Hypertrophic pyloric stenosis (HPS) is the most common surgical pathology of the neonatal period, resulting from idiopathic hypertrophy of the pyloric muscle layer causing gastric outlet obstruction. It typically presents in 2-8 week-old infants with postprandial projectile (non-bilious) vomiting. Male to female ratio is 4-5:1, with a marked predilection for firstborn males. Ultrasonography is the gold standard for diagnosis — pyloric muscle thickness ≥3 mm and channel length ≥17 mm criteria provide 95-100% sensitivity and specificity. Transverse sections show 'target sign,' and longitudinal sections show 'cervix sign.' On physical examination, the 'olive sign' (palpable pyloric mass in the right upper quadrant) is pathognomonic. Treatment is Ramstedt pyloromyotomy (laparoscopic or open).
Age Range
0-0.2
Peak Age
0.1
Gender
Male predominant
Prevalence
Common
The exact etiology of HPS is unknown, but the fundamental pathology is progressive hypertrophy and hyperplasia of the pyloric sphincter muscle. The circular muscle layer is more prominently affected, and the longitudinal muscle layer is also partly hypertrophied. This muscle thickening progressively narrows the pyloric channel lumen, eventually resulting in complete gastric outlet obstruction. Gastric contents cannot pass into the duodenum, the stomach dilates, and projectile vomiting begins. Vomiting is non-bilious because the obstruction is proximal to the ampulla of Vater. Prolonged vomiting leads to hypochloremic, hypokalemic metabolic alkalosis — HCl loss (gastric acid) creates alkalosis, and kidneys lose K+ in alkalosis. The 'target sign' on ultrasonography directly results from concentric hypertrophy of the pyloric muscle: central hypoechoic mucosa + surrounding hypoechoic thickened muscle layer creates the target appearance with different echogenicity from the outer wall. The muscle thickness ≥3 mm criterion is based on normal neonatal pyloric muscle being 1-2 mm — more than double thickening is considered diagnostic. The channel length ≥17 mm criterion is based on normal pyloric channel length of 10-12 mm.
The 'target sign' is the characteristic ultrasound finding seen on transverse US section of the pyloric region: central echogenic mucosa surrounded by concentric hypoechoic thickened pyloric muscle creates a target or donut appearance. This finding becomes prominent when pyloric muscle thickness is ≥3 mm and is diagnostic for HPS with >95% sensitivity. The 'olive sign' is a physical examination finding — a hard, mobile, 1-2 cm mass palpated in the right upper quadrant or epigastrium, representing direct palpation of the thickened pyloric muscle. Olive sign is clinically pathognomonic — when detected, diagnosis can be made without US (though US confirmation is recommended). 75-85% of experienced clinicians can palpate the olive sign. Target sign + olive sign combination confirms HPS diagnosis.
On transverse sections, the thickened muscle layer in the pyloric region appears as a hypoechoic ring, creating the 'target sign' or 'donut sign' with the central echogenic mucosa. Muscle thickness is measured at the widest cross-section of the pyloric channel from the outer serosal surface to the outer surface of the mucosa. Normal neonatal pyloric muscle thickness is 1-2 mm, while in HPS it measures ≥3 mm (typically 3-6 mm). This measurement is the most reliable single diagnostic parameter — 95-100% sensitivity and specificity. In premature infants, a threshold of ≥2.5 mm may be accepted.
Report Sentence
Concentric muscular hypertrophy with target sign appearance is seen in the pyloric region on transverse sections, with pyloric muscle thickness measuring ___ mm (≥3 mm); findings are consistent with hypertrophic pyloric stenosis.
On longitudinal (long axis) sections, pyloric channel length is measured ≥17 mm (normal: 10-12 mm). The thickened pyloric muscle distinctly separates the gastric antrum from the duodenum, creating the 'cervix sign' — the swollen pyloric muscle resembles a cervical os. On longitudinal sections, protrusion of the pyloric muscle into the fundus of the stomach is also known as 'shoulder sign.' The elongated pyloric channel is an indirect finding demonstrating that peristaltic waves at the gastric outlet are ineffective and gastric retention occurs. The elongated pyloric muscle also creates the 'railroad track sign' — echogenic mucosal line between two parallel hypoechoic muscle layers.
Report Sentence
On longitudinal sections, pyloric channel length measures ___ mm (≥17 mm), demonstrating an elongated pyloric channel consistent with cervix sign appearance.
On real-time US, the pyloric channel does not open during a 15-20 minute observation period and gastric contents do not pass into the duodenum. The normal pyloric channel periodically opens and closes (pyloric relaxation), but in HPS, muscle hypertrophy creates mechanical obstruction preventing pyloric opening. Gastric distension, vigorous peristaltic waves (to-and-fro movement), and antral fullness are secondary findings. 'Antral nipple sign' — protrusion of thickened mucosa at the pyloric channel entrance — may also be observed.
Report Sentence
On real-time US evaluation, the pyloric channel is not observed to open and gastric contents do not pass into the duodenum, consistent with gastric outlet obstruction.
Pyloric muscle volume is a supplementary parameter in addition to muscle thickness and channel length. Calculated using the prolate ellipsoid formula: Volume = π/6 × length × AP diameter × transverse diameter. Normal in neonates is <1.0 cm³ while in HPS it is ≥1.4 cm³ (typically 1.5-3.0 cm³). This parameter is particularly useful in supporting diagnosis in borderline measurements (muscle thickness 2.5-3.0 mm). Transverse measurement of pyloric diameter (pyloric diameter ≥14 mm) is also a supplementary finding.
Report Sentence
Pyloric muscle volume is calculated as ___ cm³ using the prolate ellipsoid formula (≥1.4 cm³); this volumetric measurement supports the diagnosis of hypertrophic pyloric stenosis.
On color Doppler US, increased mucosal and submucosal vascularity may be seen in the hypertrophic pyloric region. Increased blood flow in the thickened pyloric mucosa reflects inflammatory changes and mucosal hyperemia. This finding is not specific but supports B-mode findings in differentiating from pylorospasm or normal pyloric region variations. It should also be evaluated comparatively with vascularity in surrounding normal bowel loops.
Report Sentence
On color Doppler examination, increased mucosal vascularity is observed in the pyloric region.
In HPS, the stomach appears dilated due to pyloric obstruction with retained fluid/milk. Vigorous peristaltic waves are seen but gastric contents cannot pass through the pylorus — 'to-and-fro' movement (back-and-forth oscillation) occurs. This indirect finding confirms functional obstruction in addition to pyloric channel measurements. Gastric distension provides a natural acoustic window for pyloric measurements — fluid-filled stomach allows better visualization of the pyloric region.
Report Sentence
The stomach appears dilated with retained fluid; vigorous peristaltic waves are observed but pyloric passage is not achieved, consistent with gastric outlet obstruction.
CT is rarely needed for HPS diagnosis — US is sufficient and safer (no radiation). However, in atypical presentations or when US is inadequate, CT may show thickened pyloric muscle mass, elongated pyloric channel, and dilated stomach. Pyloric muscle appears as soft tissue density thickening. With IV contrast, mucosal enhancement is distinctly separated from the muscle layer. The advantage of CT is exclusion of other anomalies (malrotation, midgut volvulus).
Report Sentence
CT demonstrates thickened muscle mass in the pyloric region with an elongated pyloric channel and dilated stomach; findings are consistent with hypertrophic pyloric stenosis.
Criteria
2-8 week-old male infant (firstborn), non-bilious projectile vomiting, muscle thickness ≥3 mm, channel length ≥17 mm. 80-85% of cases fall in this category.
Distinct Features
US sufficient for diagnosis, no additional imaging needed. Pyloromyotomy performed after electrolyte imbalance correction. Prognosis is excellent — postoperative complication rate <5%.
Criteria
Muscle thickness at borderline (2.5-2.9 mm), channel length 14-16 mm. Symptoms newly onset or not fully developed. Initial US may not be diagnostic.
Distinct Features
Follow-up US recommended in 24-48 hours — muscle will progressively thicken. Differential diagnosis with pylorospasm needed. In pylorospasm, muscle thickness remains within normal limits and pyloric opening is observed during 15-20 minute observation.
Criteria
Gestational age <37 weeks. Symptom onset may be later (2-8 weeks by corrected age). US criteria may be lowered: muscle thickness ≥2.5 mm, channel length ≥14 mm.
Distinct Features
Normal pyloric measurements in premature infants are smaller than term infants — standard thresholds may not be applicable. Pyloric volume calculation may increase diagnostic value in this group.
Criteria
Age >12 weeks, female infant, or atypical symptoms (non-projectile vomiting, failure to thrive). Rare (5-10%).
Distinct Features
US measurements are generally diagnostic, though late presentation may show more prominent muscle thickness (≥5 mm). Differential diagnosis should include gastroesophageal reflux, feeding intolerance, and metabolic diseases.
Distinguishing Feature
In midgut volvulus, vomiting is bilious — in pyloric stenosis it is non-bilious. On US, volvulus shows SMA/SMV reversal and whirlpool sign; pyloric stenosis shows normal SMA/SMV relationship with pyloric muscle thickening. Volvulus requires emergency surgery, HPS is elective.
Distinguishing Feature
NEC occurs in premature infants (HPS in term), abdominal distension and bloody stools present (absent in HPS). Radiographically NEC shows pneumatosis intestinalis and portal venous gas — absent in HPS. NEC may progress to severe sepsis and multiorgan failure.
Distinguishing Feature
In Hirschsprung disease, obstruction is in distal colon presenting with abdominal distension and delayed meconium passage — in HPS obstruction is at pyloric level with vomiting as the predominant symptom. Hirschsprung diagnosis is made with contrast enema and rectal biopsy — ganglion cells are absent.
Distinguishing Feature
In GER, vomiting is non-projectile, positional, and occurs during or immediately after feeding. US shows normal pyloric measurements. GER usually resolves with conservative management. In HPS, projectile vomiting progressively worsens and requires surgical treatment.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
no-follow-upHPS requires surgical treatment as an urgent condition but is not a true surgical emergency — dehydration and electrolyte imbalance (hypochloremic, hypokalemic metabolic alkalosis) must be corrected first (typically 12-24 hours IV fluid resuscitation). Surgical treatment is Ramstedt pyloromyotomy — longitudinal incision of the pyloric muscle from serosa to mucosa. Laparoscopic approach has become standard. Postoperative feeding is initiated within 4-6 hours. Prognosis is excellent — mortality <0.1%, mucosal perforation rate <5%, recurrence is very rare. Medical treatment (pyloric relaxation with atropine) is applied as an alternative in some centers, but surgery is the gold standard.
Most common surgical pathology of the neonatal period. Delayed diagnosis can lead to hypochloremic hypokalemic metabolic alkalosis, dehydration, and failure to thrive. US is the gold standard (>95% sensitivity and specificity). Ramstedt pyloromyotomy is curative with excellent prognosis. Preoperative correction of electrolyte imbalance is critical.