Hyperthrophic Pyloric Stenosis

Question 1

What is hypertrophic pyloric stenosis (HPS)?

Answer 1

HPS is a thickening of the pyloric muscle in neonates causing stomach outlet obstruction. The exact cause is unknown.

Question 2

How does the pathophysiology of hypertrophic pyloric stenosis progress?

Answer 2

1. The pyloric muscle hypertrophies over a few days to weeks.
   
   2. Gastric outlet obstruction worsens until there is no passage of content into the duodenum.
   3. The stomach dilates.
   4. Milk vomits worsen and become projectile, but the child remains hungry.
   5. Peristalsis becomes stronger and can be seen on the anterior abdominal wall.

Question 3

What are the signs of hypertrophic pyloric stenosis in a neonate?

Answer 3

1. Projectile vomiting.
   
   2. Persistent vomiting leading to failure to thrive initially.
   3. Eventually, marked wasting and severe electrolyte derangements.
   4. Visible peristalsis on the abdominal wall.

Question 4

What electrolyte imbalances occur in hypertrophic pyloric stenosis?

Answer 4

• Hypochloraemia
• Hyponatraemia
• Hypokalaemia
• Marked metabolic alkalosis
• Occasional unconjugated hyperbilirubinaemia.

Question 5

How does vomiting in hypertrophic pyloric stenosis affect electrolyte levels?

Answer 5

Vomiting causes loss of hydrogen ions, sodium, and chloride. This results in hypochloraemia, hyponatraemia, and hypokalaemia, along with a marked metabolic alkalosis.

Question 6

What causes the paradoxical aciduria in hypertrophic pyloric stenosis?

Answer 6

The low serum potassium during severe dehydration leads to potassium moving into cells. Potassium is also preferentially retained in the kidneys via the K+/H+ pump, resulting in hydrogen ion loss in the urine despite the patient being already alkalotic. This leads to paradoxical aciduria.

Question 7

What is the incidence of hypertrophic pyloric stenosis?

Answer 7

The incidence is reported to be as high as 1:1000 live births.

Question 8

What percentage of hypertrophic pyloric stenosis cases have a family history?

Answer 8

A family history is present in 5-20% of patients.

Question 9

What is the gender distribution of hypertrophic pyloric stenosis?

Answer 9

Hypertrophic pyloric stenosis occurs more commonly in males, with a male-to-female ratio of 4:1.

Question 10

In which birth order is hypertrophic pyloric stenosis more common?

Answer 10

It is more common in the first-born child.

Question 11

Which population has a higher incidence of hypertrophic pyloric stenosis?

Answer 11

It is more common in the Caucasian population.

Question 12

What is the classic presentation of hypertrophic pyloric stenosis?

Answer 12

The classic presentation is a 6-week-old male with milk vomiting starting from 2 to 3 weeks after birth. The vomiting becomes larger, more frequent, more forceful, and eventually projectile immediately after a feed.

Question 13

What are the common signs in a baby with hypertrophic pyloric stenosis?

Answer 13

• The baby cries a lot.
• Feeds eagerly.
• Rapid weight loss.

Question 14

What is a potential complication in hypertrophic pyloric stenosis that causes vomiting?

Answer 14

Haematemesis (coffee-ground vomits) may occur in about 15% of cases due to gastritis from old milk curds irritating the gastric mucosa, as well as oesophagitis from secondary gastro-oesophageal reflux.

Question 15

What is the general appearance of a baby with hypertrophic pyloric stenosis during examination?

Answer 15

The baby appears wasted with no signs of sepsis.

Question 16

What is the dehydration status in babies with hypertrophic pyloric stenosis?

Answer 16

Many babies are 5 to 10% or more dehydrated.

Question 17

What percentage of babies with hypertrophic pyloric stenosis are jaundiced?

Answer 17

About 2% of babies with hypertrophic pyloric stenosis are jaundiced due to impaired glucuronyl transferase activity with fasting.

Question 18

What can be observed in the epigastric area of babies with hypertrophic pyloric stenosis in advanced cases?

Answer 18

In advanced cases, visible waves of gastric peristalsis can be seen after a feed in the epigastric area.

Question 19

What is the condition of the abdomen during examination?

Answer 19

The abdomen is soft and non-tender.

Question 20

What is observed during vomiting in babies with hypertrophic pyloric stenosis?

Answer 20

Projectile vomiting of stomach contents may be observed.

Question 21

How is the ‘Pyloric Tumour’ or ‘olive-shaped’ mass palpated?

Answer 21

The mass can be palpated in about 50% of cases on the right border of the right rectus muscle just above the umbilical level. The baby should be relaxed, either in the caregiver’s arms or lying on its right side after a test feed. The examiner stands on the left side and palpates deeply for the mass.

Question 22

What investigations are required to assess the degree of metabolic derangement in hypertrophic pyloric stenosis?

Answer 22

Urea and electrolytes as well as venous gas are required to assess the degree of metabolic derangement.

Question 23

What is the diagnostic investigation for hypertrophic pyloric stenosis?

Answer 23

Ultrasound is the diagnostic investigation, with nearly 100% sensitivity. The length, width, and thickness of the pyloric muscle are measured.

Question 24

What measurements of the pyloric muscle on ultrasound are considered diagnostic for hypertrophic pyloric stenosis?

Answer 24

• Muscle thickness >5mm
• Width >10mm
• Length >15mm

Question 25

Is abdominal x-ray needed for the diagnosis of hypertrophic pyloric stenosis?

Answer 25

Abdominal x-ray is often done but is not needed and should generally not be performed. If done, it may show a large distended stomach with a frothy air-fluid level and minimal distal gas.

Question 26

When is a contrast meal performed in hypertrophic pyloric stenosis, and what are its findings?

Answer 26

A contrast meal is not typically needed, but if the ultrasound is atypical despite typical metabolic derangements, it may be performed. It can show: • A long, narrow pyloric canal with a ‘string sign’ • Pyloric shouldering or the “mammary” sign.

Question 27

What is the first step in managing hypertrophic pyloric stenosis?

Answer 27

The first step is to correct dehydration and metabolic derangements.

Question 28

How is dehydration typically corrected in hypertrophic pyloric stenosis?

Answer 28

Dehydration is corrected with: • Nasogastric tube for feeding. • Intravenous fluid therapy, starting with fluid boluses of normal saline.

Question 29

What is the goal for urine output in hypertrophic pyloric stenosis management?

Answer 29

A urine output of 1 ml/kg/hour should be achieved.

Question 30

What fluids are used for maintenance after initial rehydration in hypertrophic pyloric stenosis?

Answer 30

Maintenance fluid and electrolyte replacement includes: • “Half normal saline” (0.45% NaCl) with KCl and 5% dextrose. • Fluid is given at 130-150% of normal maintenance infusion rate, i.e., 180-220 ml/kg/day.

Question 31

Why is sodium level monitoring important during management of hypertrophic pyloric stenosis?

Answer 31

There is a risk of pontine demyelination if sodium is raised too quickly, so regular blood sodium monitoring is important, especially if normal saline is being administered.

Question 32

What is the operation of choice for correcting hypertrophic pyloric stenosis?

Answer 32

The operation of choice is the Ramstedt Pyloromyotomy, which can be performed either open or laparoscopically.

Question 33

When should surgery be performed in hypertrophic pyloric stenosis?

Answer 33

Surgery is performed once electrolytes and pH have normalized, which may take 1 to 5 days.

Question 34

What are the risks of surgery if the pH, chloride, or bicarbonate levels are abnormal?

Answer 34

There is a risk of post-operative apnoea and myocardial suppression with anaesthesia if: • The pH is more than 7.5, • The chloride is less than 95mmol/L, • The serum bicarbonate is more than 30mmol/L.

Question 35

What are the approaches for the open surgery in hypertrophic pyloric stenosis?

Answer 35

The open approach can be via: • A peri-umbilical incision, • An upper midline incision, • A right upper transverse incision.

Question 36

Why is the laparoscopic approach preferred for surgery in hypertrophic pyloric stenosis?

Answer 36

The laparoscopic approach is now preferred due to better cosmesis (cosmetic results).

Question 37

What is done during the pyloromyotomy procedure?

Answer 37

The pylorus muscle is divided along the length of the ‘olive,’ leaving only the mucosa intact. This allows the pyloric canal to open up and allows milk feeds to pass through.

Question 38

What are potential complications after pyloromyotomy surgery?

Answer 38

Potential complications include: • Perforation of the mucosa, especially at the duodenal side of the myotomy. • An incomplete myotomy that may require a redo operation.

Question 39

What is the typical outcome for babies after surgery for hypertrophic pyloric stenosis?

Answer 39

These babies usually do very well. Most are on full feeds and discharged within 24 hours of surgery and return for a follow-up appointment having regained most of their weight.

Question 40

What complications can arise in the post-operative period of hypertrophic pyloric stenosis surgery?

Answer 40

There is a small incidence of wound sepsis or dehiscence due to the malnourished status of the baby at the time of surgery.

Question 41

What should be monitored in severely malnourished infants after surgery for hypertrophic pyloric stenosis?

Answer 41

Severely malnourished infants should be monitored for metabolic and electrolyte derangements due to “refeeding syndrome,” particularly potassium, phosphate, and magnesium deficiency.