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The duodenal C-loop refers to the characteristic C-shaped course of the duodenum, which curves around the head of the pancreas. It is an important anatomical landmark in abdominal imaging and surgery.

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Anatomy of Duodenum

The duodenum is the first part of the small intestine, ~25–30 cm long, extending from the pylorus to the duodenojejunal flexure.

It is divided into four parts:

1. First part (superior): from pylorus, passes horizontally to the right; intraperitoneal (proximal 2 cm, the duodenal cap/bulb).
2. Second part (descending): runs vertically alongside the head of the pancreas; contains major duodenal papilla (ampulla of Vater) and minor papilla.
3. Third part (horizontal/inferior): passes horizontally across midline, between aorta/IVC (posterior) and SMA/SMV (anterior).
4. Fourth part (ascending): ascends to the left of the aorta to reach duodenojejunal flexure, suspended by ligament of Treitz.

Together these form the C-loop, embracing the head of the pancreas.

Relations

• Medial: head of pancreas, bile duct, pancreatic duct.
• Anterior: liver, gallbladder, transverse colon.
• Posterior: right kidney, ureter, IVC, aorta.
• Superior: stomach, pylorus.

Clinical Importance

• Pathology causing C-loop widening/distortion:
  • Carcinoma head of pancreas.
  • Periampullary carcinoma.
  • Pancreatitis with pseudocyst.
  • Duodenal diverticula, ulcers, Crohn’s disease.
• Malrotation of bowel: abnormal position of duodenal C-loop.