# A 2-month-old infant is brought to the emergency department by parents who report projectile vomiting after every feeding for the past week. Which assessment finding would be most indicative of hypertrophic pyloric stenosis?

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> subject: Child Health

## 문제

A 2-month-old infant is brought to the emergency department by parents who report projectile vomiting after every feeding for the past week. Which assessment finding would be most indicative of hypertrophic pyloric stenosis?

## 보기

1. Forceful vomiting of bile-stained fluid after feeding
2. Abdominal distension with visible peristaltic waves
3. Blood-streaked stools with mucus and diarrhea
4. Palpable olive-shaped mass in the right upper quadrant **✔ 정답**

**정답: 4**

## 해설

The palpable olive-shaped mass in the RUQ is the classic diagnostic finding for pyloric stenosis. Other findings like bilious vomiting, abdominal distension, or bloody stools are not typical and suggest different conditions.

## 심화 해설

Understanding the Clinical Presentation

The question focuses on identifying the most indicative assessment finding for hypertrophic pyloric stenosis (HPS) in a 2-month-old infant. The classic history is projectile, non-bilious vomiting occurring after feedings, which aligns with the parents' report. To differentiate HPS from other causes of infant vomiting, the nurse must recognize the hallmark physical exam finding.

Analysis of the Correct Answer

The correct answer is 4. Palpable olive-shaped mass in the right upper quadrant. Infantile hypertrophic pyloric stenosis (IHPS) is characterized by hyperplasia of the smooth muscle fibers of the pylorus, leading to narrowing of the pyloric canal and gastric outlet obstruction [2]. This hypertrophied pyloric muscle is clinically palpable as a firm, movable, olive-shaped mass, typically located in the right upper quadrant or epigastrium. The presence of this "olive" is a pathognomonic sign for HPS, making it the most specific indicator among the options provided [1].

Analysis of Incorrect Answers

1. Forceful vomiting of bile-stained fluid after feeding

This finding is inconsistent with HPS. The obstruction in HPS is at the gastric outlet, proximal to the ampulla of Vater where bile enters the duodenum. Therefore, the vomiting in HPS is characteristically non-bilious [1, 2]. Bilious vomiting in an infant is a surgical emergency suggesting an obstruction distal to the duodenum, such as malrotation with volvulus, and is not typical for HPS.

2. Abdominal distension with visible peristaltic waves

While visible gastric peristaltic waves can be a classic sign of HPS, they are not the most indicative finding. Peristaltic waves, observed as a rippling movement across the upper abdomen from left to right, indicate the stomach is working hard against an obstruction [1]. However, this sign is less specific and can be difficult to elicit. More importantly, abdominal distension is not a primary feature of HPS, as the obstruction is high and vomiting relieves the gastric distension.

3. Blood-streaked stools with mucus and diarrhea

This presentation is suggestive of an intussusception or infectious colitis, not HPS. The pathophysiology of HPS involves gastric outlet obstruction and does not typically cause lower gastrointestinal bleeding. Infants with HPS may develop constipation or starvation stools due to reduced intake, but blood-streaked, mucoid stools are not a characteristic finding [2].

Key Diagnostic and Pathophysiological Considerations

The diagnosis of HPS is primarily clinical, based on the history of progressive, projectile, non-bilious vomiting in an infant typically between 3 to 5 weeks of age, though presentations can vary [2, 4]. The hypertrophied pyloric muscle causes complete or near-complete gastric outlet obstruction [1]. While the palpable "olive" is the most specific clinical sign, its detection is operator-dependent. When the diagnosis is uncertain, ultrasonography is the diagnostic modality of choice due to its high accuracy in measuring pyloric muscle thickness and canal length [1]. The classic biochemical derangement is hypochloremic, hypokalemic metabolic alkalosis from loss of gastric hydrochloric acid, though atypical presentations with metabolic acidosis have been reported, highlighting the need for a high index of suspicion .References (research sources)

- [1]Hypertrophic Pyloric Stenosis in a Four-Week-Old Infant: Radiological Diagnosis and Pitfalls.Research articlePokhrel B, Bhatta A, Basnet A, Pokhrel N, Regmi D. (2025) · DOI: 10.7759/cureus.98606

- [2]Delayed presentation of infantile hypertrophic pyloric stenosis: a case report.Case reportBerhe GK, Mengesha RE, Negash HT, Gereziher YT, GebremedhinTeklu T. (2025) · DOI: 10.1016/j.ijscr.2025.112092

## 임상 시나리오

Clinical Assessment for Hypertrophic Pyloric Stenosis

When an infant presents with projectile non-bilious vomiting, the physical assessment should prioritize the detection of a palpable **olive-shaped mass** in the right upper quadrant. This mass represents the hypertrophied pylorus and is best palpated after an episode of vomiting when the infant is calm. The abdomen should be examined with warm hands, using deep palpation in the epigastrium and right upper quadrant.

Key Diagnostic Steps

- Perform a test feed to observe for visible gastric peristaltic waves moving from left to right across the epigastrium before vomiting occurs.

- Attempt to palpate the "olive" with the infant supine and knees flexed to relax the abdominal muscles.

- Monitor for signs of dehydration and electrolyte imbalance, specifically hypochloremic, hypokalemic metabolic alkalosis due to loss of gastric hydrochloric acid.

Differential Red Flags

Be alert for **bilious vomiting**, which is never characteristic of pyloric stenosis and requires immediate surgical evaluation for malrotation with volvulus. Blood-streaked stools or diarrhea should raise suspicion for intussusception or infectious enterocolitis, not HPS.

Nursing Considerations

Maintain strict intake and output records. Position the infant with the head elevated during feedings and burp frequently to minimize vomiting. Prepare the family for a pyloric ultrasound as the diagnostic standard, and ensure preoperative stabilization including correction of fluid and electrolyte deficits before a pyloromyotomy.

## 핵심 개념

- **Pathognomonic** — A sign or symptom that is so characteristic of a disease that it can be used to make a diagnosis.
- **Pyloric Stenosis** — Hypertrophy of the pyloric sphincter causing gastric outlet obstruction, typically presenting with projectile non-bilious vomiting in infants aged 2-8 weeks.
- **Olive-shaped mass** — The palpable hypertrophied pylorus felt in the right upper quadrant or epigastrium, best appreciated after vomiting or during quiet palpation.
- **Non-bilious vomiting** — Vomiting without green bile staining, indicating an obstruction proximal to the duodenal ampulla of Vater.
- **Gastric outlet obstruction** — A mechanical blockage preventing the passage of gastric contents into the duodenum.

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