eMedicine Specialties > Pediatrics: General Medicine > Gastroenterology

Pyloric Stenosis, Hypertrophic

Author: Hisham Nazer, MB, BCh, FRCP, DCh, DTM&H, Professor of Pediatrics, Consultant in Pediatric Gastroenterology, Hepatology and Clinical Nutrition, Bushnaq Medical Centre, University of Jordan
Coauthor(s): Dena Nazer, MD, Fellow, Child Protection Center, Children's Hospital of Michigan; Daniel A Beals, MD, Attending Staff, Cornerstone Pediatric Surgery
Contributor Information and Disclosures

Updated: Oct 31, 2008

Introduction

Background

Hirschsprung wrote the first complete description of hypertrophic pyloric stenosis (HPS) in 1888. He believed the disease was congenital and represented fetal pyloric development failure. In 1907, Ramstedt described an operation to alleviate this condition. He suggested splitting the pyloric muscle and leaving it open to heal secondarily. This procedure has been used to treat infantile hypertrophic pyloric stenosis (IHPS) since that time. Although this curious disease is treated easily with surgery, its etiology remains undetermined. Hypertrophic pyloric stenosis is inherited by a multifactorial threshold model, and the generalized occurrence risk for siblings is 5-9%. Associated congenital anomalies are reported in 6-20% of patients with pyloric stenosis. A rare association with developmental delay has also been reported.¹

Pathophysiology

Diffuse hypertrophy and hyperplasia of the smooth muscle of the antrum of the stomach and pylorus proper narrow the channel, which then can become easily obstructed. The antral region is elongated and thickened to as much as twice its normal size. In response to outflow obstruction and vigorous peristalsis, stomach musculature becomes uniformly hypertrophied and dilated. Gastritis may occur after prolonged stasis. Hematemesis is occasionally noted. The patient may become dehydrated as a result of vomiting and develop marked hypochloremic alkalosis.

Researchers have investigated the cause of this muscle hypertrophy for several decades. Many believe the problem is induced by the pyloric musculature failing to relax. Results of studies of pyloric muscle innervation are inconclusive, possibly showing a tendency toward fewer or more immature ganglion cells in affected individuals. Deregulation of vasoactive intestinal peptide (VIP) and nitric oxide both have been demonstrated in patients with pyloric stenosis, although whether these factors are associative or causative is unclear.

No definitive cause for hypertrophic pyloric stenosis has been found. However, various environmental and hereditary factors have been implicated. Suspected environmental factors include infantile hypergastrinemia, abnormalities in the myenteric plexus innervation, cow's milk protein allergy, and exposure to macrolide antibiotics. Hereditary factors may also play a role; hypertrophic pyloric stenosis occurs in as many as 7% of infants of affected parents. The etiology is probably multifactorial, with both genetic and environmental factors contributing. Recognition that hypertrophic pyloric stenosis is an acquired disorder and not a congenital disorder is increasing.

Frequency

United States

Pyloric stenosis is a common cause of gastric outlet obstruction in infants. The prevalence of hypertrophic pyloric stenosis ranges from 1.5-4 cases per 1000 live births among whites, although it is less prevalent among blacks and Asian Americans.

Mortality/Morbidity

Operative therapy for hypertrophic pyloric stenosis has remained unchanged for nearly 100 years. Outcomes have improved through advances in early diagnosis, preoperative resuscitation, operative anesthetics, and nutritional management. Mortality may rarely result from late diagnosis, resulting in dehydration and shock. Mortality is also rare after pyloromyotomy. Wound infection occurs in fewer than 1% of patients. Perforation of the pyloric mucosa is also unusual, occurring in fewer than 3% of reported cases. Long-term sequelae from the disease or treatment are also minimal.

Race

Reported prevalence of hypertrophic pyloric stenosis among whites ranges from 1.5-4 cases 1000 live births; hypertrophic pyloric stenosis is less prevalent among blacks, Asians, and Hispanics.

Sex

Pyloric stenosis has a well-known predilection for occurring more often in males than in females, with reported ratios ranging from 2:1 to 5:1. First-born male children are believed to have the highest risk of developing hypertrophic pyloric stenosis.

Age

Newborns typically develop signs of gastric outlet obstruction at 4 weeks. Cases of hypertrophic pyloric stenosis have been documented from the first week of life to 3 months. Premature infants generally develop symptoms later than full-term infants.

Clinical

History

• Typical presentation of an infant with hypertrophic pyloric stenosis (HPS) is onset of initially nonbloody, always nonbilious vomiting at 4-8 weeks. Although vomiting may initially be infrequent, over several days it becomes more predictable, occurring at nearly every feeding. Vomiting intensity also increases until pathognomonic projectile vomiting ensues. Slight hematemesis of either bright red flecks or a coffee-ground appearance is sometimes observed.
• Patients are usually not ill-looking or febrile. The baby in the early stage of the disease remains hungry and sucks vigorously after episodes of vomiting.
• Prolonged delay in diagnosis can lead to dehydration, poor weight gain, malnutrition, metabolic alterations, and lethargy.
• Parents often report trying several different baby formulas because they (or their physicians) assume vomiting is due to intolerance.

Physical

• Careful physical examination provides a definitive diagnosis for most infants with hypertrophic pyloric stenosis. However, some of the classic signs that would lead to diagnosis may be absent due, in part, to the early diagnosis of hypertrophic pyloric stenosis.
• An enlarged pylorus, classically described as an "olive," can be palpated in the right upper quadrant or epigastrium of the abdomen.² In order to assess the pylorus, the patient must be calm and cooperative. A pacifier or small amount of dextrose water may help. If the stomach is distended, aspiration using a nasogastric tube is necessary. With the infant supine and the examiner on the child's left side, gently palpate the liver edge near the xiphoid process. Then displace the liver superiorly; downward palpation should reveal the pyloric olive just on or to the right of the midline. To be assured of the diagnosis, the physician should be able to roll the pylorus beneath the examining finger. The tumor (mass) is best felt after vomiting or during, or at the end of, feeding. The diagnosis is easily made if the presenting clinical features are typical, with projectile vomiting, visible peristalsis, and a palpable pyloric tumor.
• When diagnosis is delayed, the infant may develop severe constipation associated with signs of dehydration, malnutrition, lethargy, and shock.

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