Hypertrophic pyloric stenosis

Case contributed by Rad_doc


Projectile vomiting and poor weight gain

Patient Data

Age: 1 month
Gender: Male

Focused Ultrasound of the Upper Abdomen


Hypertrophied hypoechoic pylorus.

Normal comparison demonstrates a normal sized pylorus.

Cine views (not provided) demonstrate that no fluid passes through the pylorus.



After taking a look at this diagram, switch back to the ultrasound images and make sure you understand the anatomy here. 

Occasionally, young patients with vomiting may undergo abdominal radiography as part of their evaluation, especially if they are being evaluated at an institution without experienced pediatric sonographers to perform a pylorus ultrasound (which can be a challenging study to perform).

Plain Radiograph of the Abdomen


Marked gaseous distention of stomach with the so-called "caterpillar sign." This occurs from gastric contractions against a hypertrophied, obstructing pylorus. Stool and gas identified in non-dilated small bowel and colon.

When obtaining patient history from the patient's mother, she thought that some of the vomit was "green tinged." 

As previously discussed, bilious vomiting changes your differential diagnosis and an upper GI series would be the next study to further evaluate this patient. Typically, emesis in the setting of hypertrophic pyloric stenosis looks like stomach contents (e.g. formula or breast milk), rather than bilious, since the obstruction is proximal to the ampulla of Vater.

Also, at hospitals without readily available experienced ultrasonographers, the patient may undergo upper GI evaluation to confirm hypertrophic pyloric stenosis prior to surgery or transfer to a dedicated pediatric center.

Upper GI Study


Contrast administered through the NG tube pools in the distal stomach.

Small streak of contrast passes through a narrowed pyloric channel. This is the so-called "string sign." 

Clinical followup:

Patient was admitted to the inpatient unit, rehydrated, and laboratory abnormalities corrected. Laparoscopic evaluation confirmed the diagnosis of hypertrophic pyloric stenosis and patient underwent pyloromyotomy.

Case Discussion

Hypertrophic pyloric stenosis: 

The patient's clinical presentation is a common one in pediatrics with a wide differential diagnosis. In this case, the sonographic findings of a hypertrophic pylorus with no passage of gastric contents clinches the diagnosis of hypertrophic pyloric stenosis (HPS). There is an additional bonus of having an upper GI series which demonstrates suggestive findings including an elongated narrow pyloric channel ("string sign") and pooling of contrast in the distal stomach. Most patients with abdominal complaints (pain, vomiting, etc.) will get a plain radiograph of the abdomen. Unfortunately, plain film is usually non-specific in hypertrophic pyloric stenosis but may be suggestive of it when a distended stomach and a paucity of distal bowel gas are identified.

In pediatric patients presenting with vomiting, the first question that you should ask is "bilious or not?". Unfortunately, differentiating non-bilious from bilious vomit is hard! So, it is not uncommon for patients with hypertrophic pyloric stenosis to undergo an upper GI study based on history from mother of yellowish appearing vomit in order to evaluate for possible midgut malrotation and volvulus.

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