Pyloric stenosis occurs when there is hypertrophy of the pylorus muscle which narrows the pyloric canal. This causes issues with gastric contents passing into the duodenum.
It is the most common cause of gastric outlet obstruction in the first 12 weeks of life. It most commonly presents in the 2nd-4th week of life and can continue until 4 months of age. It is more common in males (4:1).
🦴 Anatomy
The pylorus is the the final portion of the stomach. It has 2 parts - an antrum and a canal. The canal ends at the pyloric orifice which is surrounded by the pyloric sphincter. The pyloric sphincter is a thick band of smooth muscle which controls the gastric emptying of contents into the duodenum.
It is innervated by the autonomic nervous system (ANS) which controls the opening and closing of the sphincter:
- Parasympathetic nervous system - the vagus nerve controls the parasympathetic innervation. Activation of the vagus nerve leads to relaxation of the sphincter and emptying of contents into the duodenum.
- Sympathetic nervous system - the greater splanchnic nerve is the origin for the sympathetic innervation of the pyloric sphincter it synapses in the celiac ganglion before reaching the pyloric sphincter. It causes contraction of the sphincter and continence of the gastric contents in the stomach.
⚠️ Pathophysiology and risk factors
The exact etiology of pyloric stenosis remains incompletely understood, but both genetic and environmental factors likely contribute. Some evidence suggests a genetic predisposition, as the condition often runs in families and is more common in first-born males. Additionally, certain risk factors such as maternal use of macrolide antibiotics during pregnancy have been associated with an increased incidence. The precise mechanisms triggering the hypertrophy are not fully understood, however.
The hypertrophy of the pylorus muscle leads to narrowing of the canal and increased resistance by the pyloric sphincter. This prevents food from passing through the sphincter and leads to forceful peristalsis by the stomach in an attempt to pass the food into the duodenum.
Risk factors include:
- Males
- Firstborns
- Maternal macrolide usage during pregnancy - predominantly erythromycin.
- Family history
- Prematurity
😷 Presentation
Pyloric stenosis typically presents in weeks 2-4 after birth.
- Projectile, non-bilious vomiting - forceful peristalsis from the stomach to the duodenum is met with strong resistance from the pyloric sphincter which causes food to be forced up the oesophagus. It generally happens 30 minutes after feeding.
- Persistence of hunger - paradoxically, even though the infant is vomiting, they may continue to exhibit hunger cues and desire to feed shortly after vomiting episodes.
- Weight loss
- Dehydration - seen as dry nappies, for example. In severe cases, it may lead to hypovolaemic shock.
- Failure to thrive
On examination, we may notice the following:
- Visible peristalsis
- Palpable olive-sized mass in the upper abdomen - this mass is felt better during feeds.
🔍 Investigations
- Blood gas - hypochloric metabolic alkalosis, as the baby is vomiting hydrochloric acid (HCl). It may also show hypokalaemia (as the kidneys excrete K+ in an attempt to get back H+ to compensate for the alkalosis).
- 🏆 Ultrasound - confirms diagnosis. Demonstrates hypertrophy of the pyloric muscle, with wall thickness >3mm length >15mm and diameter >11mm.
🧰 Management
The initial management of pyloric stenosis is to:
- Correct any metabolic abnormalities - with fluid and electrolyte replacement.
- For acute hypovolaemia: 10-20ml/kg fluid boluses
- Rehydration: should be provided at 1.5 times maintenance rate (150 ml/kg/day); with 5% dextrose + 0.45% saline (may differ based on trust policy).
- Maintenance fluids - 100ml/kg/day, commenced after correcting dehydration & electrolytes.
- Stop oral feeding
- Insert a nasogastric tube and aspirate it at 4 hourly intervals.
The definitive management is surgical using the following procedure:
- 🏆 Ramstedt pyloromyotomy - a laparoscopic procedure in which an incision is made in the sphincter to widen the canal. It carries an excellent prognosis. Babies can resume feeding after 6 hours, although there may be some residual vomiting. This is common due to gastric distension and dysmotility post-surgery.
