Vomiting is a commonly encountered complaint in neonates and infants. Whether the symptom is due to esophageal reflux or acute gastroenteritis, many visits each year across urgent cares, pediatric clinics, and family medicine offices are for vomiting.

Many times, the cause is self-limited, benign, and of no consequence.

Today’s article will review one of the rarer, but commonly tested topics, pyloric stenosis. Pyloric stenosis is a narrowing of the pyloric canal that is a result of aberrant relaxation of the pyloric muscles.

Pyloric Stenosis Anatomy

When reviewing our anatomy, we will recall that the pylorus is the structure that separates the stomach from the first part of the small intestine. Due to the abnormal relaxation, the pylorus will hypertrophy.

Due to the hypertrophy, it becomes increasingly difficult for food, in this case usually formula or breast milk, to enter to the duodenum. When this happens, the outflow from the stomach is blocked, leading to distention and subsequent vomiting.


The disease is most commonly seen in Caucasians. The male to female ratio is 4 to 1. Classically, test questions may indicate a first born male. The age of onset is usually between 3 and 6 weeks of life.

The disease is rare prior to three weeks and additionally becomes rare again after four to five months of life. There is a relative risk increase of 5 if there is a positive family history in a first degree relative.

Patient Presentation in Pyloric Stenosis

Infants presenting with concern for pyloric stenosis generally have a history of nonbilious projectile vomiting that is worse after feeding. As the condition progresses, both the timing, frequency, and severity of the vomiting may increase. Babies may be irritable due to poor feeding.

As expected, there may also be a history of decreased bowel movements from the parent. Given the vomiting, weight loss is common and should be taken seriously; one of the concerns in the acute setting is dehydration.

It should be noted that colloquially, many parents and family members have heard of pyloric stenosis and may inquire about the disease. The nature, progression, and type of vomiting should always be assessed with parents.

Asking parents to quantify and describe vomiting can be helpful, as a common misconception is what “projectile vomiting” actually is. True projectile vomiting among infants is not common and should raise suspicion for pyloric stenosis.

The Physical Exam

The evaluation and physical exam should pay close attention to weight. It is common for neonates to lose about 10% of their weight at hospital discharge. Infants who continue to lose weight should be evaluated further.

Upon examination of a child suspected of pyloric stenosis, careful attention is given to the abdominal exam. The classic description is a firm, olive shaped mass noted at the epigastrium. This is present about 70% of the time. Epigastric distention may be observed. It can be helpful for the clinician to observe the infant feeding. Occasionally, visible peristalsis can be noted in the epigastric region as well.

Differential Diagnosis for Weight Loss

The differential in an infant with weight loss includes congenital defects, genetic defects, pyloric stenosis, esophageal reflux, gastritis, or issues with inexperienced feeding. If suspicion for pyloric stenosis is high, a work up should be undertaken.

The main concern, as discussed previously is that weight loss can lead to significant dehydration. If a patient has significant vomiting and there is concern for dehydration, a basic or comprehensive metabolic panel can be obtained.

The classic finding that is commonly tested is a hypokalemic, hypochloremic metabolic alkalosis which is the result of significant electrolyte loss from vomiting. For students, this should be committed to memory.

Working Up The Patient

The work up for pyloric stenosis is fairly simple. Quite obviously, given the concern for young age and need to avoid exposure to radiation, ultrasound is the main-stay of diagnosis. An ultrasound can indicate a thickened, elongated pyloric muscle. The finding of redundant tissue is also present.

An upper GI is also a potential avenue for diagnosis. The finding on an upper GI series usually is illustrated via an elongated and stenotic pyloric canal.

Treating Pyloric Stenosis

Once the diagnosis is established, treatment is surgical.

A referral to a pediatric surgeon who is experienced in surgeries for pyloric stenosis is appropriate. The Ramstedt pyloromyomotomy is most commonly used. In this approach, the hypertrophied muscle is divided and the problem is solved. Open or laparoscopic approaches can be used.

In patients with severe dehydration or electrolyte imbalances, these should be corrected prior to proceeding with surgery. The use of judicious fluids may accomplish this. Post surgery, infants should be encouraged to resume feeding within 12 to 24 hours.

As discussed above, vomiting is a common concern from parents bringing children in to be evaluated in the office setting. Although most etiologies are benign, pyloric stenosis represents a significant cause of dehydration, weight loss in the infant population.

Once identified, the treatment is surgical.


Peralta, Ruben. Pyloric Stenosis. The 5 minute Clinical Consult. Wolters Kluwer, 2016.

This article, blog, or podcast should not be used in any legal capacity whatsoever, including but not limited to establishing standard of care in a legal sense or as a basis of expert witness testimony. No guarantee is given regarding the accuracy of any statements or opinions made on the podcast or blog.