Closed loop obstruction

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

Clinical presentation 

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

Complications

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.

Pathology

Closed loop small bowel obstructions are usually secondary to adhesions, volvulus, or hernia. A similar related pathology is the large bowel volvulus (either 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 physiology with 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 does 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 an incarcerated segment.

Associations

• internal hernias or congenital or iatrogenic defects in the mesentery or omentum: may serve to trap a segment of the bowel leading to a closed-loop obstruction a result of surgically created rents in the mesentery  
• those with a Roux-en-Y gastric bypass are also at increased risk for closed-loop obstruction ⁶. 

Radiographic features

CT

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

Treatment and prognosis

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