Annular Pancreas

A. Definition

• Annular pancreas is a rare congenital anomaly in which pancreatic tissue partially or completely encircles the second part of the duodenum.
• This ring of tissue may cause duodenal narrowing or obstruction.

B. Embryologic Theories of Development

• Three main hypotheses explain its formation:
  • Lecco’s theory: Adhesion of the right ventral pancreatic bud to the duodenal wall leads to incomplete rotation.
  • Persistence of accessory ventral bud tissue: Abnormal persistence and enlargement of ventral bud elements.
  • Hypertrophy and early fusion: Overgrowth and fusion of ventral and dorsal buds before rotation, resulting in encirclement of the duodenum.

C. Associated Conditions

• May occur in isolation or with other congenital anomalies.
• Common associations include:
  • Trisomy 21 (Down syndrome)
  • Congenital heart disease
  • Esophageal and duodenal atresia
  • Tracheoesophageal fistula
  • Imperforate anus
  • Meckel diverticulum
• Polyhydramnios may be noted prenatally due to duodenal obstruction.

D. Clinical Presentation

• Symptoms vary by age group:
  • Infants/Children:
    • Neonatal small bowel obstruction (most common pediatric presentation)
    • Feeding intolerance
    • Bilious vomiting
    • Abdominal distension
  • Adolescents/Adults:
    • Abdominal pain
    • Postprandial fullness
    • Nausea and vomiting
    • Acute or chronic pancreatitis

E. Diagnostic Evaluation

• KUB X-ray: May show “double bubble” sign indicating duodenal obstruction.
• CT/MRI/Upper GI series:
  • Can demonstrate duodenal narrowing or encircling pancreatic tissue.
  • May miss subtle or incomplete annular pancreas.
• MRCP/ERCP with endoscopic ultrasound: More sensitive for ductal anatomy and pancreatic tissue configuration.
• Laparotomy: May be required for definitive diagnosis in uncertain cases.

F. Treatment

• Duodenal bypass surgery is the standard treatment for symptomatic cases:
  • Gastrojejunostomy
  • Duodenojejunostomy
• Pancreatic tissue is typically not resected due to risk of complications.