Laboratory Studies
An electrolyte panel is essential for estimating the state of dehydration and acidosis/alkalosis in patients with pyloric stenosis. Hypochloremic hypokalemic metabolic alkalosis is the characteristic biochemical disturbance observed in pyloric stenosis.
Liver function studies are not routinely obtained or necessary for diagnosis. Jaundice occurs in approximately 2% of infants with pyloric stenosis. Although the cause is uncertain, this finding (similar to findings in Gilbert syndrome) is thought to reflect a decrease in hepatic glucuronosyltransferase activity associated with starvation, as occurs in high gastrointestinal (GI) obstruction. The jaundice resolves spontaneously and rapidly after pyloromyotomy.
Urinalysis with normalization of urinary pH (correction of paradoxic aciduria) also helps determine adequacy of resuscitation.
Radiography
Although a careful history and physical examination lead to diagnosis in the vast majority of patients with pyloric stenosis, those in whom a palpable mass is not identified require further diagnostic studies. Plain abdominal radiography may show a dilated stomach bubble, which suggests the diagnosis but should not be considered a diagnostic finding.
Upper GI (UGI) contrast studies have largely been supplanted by ultrasonography (US; see below) as the study of choice for confirming pyloric stenosis. Although UGI studies have been reported as yielding an accuracy of 96%, obvious disadvantages of such studies include radiation exposure and the risk of aspiration of contrast material.
A UGI study may be helpful in ruling out gastroesophageal reflux, duodenal atresia, and malrotation in cases in which uncertainty exists as to the nature of the emesis (ie, bilious versus nonbilious) and in which a pyloric mass is indiscernible. Failure of gastric emptying demonstrated on UGI studies is not diagnostic of pyloric stenosis, because pyloric spasm and central nervous system (CNS) lesions may be associated with delayed gastric emptying. (See the image below.)
Ultrasonography
In 1977, Teele and Smith first described the use of US in the diagnosis of pyloric stenosis. [29] Objective criteria in measuring the pylorus have increased the diagnostic accuracy of US.
On US, a diagnosis of pyloric stenosis can be made through identification of an elongated sausage-shaped mass with the following characteristics (see the image below) [30] :
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Pyloric diameter >14 mm
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Muscular thickness >4 mm
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Length >16 mm
A sensitivity of 91-100% and a specificity of 100% have been reported with these criteria. US is best performed with the stomach evacuated; food or milk curds may interfere with the study. If a hypertrophied pylorus is not demonstrated on US, a UGI examination should follow to assess for other causes of vomiting.
Longitudinal ultrasonogram of pyloric stenosis. Pyloric stenosis is diagnosed by demonstration of elongated sausage-shaped mass with pyloric diameter greater than 14 mm, muscular thickness greater than 4 mm, and length of more than 16 mm.
In 2008, Leaphart et al reported that US in infants younger than 21 days may need revising with respect to muscle thickness. [31] Of the 314 newborns with hypertrophic pyloric stenosis studied, 60 (19%) were younger than 3 weeks, and 51 (85%) of these were diagnosed on the basis of US findings. Mean muscle thickness in this subset was 3.7 mm (vs 4.6 mm in those older than 3 wk), which is concerning because the normal cutoff is less than 4 mm. Given a possible 1-4% rate of negative exploration findings reported in the literature, [32] the significance of these findings awaits further prospective research; however, this information could be useful in the assessment of borderline diagnoses.
Several studies supported the premise that surgeons [33, 34] or even residents with appropriate resident-to-resident training may be sufficiently skilled to diagnose pyloric stenosis accurately with US. The advantages of this approach include a facilitated initial assessment and expedited management.
Histologic Findings
Microscopically, circular muscle hypertrophies are apparent, with increased connective tissue in the septa between the muscle bundles. An increase in chondroitin sulfate within the extracellular matrix may account for the cartilaginous quality of the pyloric tumor. Note that a histologic specimen is not obtained, nor is it necessary, for the diagnosis of pyloric stenosis.
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Diagram of anatomic changes associated with pyloric stenosis.
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Technique used for examining infant with pyloric stenosis. Infant is best examined from right, with mild pressure applied by using first three fingers of right hand in cephalad direction. Careful examination reveals oblong, smooth, hard mass that is 1-2 cm in length. This mass is hypertrophied pylorus and is commonly referred to as olive.
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Upper gastrointestinal study used for diagnosing pyloric stenosis.
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Longitudinal ultrasonogram of pyloric stenosis. Pyloric stenosis is diagnosed by demonstration of elongated sausage-shaped mass with pyloric diameter greater than 14 mm, muscular thickness greater than 4 mm, and length of more than 16 mm.
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Open pyloromyotomy.
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Laparoscopic pyloromyotomy.
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Laparoscopic pyloromyotomy. Pyloric incision.
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Laparoscopic pyloromyotomy. Spreading of incision.
Tables
| Level of Dehydration | |||
|
Mild |
Moderate |
Severe |
Estimated volume deficit |
5% (50 mL/kg) |
10% (100 mL/kg) |
15% (150 mL/kg) |
|
|
|
|
Clinical findings |
|
|
|
Skin (touch) |
Normal |
Dry, pale |
Clammy |
Skin turgor |
Normal |
Tenting |
None |
Mucous membranes |
Moist |
Dry |
Parched |
Eyes |
Normal |
Deep-set |
Sunken |
Tearing |
Present |
Reduced |
None |
Fontanelle |
Normal (flat) |
Soft |
Sunken |
Central nervous system |
Normal |
Irritable |
Lethargic/obtunded |
Heart rate |
Normal |
Slightly increased |
Increased |
Pulse quality |
Normal |
Weak |
Feeble/impalpable |
Capillary refill |
Normal |
~2 s |
>3 s |
Urine output |
Normal |
Decreased |
Anuric |
