Closed loop

Contrast-enhanced CT demonstrates diffuse small bowel dilatation. Centrally, we see two adjacent transition points (yellow arrow and green arrow). In between these points, there is a U-shaped small bowel loop (red arrow). Proximally to this configuration, we see a dilated loop of small bowel (blue arrow). Distally, the small bowel and colon are collapsed. The involved bowel shows mild edema, with retained mural enhancement, so there are no definite CT signs of ischemia (though this is not 100% sensitive). No free intraperitoneal fluid, no pneumoperitoneum. This represents a surgical emergency because progression to strangulation, bowel infarction, and perforation may occur rapidly.

Closed-loop obstruction is one of the most important diagnoses to recognize on emergency abdominal CT.

Unlike uncomplicated mechanical bowel obstruction, obstruction at two adjacent points creates a trapped bowel segment in which intraluminal pressure rapidly increases. Venous congestion precedes arterial compromise, resulting in bowel ischemia, necrosis, and perforation if untreated.

Early recognition by the radiologist directly changes patient management by prompting urgent surgical consultation rather than conservative treatment.

Understanding the mesentery is essential.

• Small bowel is suspended by the mesentery, containing arteries, veins, lymphatics, and fat.
• A closed loop forms when both the afferent and efferent limbs become obstructed.
• Mesenteric twisting may produce the whirl sign.
• Venous outflow obstruction develops first, followed by arterial compromise.
• Common locations include the distal ileum, although any mobile small bowel segment may be involved.

Patients typically present with

• Acute abdominal pain
• Vomiting
• Abdominal distension
• Obstipation
• Elevated inflammatory markers or lactate (late finding)

A CT diagnosis of closed-loop obstruction should immediately prompt surgical review.

Urgent surgery is indicated when CT demonstrates signs of bowel compromise or strangulation.

CT protocol

• Portal venous phase CT abdomen and pelvis
• Intravenous contrast is essential
• Thin-slice multiplanar reconstructions
• Oral contrast is usually unnecessary in the acute setting

Report systematically✓ Site of obstruction✓ Cause if identifiable (adhesion, hernia, volvulus)✓ Number and location of transition points✓ Configuration of the loop (C-shaped or U-shaped)✓ Whirl sign✓ Mesenteric edema or vascular congestion✓ Free fluid✓ Bowel wall thickness✓ Bowel wall enhancement✓ Pneumatosis or portal venous gas✓ PerforationConclude explicitly whether imaging suggests simple closed-loop obstruction or strangulated closed-loop obstruction.

A diagnosis of closed-loop obstruction should be treated as time-critical.

• Immediate surgical consultation
• Intravenous fluids and electrolyte correction
• Nasogastric decompression when appropriate
• Broad-spectrum antibiotics if ischemia or perforation is suspected
• Emergency laparotomy or laparoscopy when strangulation or bowel compromise is suspected

Delayed intervention substantially increases the risk of bowel necrosis, perforation, sepsis, short bowel syndrome, and mortality.