Hypertrophic Pyloric Stenosis (HPS) is due to concentric hypertrophy of the pyloric smooth muscle, leading to gastric outflow obstruction and has an incidence of .1-.4%, with most cases occurring in Caucasians. At a ratio of 4:1, boys are more likely to be affected than girls, with first born male children having a higher susceptibility to the condition. HPS has been found to occur in 20% of male offspring and 10% of female offspring to a mother with pyloric stenosis herself. An increased incidence of HPS has been linked to infants with B and O blood groups, and there is a higher concordance of HPS in monozygotic than dizygotic twins, suggesting a genetically based predisposition. Its occurrence has been linked to macrolide use during pregnancy and erythromycin (a motilin agonist) administration in neonates, with risk increasing by a factor of 8 if administered during days 3-13 of the newborn’s life. Reduced levels of nitric oxide synthase have been found in a subset of HPS cases and is thought to play a role in its etiology.
Diagnosis and Evaluation
The presentation of HPS, characterized by post-prandial nonbilious projectile vomiting and progressive feeding intolerance, begins at 2-4 weeks of age, and pyloric narrowing is maximal at 4-8 weeks of age. On physical exam, the infant will appear underweight and dehydrated. Projectile nonbilious vomiting is a classical presentation associated with HPS, and may be associated with secondary coffee ground emesis. Whether the vomiting is projectile or not is often dependent on the progression of the stenosis. Loss of fluid, hydrogen ions, and chloride ions due to continuous vomiting can result in hypochloremic metabolic alkalosis accompanied by paradoxical aciduria. Icteropyloric syndrome, characterized by jaundice due to hyperbilirubinemia (primarily unconjugated) is the most common medical syndrome associated with HPS, and is attributed to decreased levels of glucoronyl transferase. Examination of the abdomen yields a palpable olive shaped mass, usually in the right upper quadrant along the lower border of the liver, that is most easily palpated after a period of vomiting or on an empty stomach. After feeding, gastric peristaltic waves may be visible on the abdomen.
Detection by ultrasound is the most conventional means of confirming HPS. To allow for distention of the antrum and the pyloric region, and hence better visualization, the patient is placed in the right posterior oblique position. Criteria for diagnosis by ultrasound include pyloric muscle thickness > 4mm, a pyloric channel length >16mm, and a pyloric diameter >14mm. On the short axis sonographic view, the hypertrophied hypoechoic muscle surrounding the echogenic mucosa creates the appearance of a “Bull’s eye”. The sensitivity and specificity of ultrasound in the diagnosis of HPS is 97% and 100% respectively. Alternatively, an upper GI can be used for primary diagnosis or in patients with indeterminate ultrasound findings. With the use of contrast, an elongated pyloric channel will be visible creating a “string sign”. Displacement of the pylorus into the antrum of the stomach will create what is known as the “shoulder sign” on contrast studies.
Management and Surgical Technique
Prior to operative management, correction of acid-base, electrolyte and fluid imbalances is essential to prevent postoperative complications such as anesthesia related apnea. It is imperative that the patient is not orally fed pre-operatively, as generation of stomach acid can make acid-base correction more difficult. Initially a 20ml/kg normal saline bolus is used to correct the dehydrated state. Once urine output is confirmed, 10-20mEq/L of KCL should be added. A nasogastric tube (NG) is generally not necessary.
The classic, definitive surgical treatment of HPS is a Ramstedt pyloromyotomy, in which a longitudinal incision of the anterior surface of the pylorus is made down to the level of the submucosa. A right upper quadrant transverse incision offers the most direct access to the pylorus. However, a circumumbilical approach, associated with increased cosmesis, can be used as well. The supraumbilical skin fold is incised in a curvilinear fashion, and the midline fascia is exposed one third the distance from the umbilicus to the xiphoid. A longitudinal incision of the linea alba allows entrance into the peritoneum and exposure of the pylorus. The gastroduodenal junction can easily identified by locating the vein of Mayo. The duodenum should be immobilized using the non-dominant index finger, and a transverse myotomy incision made 1-2mm proximal to the duodenum until nonhypertrophied antrum has been reached. The blunt knife end is used to separate the transverse and oblique muscle fibers. A Benson or similar pyloric spreader can then be used to separate the circular muscle fibers. Free movement of the two sides of the incision should be established. The stomach can be insufflated with air via orogastric tube to check for any leaks, though data to support this practice is scant.
Laparoscopic pyloromyotomy is increasing in preference due to its cosmetic advantages, decreased need for analgesics, and statistically decreased time interval between the operation and full feedings. A 5mm umbilical trocar is introduced via a cutdown incision. Two 3mm instruments are then placed in stab incisions, with or without the use of trocars, in the right and left epigastric region. Atraumatic forceps are introduced through the right epigastric incision, and used to stabilize the duodenum. A sheathed knife scalpal is introduced through the left epigastric port and used to linearly incise the serosa of the pylorus from the pyloric base towards the antrum. The sheathed knife scalpel is removed and replaced by a Tan or similar pyloric spreader which is then used to separate the incision and expose the submucosa. Due to manufacture discontinuation of the commonly used arthroscopy knife for this procedure, many surgeons have converted to the use of an extended tip electrocautery device for creation of the myotomy incision. An omental patch may be placed over the pyloromyotomy if bleeding becomes difficult to control.
In the event of an iatrogenic duodenotomy or gastrotomy, the defect and pyloromyotomy should be surgically closed with full thickness sutures, the pylorus rotated to the posterior surface, and a new pyloromyotomy performed in the usual fashion. Consideration can be given to gastric decompression overnight in these patients. Postoperative complications are uncommon but include wound infection, which should be treated with local wound care, bleeding, and iatrogenic injury to surrounding structures.
Alternative treatment options for HPS include the use of atropine sulfate, administered 6 times a day, 5 minutes before feeding in doses of .01 mg/k/day via IV or .05 mg/kg/day via NG. The average hospital stay associated with antimuscarinic treatment is 21-44 days. Because this means of treatment is not successful in 15-66% of patients, it is reserved for infants who are poor surgical candidates or whose parents are against surgical treatment.
After surgical treatment, vomiting of the initial feeds is quite common, but vomiting of all feeds persisting beyond 5 days may be a sign that the surgical treatment was inadequate. While a variety of elaborate feeding regimes are described, a diet of breast milk or formula ad lib immediately postoperatively is equally efficacious in reaching target feeds for discharge.
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