pyloric stenosis

Hypertrophic Pyloric Stenosis

hypertrophic pyloric stenosis (HPS) is a disease of newborns with an incidence
of 1 in 300 to 1 in 900 live births. It is most commonly identified in Caucasians of
northern European descent. Throughout the world, HPS appears to be less common
in Africans, African Americans, and Asians. HPS is more common in infants
with blood types B and O. Seasonal variation in the incidence of HPS has been reported; more infants present during the spring and fall months.

Although a genetic predisposition to HPS is suspected, the exact mode of inheritance

is unknown. Males are affected four times as often as females, and first born
males are at highest risk. Family history is relevant. When parents (mother or father)
have had HPS it occurs in 5-20% of their male children but in only 3-7% of their
female children. Children whose mothers had HPS develop pyloric stenosis 3-4
times more frequently than children whose fathers had HPS. Finally, monozygotic
twins are more likely to be concordant for HPS than are dizygotic twins.
Etiology
Despite extensive clinical and laboratory research, the cause of pyloric stenosis
remains unknown. Researchers have investigated the role of many factors (i.e., ganglion cells, maternal factors, gastric acidity, nutritional factors, prostaglandins, nitric oxide, hypergastrinemia, etc.) suspected as contributors to pyloric muscle hypertrophy,yet no conclusive etiology has been described.


Clinical Presentation
Infants with HPS generally present between the second or third week of life to
two months of age. Rare cases have been reported throughout childhood and into
adult life. Symptoms begin as mild regurgitation that gradually progresses to
nonbilious vomiting. With time, the emesis becomes more frequent and forceful
(i.e., projectile). Infants are generally consolable and hungry after vomiting episodes.
In 3-5% of cases, the vomitus will be brown or even bloody secondary to an
associated esophagitis /gastritis.
In HPS, dehydration, weight loss, and failure to thrive are the result of uncorrected
fluid losses and inadequate nutrition caused by a nearly complete gastric outlet
obstruction. Gastric secretions contain significant quantities of potassium,
hydrogen ion, and chloride. Although the kidney can initially compensate for mild
electrolyte losses, with prolonged emesis and dehydration, a hypokalemic,
hypochloremic, metabolic alkalosis develops. Indirect hyperbilirubinemia is observed
in 1-2% of patients and is caused by a decrease in hepatic glucuronyl transferase
probably as a consequence of starvation.
Physical examination often reveals a hungry child with signs of dehydration (i.e.,
sunken fontanelles, pale mucosal membranes, poor skin turgor, lethargy, hypotonicity,
poor capillary refill). Visual inspection of the abdomen may reveal peristaltic
waves traversing from left to right across the upper abdomen. Nasogastric or orogastric decompression of the stomach offers symptomatic relief and empties the stomach of retained formula/milk and mucous facilitating palpation of a hypertrophied pylorus (olive). A meal of sugar water can be administered to satiate the crying infant. As the child relaxes, palpation of the pyloric mass is often easier.


differential diagnosis

HPS is extensive and includes all causes of nonbilious

emesis in the neonate. Anatomic anomalies that mimic pyloric stenosis include duodenalstenosis, antral/pyloric webs or duplications (those 10-15% with obstruction
proximal to the ampulla of Vater). Functional problems in the differential include
gastroenteritis, gastroesophageal reflux with/without hiatal hernia and achalasia. The
metabolic differential includes congenital adrenal hyperplasia (CAH) and inborn
errors of metabolism. Intracranial pathologies, including intracerebral bleeding and
hydrocephalus are also associated with projectile vomiting.
Diagnosis
The hypertrophied pylorus (olive) is palpable on clinical exam in about 75-90%
of infants with HPS. If the olive cannot be felt or the diagnosis is in doubt, an
abdominal ultrasound is beneficial. A pyloric muscle thickness greater than 4 mm
or pyloric channel length greater than 14mm confirms the diagnosis.
Ultrasonographic detection of pyloric stenosis has a false negative rate of 5-10%. If
ultrasonography is nondiagnostic, an upper gastrointestinal study (UGI) can be
performed. UGI may be beneficial to exclude reflux, distal obstruction and malrotationas sources of emesis. The radiographic findings on UGI that suggest HPS include:
the string sign from the narrowed pyloric channel, the double track sign from
the folding of the rugal folds, and the pyloric beak or shoulder signs from the
pyloric bulge into the antrum.
Pathology
Gross pathologic findings include a firm, bulbous pylorus with a smooth and
shiny serosal surface . On cut section, the mucosa is pushed inward effectively
obliterating the pyloric channel. The lumen of the duodenum attains its full
size immediately distal to the hypertrophied pylorus unlike the proximal gastric
lumen which demonstrates progressive narrowing. Microscopic examination of the
pylorus reveals hypertrophy and hyperplasia of the circular pyloric muscle fibers.
Edema and nonspecific inflammatory changes are observed in the mucosa and
submucosa.
Treatment
The mainstay of treatment is surgical pyloromyotomy, a procedure formalized
by Ramstedt in 1912. Initial management of infants with HPS includes fluid resuscitation appropriate to the degree of dehydration and severity of electrolyte
abnormalities (i.e., hypochloremia, hypokalemia, alkalosis). A typical resuscitation
plan includes initial rehydration with normal saline (10-20 cc/kg boluses) until urine
output is established, followed by gradual potassium replenishment (i.e., D51/2 NS
with 20 meq KCl/l at 1.5-2 times maintenance rate) until electrolyte abnormalities
are corrected. Most infants can be operated upon within 24 hours of admission.


Pyloromyotomy is performed under general anesthesia. The traditional incision,
as described by Ramstedt, is a transverse right upper quadrant incision. Periumbilical
incisions are occasionally used and cosmetically superior, but have higher risk for
wound infection. The stomach is identified and the pylorus is delivered through the
incision. The hypertrophied pylorus is incised from the gastroduodenal junction
proximally to just beyond the extent of the tumor, being careful not to violate the
duodenal or gastric mucosa. The incised muscle is split further by dividing the
remaining circular muscle fibers using the blunt edge of a knife handle or other
spreading device. The intact mucosa bulges between the divided muscle edges. The
divided pylorus is grasped on each side of the pyloromyotomy and gently manipulated
to and fro to confirm complete separation of the muscle fibers. The pylorus is
replaced into the abdomen after the mucosa is closely reinspected for leak or bleeding.
Feeding is started 6-8 hours postoperatively. A pyloric feeding regimen is used to
gradually initiate and advance enteral intake. Most regimens begin with sugar water
followed by increasing concentrations and volumes of the childs formula. Occasionally,infants will continue to have small amounts of emesis when feedings are
initiated postoperatively. Parents should be forewarned and reassured regarding this
potential, usually self-limited, postoperative problem. The feeding volume is advanced every few hours. The infant is discharged when oral intake is adequate to maintainhydration and meet estimated nutritional needs.
Outcomes
Infants tolerate pyloromyotomy very well. Average hospital length of stay is 1-3
days. Overall mortality is approximately 0.3%. Two uncommon complications of
pyloromyotomy are gastric/duodenal perforation and incomplete separation of muscle
fibers. Although perforations are easily repaired at the time of surgery, an unrecognized duodenal perforation is a devastating complication presenting as diffuse peritonitis and/or intra-abdominal abscess. Incomplete pyloromyotomy results in
prolonged postoperative feeding intolerance. Recurrence of HPS is extremely rare.