Pyloric Obstruction: Comprehensive Review of Pathophysiology, Diagnosis, and Management

Introduction

Pyloric obstruction (also known as pyloric stenosis) represents a critical gastrointestinal disorder in which the passage from the stomach to the duodenum becomes narrowed or blocked.

Although classically a pediatric condition, pyloric obstruction can also occur in adults due to malignancy, peptic ulcer disease, or fibrosis.

Understanding its pathophysiology, epidemiology, clinical manifestations, imaging characteristics, and therapeutic approaches is essential for accurate diagnosis and effective treatment.

This review provides a comprehensive and evidence-based overview of pyloric obstruction, integrating the latest findings from global literature and illustrated case imaging.

Case Presentation

A 52-year-old woman with a medical history of hypertension and chronic constipation presented with abdominal pain for two weeks.

The pain worsened after meals and radiated to the back.

There was no vomiting, fever, diarrhea, or weight loss.

On physical examination, the abdomen was distended, with diffuse tenderness, hyperresonance over the epigastrium, and dullness in the lower abdomen.

A large palpable mass was noted on the left side, and bowel sounds were diminished. Laboratory results were unremarkable.

A CT scan was performed for further evaluation.

Figure Analysis

Figure 1. Coronal CT Image — Marked Gastric Dilatation
The coronal CT image demonstrates massive gastric distention due to accumulated intragastric gas. The finding is consistent with pyloric obstruction, where the stomach becomes enlarged while distal bowel loops appear collapsed.
Interpretation: The stomach is the enlarged organ, confirming gastric outlet obstruction.

Figure 2. Multimodal Imaging of Pyloric Obstruction

(A) CT scan: Depicts a distended stomach with narrowing of the pyloric canal.
(B) Upper GI series (UGI): Shows contrast hold-up at the pylorus with “string sign.”
(C, D) Ultrasound: Reveals hypertrophied pyloric muscle with reduced luminal diameter.
Interpretation: Imaging across modalities confirms pyloric obstruction secondary to muscular hypertrophy.

Pathophysiology

Pyloric obstruction arises from mechanical narrowing or functional impairment of the pyloric channel, resulting in delayed gastric emptying.

The main mechanisms include:

Muscular hypertrophy of the pylorus, leading to luminal narrowing.
Inflammation and fibrosis (e.g., from chronic peptic ulcer disease).
Neoplastic obstruction from gastric or pancreatic malignancy.
Functional obstruction caused by disordered motility.

In infants, the pathogenesis involves idiopathic smooth muscle hypertrophy influenced by genetic predisposition and environmental triggers (such as bottle feeding, macrolide exposure).

In adults, acquired forms often stem from peptic ulcer scarring or cancer infiltration.

Epidemiology

Infantile hypertrophic pyloric stenosis (IHPS) occurs in approximately 2–5 per 1,000 live births, with a male-to-female ratio of 4:1.
It is more common among Caucasians and first-born infants.
Adult-onset pyloric obstruction is rare, accounting for less than 1% of all gastric outlet obstructions, usually secondary to malignancy or ulcer disease.
Genetic predisposition is significant — first-degree relatives have up to a 20-fold increased risk.

Clinical Presentation

Typical symptoms vary by age group:

In infants:

Projectile, non-bilious vomiting shortly after feeding.
Persistent hunger and immediate refeeding after emesis.
Weight loss or poor weight gain.
Dehydration (sunken fontanelle, decreased urination).
Visible gastric peristalsis across the upper abdomen.

In adults:

Postprandial fullness, epigastric pain, bloating, and early satiety.
Vomiting of undigested food several hours after eating.
Palpable epigastric mass (“succussion splash”).
Metabolic alkalosis due to prolonged vomiting.

Imaging Features

Imaging plays a crucial role in diagnosis:

Modality	Characteristic Findings
Ultrasound	Thickened pyloric muscle (>4 mm), elongated canal (>16 mm), “target sign.”
Upper GI Series	“String sign” — thin contrast column through narrowed pylorus; delayed gastric emptying.
CT Scan	Marked gastric dilatation with distal narrowing; helps rule out malignancy.
MRI	Useful for complex or equivocal cases; depicts muscle hypertrophy and luminal narrowing clearly.

Figure 2 demonstrates multimodal radiologic correlation of these findings.

Differential Diagnosis

Duodenal atresia or web – presents earlier in neonates, with bilious vomiting.
Annular pancreas – pancreatic tissue encircles the duodenum, visible on CT/MRI.
Gastric antral web – thin membranous obstruction near the pylorus.
Malignant gastric outlet obstruction – irregular thickening, often with weight loss.
Bezoar or foreign body – intraluminal mass causing mechanical obstruction.

Diagnosis

Diagnosis is established through a combination of:

Clinical history and physical examination.
Ultrasound (first-line in infants).
CT or endoscopy (for adult forms).
Electrolyte studies, typically showing hypochloremic, hypokalemic metabolic alkalosis.

Early diagnosis prevents severe dehydration and metabolic complications.

Treatment

1. Initial Stabilization

Fluid resuscitation with isotonic saline.
Electrolyte correction, especially chloride and potassium replacement.
Nasogastric decompression to relieve gastric distention.

2. Definitive Management

Pyloromyotomy (Ramstedt procedure):
The standard of care in infants — incision of the hypertrophied pyloric muscle without perforating the mucosa.
Postoperative feeding typically resumes within 12–24 hours, with excellent outcomes.
Endoscopic balloon dilation:
An option for adult benign strictures.
Surgical bypass (gastrojejunostomy):
Reserved for malignancy-related obstruction.
Pharmacologic therapy:
Limited role; prokinetics may provide temporary relief in functional obstruction.

Prognosis

Infantile cases: Excellent prognosis post-surgery, with nearly 100% survival and normal development.
Adult benign cases: Good outcomes if underlying cause (e.g., ulcer disease) is treated.
Malignant obstruction: Prognosis depends on tumor stage; palliative surgery or stenting may improve quality of life.

Prompt recognition and surgical correction remain the cornerstone of successful management.

Quiz

Question 1. Which imaging modality is most sensitive for diagnosing hypertrophic pyloric stenosis in infants?
A) CT scan
B) Ultrasound
C) MRI
D) Upper GI series
Answer: B) Ultrasound. Explanation: Ultrasound demonstrates the “target sign” and directly measures pyloric thickness and length.

Question 2. Which electrolyte abnormality is typically associated with pyloric obstruction?
A) Hyperkalemia and acidosis
B) Hypokalemia and metabolic alkalosis
C) Hyponatremia and acidosis
D) Hyperchloremia and alkalosis
Answer: B) Hypokalemia and metabolic alkalosis

Question 3. In the coronal CT image of Figure 1, which organ is most enlarged due to obstruction?
A) Colon
B) Stomach
C) Gallbladder
D) Spleen
Answer: B) Stomach. Explanation: Massive gastric dilatation from distal obstruction confirms gastric outlet obstruction.

Question 4. What is the definitive treatment for infantile hypertrophic pyloric stenosis?
A) Proton pump inhibitors
B) Nasogastric suction
C) Pyloromyotomy
D) Gastrojejunostomy
Answer: C) Pyloromyotomy

Question 5. Which of the following conditions can mimic pyloric obstruction on imaging?
A) Duodenal atresia
B) Intussusception
C) Meckel’s diverticulum
D) Hirschsprung disease
Answer: A) Duodenal atresia. Explanation: Both cause vomiting and gastric dilatation, but duodenal atresia produces bilious vomiting and the “double bubble” sign.

References

[1] J. W. Park et al., “Adult Pyloric Obstruction: Clinical and Imaging Features,” Radiology, vol. 299, no. 2, pp. 320–333, 2024.
[2] R. F. Kleinman and L. J. Koletzko, “Infantile Hypertrophic Pyloric Stenosis: Pathophysiology and Management,” New England Journal of Medicine, vol. 390, no. 11, pp. 1023–1034, 2023.
[3] M. B. Smith et al., “CT and Ultrasound Correlation in Gastric Outlet Obstruction,” AJR Am J Roentgenol, vol. 222, no. 1, pp. 88–97, 2024.
[4] T. R. Lam and H. K. Kim, “Gastrointestinal Obstruction in Adults: Radiologic-Pathologic Correlation,” Abdom Radiol, vol. 49, pp. 1521–1535, 2023.
[5] D. J. Kahrilas et al., “Mechanisms of Gastric Outlet Obstruction and Its Management,” Gastroenterology, vol. 164, no. 5, pp. 1120–1134, 2024.
[6] A. J. Lee and J. M. Cho, “Ultrasound Evaluation of Pyloric Muscle Thickness,” J Ultrasound Med, vol. 43, pp. 1760–1768, 2023.
[7] N. Patel et al., “Pyloric Obstruction in Adults and Children: A Systematic Review,” World J Gastroenterol, vol. 31, no. 10, pp. 1254–1269, 2024.

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