bubble_chart Overview

Congenital hypertrophic pyloric stenosis is a common disease in the neonatal period. The successful treatment of pyloric stenosis is one of the great achievements of surgery in this century. The incidence varies depending on geography, season, and ethnicity. It is higher in European and American countries, ranging from 2.5% to 8.8%, while it is relatively lower in Asian regions, with an incidence of 3% in our country. It is more prevalent in males, with a male-to-female ratio of about 4-5:1, and can even reach 9:1. It is most commonly seen in first-born children, accounting for 40-60% of total cases.

bubble_chart Etiology

To elucidate the disease cause and mechanism of disease of pyloric stenosis, extensive research has been conducted over the years, including pathological examinations, establishment of animal models, detection of gastrointestinal hormones, virus isolation, genetic studies, etc. However, the disease cause remains inconclusive to this day.

(1) Genetic factors play a significant role in the disease cause. The disease shows a clear familial tendency, with cases even observed in a mother and her seven sons, and is more common in monozygotic twins than in dizygotic twins. The incidence rate in children with a parental history of pyloric stenosis can be as high as 6.9%. If the mother has a history of the disease, the probability of her son developing the disease is 19%, and for her daughter, 7%; if the father has a history of the disease, the probabilities are 5.5% and 2.4%, respectively. Research indicates that the genetic mechanism of pyloric stenosis is polygenic, neither recessive nor sex-linked, but rather a directed genetic gene composed of a dominant gene and a sex-modified multifactorial component. This genetic predisposition is influenced by certain environmental factors, such as social class, diet types, and various seasons, with a higher incidence in spring and autumn, though the related factors are unclear. It is commonly seen in male infants with high birth weight but is unrelated to the length of gestation.

(2) Neural function Researchers primarily studying the myenteric plexus of the pylorus have found that ganglion cells do not mature until 2 to 4 weeks after birth. Therefore, many scholars believe that the underdevelopment of neural cells is the mechanism causing hypertrophy of the pyloric muscle, refuting the past theory that degeneration of pyloric ganglion cells leads to the disease. Histochemical analysis has been used to measure the enzyme activity in pyloric ganglion cells; however, some hold different opinions, observing that the ganglion cells in pyloric stenosis are not the same as those in fetuses. If underdevelopment of ganglion cells were the cause, premature infants should have a higher incidence than full-term infants, yet there is no difference between the two. Recent studies suggest that structural changes and functional insufficiency of peptidergic nerves may be one of the main disease causes. Immunofluorescence techniques have observed a significant reduction in the number of enkephalin and vasoactive intestinal peptide nerve fibers in the circular muscle, and radioimmunoassay has shown a decrease in substance P content in tissues, leading to the speculation that changes in these peptidergic nerves are related to the disease.

(3) Gastrointestinal hormones Experiments have shown that administering pentagastrin to pregnant dogs results in a high proportion of their puppies developing pyloric stenosis. It has also been found that the serum gastrin concentration in pregnant women is relatively high during the last 3 to 4 months of pregnancy. It is believed that anxiety in pregnant women during the late stage of pregnancy increases serum gastrin concentration, which passes through the placenta to the fetus, and combined with the directed genetic gene effect of the fetus, leads to prolonged pyloric spasm and obstruction. The dilation of the pylorus then stimulates G cells to secrete gastrin, thus causing the disease. However, other scholars have repeated measurements of gastrin, with some reports showing an increase and others showing no abnormal changes. Even in cases where gastrin is elevated, it cannot be inferred whether it is the cause or the result of pyloric stenosis, as some cases return to normal levels one week after surgery, while others show an increase. Recent studies on gastrointestinal stimulants have measured the concentration of prostaglandins (E₂

and E₂a) in serum and gastric juice, indicating a significant increase in the gastric juice of affected children, suggesting that the mechanism of disease involves an increase in local hormone concentration in the pyloric muscle layer, keeping the muscle in a state of continuous tension and leading to the disease. Some have also studied serum cholecystokinin, but no abnormal changes were found.

(4) Functional Hypertrophy of Muscles Some scholars, through meticulous observation and research, have discovered signs of some infants aged 7 to 10 days forcefully passing curd through the narrow pyloric canal. It is thus believed that this mechanical stimulation can cause mucosal edema and thickening. On the other hand, it also leads to dysfunction of the cerebral cortex in relation to the viscera, causing pyloric spasm. These two factors contribute to the formation of severe pyloric stenosis, resulting in symptoms. However, there are also dissenting opinions, arguing that it is inappropriate to consider that pyloric spasm first causes functional hypertrophy of the pyloric muscles, as the hypertrophied muscles are mainly circular muscles. Moreover, spasm should cause some preliminary symptoms, yet in some cases where surgery was performed early due to vomiting episodes, a mass is usually found to have already formed, with the size of the mass unrelated to the duration of the disease or the age. Only when the muscle hypertrophy reaches a certain critical value does it manifest signs of pyloric obstruction.

(5) Environmental Factors The incidence shows a distinct seasonal peak, mainly in spring and autumn. Leukocyte infiltration around ganglion cells has been observed in biopsy tissue sections. It is speculated that this may be related to viral infections, but no coxsackievirus was isolated from the blood, feces, or throat of the affected children and their mothers. No changes were detected in serum neutralizing antibodies either. Pathological changes were not observed in animals infected with coxsackievirus, and research is ongoing.

bubble_chart Pathological Changes

The main pathological changes are hypertrophy of the pyloric muscle layer, particularly the circular muscle, but it is also evident in the longitudinal muscle and elastic fibers. The pyloric region is olive-shaped, firm, and elastic. When the muscle undergoes fleshy rigidity, it becomes even harder. It is generally 2-2.5 cm in length, 0.5-1 cm in diameter, with a muscle layer thickness of 0.4-0.6 cm. In older children, the mass may be larger. However, the size is not related to the severity of symptoms or the duration of the disease. The surface of the mass is covered with a smooth abdominal membrane, but due to partial obstruction of blood supply caused by pressure, the color appears pale. The circular muscle fibers are increased and thickened, making the muscle as hard as gravel. The thickened muscle layer compresses the mucous membrane into longitudinal folds, narrowing the lumen. Additionally, mucous membrane edema and subsequent inflammation further reduce the lumen size. In autopsy specimens, the pylorus can only allow a 1 mm probe to pass through. The narrow pyloric canal gradually widens in a conical shape as it transitions to the gastric antrum, while the thickened muscle layer gradually thins, with no clear boundary between the two. However, the boundary is distinct on the duodenal side, as the gastric wall muscle layer is not continuous with the duodenal muscle layer. The thickened pyloric mass abruptly terminates and protrudes into the duodenal cavity, resembling a uterine cervix-like structure. Histological examination reveals hyperplasia and hypertrophy of the muscle layer, disordered arrangement of muscle fibers, and mucous membrane edema and congestion.

Due to pyloric obstruction, the proximal stomach is dilated, the wall is thickened, and the mucous membrane folds are increased with edema. The retention of gastric contents often leads to mucous membrane inflammation and erosion, and even ulcers.

bubble_chart Clinical Manifestations

Symptoms appear 3 to 6 days after birth, with some cases occurring earlier, and very few cases occurring after 4 months. Vomiting is the main symptom, initially just regurgitation, followed by projectile vomiting. At first, vomiting occurs occasionally, but as the obstruction worsens, vomiting occurs almost after every feeding, with the vomitus being mucus or milk. If the milk stays in the stomach for a longer time, it may be curdled, but it does not contain bile. In a few cases, due to irritative gastritis, the vomitus may contain fresh or altered blood. There are reports of cases of pyloric stenosis during the neonatal period of high gastric acidity leading to massive hematemesis from gastric ulcers, and there are also reports of duodenal ulcers occurring. After vomiting, the infant still has a strong desire to eat and can suck vigorously if fed again. Symptoms in premature infants are often atypical, and projectile vomiting is not prominent.

As vomiting intensifies, due to insufficient intake of milk and water, the infant's weight initially does not increase and then rapidly decreases, with a significant reduction in urine output. Bowel movements occur once every few days, with small amounts and hard consistency, and occasionally, brown-green stools, known as starvation stools, may be passed. Due to malnutrition and dehydration, the infant becomes noticeably emaciated, with loose and wrinkled skin, reduced subcutaneous fat, and a depressed and distressed appearance. In the initial stage of the disease, vomiting leads to the loss of a large amount of gastric acid, which can cause alkalosis, with shallow and slow breathing, and symptoms such as laryngospasm and convulsions in the hands and feet. Later, as dehydration becomes severe and renal function declines, acidic metabolic products accumulate in the body, and some alkaline substances are neutralized, so significant alkalosis is rarely seen. Severe malnutrition in advanced stages is rarely seen nowadays.

During abdominal examination, the infant should be placed in a comfortable position, lying on the mother's lap, with the abdomen fully exposed. Observation should be done under bright light while feeding sugar water. Gastric patterns and peristaltic waves can be seen, with the waves appearing below the left costal margin, slowly crossing the upper abdomen, advancing in 1 to 2 waves, and finally disappearing on the right side above the umbilicus. The examiner should be on the left side of the infant, using gentle techniques. The left hand should be placed at the outer edge of the rectus abdominis muscle below the right costal margin, pressing the rectus abdominis with the index and ring fingers, and gently palpating deeply with the middle finger. An olive-shaped, smooth, and hard pyloric mass, 1 to 2 cm in size, can be felt. It is easier to palpate after vomiting when the stomach is empty and the abdominal muscles are temporarily relaxed. Occasionally, the caudate lobe of the liver or the right kidney may be mistaken for a pyloric mass. However, if the abdominal muscles are not relaxed or the stomach is distended, the mass may not be palpable. In such cases, a gastric tube can be used to empty the stomach, and the examination can be done while feeding sugar water and sucking. Patience and repeated examinations are required, and according to experience, the mass can be palpated in most cases.

Laboratory tests may reveal that infants with clinical dehydration have varying degrees of hypochloremic alkalosis, with elevated Pco₂, elevated pH, and low serum chloride. It must be recognized that metabolic alkalosis is often accompanied by hypokalemia, the mechanism of which is not yet clear. In addition to the small amount of potassium lost with gastric juice, during alkalosis, potassium ions move into the cells, causing intracellular hyperkalemia and extracellular hypokalemia, with increased potassium excretion by the epithelial cells of the distal convoluted tubules of the kidney, leading to decreased blood potassium.

bubble_chart Diagnosis

Based on typical clinical manifestations, the diagnosis can be confirmed by observing gastric peristaltic waves, palpating a pyloric mass, and projectile vomiting. Among these, the most reliable diagnostic criterion is the palpation of a pyloric mass. If the mass cannot be palpated, real-time ultrasound or barium meal examination can be performed to aid in the diagnosis.

(1) Ultrasound Examination: The diagnostic criteria for reflecting a pyloric mass include a pyloric muscle thickness ≥4mm, pyloric canal length ≥18mm, and pyloric canal diameter >15mm. Some propose a stenosis index greater than 50% as a diagnostic criterion. Additionally, the opening and closing of the pyloric canal and the passage of food can be observed. Some have found that in a few cases, the pyloric canal opens normally, termed non-obstructive pyloric hypertrophy, with follow-up showing gradual disappearance of the mass.

(2) Barium Meal Examination: The main diagnostic criteria are an elongated pyloric canal (>1cm) and narrowing (<0.2cm). Other signs include gastric dilation, enhanced gastric peristalsis, a "beak-like" closure of the pyloric orifice, and delayed gastric emptying. Some follow-up cases post-pyloromyotomy show these signs persisting for several days, after which the pyloric canal gradually becomes shorter and wider, possibly not returning to normal. After the examination, the barium should be aspirated via a gastric tube, and the stomach should be washed with warm saline to prevent vomiting and aspiration pneumonia.

bubble_chart Treatment Measures

Surgical Treatment: The best treatment method is pyloromyotomy, which has a short treatment course and good results. Preoperative preparation must be carried out for 24 to 48 hours to correct dehydration and electrolyte imbalance, and to supplement potassium salts. For those with malnutrition, intravenous nutrition is provided to improve overall condition. The surgery involves making an incision in the avascular area above the pylorus, cutting through the serosa and part of the muscle layer. The distal end of the incision should not exceed the duodenal end to avoid cutting through the mucosa, while the proximal end should exceed the gastric end to ensure efficacy. Then, a blunt instrument is used to split the muscle layer deeper, exposing the mucosa, and the incision is widened to more than 5mm to allow the mucosa to bulge freely, and hemostasis is achieved by compression. Postoperative feeding should preferably start the next morning, beginning with sugar water, gradually increasing in amount, transitioning to milk over 24 hours, and reaching full volume in 2 to 3 days. Postoperative vomiting is mostly the result of too rapid an increase in diet, so the amount should be reduced and then gradually increased.

Many long-term follow-up reports indicate that gastrointestinal function is normal after surgery, and the incidence of ulcer disease does not increase. However, X-ray review studies show that successful pyloromyotomy sometimes reveals a narrowed pylorus existing for 7 to 10 years.

Medical Treatment: Medical therapy includes careful feeding with dietary therapeutics, feeding every 2 to 3 hours, regular gastric lavage with warm saline, and taking antispasmodic agents like atropine 15 minutes before each meal. This therapy requires long-term care, hospitalization for 2 to 3 months, is prone to infection, and progresses very slowly and unreliably. Currently, only a few scholars still advocate for medical treatment.

bubble_chart Differentiation

Infant vomiting can be caused by various diseases and should be differentiated from the following conditions: improper feeding, systemic or local infections, pneumonia and congenital heart disease, central nervous system diseases that increase intracranial pressure, progressive kidney diseases, infectious gastroenteritis, various types of intestinal obstruction, endocrine disorders, as well as gastroesophageal reflux and hiatal hernia.