You are in: eMedicine Specialties > Radiology > PEDIATRICS Hypertrophic Pyloric StenosisArticle Last Updated: Jun 29, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Janet R Reid, MD, FRCP(C), Associate Professor of Radiology, Section Head of Pediatric Radiology, Children's Hospital of Cleveland Clinic Janet R Reid is a member of the following medical societies: American Association for Women Radiologists, American Society of Neuroradiology, Ohio State Medical Association, Radiological Society of North America, Royal College of Physicians and Surgeons of Canada, and Society for Pediatric Radiology Editors: Robert J Starshak, MD, Medical Director, Assistant Clinical Professor, Department of Radiology, Medical College of Wisconsin, Falls Medical Group; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; David A Stringer, BSc, MBBS, FRCR, FRCPC, Professor, National University of Singapore; Head, Diagnostic Imaging, KK Women's and Children's Hospital, Singapore; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; John Karani, MBBS, FRCR, Consulting Staff, Department of Radiology, King's College Hospital, London Author and Editor Disclosure Synonyms and related keywords: idiopathic hypertrophic pyloric stenosis, infantile hypertrophic pyloric stenosis, pyloric stenosis, HPS, IHPS, projectile vomiting, nonbilious infantile projectile vomiting INTRODUCTIONSection 2 of 11
  BackgroundHypertrophic pyloric stenosis (HPS) is commonly encountered in pediatric practice. The typical infant presents with nonbilious projectile vomiting and dehydration (with hypochloremic metabolic alkalosis) if the diagnosis is delayed. HPS accounts for one third of nonbilious vomiting occurrences in infants and is the most common reason for laparotomy before age 1 year. Despite its status as a common disease, the cause of HPS is unclear; however, a definite genetic component exists because up to a 5-fold increase in HPS incidence is observed in families in which a sibling or parent has had the disease. Pyloric stenosis and esophageal atresia may coexist.1 PathophysiologyFull-thickness biopsies in patients with HPS demonstrate both hypertrophy and hyperplasia of the circular muscle layer of the pylorus. No clear pathophysiologic sequence or etiology has been described; however, proposed theories include, among others, abnormal circular muscle innervation, immature ganglion cells, decreased nitric-oxide stimulation of muscle fibers, immature ganglion cells, and abnormal gastrin levels. Interestingly, pyloromyotomy works by 2 mechanisms: initially, the pyloric channel widens as a result of incising the muscle; afterward, the procedure secondarily induces regression of muscle hypertrophy and, over time, the disease itself. FrequencyUnited StatesHPS is seen in 2-5 infants per 1000 in North America and accounts for 30% of all patients who present with nonbilious vomiting before age 1 year. The onset of vomiting may occur as early as the first week of life and as late as age 5 months. A striking male preponderance is seen, with a male-to-female ratio of 4-6:1. InternationalHPS is more common in the white population; the incidence in the Asian, Indian, and black populations is one third to one fifth lower than the incidence in whites. Mortality/MorbidityDeaths resulting from HPS are rare. Morbidity is linked directly to the duration and frequency of the patient's vomiting. Protracted vomiting causes decreased intake and increased loss of essential nutrients and electrolytes, which then results in dehydration and metabolic alkalosis. In a 25-year review of 901 infants with surgically proven HPS, Hulka et al describe a trend toward shorter duration of symptoms, earlier presentation, and a 50% reduction in hypochloremic metabolic alkalosis and dehydration.2 This improving trend is, in part, a result of the accessibility and accuracy of US in the diagnosis of HPS. RaceHPS is more common in whites and is seen less commonly in black infants or infants of Asian descent. SexMales are significantly more affected than females at a rate of 4-6:1. AgeHPS is most commonly seen in infants aged 3-6 weeks. The thickness of the circular muscle in HPS parallels the patients' age; those presenting at an older age have a muscle thickness (MT) greater than those who present in the usual age range. Premature infants tend to present at 3-6 weeks from birth—not at 3-6 weeks from the due date—and these infants may have borderline normal MT because they are comparatively smaller. A large epidemiologic study reported that the interval between birth and the onset of symptoms in preterm infants was longer than that in full-term infants.3 HPS is rarely seen in children older than 6 months. AnatomyIn HPS, the circular muscle layer becomes thickened, which narrows the pyloric channel and elongates the pylorus. During this process, the mucosa becomes redundant and may appear hypertrophic. With elongation and thickening of the muscle, the pylorus deviates upward toward the gallbladder, which serves as a marker, because in HPS, the pylorus can be seen adjacent to the gallbladder and anteromedial to the left kidney. The thickened pylorus narrows the pyloric channel, resulting in gastric outlet obstruction, gastric distention, and retrograde peristalsis in the stomach. Clinical DetailsHPS is the most common indication for laparotomy in infants and accounts for 30% of patients who present with nonbilious vomiting. Parents may describe the vomiting as occurring with every feeding or intermittent vomiting that may be projectile; the vomiting worsens over time. Bilious vomiting is rare. Workup of the vomiting child first requires a detailed history, followed by a complete physical examination. Preferred ExaminationThe preferred diagnostic test for HPS is a contentious topic, with a wealth of articles that discuss the cost-effectiveness and the changing face of this disease.7, 8, 9 The first and most important step in patient workup of suspected HPS is a thorough physical examination. If the pyloric olive is felt, the patient may proceed directly to the operating room without imaging.5 However, many surgeons are uncomfortable with this protocol because a false-positive physical examination then leads to a negative laparotomy. Therefore, US is recommended because its sensitivity and specificity are close to 100% for this disease.10, 11 If the clinical suspicion for HPS is moderate to high, US is also recommended. If the vomiting infant is outside the usual age range for HPS or if the clinical suspicion is low, an upper gastrointestinal (UGI) study is recommended because it more effectively rules out other problems such as malrotation and gastroesophageal reflux.9 Some investigators have reported that a UGI study is the most cost-effective study8 (more than US) in the vomiting infant because a negative US often leads to a UGI study to rule out other diagnoses that a focused US evaluation does not detect.9 A second test, such as US, rarely follows a negative UGI study for HPS.8, 9 In experienced hands, US is the preferred modality in the workup of any vomiting infant. The technique includes feeding glucose water to the baby, which often improves visualization of the pylorus and, in the case of a negative study, allows continuous observation of the gastroesophageal junction to diagnose reflux. The radiologist's skill and clinical suspicion ultimately determine which test is appropriate. Limitations of TechniquesUS has high sensitivity, specificity, and accuracy in the diagnosis of HPS. However, errors in diagnosis do occur and relate to the following: False negatives Operator inexperience: The pylorus may not be identified. Distended formula and gas-filled stomach: These cause the pylorus to fold backward on itself such that it may remain hidden behind the stomach. The overdistended antrum may be mistaken for the pylorus; in such cases and in any infant whose pylorus is not visualized on US, place a nasogastric tube and withdraw the gastric secretions.MT increases with patient size. Borderline measurements are seen early in the disease and with premature infants. Some clinicians advocate observation and then repeating the US study in 2-3 days to confirm the diagnosis if the patient is stable and is not dehydrated. False positives Pylorospasm: The normal pylorus opens at least once every 15 minutes. Pylorospasm is a dynamic process that changes over time. The thickened muscle and elongated pylorus should be fixed. Postoperative appearance: Symptoms may take time to clear and, therefore, so do the abnormalities on US. US may show HPS (thickened MT) for up to 12 weeks following pyloromyotomy. In these cases, a UGI study may provide more information than US to rule out incomplete myotomy. DIFFERENTIALSSection 3 of 11
Midgut Volvulus Other Problems to Be ConsideredMalrotation, with or without midgut volvulus RADIOGRAPHSection 4 of 11
FindingsAbdominal radiographs may show a fluid-filled or air-distended stomach, suggesting the presence of gastric outlet obstruction. A markedly dilated stomach with exaggerated incisura (caterpillar sign) may be seen, which represents increased gastric peristalsis in these patients (see Image 1). If the patient has recently vomited or has a nasogastric tube in place, the stomach is decompressed and the radiographic findings are normal. A UGI study was once considered the test of choice for HPS. Findings on UGI studies include the following:
Degree of ConfidencePlain film radiography provides a low degree of confidence in making the diagnosis of or in ruling out HPS. A UGI study has high sensitivity (>90%) and low specificity. False Positives/NegativesHigh intestinal obstruction can be seen with midgut volvulus, duodenal obstruction (from stenosis, duodenal web, annular pancreas), gastric outlet obstruction caused by focal foveolar hyperplasia, and eosinophilic gastroenteritis, among others. False-negative radiographs can be seen in a child who has recently vomited. CT SCANSection 5 of 11
FindingsDo not perform computed tomography (CT) scanning for the diagnosis of HPS. MRISection 6 of 11
FindingsDo not perform magnetic resonance imaging (MRI) for the diagnosis of HPS. ULTRASOUNDSection 7 of 11
FindingsAlthough a false-negative clinical diagnosis causes diagnostic delay, a false-positive diagnosis results in a negative laparotomy. Therefore, imaging has become more important in the diagnosis of HPS. US is the method of choice for both the diagnosis and exclusion of HPS because this modality has a sensitivity and specificity of approximately 100%.10, 11 US is recommended in patients whose disease is clinically suspected but in whom the pyloric olive cannot be felt.5, 10 US is performed with a 7.5- to 13.5-MHz linear transducer in the supine child. Transverse images at the epigastrium identify the pylorus to the left of the gallbladder and anteromedial to the right kidney. A distended stomach, however, displaces and distorts the pylorus and may require the placement of a nasogastric tube to withdraw the stomach's contents. A gastric aspirate of more than 5 mL in a baby who has been without oral intake (NPO) for several hours indicates gastric outlet obstruction. Right posterior oblique positioning and scanning from a posterior approach may help to improve visualization of the pylorus.12 US signs of HPS, originally described in 197713 and further defined, are as follows:
Degree of ConfidenceA positive HPS finding by US almost always indicates HPS. A negative examination can be false in a patient who is seen early in the disease or in a younger patient whose MT is less than 3 mm. False Positives/NegativesThe diagnostic accuracy of US for HPS is high. Sensitivity and specificity approach 100%.10, 11 Possible sources of false negatives (see Limitations of Techniques) are an overdistended stomach (the pylorus is hidden behind the antrum), failure to identify the pylorus (eg, operator inexperience in performing US for evaluation of HPS), and a small infant or early presentation. Another possible source for a false-positive finding is pylorospasm (typically transient). NUCLEAR MEDICINESection 8 of 11
FindingsNuclear medicine scanning is not routinely used for HPS; however, possible findings include delayed gastric emptying. Degree of ConfidenceThe degree of confidence is poor. False Positives/NegativesNuclear medicine scanning has a high sensitivity but low specificity for HPS. INTERVENTIONSection 9 of 11
Although surgical pyloromyotomy remains the definitive treatment for HPS, small trials have reported the success of balloon catheter dilatation through an endoscope. The reliability of circular muscle disruption is unknown; in 2 of 6 patients in a small case series, incomplete disruption of the circular muscle ring was noted, and in 1 of 6 patients, a mucosal tear necessitated a full-thickness pyloric repair. Medical/Legal Pitfalls
MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Hypertrophic Pyloric Stenosis excerpt Article Last Updated: Jun 29, 2007 | |||||||||||||||||||||||||||||||||||||||||||||||||
