Congenital hypertrophic pyloric stenosis is an incomplete obstructive disorder of the upper gastrointestinal tract caused by hypertrophy and hyperplasia of the pyloric circular muscle, leading to narrowing of the pyloric lumen. Its incidence ranges from 1/3,000 to 1/1,000 and ranks as the third most common gastrointestinal malformation. It occurs more often among firstborn infants and appears predominantly in males, with a male-to-female ratio of approximately 5:1. Most affected infants are full-term, while it is less commonly seen in preterm infants.
Etiology and Pathogenesis
The exact cause of this condition is not fully understood, but it is generally associated with the following factors:
Genetic Factors
This disorder is considered a polygenic hereditary disease.
Disruption of Gastrointestinal Hormones and Other Bioactive Substances
Abnormalities in the pyloric circular muscle, such as decreased levels of enkephalins, substance P, and vasoactive intestinal peptides, have been observed in affected infants. Elevated levels of serum gastrin and prostaglandins have also been identified. Infants receiving exogenous prostaglandin E for the maintenance of a patent ductus arteriosus may be more prone to developing pyloric stenosis.
Congenital Abnormalities in Pyloric Muscle Development
During embryonic development, particularly between the fourth and sixth weeks, excessive muscle growth may occur in the pylorus, particularly in the circular muscle layer, resulting in hypertrophy and subsequent obstruction.
Pathology
Hypertrophy and hyperplasia affect all muscular layers of the pylorus, with the circular muscle layer most prominently involved. The pylorus becomes markedly enlarged, taking on an olive-like appearance. It is pale in color, smooth in texture, and has the consistency of firm rubber. The mass progressively enlarges with age. The thickened muscle layer gradually extends into the gastric wall, resulting in poorly defined boundaries in the gastric antrum. In contrast, the duodenal side has clear boundaries, with the hypertrophic tissue abruptly terminating at the duodenal bulb. Strong gastric peristalsis pushes part of the pyloric canal into the duodenum, causing a folding of the duodenal mucosa resembling a "cervical appearance."
Clinical Manifestations
The hallmark symptoms include non-bilious projectile vomiting, accompanied by physical findings of gastric peristaltic waves and a palpable mass in the right upper quadrant of the abdomen.
Vomiting
Vomiting is the primary symptom, typically manifesting 2 to 4 weeks after birth, although some cases present as early as the first week or as late as 2 to 3 months after birth. Initial symptoms often include mild regurgitation, which progresses to severe projectile vomiting, occurring almost after every feeding session within 30 minutes and forcefully expelled through the mouth or nose. The vomitus contains curdled milk but no bile. In some cases, frequent vomiting leads to gastric mucosal capillary rupture, resulting in vomitus that contains coffee-ground-like material or blood. Despite frequent vomiting, affected infants remain hungry and feed eagerly. Severe vomiting results in the expulsion of most ingested food, leading to decreased stool frequency and oliguria. Prolonged vomiting results in inadequate intake of nutrients and fluids, along with significant loss of H+ and Cl- ions. This leads to failure to thrive, malnutrition, dehydration, and hypochloremic alkalosis. In advanced stages, dehydration worsens, tissue hypoxia occurs, and complications such as lactic acidosis, hypokalemia, and metabolic acidosis may develop, particularly when renal function becomes impaired.
Jaundice
Jaundice is observed in approximately 2% to 8% of cases and is characterized by elevated levels of unconjugated bilirubin. It spontaneously resolves within a few days following surgical intervention. Although the exact mechanism is uncertain, potential causes include starvation, immature liver function, reduced glucuronyl transferase activity, limited stool output, and increased enterohepatic circulation of bilirubin.
Abdominal Signs
The upper abdomen may appear distended, while the lower abdomen remains soft and flat. Visible gastric peristaltic waves can often be observed migrating from the left subcostal region to the right upper abdomen, especially during feeding or just before vomiting. These waves can sometimes be elicited by gently tapping the upper abdomen. A characteristic sign of this condition is the palpable olive-shaped mass in the right upper quadrant, just below the right costal margin along the lateral edge of the rectus abdominis muscle. This firm, mobile mass is a key diagnostic feature.
Auxiliary Examinations
Abdominal Ultrasound
Ultrasound is the preferred non-invasive diagnostic method. It reveals a hypoechoic, circular thickening of the hypertrophic pyloric muscle with a hyperechoic central mucosal layer. Measurements of the thickened muscle layer, pyloric diameter, and pyloric canal length aid in diagnosis. A muscle thickness ≥4 mm, pyloric diameter ≥13 mm, and canal length ≥17 mm provide diagnostic accuracy ranging from 81% to 93%.
X-Ray with Contrast (Barium Meal Study)
Fluoroscopy may show gastric dilation, delayed passage of contrast through the pylorus, and prolonged gastric emptying time. Detailed observation often reveals elongation of the pyloric canal with its cranial curve, the "beak sign" in the pyloric antrum, narrowing of the lumen into a string-like structure, and characteristic X-ray findings such as the "mushroom sign" and "double shoulder sign" in the duodenal bulb.
Differential Diagnosis
For cases with atypical clinical manifestations, the following conditions should be considered as differential diagnoses:
Improper Feeding
Overfeeding, feeding too quickly, air ingestion during bottle feeding, or inappropriate positioning after feeding are common causes of vomiting in neonates. Symptoms generally resolve after modifying feeding techniques, such as bringing the infant upright after feeding and gently patting their back to release trapped gastric air.
Pylorospasm
Intermittent and irregular vomiting, usually of a small quantity, often begins shortly after birth without progressive worsening. Gastric peristaltic waves may occasionally be observed, but no palpable mass is present in the right upper quadrant. Affected infants typically exhibit good overall health, with no significant dehydration or malnutrition. Ultrasound findings reveal no hypertrophy of the pyloric muscle layer. Treatment with antispasmodic or sedative medications, such as atropine or chlorpromazine, often leads to clinical improvement.
Gastroesophageal Reflux (GER)
Vomiting is usually non-projectile, with no signs of gastric peristaltic waves or an olive-shaped mass in the right upper quadrant. Positioning therapy and the use of thickened feeds can reduce vomiting. Diagnostic confirmation may involve imaging studies, such as X-ray with contrast (barium swallow), or 24-hour pH monitoring of the esophagus.
Gastric Volvulus
Vomiting typically emerges within weeks after birth and worsens with changes in body position. X-ray with barium studies may reveal:
- Crossed esophagogastric mucosal lines,
- The greater curvature of the stomach positioned above the lesser curvature,
- The gastric antrum located higher than the duodenal bulb,
- Double air-fluid levels or double-bubble appearance in the stomach,
- Lengthening of the abdominal segment of the esophagus, with its opening displaced below the stomach.
Gastroscopy can both confirm the diagnosis and provide therapeutic intervention via endoscopic reduction of the volvulus.
Other Congenital Gastrointestinal Anomalies
Conditions such as prepyloric membrane, annular pancreas, malrotation of the intestines, and meconium peritonitis with intestinal obstruction should also be considered. Clinical symptoms, timing of onset, and the nature of the vomitus vary depending on the location and severity of the obstruction caused by these anomalies. Vomiting typically begins shortly after birth and is accompanied by decreased or absent bowel movements.
Prepyloric Membrane
Vomiting resembles that seen in hypertrophic pyloric stenosis, but there is no abdominal mass or the characteristic findings on X-ray imaging.
Annular Pancreas, Malrotation of the Intestines, or Meconium Peritonitis with Intestinal Obstruction
Vomitus may contain bile or even fecal-like material. Abdominal X-rays may reveal varying degrees of gastric and duodenal dilation, presenting classical "double-bubble" or "triple-bubble" appearances indicative of duodenal obstruction. In annular pancreas, the descending portion of the duodenum may appear constricted, linear, or segmentally narrowed. In cases of malrotation, barium enema studies may show atypical positioning of the cecum and ascending colon in the right upper quadrant or central upper abdomen. Meconium peritonitis with intestinal obstruction may present with calcifications within the abdominal cavity.
Treatment
Once the diagnosis is confirmed, early correction of nutritional status is necessary. Surgical pyloromyotomy is performed using a laparoscopic approach, which is simple and highly effective. With advancements in endoscopic techniques, pyloromyotomy can now be performed under direct visualization via gastroscopy, offering less invasive treatment with minimal trauma and no visible skin scars.