Embryology
A general understanding of the embryologic development of the stomach is essential to the management of congenital and acquired surgical disorders of the stomach. The primordial stomach is a foregut organ that begins as a pharyngeal structure and then dilates and elongates to form the esophagus and stomach. The dorsal border of the primordial stomach grows faster than the ventral border, resulting in the greater and lesser curvature, respectively. By the end of the seventh week of gestation, the stomach has undergone rotation around both the vertical and anteroposterior axes to come to rest in its normal anatomic position (see also Chapter 24 ).
Hypertrophic Pyloric Stenosis
History, Incidence, and Etiology
Hypertrophic pyloric stenosis (HPS) is the most common gastric surgical disorder in neonates. It was first described clinically by Hildanus in 1627, with subsequent accounts provided by Blair in 1717, Beardsley in 1788, and others. Not until 1888 was the disease generally appreciated following Harald Hirschsprung’s description with postmortem clinicopathologic correlation and introduction of the term congenital pyloric stenosis . The first surgical treatment performed by Löbker in 1898 was a gastroenterostomy bypass of the pyloric obstruction. Extramucosal splitting of the muscle with transverse pyloroplasty was demonstrated by Dufour and Fredet in 1908, and then modified to solely a muscle-splitting procedure by Ramstedt in 1911. Ramstedt’s pyloromyotomy became the procedure of choice in the early 20th century.
The prevalence of HPS ranges from 1.5 to 4.0 per 1000 live births and varies with geographical region. In the United States it is more prevalent in Caucasian populations compared to African Americans or Asians. Multiple studies focusing on epidemiologic developments have found divergent results; although numerous studies have claimed trends in prevalence of HPS, more recent epidemiologic studies suggest that the prevalence has been stable over time. The ratio of males to females remains constant at approximately 4:1. The prevalence of a positive family history demonstrates the polygenic mode of inheritance; the children of mothers who had pyloric stenosis are more likely to have the anomaly than are children of fathers who had the disease.
Hypertrophic pyloric stenosis is a result of progressive hypertrophy of the circular muscle, leading to a temporary high-grade or complete gastric outlet obstruction.
Despite considerable research efforts, no single etiology has been identified for HPS. Genetic as well as environmental factors seem to contribute to the pathophysiology. Environmental investigations found a potential influence of method of feeding, erythromycin treatment, maternal smoking, and infant sleeping position on development of HPS. A genetic predisposition seems beyond question; strong familial aggregation supports this theory. So far, five genetic loci have been identified as being associated with the development of HPS. One of them encodes the nitric oxide synthetase, a key player in smooth muscle relaxation. Other theories revolve around hyperacidity leading to spasms and edema, abnormal innervation, reduction of neurotrophins, growth factors and gastrointestinal peptides, and abnormal motility.
Clinical Presentation
The typical patient presents between 3 and 6 weeks of age. Premature infants may show clinical findings at an older age. Parents provide a history of prolonged emesis that has progressively become more forceful and “projectile.” The emesis is nonbilious, but may become brown-colored or have blood streaks due to minor mucosal hemorrhage from gastritis. Emesis occurs soon after feeds, and the infant will usually appear hungry following emesis. Often several formula changes have been made by the parent or pediatrician prior to workup for HPS. A prolonged period of vomiting may lead to dehydration, lethargy, weight loss, and failure to thrive. Decreased urine output and hypochloremic, hypokalemic metabolic alkalosis develop in tandem. In response to hypovolemia, there are increases in serum aldosterone levels and renal absorption of sodium ions and water. In an attempt to conserve sodium at the expense of hydrogen ions, paradoxical aciduria may occur late in the process. Jaundice due to unconjugated hyperbilirubinemia is found in 1% to 2% of infants and is believed to be secondary to starvation, an immature liver, and decreased levels of glucuronyl transferase activity. The jaundice usually resolves after surgery. The differential diagnosis of nonbilious vomiting at this age includes overfeeding, gastroesophageal reflux, pylorospasm, increased intracranial pressure, infectious gastroenteritis, metabolic disorders, and other uncommon causes of gastric outlet obstruction.
Diagnostic Evaluation
In a cooperative patient, the diagnosis of HPS can be made by physical examination in the setting of an appropriate history. Signs of dehydration and a palpable olive-shaped mass in the epigastric region under the liver’s edge are the cardinal physical findings. Palpation may be assisted by placing a nasogastric (NG) tube to decompress the distended stomach and subsequently feeding the infant a small amount of dextrose water. The NG tube is removed when the examination is complete. With ultrasound reading available, in most clinical settings we advocate early ultrasonographic investigation to avoid potentially stressful and frequently unsuccessful examinations for patients and parents. The characteristic appearance of pyloric stenosis on ultrasonography is a target sign consisting of an outer ring of low-echo-density musculature and an inner ring of high-echo-density mucosa. A pyloric thickness greater than 3.5 to 4 mm and a length of 16 mm are widely accepted as diagnostic criteria for pyloric stenosis. A recent review showed that ultrasound by trained technicians is 100% sensitive and 99% specific for HPS with measured thicknesses of 3 mm or greater; pyloric lengths of 15 mm or greater had a 100% sensitivity and 97% specificity, independent of patient age and weight ( Figure 25-1 ).
Often the sonographer can comment on whether there is passage of gastric contents during the period of examination, which—if negative—further substantiates the diagnosis. Given that ultrasonography is accurate, noninvasive, cost-effective, and without risk of contrast aspiration, it has replaced the upper gastrointestinal (UGI) series as the gold standard for imaging diagnosis of pyloric stenosis. In the event of a nondiagnostic ultrasound, a UGI series may differentiate between pyloric stenosis and other possible causes of nonbilious emesis, such as gastroesophageal reflux and antral or pyloric webs. On UGI, the narrowed pyloric channel of HPS produces a “string sign” of contrast; a “double track” sign illuminates the infolding mucosa, and a “shoulder sign” is caused by the muscle bulging into the distal antrum ( Figure 25-2 ).
Treatment
Treatment of HPS itself is never a surgical emergency, but it may present as a medical emergency due to accompanying hypovolemia and electrolyte disturbances. The goal of initial therapy is to correct the dehydration and metabolic alkalosis before surgery. This requires rapid analysis of electrolytes and establishment of intravenous (IV) access. Intravenous fluid resuscitation is initiated with boluses of 10 to 20 mL/kg of 0.9% normal saline to correct hypovolemia. Thereafter, an IV infusion of 5% dextrose in 0.45% saline is begun at 1.5 times the maintenance rate. Once urine output is established, 10 to 20 mEq/L of potassium chloride can be added to the infusion. Electrolyte levels should be checked every 12 hours until they are normalized. The infant should be maintained on strict fasting. NG tube suction should be avoided, because it will only further contribute to electrolyte disturbances.
Preoperative preparation may require 24 to 48 hours to correct electrolyte dehydration and electrolyte abnormalities in order to prevent postanesthetic intra-operative hypotension and postoperative apnea. Many pediatric anesthesiologists will require a chloride level greater than 100 mmol/L and serum carbon dioxide less than 28 mmol/L before general anesthesia. Immediately before induction, the stomach should be aspirated with an orogastric tube, especially if the infant previously underwent a UGI contrast study.
Standard surgical correction of HPS is a muscle-splitting longitudinal extramucosal pyloromyotomy using an open or minimally invasive approach ( Figure 25-3 ). An open pyloromyotomy may be performed through a traditional 2- to 3-cm right upper quadrant incision or a supraumbilical curved incision introduced by Tan and Bianchi in 1986. Many surgeons prefer to perform laparoscopic pyloromyotomy, as first described by Alain et al. in 1991, with an umbilical incision and two stab incisions (see Figures 25-3 A and B ). Regardless of the means of access, the elements of the procedure are the same. The serosa and outer muscle fibers are incised sharply from just proximal to the pyloroduodenal junction to just proximal to the antropyloric junction on the stomach. The deeper muscle fibers are bluntly split with the handle of the scalpel (open) or a shielded, extended cautery blade or retractible arthrotomy blade. A Benson or laparoscopic pyloromyotomy spreader is used to complete the muscle-splitting to the level of the submucosa. Adequacy of the pyloromyotomy is ensured when the two muscular cutting edges can be moved independently. Great care should be applied at the distal portion of the pyloromyotomy at the pyloroduodenal junction, as it bears the greatest risk for a mucosal tear and full-thickness myotomy into the lumen. After completion of the pyloromyotomy, the stomach can be insufflated with 45 to 60 mL of air with use of an orogastric tube to check for air bubbles or bilious fluid that would be indicative of a mucosal injury. A full-thickness enterotomy can be repaired primarily with absorbable sutures for the mucosa and submucosa with an omental patch, or closure of the initial myotomy and a new pyloromyotomy on the opposite side.
A nonlaparoscopic, transumbilical, intracavitary pyloromyotomy variation combining the advantages of open and laparoscopic techniques has been described by Gauderer.
Most surgeons will initiate feeds within 4 to 8 hours after surgery. A recent review showed that a postoperative period of 4 to 6 hours of fasting may decrease the frequency of postoperative emesis and decrease hospital length of stay. Feeding protocols will vary depending on the surgeon’s preference. There is no consensus on timing and type of feedings postoperatively. Based on the current literature, an ad libitum feeding regimen starting 4 hours after surgery may be superior to a variety of scheduled, incremental feeds. A common protocol starts with 
to 1 ounce of electrolyte solution and progresses every 2 to 3 hours to 2 ounces of formula or breast milk. Feeds are held for 2 hours after emesis. Most infants can be discharged home within 24 to 48 hours without any antacids or prokinetic medications.
Surgical correction is the standard of care throughout the world. Under extenuating circumstances, when surgical treatment is risky, unavailable, or undesirable, HPS may be medically treated with a course of intravenous and subsequent oral atropine (mean 51 days, range 29 to 137 days). Atropine suppresses muscular contractions and decreases gastrointestinal peristalsis. Kawahara et al. found an 87% success rate with atropine with a median 13-day hospital stay (range 6 to 36 days).
Outcomes
HPS can be surgically corrected with minimal risk of mortality and morbidity. Transient small-volume postoperative emesis is common and is generally thought to be caused by persistent edema, gastritis, and gastric dysmotility, rather than a postoperative complication. Possible complications include a mucosal tear, incomplete pyloromyotomy, wound infection, and wound dehiscence. Significant complications are rare. Persistent vomiting may be a sign of an incomplete myotomy. Unexpected abdominal tenderness, abdominal distension, and clinical deterioration may be signs of an unrecognized mucosal perforation. Postoperative sonography and water-soluble contrast studies are sometimes helpful, but edema and the radiologic appearance of muscular hypertrophy are slow to resolve.
Studies have compared the right upper quadrant (RUQ) incision surgical approach to the circum-umbilical incision approach, and the open operation to laparoscopic repair. In 1999, Leinwand et al. retrospectively analyzed the RUQ approach compared to the circum-umbilical approach and found the circum-umbilical approach to be cosmetically superior but with an increased rate of mucosal perforation, serosal tears, and wound infections. Kim et al. performed a retrospective review in 2005, comparing laparoscopic, circum-umbilical, and RUQ techniques, and found that the laparoscopic approach resulted in a shorter operative time without higher complication or costs. Prospective randomized studies have demonstrated that laparoscopic repair is as safe and effective as open repair, with the benefits of less pain and earlier return to feeding. The latest meta-analysis from Sola et al. (2009), Jia et al. (2011), and Oomen et al. (2013) confirm that laparoscopic pyloromyotomy has a comparable to reduced rate of total complications, and tendency for shorter postoperative time to feeding and length of stay.
Foveolar Hyperplasia
Focal foveolar hyperplasia (FFH) is a rare cause of gastric outlet obstruction and is characterized by mucosal hyperplasia and mucosal polyps. It has been considered by some authors as a localized Ménétrier’s disease (diffuse foveolar hyperplasia). It is rarely encountered as an isolated finding, but more frequently in association with infantile hypertrophic pyloric stenosis. Only a handful of cases have been reported. The histopathology reveals elongated, tortuous, polypoid gastric pits. The etiology remains unclear. Some cases of FFH have been reported to be associated with prostaglandin therapy, cow’s milk hypersensitivity, and infections caused by Helicobacter pylori . Ultrasonography can be helpful for diagnosis of this rare finding; hyperechoic mucosa with polypoid mucosal thickening of the gastric antrum without extension into the lamina propria has been described. The addition of Doppler ultrasonography further characterizes the lesion, with documentation of intense hyperemia of the antral wall deeper than the superficial mucosa. Lesions are found in the antrum; they often occur in groups, and measure up to 5 mm. If the polyp is obstructive, excision is indicated, which is feasible endoscopically with snare polypectomy and electrocautery, or surgically. In a retrospective review of ultrasonographic images of patients with HPS managed by pyloromyotomy, 12% of patients were found to have coexisting foveolar cell hyperplasia, suggesting that foveolar hyperplasia is an unrecognized clinical entity that may lead to persistent postoperative emesis following myotomy. Tan et al. suggested that FFH occurring concurrently with HPS is adequately treated by routine extended pyloromyotomy. Zhao et al. describe difficulties in correctly diagnosing cases of isolated foveolar hyperplasia in three children that required excision via laparotomy.
Congenital Gastric Outlet Obstruction
Congenital gastric outlet obstruction (GOO) not caused by HPS is rare and is caused primarily by distal gastric webs, atresias, or gastroduodenal duplications. Gerber classified distal gastric webs or atresias as pyloric or antral (1 cm or more proximal to pylorus). Atresia may be subclassified as segmental gap atresia or pyloric aplasia, appearing as solid fibrous cords. Among these rare lesions, the relative frequencies are pyloric webs > pyloric atresia > antral web > antral atresia ( Figure 25-4 ).
Webs are obstructing membranes of mucosa and submucosa. Prepyloric webs may be windsock-like lesions with redundant tissue prolapsing into the duodenum ( Figure 25-5 ). Gastric webs in the body of the stomach have also been reported.
Pyloric atresia has a prevalence of about one in 100,000 live births. Pyloric atresia is estimated to cause only 1% of intestinal atresias. Associated anomalies are common and occur in 54% of children and include epidermolysis bullosa, other intestinal atresias, and gallbladder agenesis. It is these associated anomalies that account for the reported high mortality in patients with congenital GOO, which may result from developmental arrest between the 5th and 12th weeks of gestation. Because of the high incidence of associated anomalies, all patients with pyloric atresia should be screened for other anomalies. Epidermolysis bullosa is most frequently concomitant with pyloric atresia and may involve the mucosa of the urinary tract, necessitating renal ultrasonography to rule out vesicoureteric obstruction and hydronephrosis.
Clinical Presentation
The presentation of antral or pyloric webs will depend on the degree of obstruction. Atresias may be suspected with antenatal polyhydramnios, gastric dilation, and narrowed gastric outlet. Neonates with high-grade or total obstruction present soon after birth with nonbilious vomiting, feeding intolerance, and gastric distension. Delayed diagnosis can lead to aspiration, dehydration, hypochloremia, hypokalemic metabolic alkalosis, and gastric perforation. Older children or adults with fenestrated webs are more likely to present with intermittent epigastric distension, nausea, vomiting, early satiety, and weight loss.
Diagnostic Evaluation
The diagnosis of GOO will be suggested by gastric distension with minimal or no air distally to the pylorus on a plain abdominal film (solitary gastric bubble). Neonates and infants with nonbilious emesis will frequently undergo ultrasonographic evaluation. Ultrasound of an antral web may demonstrate a persistent echogenic diaphragm-like structure in the antral region, gastric dilation, and a normal pylorus. Upper gastrointestinal (UGI) contrast studies may help to confirm the diagnosis of a complete or incomplete obstruction. A complete obstruction can present as a stretched-out peak at the pylorus or a thin septum projecting into the antral lumen perpendicular to the longitudinal axis of the stomach ( Figure 25-6 ). A pyloric dimple sign may be formed by the shallow pyloric cavity at the proximal end on UGI. A prolapsed prepyloric web can produce a double-bubble sign. If the UGI series is inconclusive, upper endoscopy serves as alternative for direct visualization. Webs are usually 1 to 4 mm thick and located 1 to 2 cm proximal to the pylorus with an aperture of varying size.
Treatment
As in HPS, correction of dehydration and electrolyte disturbances must be addressed first. Immediate and continuous nasogastric decompression may be necessary in cases of complete obstruction. Webs can be treated by surgical excision via an incision over and across the web with transverse closure to widen the lumen (Heineke-Mikulicz type pyloroplasty) or by endoscopic incision or dilation. Gastrotomy with dilation without pyloroplasty has also been described. Incidentally found or asymptomatic antral webs may be expectantly treated solely with small, thickened feeds and antispasmodics.
For atresias, a short segment may be bypassed with a Finney or Heineke-Mikulicz pyloroplasty. For longer atresias or a segmental gap, a gastroduodenostomy is preferable to a gastrojejunostomy. A catheter must be passed distally to eliminate the possibility of any other atresias. Prokinetics may be useful for postoperative delayed gastric emptying. The overall mortality of pyloric atresia is greater than 50%, with the main cause of death related to associated anomalies or septicemia. The association of pyloric atresia with epidermolysis bullosa translates into increased mortality if not addressed early and treated aggressively.
Gastric Volvulus
Etiology and Pathophysiology
Gastric volvulus is a twisting of the stomach that causes foregut obstruction with risk of ischemia and subsequent necrosis of the stomach. It is a rare and potentially life-threatening cause of nonbilious emesis in children. Cribbs et al. reviewed 581 cases of gastric volvulus in children between 1929 and 2007, describing the disorder comprehensively. The stomach is tethered by the four gastrohepatic, gastrosplenic, gastrocolic, and gastrophrenic ligaments and the duodenum and esophagus ( Figure 25-7 ). Volvulus may occur because of absence or stretching of these anatomic attachments (primary volvulus), or is associated with other abdominal pathologies such as diaphragmatic hernia, eventration, or wandering spleen (secondary volvulus). Secondary volvulus can also be caused by gastric dilation. Gastric volvulus is classified according to the plane of rotation. Rotation around the longitudinal axis of the stomach produces an organoaxial volvulus ( Figure 25-8 ). Rotation around the transverse axis of the stomach causes a mesenteroaxial volvulus ( Figures 25-9 and 25-10 ). Organoaxial volvulus is the most prevalent type, although mixed biplanar types have been described. Acute volvulus is more likely to be associated with anomalies, whereas chronic volvulus occurs more commonly as a primary etiology.
Clinical Presentation
Gastric volvulus in adults was first described with the classic triad of sudden onset of epigastric pain, intractable retching without vomiting, and inability to pass a nasogastric tube. Gastric volvulus can occur as acute, chronic, intermittent, recurrent, or acute-on-chronic event. The acute presentation in children includes nonbilious vomiting (75%), rather than intractable nonproductive retching, epigastric distension, and severe abdominal pain. Acute volvulus is more frequent in infants. The acute presentation in infants also more often includes respiratory distress and cyanosis compared to adults. Chronic volvulus is more common and more difficult to diagnose. Chronic or recurrent volvulus presents with signs of recurrent emesis and respiratory infections, abdominal distension, feeding difficulties, and failure to thrive.
Diagnostic Evaluation
Plain films and UGI contrast studies are the imaging modalities of choice. Plain abdominal film may demonstrate gastric distension in the epigastric region or left upper quadrant with or without high riding greater curvature. UGI series demonstrates esophageal obstruction and malposition of the stomach with a misplaced gastroesophageal junction or pylorus. An elevated hemidiaphragm on plain radiography is a sign of an underlying diaphragmatic abnormality precipitating a secondary volvulus. Especially in cases with associated anomalies, computed tomography (CT) scans can be of diagnostic value.
Treatment
Acute volvulus is a surgical emergency, and complete obstruction and strangulation can lead to necrosis and perforation of the stomach. Associated mortality remains high because of delayed diagnosis. Resuscitation and decompression with an NG tube should be performed immediately, followed by an emergent operation. Surgical treatment consists of detorsion of the stomach, resection or repair of areas of perforation or necrosis, and gastric fixation. Gastric fixation may be performed by placement of a gastrostomy tube creation of a fundic or anterior gastropexy. Any associated diaphragmatic abnormalities (hernia or eventration) should be repaired at the same time. Some surgeons advocate fundoplication in those infants with preexisting gastroesophageal reflux. Chronic volvulus may be reducible endoscopically or laparoscopically with gastropexy or gastrostomy tube placement. Nonoperative treatment involving positioning on the right side or prone with the head elevated following feeds has been more popular for treating mildly symptomatic chronic volvulus outside of North America and should not be considered as long-term treatment.
Congenital Microgastria
Congenital microgastria is a rare anomaly of impaired foregut development, characterized by a hypoplastic tubular stomach with abnormal function and megaesophagus. The condition leads to gastroesophageal reflux, vomiting, and failure to thrive. The first case was described in 1894. Recent reviews have identified approximately 60 reported cases. Associated gastroesophageal reflux can lead to aspiration pneumonia and esophageal ulceration. Diarrhea may result from rapid gastric transit and dumping. Microgastria has been associated with numerous other malformations including malrotation, esophageal atresia, duodenal atresia, imperforate anus, situs inversus, asplenia, and renal, cardiac, and skeletal anomalies. Microgastria is usually discovered on a UGI contrast study performed for the evaluation of reflux symptoms. A dilated esophagus and massive gastroesophageal reflux are also typically seen ( Figure 25-11 ).
