HYPERTROPHIC PYLORIC STENOSIS
Hypertrophic pyloric stenosis is predominately a neonatal disorder. Its exact cause and pathogenesis remain debated. It may be due to a lack of localized nitric oxide synthase, which normally allows for smooth muscle relaxation. It is unknown if the lack of nitric oxide synthase is a primary or secondary event, as it is not seen in all cases. In hypertrophic pyloric stenosis, the interstitial cells of Cajal, which are the pacemaker cells of the gastrointestinal tract, are only seen near the submucosa rather than throughout the entire pylorus. Epidermal growth factors (EGFs), their receptors, and heparin-binding EGF-like growth factors are also increased in smooth muscle cells in hypertrophic pyloric stenosis, but the trigger for these increased growth factors remains unknown.
The term hypertrophic
pyloric stenosis is a misnomer, because the disorder is not due to
hypertrophy but rather to hyperplasia of the smooth muscle layers of the
prepyloric region, particularly the circular layer. The increase in muscular
mass diminishes the size of the lumen, causing obstruction. Depending
upon the degree of the obstruction and its duration, the stomach may be
enormously dilated. The pylorus bulges forward like a tumor, terminating
abruptly at the beginning of the duodenum at one end and, on average, about 2
cm proximally at the other end. The consistency of the pylorus in this
condition is remarkably firm, almost as hard as that of cartilage. The condition
occurs five to seven times more frequently in boys than in girls and occurs in
about 3 in 1000 live births. It is more common in those of Northern European
descent.
Vomiting is
classically the first symptom and may appear between the second and sixth weeks
of life. It may begin with mild spitting, but increases in frequency and
severity that progresses to projectile vomiting. The infants cry, indicating
hunger and willingness to take food. With less food and fluid passing through
the obstructed pylorus, the patients lose weight and become dehydrated.
In this stage a metabolic alkalosis may present a serious problem. The
enlarged pylorus may be palpated as the classic “olive,” and strong peristaltic
movements of the stomach may be observed on simple inspection of the abdominal
wall. Adults typically present with nausea, vomiting, early satiety, and
postprandial epigastric pain. The enlarged pylorus is less readily palpable on
the adult physical examination.
Diagnosis in
infants can often be made by the history and physical examination. X-ray
examination may be done prior to surgical repair. On a barium study, the
stomach appears abnormally large and dilated, with no passage of contrast in
the duodenum until 1/2 hour to 2 hours later. Diagnosis can be confirmed using abdominal
ultrasound, which will show a hypertrophied canal that appears as a sonolucent
3-mm “doughnut.” In adults,
upper endoscopy is recommended to rule out chronic peptic or malignant disease.
Treatment
for hypertrophic pyloric stenosis begins with fluid resuscitation and
correction of electrolyte abnormalities. Medical therapy with anticholinergics
has a high failure rate, and is therefore rarely used. Definitive treatment is
with Ramstedt pyloromyotomy, where a longitudinal incision is made through the
hypertrophied muscle down to the submucosa. An alternative surgery is pyloric
trauma myoplasty, where the
pylorus is grasped with a Babcock clamp, causing displaced muscle at two
locations. Laparoscopic pyloromyotomy has become increasingly common. Infants
resume normal growth and development after pyloromyotomy. The resulting cure is
permanent, leaving no tendency to diseases of the upper gastrointestinal tract.
In adults, resection of the pylorus is recommended to rule out malignancy. The
pylorus can also be endoscopically dilated, but this is associated with a
higher failure rate.
