# A 3-week-old infant is brought to the emergency department by parents who report projectile vomiting after every feeding for the past 5 days. Which assessment finding would be most indicative of hypertrophic pyloric stenosis?

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## 문제

A 3-week-old infant is brought to the emergency department by parents who report projectile vomiting after every feeding for the past 5 days. Which assessment finding would be most indicative of hypertrophic pyloric stenosis?

## 보기

1. Palpable olive-shaped mass in the right upper quadrant **✔ 정답**
2. Bilious vomiting with abdominal distension
3. Bloody stools with mucus and diarrhea
4. High-pitched bowel sounds with cramping

**정답: 1**

## 해설

The palpable olive-shaped mass in the RUQ is the pathognomonic sign of hypertrophic pyloric stenosis, representing the hypertrophied muscle. Other options are not characteristic: bilious vomiting suggests intestinal obstruction, bloody stools indicate other GI issues, and high-pitched sounds are nonspecific.

## 심화 해설

Clinical Presentation of Hypertrophic Pyloric Stenosis

The classic presentation of infantile hypertrophic pyloric stenosis (IHPS) involves a specific sequence of symptoms that directly relates to the underlying pathology. The condition is characterized by hyperplasia of the smooth muscle fibers of the pylorus, which leads to a narrowing of the pyloric canal and a progressive gastric outlet obstruction [1]. As the obstruction becomes more severe, the infant develops forceful, projectile, non-bilious vomiting because the blockage is proximal to the bile duct entry point at the duodenum [1,2]. The infant typically remains hungry and will attempt to feed well immediately after an episode of vomiting, which distinguishes this condition from many other causes of pediatric emesis [1]. The onset of symptoms is highly predictable, usually occurring between the 3rd and 5th weeks of life, making the age of this 3-week-old infant a critical clue [1].

Rationale for the Correct Answer

The most indicative physical assessment finding for hypertrophic pyloric stenosis is a palpable olive-shaped mass in the right upper quadrant of the abdomen. This mass is the hypertrophied pyloric muscle itself. Palpation of this "olive" is a classic, pathognomonic sign of the condition, although its detection is highly dependent on the examiner's skill and the infant's state of relaxation [2]. To successfully palpate the mass, the infant should be calm, with relaxed abdominal muscles, and the stomach should be empty, often after an episode of vomiting. This finding provides direct physical evidence of the pyloric muscle hypertrophy that defines the disease.

Analysis of Incorrect Options

**Option 2: Bilious vomiting with abdominal distension.** This finding is inconsistent with IHPS. The obstruction in pyloric stenosis is located at the gastric outlet, which is anatomically proximal to the ampulla of Vater where bile enters the gastrointestinal tract. Therefore, the vomiting in IHPS is characteristically non-bilious [1,2]. The presence of bilious (green) vomiting is a surgical emergency that suggests an obstruction distal to the duodenum, such as malrotation with midgut volvulus, and is not indicative of pyloric stenosis.

**Option 3: Bloody stools with mucus and diarrhea.** This clinical picture is not associated with IHPS. Bloody, mucoid stools are more suggestive of an inflammatory or infectious process, such as bacterial colitis or intussusception. Intussusception, in particular, classically presents with "currant jelly" stools and episodes of severe, cramping abdominal pain. The pathology of IHPS is a mechanical obstruction of the stomach outlet and does not involve the intestinal mucosa in a way that would cause bleeding or diarrhea [1].

**Option 4: High-pitched bowel sounds with cramping.** While IHPS is a mechanical obstruction, the classic auscultatory and pain patterns differ. High-pitched, hyperactive bowel sounds and visible peristaltic waves can be present in IHPS as the stomach attempts to overcome the obstruction [2]. However, the pain is not typically described as intermittent cramping. The hallmark of the history is the progressive, projectile vomiting. The finding of high-pitched bowel sounds is nonspecific and can be found in many types of intestinal obstruction, making the palpable mass a far more specific and therefore "most indicative" finding for this particular diagnosis.

Diagnostic Confirmation and Clinical Implications

While the palpable "olive" is a classic sign, it is not always easily appreciated. When the diagnosis is suspected based on the history of projectile, non-bilious vomiting in a 3- to 5-week-old infant, the diagnostic modality of choice is ultrasonography due to its high accuracy and non-invasive nature [2]. Ultrasound allows for direct measurement of pyloric muscle thickness and canal length against established diagnostic thresholds, confirming the diagnosis and differentiating IHPS from conditions like transient pylorospasm, which can resolve without surgery [2]. Early and accurate diagnosis is critical to prevent the complications of prolonged vomiting, including dehydration, weight loss, and a characteristic hypochloremic, hypokalemic metabolic alkalosis [1].References (research sources)

- [1]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

- [2]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

## 임상 시나리오

Clinical Assessment for Hypertrophic Pyloric Stenosis

1. Pre-Palpation Preparation

Ensure the infant is calm and the stomach is empty. Palpation is best performed after the infant has vomited. A pacifier dipped in oral sucrose may help soothe the infant and relax the abdominal muscles. Position the infant supine with knees slightly flexed to reduce abdominal wall tension.

2. Locating the Mass

Stand on the infant's right side. Use the flat pads of your fingers to palpate deeply but gently in the right upper quadrant, starting from the liver edge and moving medially toward the epigastrium. The hypertrophied pylorus feels like a firm, movable, olive-shaped mass approximately 1 to 2 cm in length. It is most easily appreciated when the abdominal muscles are relaxed, often during quiet breathing or sleep.

3. Adjunctive Maneuvers

If the mass is not immediately palpable, attempt to empty the stomach with a nasogastric tube and repeat the examination. Administering small amounts of clear fluid can help delineate the pyloric region by transiently distending the stomach. Observing visible gastric peristaltic waves moving from left to right across the epigastrium before vomiting supports the diagnosis.

4. Confirming the Diagnosis

When the olive mass is palpated by an experienced clinician, the diagnosis is essentially confirmed, and imaging may be deferred to avoid delays in surgical correction. If the mass cannot be felt, abdominal ultrasound is the diagnostic imaging of choice, revealing a thickened pyloric muscle wall (>3 mm) and an elongated pyloric channel (>15 mm). Serum electrolytes must be checked urgently to identify hypochloremic, hypokalemic metabolic alkalosis, which requires correction before pyloromyotomy.

## 핵심 개념

- **Hypertrophic Pyloric Stenosis** — Hyperplasia of the smooth muscle of the pylorus causing progressive gastric outlet obstruction, typically presenting with projectile non-bilious vomiting in infants aged 3 to 5 weeks.
- **Olive-shaped mass** — The pathognomonic palpable finding of the hypertrophied pyloric muscle located in the right upper quadrant or epigastrium, best felt after vomiting when the infant is calm.
- **Non-bilious vomiting** — Vomitus without bile, indicating that the obstruction is proximal to the duodenal papilla, characteristic of gastric outlet obstructions like pyloric stenosis.
- **Projectile vomiting** — Forceful expulsion of stomach contents that can travel several feet, caused by vigorous gastric peristalsis against a narrowed pyloric channel.
- **Right upper quadrant** — The anatomical region of the abdomen where the hypertrophied pylorus is typically palpated, bordered by the liver edge and the right costal margin.

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