Pediatric Hypertrophic Pyloric Stenosis 

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]

HPS occurs secondary to hypertrophy and hyperplasia of the muscular layers of the pylorus, which cause a functional gastric outlet obstruction. 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. Recently, genetic studies have identified susceptibility loci for infantile HPS and molecular studies have concluded that smooth muscle cells are not properly innervated in infantile HPS.^[2]

Frequency

United States

Pyloric stenosis is the most common cause of gastric outlet obstruction in infants. It is also the most common surgical cause of vomiting 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 3-4 weeks. Cases of hypertrophic pyloric stenosis have been documented from the first week of life to 3 months. Approximately 95% of infantile hypertrophic pyloric stenosis cases are diagnosed in those aged 3-12 weeks. Premature infants generally develop symptoms later than full-term infants, which may lead to a delay in diagnosis.