Lesions of the Stomach

Etiology

The cause of HPS is unknown, but genetic and environmental factors appear to play a significant 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 , and APOA1 have been associated with HPS. Environmental factors associated with HPS include the method of feeding (breast vs formula), seasonal variability, exposure to erythromycin, environmental pesticides, 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.

Diagnosis

The classic presentation of HPS is nonbilious, projectile vomiting in a full-term neonate who is between 2 and 8 weeks old. Initially, the emesis is infrequent and may appear to be symptomatic of GERD. 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 neonate 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 neonate must be relaxed. Techniques for relaxing the patient include bending the newborn’s 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 French to 12 French 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 patience and an optimal examination setting. If palpated, no further studies are needed. If the hypertrophied pylorus cannot be palpated, ultrasound (US) is the next step.

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 ≥4 mm and a pyloric length of ≥16 mm ( Fig. 29.1 ). A thickness of >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. There are reports of nonradiologists performing US for diagnosing HPS, 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. 29.2 ).

In the past, the diagnosis was often delayed and profound dehydration with metabolic derangements was common. Today, however, primary care physicians are more aware of the problem and the availability of US facilitates an earlier diagnosis and treatment of HPS. However, the complete differential diagnosis for nonbilious vomiting should be considered. This includes medical causes such as GERD, 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.

Treatment

The mainstay of therapy is typically resuscitation followed by pyloromyotomy. There are reports of medical treatment with atropine and pyloric dilation, but these treatments require long periods of time and are often not effective.

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 all of 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 <24 hours after presentation. A basic metabolic panel should be ordered, and the resuscitation should be directed toward correcting the abnormalities. Most surgeons use the serum carbon dioxide (<30 mmol/L), chloride (>100 mmol/L), and potassium (4.5–6.5 mmol/L) levels as markers of adequate resuscitation. Initially, a 10- to 20-mL/kg bolus of normal saline should be given if the electrolyte values are abnormal. Then D5/½NS with 20–30 mEq/L of potassium chloride is started at a rate of 1.25–2 times the calculated maintenance rate. Electrolytes should be checked every 6 hours until they normalize and the alkalosis has resolved. Subsequent fluid boluses are given if the electrolytes remain abnormal. Then the patient can safely undergo anesthesia and operation. It is important to appreciate that HPS is not a surgical emergency and resuscitation is of the utmost priority. Inadequate resuscitation can lead to postoperative apnea due to decreased respiratory drive secondary to metabolic alkalosis.

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 the open technique or by the minimally invasive approach. The laparoscopic technique has become the standard approach in the last 5–10 years. 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 seems to be used most commonly ( Fig. 29.3 ). 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.