypertrophied muscle
9. Retained secretions and retrograde peristalsis

Ultrasound for HPS is operator-dependent but easy for the experienced radiologist. UGI exposes the child to unnecessary radiation and the rare risk of barium aspiration. Some studies in the surgical literature have found the UGI to be the most cost-effective test for the vomiting infant: if the study is negative for HPS, additional information can be gathered to rule out malrotation, gastroesophageal reflux, and other GI conditions causing the vomiting. Although ultrasound can be used to diagnose gastroesophageal reflux, it is not reliable for malrotation as there is a false negative rate of 33% for inversion of the superior mesenteric vessels.

Pyloromyotomy is the treatment of choice whereby the hypertrophic musculature is incised, effectively widening the pyloric channel. This is performed once the baby is stabilized (correcting the metabolic alkalosis and dehydration). The hypertrophic musculature regresses in response to pyloromyotomy within 12 weeks of surgery; the ultrasound remains abnormal during this postoperative period.