Chapter 40 Hypertrophic Pyloric Stenosis
PATHOPHYSIOLOGY
Hypertrophic pyloric stenosis is one of the more frequently occurring conditions requiring surgery within the first 6 months of life. Hypertrophy (increased size) and hyperplasia (increased mass) of the circular muscle of the pylorus cause obstruction at the pyloric sphincter. The circular muscle increases to as much as twice the normal thickness, and the pylorus lengthens, which results in severe narrowing of the lumen. In addition, the stomach dilates, and hypertrophy of the gastric antrum occurs. The cause is unknown, but multiple factors have been implicated, and evidence suggests that local innervation is involved. Immaturity of function and the absence of pyloric ganglion cells has been suggested. Hypertrophic pyloric stenosis may be associated with intestinal malrotation, esophageal or duodenal atresias, and anorectal anomalies. In addition, there is a genetic predisposition. In 1999, the Centers for Disease Control and Prevention (CDC) reported a possible link between the use of oral erythromycin in infants and hypertrophic pyloric stenosis. The CDC does not recommend that physicians stop prescribing erythromycin, just that they be aware of the possible risk. A study done in Denmark determined that the maternal use of macrolides such as erythromycin during breast feeding increased the risk of infantile hypertrophic pyloric stenosis.
INCIDENCE
1. Hypertrophic pyloric stenosis occurs in 1 to 4 cases per 1000 live births, usually 2 to 8 weeks after birth, with peak incidence within the first 3 to 5 weeks of life.
2. Hypertrophic pyloric stenosis is less common in African Americans and is rare in Asian individuals. It is most commonly seen in white children.
3. Male/female ratio is 5:1. This ratio is not observed as much in children of low birth weight (<2500 g) as in children of birth weight over 2500 g.
CLINICAL MANIFESTATIONS
1. Nonbilious vomitus; may be blood-streaked (initial symptom)
2. Vomiting, usually occurring 30 to 60 minutes after feeding
3. Vomiting that becomes progressively more projectile, projecting up to 3 feet from the infant
4. Appears hungry; eagerness to be fed after vomiting
5. Vomiting of retained feeding with current feeding
6. Signs of dehydration (decreased tears, poor skin turgor, dark circles under eyes, sunken fontanelle)
8. Failure to gain weight or weight loss
10. Distended upper abdomen after feeding
12. Visible left-to-right gastric peristaltic waves
13. Palpable firm, movable, olive-shaped mass in right upper quadrant
LABORATORY AND DIAGNOSTIC TESTS
Refer to Appendix D for normal values and/or ranges of laboratory and diagnostic tests.
1. Complete blood count—elevated hemoglobin and hematocrit, due to hemoconcentration—used to determine fluid balance, specifically dehydration status
2. Serum electrolyte levels—hypochloremia, hypernatremia, hypokalemia (may be masked by hemoconcentration from extracellular fluid depletion)—used to determine electrolyte levels, which may be imbalanced as a result of vomiting
3. Arterial blood gas values—used to determine acid/base balance, specifically metabolic alkalosis related to vomiting
4. Upper gastrointestinal barium studies—diagnostic; show delayed gastric emptying and narrowing of the pyloric channel (barium is aspirated through a nasogastric tube after the procedure to decrease risk of aspiration)
5. Abdominal ultrasonography—first-line diagnostic study. Used to visualize hypertrophy and hyperplagia of pyloric sphincter
6. Urine specific gravity—used to determine hydration status
