Hypertrophic Pyloric Stenosis

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Diagnosis and reasoning

'Vomiting' in early infancy is an extremely common concern; in most cases, it is because regurgitation has been confused with frank vomiting. Thus, it is very important to clearly describe the differences between the two, so that anxious parents can distinguish between them. Even frank vomiting per se is usually due to completely benign causes (such as overfeeding or mild gastroesophageal reflux disease). However, it should be kept in mind that vomiting may also be a manifestation of serious underlying disease; thus, it is essential to look for 'red flags' which might signify this. Key red flags include lethargy and listlessness, inconsolability, a bulging fontanelle, persistent vomiting with poor growth or development, and projectile or bilious vomiting. Perusal of this infant's history shows that a red flag is indeed present: projectile vomiting. Note that non-bilious projectile vomiting is classically associated with gastric outflow obstruction. Considering his age, this raises the suspicion of hypertrophic pyloric stenosis (HPS); the history of vomiting following feeds is highly compatible with this, as is the presence of visible peristalsis following a feed. Pyloric ultrasound is the test of choice in suspected HPS; this shows a thickened and elongated pyloric channel, confirming the diagnosis. Estimation of serum electrolytes and arterial blood gases is essential, as derangements are common in these children; the hypochloremic, hypokalemic metabolic alkalosis seen here is what one would expect from recurrent loss of upper GI tract fluids. The immediate management should consist of fluid resuscitation and correction of the metabolic derangements; oral feeds should be temporarily stopped, while nasogastric (NG) tube insertion should be considered in view of the recurrent vomiting. Definitive management involves relaxation of the pyloric sphincter via a pyloromyotomy. Anti-emetics are of litte value here, as the vomiting is due to a mechanical obstruction.


Discussion

HPS is the most common surgical cause of vomiting in infancy, with an incidence of approximately 3 per 1000 live births in the United States. It is most common in whites of northern European ancestry, less common in African-Americans, and rare in Asians. Boys (particularly firstborns) are affected almost 4 times more often than girls. HPS displays a familial (but non-Mendelian) pattern of inheritance. The offspring of these individuals have around a 7% risk of developing the condition if the father was affected, and a 10% to 20% risk if the mother was affected. An increased incidence has also been reported in infants of blood groups B and O; in infants exposed prenatally to thalidomide, hydantoins, or trimethadione; and in infants exposed postnatally to erythromycin. HPS may be associated with other GI anomalies, such as tracheoesophageal fistulas, pyloric atresia, and gastric volvulus; it has also been linked to disease states such as eosinophilic gastroenteritis, epidermolysis bullosa, trisomy 18, Turner Syndrome, Smith-Lemli-Opitz syndrome and Cornelia de Lange syndrome. The exact etiology of HPS is unclear. Hypotheses include maternal stress during the third trimester; abnormal innervation of the pyloric muscle; and abnormalities in hormonal control. Most infants with HPS present in the first 2 to 12 weeks of life; the initial presenting symptom is nonbilious vomiting. The vomiting is initially intermittent, but increases in frequency until it ultimately occurs following all feedings. The intensity depends on the degree of stenosis, but it ultimately becomes projectile in nature. The infant is often hungry afterwards and wants to feed again; 10% of cases may have blood-tinged vomitus because of gastritis. On examination, the infant may be dehydrated and may exhibit poor weight gain or even weight loss. Around 1% to 2% will be jaundiced, secondary to decreased levels of glucuronyl transferase associated with the bowel obstruction. Following a test feed (a milk feed given to the hungry infant, calming him and allowing examination) a wave of gastric peristalsis may be seen traversing the abdomen from left to right, representing intense contractions against an obstruction. Note that it takes patience to observe visible peristalsis, as it may not be particularly obvious (especially at the beginning). Abdominal examination may reveal the hypertrophied pylorus as a firm, mobile, olive-shaped mass about 2 cm in length. It is best felt in the in the right upper quadrant of the abdomen, beneath the edge of the liver. This finding is called a pyloric 'olive' and is pathognomonic of HPS, although it is difficult to feel. Overall, even an experienced examiner can palpate it in only 60% to 80% of cases. Repeated vomiting results in loss of fluid, hydrogen ions, and chloride leading to the classic laboratory finding of hypochloremic, hypokalemic metabolic alkalosis; however, due to expedient diagnosis and treatment, more than 90% of patients show no metabolic disturbances at presentation. The diagnostic test of choice is ultrasonography, which has a sensitivity of approximately 90%; criteria for diagnosis include an elongated pyloric channel (longer than 16 mm), an enlarged pyloric diameter (greater than 14 mm), and a thickened muscle wall (greater than 3.5 mm). In patients with high clinical suspicion but a negative ultrasound, an upper GI contrast study may be considered; characteristic imaging findings include the "shoulder sign" (representing the hypertrophied pylorus bulging into the antrum) and the "string sign" or "double track sign" (streaks of barium through a narrow pyloric channel). Although HPS is not a surgical emergency, it can be a medical emergency requiring aggressive fluid and electrolyte resuscitation; typically this requires hospitalization and intravenous replacement of fluids and electrolytes. Note that correction of any alkalosis is imperative to prevent postoperative apnea or hypoventilation. The infant should be kept nil by mouth; NG tube insertion and suction may be required if the vomiting does not stop. Ramstedt pyloromyotomy is the surgical procedure of choice, with a mortality rate of between 0% to 0.5%. Laparoscopic pyloromyotomy is also gaining increasing acceptance. Following surgery, postoperative vomiting may occur secondary to edema of the pylorus at the incision site; however, persistent vomiting suggests an incomplete pylorotomy, gastritis, gastroesophageal reflux disease or an additional cause of obstruction. In cases of incomplete pyloromyotomy, endoscopic balloon dilation has been successfully used. Feeding is usually restarted between 12 to 24 hours post-operatively; the infants are usually discharged within 3 days. The prognosis of HPS is good, with most patients showing excellent short-term and long-term outcomes following pyloromyotomy.


Take home messages

  1. HPS is the commonest surgical condition causing vomiting in infancy.
  2. Visible peristalsis following a test feed is suggestive of HPS, but requires patience for observation.
  3. HPS is not a surgical emergency and can be corrected electively.
  4. HPS can present as a medical emergency requiring aggressive fluid and electrolyte resuscitation.

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