The cause of HPS is unknown, but genetic and environmental factors appear to play a large role in the pathophysiology. A genetic predisposition has been inferred from race discrepancies, the increased frequency in males, and the association with birth order (first-born infants with a positive family history). Variants near several loci including MBNL1 , NKX2-5 , APOA1 , EML4 , and BARX1 have been associated with HPS. Environmental factors associated with HPS include the method of feeding (breast vs. bottle), seasonal variability, postnatal exposure to erythromycin (excluding breast milk), environmental pesticides, maternal smoking, and transpyloric feeding in premature infants. ^{, ,} Additionally, there has been interest in several gastrointestinal peptides or growth factors that may facilitate pyloric hypertrophy. Some of these include excessive substance P, decreased neurotrophins, deficient nitric oxide synthase, and gastrin hypersecretion. ^, Thus, the etiology of HPS is likely multifactorial with environmental influences.

The classic presentation of HPS is nonbilious, projectile vomiting in a full-term neonate who is between 2 and 8 weeks of age. Initially, the emesis is infrequent and may appear to be symptomatic of gastroesophageal reflux disease. However, over a short period of time, the emesis occurs with every feeding and becomes forceful (i.e., projectile). The contents of the emesis are usually the recent feedings, but signs of gastritis are not uncommon (“coffee-ground” emesis). On physical examination, the neonate usually appears well if the diagnosis is made early. However, depending on the duration of symptoms and degree of dehydration, the infant may be gaunt and somnolent. Visible peristaltic waves may be present in the mid to left upper abdomen. The pylorus is palpable in 70%–90% of patients. ^, To palpate the pyloric mass (i.e., “olive”), the baby must be relaxed. Examination aides include bending the knees and flexing the hips and using a pacifier with sugar water. These techniques should be attempted after the stomach has been decompressed with a 10-Fr to 12-Fr orogastric tube. After palpating the liver edge, the examiner’s fingertips should slide underneath the liver in the midline. Slowly, the fingers are pulled back down, trying to trap the “olive.” Palpating the pylorus requires experience, patience, and an optimal examination setting. If an olive is palpated, no further studies are needed. If the pylorus cannot be palpated, ultrasound (US) is the next step. In a large systematic review and metaanalysis, the sensitivity of a palpable olive has decreased over time from the classically described 80%–90% to 10%, likely reflecting increased use of US.

US has become the standard technique for diagnosing HPS and has supplanted the physical examination at most institutions. The diagnostic criteria for pyloric stenosis is a muscle thickness of greater than or equal to 4 mm and a length of greater than or equal to 16 mm ( Fig. 27.1 ). A thickness of more than 3 mm is considered positive if the neonate is younger than 30 days of age. The study is dependent on the expertise of the US technician and radiologist.

Ultrasonography has become the standard imaging study for diagnosing pyloric stenosis and has supplanted physical examination at most institutions. The (A) transverse and (B) longitudinal views of hypertrophic pyloric stenosis are seen here. Muscle thickness ≥4 mm on the transverse view or a length ≥16 mm on the longitudinal view is diagnostic of pyloric stenosis. On this study, the pyloric wall thickness was 5 mm and the length ( arrows ) was 20 mm.

There are reports of nonradiologists, including surgeons, reliably performing and teaching US for diagnosing HPS (point of care US), which would obviously reduce the need for the US technician. If the US findings are equivocal, then an upper gastrointestinal series can be helpful in confirming the diagnosis ( Fig. 27.2 ).

At some hospitals outside of urban centers, ultrasound technicians and radiologists proficient in performing an ultrasound study for pyloric stenosis are not available. Also, in some instances, an ultrasound study can be equivocal. An upper gastrointestinal series can be helpful in making the diagnosis of pyloric stenosis or confirming an equivocal ultrasound study. In this upper gastrointestinal study, note the “string sign” indicating a markedly diminished pyloric channel ( arrow ) and subsequent gastric outlet obstruction. It is important to evacuate the contrast material after this study to reduce the risk of aspiration and pulmonary complications.

In the past, the diagnosis was often delayed and profound dehydration with metabolic derangements was common. Today, primary care physicians are more aware of the problem, and the availability of US facilitates earlier diagnosis and treatment of HPS. However, the complete differential diagnosis for nonbilious vomiting should be considered. This includes medical causes such as gastroesophageal reflux, gastroenteritis, increased intracranial pressure, and metabolic disorders. Anatomic causes include an antral web, foregut duplication cyst, gastric tumors, or a tumor causing extrinsic gastric compression.

The mainstay of therapy is typically resuscitation followed by pyloromyotomy. There are reports of medical treatment with atropine and pyloric dilation, but these treatments have longer lengths of stay, higher failure rates, and higher complication rates due to medication side effects.

Once the diagnosis of HPS is made, feedings should be withheld. Gastric decompression is usually not necessary but occasionally may be required in extreme cases. If a barium study was performed, it is important to remove the contrast material from the stomach to prevent aspiration.

The hallmark metabolic derangement of hypochloremic, hypokalemic metabolic alkalosis is usually seen to some degree in most patients. Profound dehydration is rarely seen today, and correction is usually achieved in less than 24 hours after presentation. A basic metabolic panel should be ordered, and resuscitation should be directed toward correcting the abnormalities and normalizing urine output. Most surgeons use the serum bicarbonate (>30 mEq/L), chloride (>100 mmol/L), and potassium (4.5–6.5 mmol/L) levels as markers of adequate resuscitation. The institution of a resuscitation protocol has been shown to decrease lab draws, reduce time to laboratory normalization, and decrease hospital length of stay. In the absence of extreme laboratory derangements or ongoing sequelae of dehydration and alkalosis, children with HPS have been shown to reliably and predictably resuscitate with fluids. One example protocol begins with 20 mL/kg 0.9% saline boluses, with the number of boluses (1–3) determined by the severity of the chloride abnormality. D5W with 0.9% saline is then initiated at 1.5 times the maintenance rate, with the addition of 20 mEq/L of potassium added when the serum potassium normalizes. Electrolytes are reevaluated once the boluses are completed. Subsequent fluid boluses are given if the electrolytes remain abnormal. ^, After successful correction of fluid deficits and electrolyte abnormalities, the patient can safely undergo anesthesia and operation. It is important to appreciate that HPS is not a surgical emergency, and resuscitation is the initial primary focus. Inadequate resuscitation is thought to lead to postoperative apnea due to decreased respiratory drive secondary to metabolic alkalosis; however, the evidence base for this is weak. ^,

After general anesthesia has been induced, an abdominal examination should be performed to physically check for an “olive” if one was not detectable preoperatively. The pyloromyotomy may be performed by open or laparoscopic technique, with the latter now the predominant approach. The anesthesiologist can pass and leave a suction catheter in the stomach for decompression and for instilling air after the pyloromyotomy to check for a leak.

The Open Approach

Historically, several different incisions have been described for the open approach. The typical right upper quadrant transverse incision is the most common ( Fig. 27.3 ). An alternate, more cosmetically pleasing incision involves an omega-shaped incision around the superior portion of the umbilicus followed by incising the linea alba cephalad. With either incision, the pylorus is exteriorized through the incision. A longitudinal serosal incision is made in the pylorus approximately 2 mm proximal to the junction of the duodenum and is carried onto the anterior gastric wall for approximately 5 mm. Blunt dissection is used to divide the firm pyloric fibers. This can be performed using the handle of a scalpel. Once a good edge of fibers has been developed, a pyloric spreader or hemostat can be used to spread the fibers until the pyloric submucosal layer is seen. The pyloromyotomy is then completed by ensuring that all fibers are divided throughout the entire length of the incision. This is confirmed by visualizing the circular muscle of the stomach proximally as well as a slight protrusion of the submucosa. The most common point of mucosal entry is at the distal part of the incision at the duodenal–pyloric junction. Therefore, care must be exercised when dividing the fibers in this region. The pyloromyotomy can be checked for completeness by rocking the superior and inferior edges of the myotomy back and forth to ensure independent movement. The mucosal integrity can be checked by instilling air through the previously placed suction catheter. If there are no leaks, the air should be suctioned. Minor bleeding is common and should be ignored because it will cease after the venous congestion is reduced when the pylorus is returned to the abdominal cavity. The abdominal incision is then closed in layers.

These two children underwent open pyloromyotomy through a right upper quadrant transverse incision. Over time, the cosmetic appearance of their incision is not as attractive as that seen after the laparoscopic operation.

The Laparoscopic Operation

Neonatal laparoscopy has grown in popularity with the refinements in technique and smaller instruments. The first reported laparoscopic pyloromyotomy in the English language was in 1991 (the authors had reported the first case in the French literature in 1990). Since then, this procedure has been accepted by most pediatric surgeons.

The technique involves entering the abdomen through an umbilical incision. A Veress needle is placed at the base of the umbilicus between the umbilical arteries. It is paramount to ensure proper placement of the Veress needle before insufflation. This can be done by several simple methods, including the “blind man’s cane” sweep and the water drop test. Alternatively, an open approach can be used to introduce the umbilical cannula. The abdomen is then insufflated to a pressure of 10 mmHg and a 3- or 5-mm port is introduced for the telescope and camera. Two 3 mm incisions are made. One stab incision is in the right paramedian side of the abdomen at the level of the umbilicus, and the other is in the left paramedian side of the abdomen just superior to the umbilicus.

Local anesthesia is used at all incisions. An atraumatic bowel grasper is placed through the left incision, and a knife or long cautery tip is introduced through the right incision ( Fig. 27.4 ). The duodenum is grasped firmly just distal to the pylorus, and the pylorus is maneuvered into view. Occasionally, a transabdominal stay suture around the falciform ligament is helpful to elevate the liver away from the pylorus. A longitudinal pyloromyotomy is then made with either the knife or the electrocautery in a manner similar to the open technique ( Fig. 27.5 ). Initially, a retractable arthrotomy knife was used. However, this is no longer on the market in the United States. Most surgeons now use an unguarded arthrotomy knife or the extended electrocautery tip with or without electrocautery, which appear equivalent in operative time and complications. A laparoscopic pyloric spreader or a box-type grasper can be used to complete the myotomy. Completeness of the myotomy and mucosal integrity are evaluated similar to the open technique. Omentum can be placed over the myotomy to help with hemostasis, if necessary. The stomach may be inflated with air through an orogastric tube to evaluate for perforation. However, in one study in which there were two perforations, inflating the stomach did not detect the leak. The leaks were detected by careful inspection of the pyloromyotomy. The pneumoperitoneum is evacuated after the instruments are removed. The umbilicus is closed with absorbable suture, and the 3 mm incisions are closed with skin adhesive.

For laparoscopic pyloromyotomy, a 3- or 5-mm cannula is introduced through the umbilicus and insufflation achieved to a pressure of 10 mmHg. Through a stab incision in the right upper abdomen, an atraumatic bowel grasper is introduced for grasping and stabilizing the duodenum. The myotomy device and pyloric spreader are introduced through the stab incision in the patient’s left upper abdomen.

Technique of laparoscopic pyloromyotomy. (A) With the duodenum stabilized, a seromuscular incision is made in the hypertrophied pylorus with the cautery blade. (B) Next, the blade is used to further bluntly divide the pyloric muscle. (C) Then, a pyloric spreader can be introduced to completely divide the hypertrophied muscle. (D) After pyloromyotomy, omentum can be placed over the myotomy to help with hemostasis.

Postoperative care is similar for both surgical techniques, assuming the submucosa is intact. Structured feeding programs have been advocated in the past. Recent studies support the use of ad libitum feeds in the early postoperative period. This results in a faster time to full feeds and quicker discharge with no increase in return hospital visits. If postoperative emesis is encountered, it is suggested to “feed through it.” There are data to suggest that the degree and duration of metabolic derangement affects postoperative feeding. Patients who required more complicated resuscitation tend to take longer to reach full feeds and discharge.

Pain is usually controlled with acetaminophen. Intravenous fluids are discontinued when the patient tolerates two to three feedings. The infant can be discharged when tolerating full feeds without pathologic emesis (spit ups will still occur), which is usually on the first postoperative day.

The major complications of pyloromyotomy include mucosal perforation, wound infection, incisional hernia, prolonged postoperative emesis, incomplete myotomy, and duodenal injury.

Critics of the procedure argue that laparoscopic pyloromyotomy exposes the patient to undue risks compared with the open technique. Initial prospective and retrospective studies did not show any difference in complication rates between the laparoscopic and open techniques. Randomized prospective trials and subsequent metaanalyses also suggest no difference in complication rates. ^, More recently, a Cochrane analysis had the same conclusions as a recent metaanalysis: that the laparoscopic approach appears to carry a slightly increased risk of mucosal perforation. ^, A large national database review suggested that open pyloromyotomy is associated with an increased length of stay compared to laparoscopic pyloromyotomy; however, recent larger studies suggested that time to feeding and length of stay are comparable. ^{, ,}

In pooled analyses, perforation occurs in approximately 1%. If the disruption occurs at the duodenopyloric junction, a simple interrupted absorbable suture can be placed to close the defect and a patch of omentum used to bolster the repair. This can be accomplished laparoscopically, depending on the experience of the surgeon. Otherwise, the operation should be converted to open. If the perforation is large or in the middle of the myotomy, then the myotomy should be closed with absorbable suture. A new myotomy can then be made 90–180° from the original incision. Repairing this injury is difficult to perform laparoscopically and conversion is usually necessary. Feedings should be held for 24 hours and then restarted. A water-soluble contrast study can be performed if desired.

Duodenal injuries also can occur with either the laparoscopic or open approach. In a 25-year retrospective review of 901 open pyloromyotomies performed between 1969 and 1994, there were 39 duodenal perforations that were recognized intraoperatively and repaired. There were no unrecognized duodenal perforations that developed after the operation.

Postoperative emesis is common, occurring in most patients at some point. Prolonged emesis is less common and ranges in incidence from 2% to 26%. Most commonly, this is due to gastroesophageal reflux (25%) but can be secondary to incomplete myotomy (0%–6%). The laparoscopic approach was once thought to be a risk factor for inadequate myotomy, but recent studies do not show this to be true. ^{, ,} At this point in our cumulative experience with the laparoscopic technique, surgeon experience rather than mode of access is likely the primary factor contributing to perforation, incomplete myotomy, and the ability to recognize and correct those intraoperatively.

Incisional hernias and wound dehiscence occur in approximately 1% of cases. Most hernia defects require repair at some point. Laparoscopically, port-site hernias usually involve omentum protruding through the incision. This can sometimes be managed at the bedside by cleansing the area with povidone-iodine (Betadine), ligating and trimming the extracorporeal omentum, elevating the abdominal wall to get the omentum back into the peritoneal cavity, and using fine absorbable suture to close the skin. The best available evidence suggests no difference in wound infections or incisional hernias between the two techniques. ^,

In the early history of pyloromyotomy, the mortality from pyloric stenosis was considerable and approached 50%. However, nowadays mortality is nearly zero with improvements in neonatal resuscitation and anesthesia, as well as surgical techniques. Morbidity is also significantly lower than in the past, with an overall complication rate of between 1% and 2%. Additionally, with more pyloromyotomies being performed laparoscopically, the cosmetic advantage of the minimally invasive techniques is significant ( Fig. 27.6 ).

The cosmetic advantage of the laparoscopic approach cannot be overemphasized. These photos show an open pyloromyotomy 5 years after the operation on the left, a child with no operations in the middle and a child with laparoscopic pyloromytomy on the right.