Approach

Nonbilious projectile post-feeding emesis in a 2- to 12-week-old infant with a palpable pylorus is pathognomonic for pyloric stenosis. Ultrasound is commonly used in cases where a palpable pylorus is not initially appreciated.

History

Parents typically report a history of progressive nonbilious vomiting after feeding. There may be a history of formula changes without resolution of symptoms. Gastroesophageal reflux may have been tentatively diagnosed.

The infant may also have poor weight gain, constipation, or symptoms of volume depletion (e.g., decreased wet diapers).

The incidence is four times greater in male infants than in female infants.[19] The disease is also associated with a non-Mendelian familial pattern.[17][19][33]

The diagnosis of pyloric stenosis in premature infants may be challenging as they present at a later chronological age (40 days vs. 33 days in full-term infants), but at an earlier postmenstrual age (42 weeks vs. 45 weeks in full-term infants), than full-term infants.[24] One retrospective study demonstrated that a greater degree of prematurity was associated with older chronological age at presentation; the authors concluded that pyloric stenosis is likely to present at a postconceptional age of 44 to 50 weeks in both term and preterm infants.[42]

Exam

If the presenting history is suggestive, palpation of an olive-shaped upper abdominal mass (often known as an "olive") confirms the diagnosis. The mass, which is the hypertrophied pyloric muscle, can be palpated in the epigastrium and right upper quadrant. Usually the infant is not calm and is crying; therefore, patience and experience are of utmost importance. The examination is aided by the placement of an orogastric tube for gastric decompression followed by sham feeding with a pacifier dipped in formula or glucose water. The examination should reveal a firm, mobile mass inferior to the liver edge.

The infant may also show peristaltic waves traveling from left to right across the abdomen on examination. This is due to the stomach attempting to force its contents past the narrowed pyloric outlet. Signs of volume depletion may be present, such as dry mucous membranes, flat or depressed fontanelles, or tachycardia.

Physical examination has a sensitivity of 74% to 79%.[43][44][45] There is a decreasing trend in physicians diagnosing this condition based on physical examination because of the availability of imaging, and ultrasound evaluation has become standard practice in many facilities.[46][47]

Laboratory evaluation

An electrolyte panel should be ordered in all suspected cases; common findings include hypokalemia, hypochloremia, and metabolic alkalosis as a result of prolonged vomiting. The degree of electrolyte abnormalities depends on the duration of symptoms prior to presentation.[48] Due to earlier diagnosis, fewer infants present with classical findings.[45]

Imaging

Ultrasonography is the most commonly employed investigation for diagnosis.[49] The sensitivity of ultrasound in diagnosing pyloric stenosis is reported to be 97% to 99%.[5][8][50][51][52] Pyloric muscle thickness >3 mm and pyloric canal length >15 mm meet the diagnostic criteria for full-term infants.[11][53] Ultrasound also allows real-time examination of pyloric channel function. Patients will have abnormal flow and peristalsis.

Upper GI contrast investigations have been described in the diagnosis of pyloric stenosis. A positive upper GI contrast observation shows a thin strand of contrast (a string sign) as a result of a narrow pylorus. However, it may lead to further vomiting and increase the risk of aspiration. Due to this increased risk, it is not a recommended method for the diagnosis of pyloric stenosis.[Figure caption and citation for the preceding image starts]: Pyloric ultrasound. <1> interval: length; <2> interval: muscle widthFrom the collection of Dr Jeffrey S. Upperman; used with permission [Citation ends].com.bmj.content.model.Caption@5cbbb6de

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