eMedicine Specialties > Radiology > Pediatrics

Hypertrophic Pyloric Stenosis

Janet R Reid, MD, FRCP(C), Associate Professor of Radiology, Section Head of Pediatric Radiology, Children's Hospital of Cleveland Clinic

Updated: Aug 3, 2009

Introduction

Background

Hypertrophic 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.

Longitudinal sonogram of the pylorus in a patient with surgically proven hypertrophic pyloric stenosis. Note the thickened circular muscle, elongated pylorus, and narrowed pyloric channel.

Transverse sonographic image in a patient with proven hypertrophic pyloric stenosis demonstrates the target sign and heterogeneous echo texture of the muscular layer (pylorus is deep to the anechoic gallbladder).

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.^1,2

Ultrasonography (US) is important in the diagnosis of HPS and has likely contributed to the changing face of the disease, because this modality results in earlier diagnosis and treatment.

Recent studies

Wang et al studied infantile HPS in Texas, from 1999 through 2002, in relation to the effect of maternal nativity, maternal Hispanic ethnicity, subtypes of maternal Asian ethnicity, and the timing of the infant's pyloromyotomy. Infantile HPS was found to occur predominantly in boys. Compared with whites, there was a lower prevalence among blacks, foreign-born Hispanics, Chinese, Vietnamese, Asian Indians, and Filipinos. Foreign-born Asians had a lower risk of infantile HPS than whites. The authors saw no decrease in the risk of infantile HPS among US-born Asians or US-born Hispanics. According to the researchers, the strength of these risk factors did not vary according to the timing of the pyloromyotomy, and they felt the findings may be explained by differences in the frequency of behavioral risk factors for infantile HPS or differences in the frequency of ascertainment of mild cases of infantile HPS by ethnicity or nativity.³

Pedersen et al studied epidemiologic data on infantile HPS from 7 European regions for the period of 1980-2002. A total of 2534 infants were diagnosed with infantile HPS during the study period, giving an overall incidence of 2.0 per 1000 live births, ranging from 0.86 per 1000 to 3.96 per 1000, depending on region. Young maternal age (<20 y) was associated with a 29% increased risk of HPS, and maternal age of 30 years and older was found to be associated with a decreased risk.⁴

Leaphart et al studied the diagnostic criteria for HPS in newborns younger than 21 days from 2000 to 2006.  According to the authors, by current standards, ultrasonography confirms HPS when the pyloric muscle thickness (MT) is greater than 4 mm and the pyloric channel length (CL) is greater than 15 mm. They found that ultrasound measurement of HPS was significantly decreased in younger patients versus older newborns (MT, 3.7 +/- 0.65 vs 4.6 +/- 0.82 mm, P < .05; CL, 16.9 +/- 2.8 vs 18.2 +/- 3.4 mm, P < .05). Of important note, the mean ultrasound measurement for young newborns with HPS typically fell within the range currently defined as normal or borderline. They found that a linear relationship existed between pyloric MT and CL and patient age, suggesting 3.5 mm MT be considered the cutoff in younger patients.⁵

Pathophysiology

Full-thickness biopsies in patients with hypertrophic pyloric stenosis (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.

Frequency

United States

Hypertrophic pyloric stenosis (HPS) 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.

International

Hypertrophic pyloric stenosis (HPS) 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/Morbidity

Deaths resulting from hypertrophic pyloric stenosis (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.⁶ This improving trend is, in part, a result of the accessibility and accuracy of US in the diagnosis of HPS.

Race

Hypertrophic pyloric stenosis (HPS) is more common in whites and is seen less commonly in black infants or infants of Asian descent.

Wang et al studied infantile HPS in Texas, from 1999 through 2002, in relation to the effect of maternal nativity, maternal Hispanic ethnicity, subtypes of maternal Asian ethnicity, and the timing of the infant's pyloromyotomy. Infantile HPS was found to occur predominantly in boys. Compared with whites, there was a lower prevalence among blacks, foreign-born Hispanics, Chinese, Vietnamese, Asian Indians, and Filipinos. Foreign-born Asians had a lower risk of infantile HPS than whites. The authors saw no decrease in the risk of infantile HPS among US-born Asians or US-born Hispanics. According to the researchers, the strength of these risk factors did not vary according to the timing of the pyloromyotomy, and they felt the findings may be explained by differences in the frequency of behavioral risk factors for infantile HPS or differences in the frequency of ascertainment of mild cases of infantile HPS by ethnicity or nativity.³

Sex

Males are significantly more affected than females at a rate of 4-6:1.

Age

Hypertrophic pyloric stenosis (HPS) 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.⁷ HPS is rarely seen in children older than 6 months.

Anatomy

In hypertrophic pyloric stenosis (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.

Presentation

Hypertrophic pyloric stenosis (HPS) 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.

In the past and with experience,^8,9 the pyloric olive, which represents the thickened and elongated pylorus, was said to be felt by surgeons in up to 80% of patients. Review of the more recent radiologic and surgical literature indicates that the olive currently is felt much less frequently (23% of the time in one reported case series).

The low rate of positive palpation for the pyloric olive may be the result of several factors. Patients present at an earlier age when the olive is smaller; with earlier presentation, the incidences of dehydration, metabolic alkalosis, weight loss, and failure to thrive as manifestations of HPS decrease dramatically.⁶ Consequently, infants who present at a younger age are better nourished such that abdominal wall fat may obscure palpation of the mass. In addition, the skill of palpation may become lost as more medical school graduates come to rely heavily on US for diagnosis.¹⁰

Preferred Examination

The preferred diagnostic test for hypertrophic pyloric stenosis (HPS) is a contentious topic, with a wealth of articles that discuss the cost-effectiveness and the changing face of this disease.^11,12,13

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.⁹ 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.^14,15 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.¹³

Some investigators have reported that a UGI study is the most cost-effective study¹² (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.¹³ A second test, such as US, rarely follows a negative UGI study for HPS.^12,13 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 Techniques

US has high sensitivity, specificity, and accuracy in the diagnosis of hypertrophic pyloric stenosis (HPS). However, errors in diagnosis do occur and relate to the following:

False negatives

Operator inexperience: The pylorus may not be identified.

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.

Differential Diagnoses

Midgut Volvulus

Other Problems to Be Considered

Malrotation, with or without midgut volvulus
Antral polyp
Gastric duplication
Focal foveolar hyperplasia
Pylorospasm

Radiography

Findings

Abdominal 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.

Supine radiograph in an infant with vomiting demonstrates the caterpillar sign.

A UGI study was once considered the test of choice for hypertrophic pyloric stenosis (HPS). Findings on UGI studies include the following:

• Delayed gastric emptying (if severe, this may prevent barium from passing into the pylorus and severely limit the study)
• Cephalic orientation of the pylorus
• Shouldering (ie, filling defect at the antrum created by prolapse of the hypertrophic muscle)
• Mushroom or umbrella sign (ie, thickened muscle that indents the duodenal bulb; the name refers to the impression made by the hypertrophic pylorus on the duodenum)
• Double-track sign (ie, redundant mucosa in the narrowed pyloric lumen, which results in separation of the barium column into 2 channels) (see Image 5)

Lateral view from an upper gastrointestinal study demonstrates the double-track sign.

• String sign (ie, barium passing through the narrowed channel, creating a single, markedly attenuated, and elongated track) (see Image 6)

Upper gastrointestinal study from a child shows the string sign (see inset).

• Pyloric tit (ie, outpouching created by distortion of the lesser curve by the hypertrophied muscle)
• Retained secretions and retrograde peristalsis

Degree of Confidence

Plain 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/Negatives

High 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.

Ultrasonography

Findings

Although 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%.^14,15 US is recommended in patients whose disease is clinically suspected but in whom the pyloric olive cannot be felt.^{9,14,16,17,18,19}

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.²⁰

US signs of HPS, originally described in 1977²¹ and further defined, are as follows:

• MT (serosa to mucosa) greater than 3 mm (a correlation between MT and the patient's age exists; the most reliable US sign is an MT greater than 3 mm. Because this measurement can be increased falsely with off-axis imaging, attention to technique is important.)
• Target sign on transverse images of the pylorus (see Image 3)

Transverse sonographic image in a patient with proven hypertrophic pyloric stenosis demonstrates the target sign and heterogeneous echo texture of the muscular layer (pylorus is deep to the anechoic gallbladder).

• Pyloric channel length greater than 17 mm
• Pyloric thickness (serosa to serosa) of 15 mm or greater
• Failure of the channel to open during a minimum of 15 minutes of scanning
• Retrograde or hyperperistaltic contractions
• Antral nipple sign²² (ie, a prolapse of redundant mucosa into the antrum, which creates a pseudomass) (see Image 4)

Longitudinal sonogram in a patient with hypertrophic pyloric stenosis demonstrates a redundant mucosa that creates the antral nipple sign.

• US double-track sign^23,24 (ie, redundant mucosa in the narrowed lumen, which creates 2 mucosal outlines) (see Image 5)

Lateral view from an upper gastrointestinal study demonstrates the double-track sign.

• Other findings - Reversible portal venous gas; nonuniform echogenicity of the pyloric muscle (see Image 3)

Degree of Confidence

A 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/Negatives

The diagnostic accuracy of US for HPS is high. Sensitivity and specificity approach 100%.^14,15 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 Imaging

Findings

Nuclear medicine scanning is not routinely used for HPS; however, possible findings include delayed gastric emptying.

Degree of Confidence

The degree of confidence is poor.

False Positives/Negatives

Nuclear medicine scanning has a high sensitivity but low specificity for HPS.

Intervention

Although surgical pyloromyotomy remains the definitive treatment for hypertrophic pyloric stenosis (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.^25,26,27

Medicolegal Pitfalls

• Failure to choose the best radiologic investigation for the vomiting infant
  • A thorough physical examination performed by a surgeon with pediatric expertise is required. A child with a palpable pyloric olive has hypertrophic pyloric stenosis (HPS); if imaging is still requested, confirm HPS by US. Following rehydration, perform pyloromyotomy when the child is clinically stable.
  • If the clinical history suggests HPS and the child is stable, perform US to diagnose or rule out HPS. If the US findings are negative, perform a UGI study to confirm or rule out other pathology.
  • If concern exists about malrotation, with or without volvulus (no olive is felt; patient is sick), a UGI study is necessary.
• Failure to choose the best test, which is dictated by patient history, physical examination, and the surgeon's level of suspicion
• US, although reliable for diagnosing HPS, may miss malrotation, which is the most serious cause of vomiting in infants. These children require a UGI examination.

Multimedia

Media file 1: Supine radiograph in an infant with vomiting demonstrates the caterpillar sign.

Media file 2: Longitudinal sonogram of the pylorus in a patient with surgically proven hypertrophic pyloric stenosis. Note the thickened circular muscle, elongated pylorus, and narrowed pyloric channel.

Media file 3: Transverse sonographic image in a patient with proven hypertrophic pyloric stenosis demonstrates the target sign and heterogeneous echo texture of the muscular layer (pylorus is deep to the anechoic gallbladder).

Media file 4: Longitudinal sonogram in a patient with hypertrophic pyloric stenosis demonstrates a redundant mucosa that creates the antral nipple sign.

Media file 5: Lateral view from an upper gastrointestinal study demonstrates the double-track sign.

Media file 6: Upper gastrointestinal study from a child shows the string sign (see inset).

References

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Keywords

idiopathic hypertrophic pyloric stenosis, infantile hypertrophic pyloric stenosis, pyloric stenosis, HPS, IHPS, projectile vomiting, nonbilious infantile projectile vomiting

Contributor Information and Disclosures

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, MD, FRCP(C) 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
Disclosure: Nothing to disclose.

Medical Editor

Robert J Starshak, MD, Medical Director, Assistant Clinical Professor, Department of Radiology, Medical College of Wisconsin, Falls Medical Group
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

Managing Editor

David A Stringer, MBBS, FRCR, FRCPC, Professor, National University of Singapore; Head, Diagnostic Imaging, KK Women's and Children's Hospital, Singapore
David A Stringer, MBBS, FRCR, FRCPC is a member of the following medical societies: British Columbia Medical Association, Canadian Association of Radiologists, European Society of Paediatric Radiology, Ontario Medical Association, Radiological Society of North America, Royal College of Physicians and Surgeons of Canada, Royal College of Radiologists, and Society for Pediatric Radiology
Disclosure: Sirius d'innovation None Board membership

CME Editor

Robert M Krasny, MD, Resolution Imaging Medical Corporation
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

John Karani, MBBS, FRCR, Clinical Director of Radiology and Consultant Radiologist, Department of Radiology, King's College Hospital, London
John Karani, MBBS, FRCR is a member of the following medical societies: British Institute of Radiology, British Society of Interventional Radiology, Cardiovascular and Interventional Radiological Society of Europe, European Society of Gastrointestinal and Abdominal Radiology, European Society of Radiology, Radiological Society of North America, and Royal College of Radiologists
Disclosure: Nothing to disclose.

Related eMedicine topics

Pediatrics, Pyloric Stenosis (Emergency Medicine)

Pyloric Stenosis, Hypertrophic (Pediatrics)

Hypertrophic Pyloric Stenosis, Surgical Treatment (Pediatrics)

Evidence based clinical practice guideline hypertrophic pyloric stenosis. Cincinnati Children's Hospital Medical Center - Hospital/Medical Center.  2001 Aug 8 (revised 2007 Nov 4).  17 pages.  NGC:006224

Clinical guidelines

ACR Appropriateness Criteria® vomiting in infants up to 3 months of age. American College of Radiology - Medical Specialty Society.  1995 (revised 2005).  7 pages. [NGC Update Pending] NGC:004792

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