Infantile Hypertrophic Pyloric Stenosis
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Infantile hypertrophic pyloric stenosis (IHPS) is a common surgical condition encountered in early infancy. Despite the extensive research, the etiology of IHPS remains still obscure. Genetic, environmental, and hormonal factors have been implicated in the pathogenesis of this condition. In terms of the pathophysiology, abnormalities of smooth muscle cells, growth factors, extracellular matrix, nerve and supporting systems, neurotransmitter, and intestinal cell of Cajal have been also reported. The incidence is approximately 1–5:1,000 with a peak incidence of 2–8 weeks. Also, epidemiologically, wide variations of incidence have been reported with geographic location, season, and ethnic origin. Although extramucosal pyloromyotomy is the procedure of choice, the best way to approach the pylorus is debated; conventional right upper quadrant open procedure, transumbilical approach, and more recently laparoscopic procedure. This chapter outlines the new insights into the etiology and pathogenesis and also the important elements necessary to care for the patients in safe and effective manner.
KeywordsHypertrophic pyloric stenosis Epidemiology Etiology Genetics Environmental and extrinsic factors Diagnosis Preoperative care Surgical technique Postoperative care
Infantile hypertrophic pyloric stenosis (IHPS) is well known, the most common surgical condition of vomiting in infants. The first clinical description of IHPS was in 1627 by Fabricius Hildanus, but it was subsequently more clearly defined at a conference by Harold Hirschsprung in 1888. The pyloric muscle is hypertrophied, and the pyloric channel becomes narrow and elongated, causing gastric outlet obstruction. Treatment is by pyloromyotomy which was introduced a century ago. Because advances in medical and surgical care have resulted in minimal mortality and morbidity, in modern times, pyloromyotomy has been considered a relatively minor surgical procedure. However, despite extensive research, the etiology or causes of circular muscle hypertrophy is not fully understood. The occurrence of IHPS has been thought to be associated several variables such as genetics and environmental and mechanical factors. Pyloric sphincter function and motility is under a complex control system which involves the enteric nervous system and gastrointestinal hormones, and smooth muscle cells have a close relationship and interact with extracellular matrix proteins. One of these factors may be a causative factor of abnormal hypertrophied muscle. Elucidation of molecular background of this condition may give a clear understanding of the pathophysiology and possibly lead to identification of environmental risk factors that may be target for preventive factors. This chapter provides update on IHPS, focused on epidemiology, etiology, and pathophysiology including genetics, pre- and postoperative care, various surgical techniques, complications, and medical care.
The incidence of IHPS has been reported to be approximately in 1–5 per 1,000 live births. However epidemiologically, the incidence of IHPS varies widely between different regions and countries. IHPS prevalence varies by maternal race/ ethnicity. IHPS occurs in approximately 2–4 per 1,000 live births in the Western population, whereas the incidence has been reported to be approximately four times lower in the Southeast Asian and Chinese populations. Studies in the USA generally report higher prevalence of IHPS among white non-Hispanic mothers, with significant lower prevalence of IHPS among non-Hispanic black mothers and Asian mothers (Ranells et al. 2011; Wang et al. 2008). Young maternal age also appears to be a risk factor, according to epidemiologic data from European surveillance of congenital anomalies (Pedersen et al. 2008), whereas McMahon shows that there is no consistent association between maternal age and IHPS (MacMahon 2006). The risk of IHPS is strikingly four to five times more common in male than female infants. However the prevalence of IHPS seems to decline with increasing birth order. Thus first-born white male predominance on IHPS is well documented (MacMahon 2006). Concordance rate of 46% is reported in monozygotic twins compared with 8% in dizygotic twins (Krogh et al. 2011). Recently, declining IHPS incidence has been reported in Scotland, Sweden, the USA, Denmark, and Germany, but the reason of this evidence is still obscure (Laffoklie et al. 2012).
Regarding to the prevalence of IHPS studies, interestingly, the most recent national report on prevalence of birth defects for 2003–2007 in the USA shows state-level prevalence of IHPS ranging by almost an order of magnitude, from 0.5 to 4.21 per 1,000 live birth (National Birth defect Prevention Network 2010). Thus, it gave warning that the literature on descriptive epidemiology of IHPS seems enigmatic at first glance, a close look at the data suggests that surveillance and ascertainment issues may account for much of the reported validity.
Male gender and family history of IHPS are consistently reported risk factors and suggest a genetic predisposition to the development of this condition. Various genetic loci associated with IHPS have been identified. Nitric oxide is a major inhibitory neurotransmitter in the gut causing smooth muscle relaxation. The synthesis of nitric oxide is catalyzed by enzyme neuronal nitric oxide synthase (NOS) coded by the NOS1 gene (IHPS1; chromosomal locus 12q24.2-q24.31). A mouse model with targeted disruption of NOS1 gene shows a phenotype consistent with IHPS with a hypertrophic pyloric muscle and distended stomach (Huang et al. 1993). Also, in hypertrophic pyloric stenosis tissue, the NOS1 gene expression has been found to be significantly reduced (Kusafuka and Puri 1997). NOS1 gene has therefore been subject to extensive investigation in IHPS patients. NOS1 is to date the only gene reported with evidence as an IHPS susceptibility locus. Linkage to chromosome 16p12-p13 and 16q24 was found in two different large Caucasian families with autosomal dominant inheritance. However this could not be replicated in any other families of same ancestry investigated, indicating locus heterogeneity of disease (Capon et al. 2006; Everett et al. 2008a). 11q14-q22 and Xq23-24 were identified via genome-wide linkage analysis of families with two or more affected individual (Everett et al. 2008b). Recently rearranged during transfection (RET) proto-oncogene located at 10q11.2 of which variants are seen in Hirschsprung’s disease was reported to be responsible of IHPS (Serra et al. 2011). Recent Swedish studies identified two candidates regions with significant linkage on chromosome 2p24 and 7p 22 and additional suggestive linkage on chromosome 6p21 and 12 p24 (Svenningsson et al. 2012). However in terms of the genomic evaluation, further study must be needed to conclude the clear relation and identification of responsible gene for IHPS.
Although no definite specific gene has been clearly identified as the cause of IHPS, genetic syndrome, such as Smith-Lemli-Opitz, Cornelia de Lange, and other chromosomal abnormalities have been associated with IHPS.
Extrinsic Factors/Environmental Factors
On the other hand, the changes in IHPS incidence reported in several countries indicate that environmental factors may be also important. Younger maternal age and maternal smoking are thought to influence the incidence of IHPS, but studies have been inconclusive. Parallels between breast feeding and IHPS risk have been documented in various countries raising discussion about whether breast feeding protects or is a risk factor of IHPS. Early exposures such as feeding practices are thought to be important risk factor because symptoms usually do not arise until the second or third week after birth. Study in Nigeria suggests that exclusive breast feeding was associated with reduced risk of IHPS, and study in Denmark suggests that bottle-feeding had a 4.6-fold increased risk of developing IHPS compared with infants who were not bottle-fed (Krohg et al. 2012). However this observation requires confirmation with a larger population-based study that includes a control group. Also recently, relation or common cause between IHPS and sudden infant death syndrome (SIDS) was reported from Sweden. The incidence of IHPS in Sweden from 1970 to 1997 has been reported to parallel the incidence of SIDS. The prone sleeping position has been suggested as possible risk factor given the fact that it has been associated with increased risk of SIDS, and the launch of the “back to sleep” campaign to prevent SIDS has coincidence with the decline in the incidence of both IHPS and SIDS (Persson et al. 2001). Thus prone sleeping may be an environmental risk factor for IHPS, which also could account for lower occurrence of IHPS in Asian people, who routinely place infants in supine position for sleep. It has been speculated that pooling of a feed in antrum, with prone sleep position, may lead to dysmotility of stomach or pylorus caused by effect on function of stomach and pylorus via proteins sensitive to change in volume, pressure, or solute concentration.
Pharmaceutical agents, hormones, and growth factors have also all been linked to IHPS through small case reports. Especially erythromycin has been associated with an increased risk of IHPS (Murchison et al. 2016) as it acts as a motilin agonist and induces strong gastric and pyloric contractions that may eventually thought to lead to hypertrophy of pylorus. Infants of mothers exposed to erythromycin during lactation have been reported to be at a higher risk of IHPS (Sorensen and Skriver 2003), while prenatal exposure has not been found to be associated with an increased risk (Cooper and Ray 2002). Although neonates treated with erythromycin showed a tenfold increase in the incidence of IHPS (Mahon et al. 2001). Prostaglandins have also been implicated as causative agent of IHPS. High level of prostaglandins has been found to be present in infants with IHPS, which suggests a positive association (Shinohara and Shimizu 1998). The debate over a genetic or environmental origin of IHPS has not yet reached a final condition. Multifactorial background, such as genetic/environmental interaction as the cause of this condition, is highly suspected.
The characteristic gross pathological feature in IHPS consists of thickening of antropyloric portion of the stomach (“olive-like mass”) and crowding of redundant and edematous mucosa within the lumen. Abnormally circumferentially thickened antropyloric muscle separates normally distendable portion of antrum from the duodenal cap. It stops abruptly at both ends. The rigid antropyloric canal is unable to accommodate the redundant mucosa, which protrudes into gastric antrum. These anatomical abnormalities cause obstruction to passage of gastric contents. According to the review by Panteli, the pyloric sphincter contracts tonically and phasically to effect gastric emptying (Panteli 2009). Sphincter function is controlled by a complex system involving the enteric nervous system, gastrointestinal hormones, and intestinal cells of Cajal. Abnormalities in hormonal control, extracellular matrix, smooth muscle fibers, growth factors, intestinal cells of Cajal, and pyloric innervations have been implicated in the pathogenesis of IHPS. Histologically, IHPS is characterized by thickened, hypertrophied, and edematous mucosa and its relationship to the underlying hypertrophied musculature, primarily involving the circular muscle.
Although the exact mechanism that leads to muscle hypertrophy in IHPS is still obscure, there is evidence that the growth of smooth muscle cell is regulated by various growth factors and/or neurological stimulations. Histochemical analysis using surgical samples revealed abnormal peptidergic innervation, abnormal distribution of nerve terminals and supporting cells, altered nitric oxide production, and abnormal expression of various growth factors such as insulin-like growth factor-1(IGF-1), platelet-derived growth factor-BB, platelet-derived endothelial cell growth factor, transforming growth factor –alpha, and epidermal growth factor. Among these growth factors, histochemical expression and in situ hybridization of IGF-1 have been extensively studied. It stimulates proliferation and differentiation in many tissues and acts as the mediator of most anabolic effects of growth hormone. Using histochemical analysis, the expression of IGF-1 and its receptor in controls was either absent or weak as opposed to increased expressions in the hypertrophied muscle in IHPS patients. Intestinal cell Cajal are nonneuronal cells that form network alongside the enteric nervous system and serve as electrical pacemakers and mediators of motor neurotransmission in the gastrointestinal tract. Ultrastructural abnormalities of enteric nerves and intestinal cells of Cajal are also reported. Extracellular matrix (ECM) molecules have characteristic patterns: chondroitin sulfate was markedly increased, with smaller increases in fibronectin and laminin. This constellation of abnormalities leads to failure of pyloric motility and then induced subsequent muscular hypertrophy.
Clinical Presentation and Evaluation
Babies of IHPS are commonly term infants who are otherwise healthy. The usual onset of symptoms occurs between 2 and 8 weeks of age with peak occurrence at 3–5 weeks of age. The infant presents with non-bloody, non-bilious emesis, which is often described as projectile in nature. However the clinical features vary with the length of the symptoms. Initially the vomiting may not be frequent and forceful, but over several days, it progresses to every feeding and become forceful non-bilious vomiting described as “projectile.” The emesis consists of gastric contents, which may become blood tinged with protracted vomiting and likely related to gastritis, with “coffee-ground” appearance (17–18% of cases). Infants with IHPS do not appear ill or febrile in early stage; however significant delay in diagnosis leads severe dehydration and weight loss due to inadequate fluid and calorie intake. Severe starvation can exacerbate diminished glucuronyl transferase activity and jaundice associated with indirect hyperbilirubinemia as seen in 2–5% of infants with IHPS.
The diagnosis of IHPS is usually based on clinical history of projectile vomiting, visible gastric peristaltic waves in left upper abdomen, and palpable enlarged pylorus (“olive-like mass”). It should be possible to diagnose IHPS on clinical features alone in 80–90%. During examination, one must take advantage of the time when the infant is resting or sleeping to palpate the mobile enlarged pylorus or “olive.” In cases with adequate passage of gas through the pylorus, abdominal distension interferes with palpation of the enlarged pylorus. Aspiration using nasogastric tube facilitates the successful palpation of an enlarged pylorus. After the edge of the liver has been identified with a fingertip, applied gentle pressure deep to the liver and progress caudally reveals the enlarged pylorus. In most cases, an enlarged pylorus is located just above the umbilicus at the lateral border of the rectal muscle below the liver edge. Palpating the “olive” has a 99% positive predictive value; however in recent times, there has been a shift in practice methods with an increased emphasis on imaging for diagnosis. In a retrospective chart review, Macdessi and Oates determined that over two study periods (1974–1977 compared with 1988–1991), the incidence of palpable enlarged pylorus(“olive”) being reported decreased from 87% to 49%, whereas the use of ultrasonographic examination (US) increased 20–61% (Macdessi and Oates 1993). Regarding the visible peristaltic wave, it would be easy to observe after test feeding in warm environment; however, this approach has unacceptably high false-positive and false-negative rates and is not used extensively.
The assessment of hydration status is also important. This can be judged by inquiring about the vomiting pattern and frequency as well as assessing the fontanelles, mucous membranes, and skin turgor.
The increasing reliance on imaging studies has resulted in diagnosis being made before serious dehydration and alkalosis have developed. Serum sodium, chloride, potassium, and bicarbonate value should be obtained when establishing intravenous access. An abnormally low chloride and high bicarbonate level is characteristic findings of a patients with IHPS .
Differential diagnosis of IHPS
Gastroesophageal reflux disease
Preampullar duodenal stenosis
Ectopic pancreas within the pyloric muscle
Increased intracranial pressure
Recurrent and persistent vomiting in these patients results in hypochloremic, hopokalemic, and metabolic alkalosis. Blood chemistries are evaluated for chloride, bicarbonate, sodium, potassium, urea nitrogen, and hematocrit. After determining the state of dehydration, and acid-base abnormalities prompt establishment of venous access, and fluid administration should be commenced. Infants currently present earlier, with corresponding reductions in frequency of metabolic disturbances and moderate to severe dehydration on admission. Although there are many algorithms in initial fluid administration for the patients with IHPS on admission, maintenance fluid with 5% dextrose in 0.45% normal saline containing 20–40 mEq/L potassium chloride can be administered. Initial maintenance rate of fluid administration is depending on the dehydration status of the patients, and standard initial fluid administration doses is 120–150% of standard maintenance doses. An initial goal is 1 ml/kg/h to 2 ml/kg/h of urine output. Once acceptable urine output is obtained, decreasing the input of fluid administration to usual maintenance dose is appropriate. It is relevant to confirm that blood electrolytes and bicarbonate returned to normal prior to carry out the surgery. There has been a debate in terms of preoperative placement of the nasogastric tube. Most infants with IHPS do not have complete gastric outlet obstruction and can tolerate their gastric secretion. A nasogastric tube removes additional fluid and hydrochloric acid from the stomach.
A nasogastric tube must be placed before induction of anesthesia, and it will be useful later for a leak test to ensure that the submucosa has not been injured during the procedure. Fredet first described a full thickness incision of the pylorus followed by transverse closure in 1908. Ramstedt modified the technique in 1912 and later described extramucosal longitudinal splitting of the pyloric muscle. Since then this extramucosal pyloromyotomy has been the standard surgical procedure of IHPS for more than 100 years. The pyloric muscle is split longitudinally which allows the submucosal layer to bulge out to the level of serosa and the stricture will be released. Since Ramstedt introduced the longitudinal pyloromyotomy in 1912, the treatment of IHPS has remained essentially the same; what has changed, however, is the way in which the abdomen is opened. Nowadays, there are three surgical approaches to carry out extramucosal longitudinal pyloromyotomy for IHPS: right upper abdominal open, transumbilical, and laparoscopic.
The surgeon should then hold the pylorus between the thumb and index finger to stabilized and assess the extent of hypertrophied muscle. A seromuscular longitudinal incision is made over the avascular area of pylorus with a scalpel, commencing 1 ~ 2 mm proximal to the prepyloric vein along the gastric antrum. The incision should go far enough onto the gastric antrum at least 0.5 ~ 1.0 cm from the antropyloric junction where the muscle is thin. At this point, scalpel handle can be used to press down on the incision, essentially cracking the muscle such that the submucosa is seen. Then pyloric spreader is spread widely. Spreader should be placed at midpoint of incision line, and the muscle is spread perpendicularly, and spreading is continued proximally and distally. Loose prolapsing of intact mucosa is evidence of a satisfactory myotomy (Fig. 3b). The anesthesiologist then inflates the stomach using nasogastric tube, and passage of air through the pylorus to duodenum is confirmed. This operative approach and procedure is the most common, reliable, and safe for junior pediatric surgeon who is not experienced in doing laparoscopic surgery in small infants. Pyloromyotomy has a low intraoperative and postoperative complication rate. The major complications following pyloromyotomy are wound infection, mucosal perforation, and inadequate pyloromyotomy. Mucosal perforation should be rare event, but if this occurred, myotomy site is reapproximated and rotate the pylorus 180° and perform a new pyloromyotomy on the posterior wall. Another option to repair is that the submucosa of perforated site is approximated using fine absorbable suture material, and then repair site is covered with the omentum.
Because it provides a better cosmetic appearance, transumbilical approach has been suggested. This transumbilical approach was first described by Tan and Bianchi in 1986 (Tan and Bianchi 1986). Since then, various modification techniques through umbilical route approach have been reported. In the transumbilical approach, a supraumbilical incision is made around two-thirds of the circumference of umbilicus and carried down to the abdominal wall fascia with sharp dissection. The midline fascia was exposed in a cephalad direction by undermining the epigastric skin. The peritoneal cavity is entered in the midline. Ordinary extramucosal pyloromyotomy is then carried out either intracavitary (in situ pyloromyotomy) or extracavitary (delivering the pylorus through the umbilical incision) techniques.
The approach to the pylorus to perform pyloromyotomy is still debated, and many authors in recent years have compared these three approaches looking for the best, considering the operative time, complication rates, length of postoperative hospital stay, time to restart feeding, and cosmetic appearance (Hall et al. 2004; Leclair et al. 2007; Sola and Neville 2009; St Peter et al. 2006; St Peter and Osstli 2008). A recent meta-analysis showed absolute incidence of major postoperative complications of 4.9% in laparoscopic group. Also this meta-analysis showed that laparoscopic procedure did not lead to significantly more major postoperative complications (ARR3%, 95%CI-3 to 8%) than open procedure. The mean difference in time to full feed was significant (2.27 h 95%CI-4.26 to -0.29 h), and the mean difference in postoperative hospital stay tended to be shorter, both in favor of laparoscopic approach (Oomen et al. 2012). Another meta-analysis which is reported by Sola and Naville demonstrates that laparoscopic approach has a significantly lower incidence of wound infection, shorter postoperative stay, and decreased time to feeding. The incidence of inadequate pyloromyotomy ranged between 1.4% and 5.6%. There was no difference in rates of mucosal perforation (Sola and Neville 2009). In terms of the operative time, Kim et al. reported that the transumbilical approach had the longest operative time, compared with laparoscopic and open procedures (Kim et al. 2005). Hence, laparoscopic pyloromyotomy may preferably be performed in centers with pediatric surgeons and anesthesiologists with experience in various laparoscopic procedures.
Although the extramucosal pyloromyotomy is the gold standard therapy for IHPS, many studies with nonoperative medical treatment for IHPS have been reported over the past 50 years. However, medical treatment with oral anticholinergic drugs such as atropine sulfate or methyl scopolamine nitrate has not worked consistently and been virtually abandoned since 1960. Recently, researchers from Japan have reviewed this medical treatment with reports of a new methods using methyl atropine nitrate intravenously (IV) and obtained successful results (Takeuchi et al. 2013; Koike et al. 2013). Atropine is administered intravenously at dose of 0.01 mg/kg six times a day, 5 min before feeding. Recently, Takeuchi et al. reported that overall success rate of IV atropine was 78.9% (142/180) and concluded that atropine therapy for IHPS should be reserved for patients who are medically unfit to undergo general anesthesia and surgery (Takeuchi et al. 2013).
Antibiotic policy for pyloromyotomy highlights wide variation in clinical practice (Tan and Bianchi 1986; Alain et al. 1991; Nour et al. 1996; Ladd et al. 2005). The efficacy of preoperative antibiotics in preventing wound infections after an open umbilical approach demonstrated that their routine use reverted the wound infection rate back to that which would be expected for a clean case (Ladd et al. 2005). Katz et al. recently reported that the use of prophylactic antibiotics does not significantly decrease the rate of wound infection or other wound complications after laparoscopic pyloromyotomy (Katz et al. 2011). In relation to the postoperative use of prophylactic antibiotics still remains a subject to debate, and nationwide survey or controlled study must be needed.
There has been still debate in relation to the timing of initiation of the enteral feeds following pyloromyotomy. Some surgeons advocated a delay of 4 or more hours before starting oral intake, followed by gradual and strictly regimented increase in the volume and concentration of the feeds (Schari and Leditschke 1968; Georgeson et al. 1993; Turnock and Rangercroft 1991). Other reports recommend that early, full-strength feeding may decrease the average length of hospital stay without increasing the risk of postoperative emesis (Garza et al. 2002; Purapong et al. 2002). Also ongoing debate arises over whether a physician chooses a standardized, incremental feeding regimen versus an ad libitum feeding schedule which allows the infant to decide when and how much to eat. Most recent reports recommend early full-strength ad libitum feeding protocol (Sullivan et al. 2016; Markel et al. 2016). Infants are fed ad libitum full-strength breast milk or formula when they are in awake and alert after operation. This feeding regimen shortened hospital stay and also resulted that frequency of postoperative emesis is not increased. They concluded that ad libitum feeds are a safe way to advance feedings in infants after pyloromyotomy, and the advantages include the simplicity of the regimen and the potential for earlier tolerance of full feedings and earlier discharge from the hospital (Adibe et al. 2007). Withholding feeds for a day or 12 h decreased vomiting overall but will delay the infant who is ready to progress. The ultimate goal of initiating early feeding is to achieve full feeds more quickly and therefore safely decrease total hospital stay. Starting feeds shortly after recovery (earlier than 6 h postoperatively) is an accepted method for feeding and allows most infants to advance to full feedings without any complications and risk.
Other Postoperative Considerations
Most of the infants with IHPS are in the 2–10 weeks of age and have a risk of postoperative apnea because of their immaturity. The postoperative apnea thought to persist until 52 weeks of postconceptional age. For this reason, the patients should be monitored using a cardiac and apnea monitor for at least 24 h postoperatively.
Important aspect of the perioperative management of IHPS is to inform parents that vomiting after surgery is common, expected, and essentially harmless. In most cases, when pyloromyotomy is adequate by intraoperative testing, vomiting that occur postoperatively will be because of pyloric and antral spasm and will resolve with continued feedings.
Conclusion and Future Directions
Hypertrophic pyloric stenosis is a well-known surgical problem within a pediatric population and is easily diagnosis by US. When prompt diagnosis and proper resuscitation with adequate electrolytes replacement and volume administration are performed, perioperative course is usually smooth. Pyloromyotomy is the treatment of choice in most of Western countries, with the laparoscopic approach favored, because of shorter length of hospital stay, superior cosmetic result, and rather lower incidence of complication rates. Recently natural orifice transluminal endoscopic surgery (NOTES) has gained attention for the treatment of IHPS, and various experimental studies are performing at the several institutions (Kawai et al. 2012). Future advance technology will make NOTES technique clinically applicable shortly. Thus the clinical treatment protocol seems to be already established and matured. Although genetic and environmental research works have explored several potentially causative factors of the IHPS, pathogenesis of IHPS is still not yet fully understood. The debate over a genetic or an environmental origin of IHPS has not yet reached a final conclusion. A future combined study of genes and environmental factors in different populations including monozygotic and dizygotic twins may provide the important data for the background of IHPS. And also future research should be focused on linkage analysis and next-generation molecular technique in well-defined families with multiple affected members.
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