Closed loop obstruction

Last revised by Daniel J Bell on 23 Mar 2024

Closed loop obstructions are a specific type of bowel obstruction in which two points along the course of the bowel are obstructed, usually but not always the transition points are adjacent at a single location. The closed loop refers to a segment of bowel without proximal or distal outlets for decompression.

Patients present with signs and symptoms of bowel obstruction, including crampy abdominal pain, vomiting, abdominal distension, and high-pitched or absent bowel sounds.

Closed loop obstructions are at higher risk than non-closed loop obstructions for strangulation (compromised blood supply) or distension-related ischemia, resulting in intestinal necrosis and perforation.

Closed loop small bowel obstructions are usually secondary to adhesions, volvulus, or hernia (external or internal). Those with a Roux-en-Y gastric bypass are at increased risk for closed loop obstruction, a result of surgically created rents in the mesentery 6.

A similar pathology is the large bowel volvulus (sigmoid or cecal). Large bowel obstructions occurring at a single point combined with a competent ileocecal valve, which occurs in 75% of patients, also create closed loop pathophysiology with a risk of cecal perforation 8.

Some publications describe two separate components of the obstruction 15.

  • closed loop syndrome

    • incarcerated loop (closed loop) continues to secrete fluid and distends, inducing parietal vascular constraints (normally it contains very little or no gas with the exception of when it involves the colon (fermentation gases)

    • induced extravasation of blood and plasma from venous stasis both in the excluded loop and in the adjacent mesentery, increasing the intestinal distension

  • supralesional syndrome

    • segment of intestine upstream from proximal point of obstruction progressively distends to the stomach

    • slower than in case of the incarcerated segment, and usually less dilated than the incarcerated segment

CT findings of a closed-loop obstruction depend in part on the orientation of the loop relative to the plane of imaging. Some or all of the following signs may be demonstrated on CT:

  • marked distension of a segment of small bowel

    • >3 cm is the generally accepted caliber for distended small bowel (see the 3-6-9 rule)

  • radially distributed, C or U-shaped small bowel loops

  • "double beak sign": tapering bowel loops at the point of obstruction

  • "whirl sign": of the tightly twisted mesentery

  • two adjacent collapsed loops of bowel

If strangulation is present, signs of bowel ischemia progressing to necrosis are 10:

  • increased attenuation of bowel wall due to hemorrhage

  • increased attenuation of bowel contents due to hemorrhage

  • mesenteric stranding and fluid

Increased attenuation of bowel content in the closed loop (>8 HU) compared to content in the dilated proximal loop is easy to measure and, unlike bowel wall attenuation, is not affected by contrast medium administration. In a single study, sensitivity was 64% and specificity was 99%10.

Two variants of closed loop obstruction may account for 25% of cases 11, the first is a collapsed closed loop with proximal dilatation. The second has been termed ‘flat-belly’ closed loop. The closed loop is distended but the proximal bowel is decompressed due to vomiting or nasogastric aspiration.

Risk of strangulation leads to high morbidity and mortality in closed loop bowel obstructions. Immediate surgical intervention is required especially in the setting of ischemia 6.

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