What is a closed loop obstruction?

Closed Loop Obstruction: Definition and Imaging Characteristics

I cannot provide you with an actual picture or image, but I can describe what closed loop obstruction looks like on imaging and its key diagnostic features.

What is a Closed Loop Obstruction?

A closed loop obstruction occurs when a segment of bowel is obstructed at two points simultaneously, creating an isolated section with no outlet for decompression, which rapidly leads to increased intraluminal pressure, impaired capillary perfusion, and potential strangulation. 1

Mechanism of Injury

• The trapped fluid and gas cause progressive distension of the isolated bowel segment 1
• Vascular compromise develops quickly due to increased intraluminal pressure 1
• Eventual ischemia and necrosis occur if not promptly addressed, with mortality rates reaching 70% if untreated 1

Imaging Appearance on CT Scan

CT scan with IV contrast is the preferred imaging modality, with approximately 90% accuracy for diagnosing closed loop obstruction. 1, 2

Key Radiological Features to Look For:

• "Bulb-like" appearance: The obstructed loop appears as a dilated, fluid-filled segment that resembles a bulb on both ultrasound and CT 3
• U-shaped or C-shaped configuration: The closed loop creates a characteristic curved appearance of the obstructed segment 1
• Two transition points: Unlike simple obstruction with one transition point, closed loop shows obstruction at two adjacent locations 4
• Radial distribution of mesenteric vessels: The mesenteric vessels converge toward the point of torsion or obstruction 1
• "Whirl sign": When volvulus is the cause, the mesentery twists around itself creating a whirled appearance 1

Signs of Complications (Ischemia/Strangulation):

• Abnormal bowel wall enhancement or lack of enhancement 1
• Bowel wall thickening 1
• Mesenteric edema 1, 2
• Pneumatosis (gas in the bowel wall) 1
• Free intraperitoneal fluid 5, 2

Common Causes

• Post-surgical adhesions are the most common cause, particularly in patients with previous abdominal surgeries 1
• Sigmoid volvulus accounts for approximately one-third of colonic emergencies in elderly patients 1
• Internal hernias (Spigelian, perineal) can create closed loop scenarios 6, 3
• Obstructing colorectal tumors combined with a competent ileocecal valve 1

Special Scenario - Double Closed Loop:

A rare but devastating situation occurs when sigmoid volvulus combines with a competent ileocecal valve, creating two closed loops simultaneously and causing gangrene of the entire colon 7

Clinical Urgency

This is a surgical emergency requiring prompt recognition and intervention. 1

• Closed loop obstructions rapidly progress to strangulation and ischemia 1
• Delayed diagnosis significantly increases morbidity and mortality, with intestinal necrosis observed in up to 70% of cases 1
• Relying solely on plain radiographs is inadequate due to their limited sensitivity (50-60%) 1

Indications for Urgent Surgery:

• Signs of ischemia on imaging 1, 2
• Abnormal bowel wall enhancement 1
• Mesenteric edema 1
• Pneumatosis 1
• Clinical signs of sepsis, acidosis (pH <7.2), hypothermia (<35°C), or coagulopathy 1

Important Pitfall

CT may not be very sensitive for identifying early ischemia, with prospective sensitivity as low as 14.8% in initial radiology reports. 5 Therefore, when closed loop obstruction is identified on imaging, assume high risk for ischemia and proceed urgently even if definitive ischemic changes are not yet visible 5, 1