large bowel obstruction

LBO occurs when there is blockage of the colonic lumen, leading to proximal dilation and accumulation of gas and stool. Etiologies (in order of frequency in adults): colorectal cancer (most common, ~60%), sigmoid or cecal volvulus, diverticular disease with stricture formation, and less commonly hernias, adhesions, or fecal impaction. Pseudo-obstruction (Ogilvie syndrome) is a functional mimic without mechanical cause, often seen in critically ill or postoperative patients, and is associated with electrolyte imbalances and opioid use.

Pathophysiology: Colonic distension proximal to the obstruction leads to increased luminal pressure, bowel wall ischemia, and risk of perforation—especially dangerous at the cecum due to Laplace's law (larger radius = greater wall tension for a given pressure). If the ileocecal valve is competent, the colon forms a closed loop, increasing risk of ischemia and perforation compared to an incompetent valve where retrograde decompression into the small bowel occurs.

Clinical features: Progressive abdominal distension, obstipation (failure to pass stool or flatus), crampy abdominal pain, and vomiting (often a late finding compared to small bowel obstruction). Physical exam may reveal tympanic distension and high-pitched or absent bowel sounds. Signs of peritonitis (rebound, guarding, rigidity) suggest ischemia or perforation and warrant emergent surgery.

Diagnosis: Abdominal X-ray may show dilated colon with haustral markings; CT abdomen/pelvis with contrast is the gold standard, identifying the transition point, cause, and complications (e.g., pneumatosis, free air, closed-loop obstruction). Sigmoid volvulus classically shows a 'coffee bean' sign on X-ray; cecal volvulus can show a similar sign in the upper abdomen or 'comma sign.'

Management: Depends on etiology and stability. Sigmoid volvulus is often managed initially with endoscopic decompression. Malignant obstructions may require surgical resection or stenting as a bridge to surgery. Cecal volvulus typically requires surgery (right hemicolectomy) due to higher risk of ischemia. Signs of strangulation, perforation, or peritonitis mandate emergent laparotomy. Supportive care includes NG tube decompression, IV fluids, electrolyte correction, and NPO status.

Complications: Bowel ischemia, perforation, sepsis, and death if untreated. Cecal perforation is particularly life-threatening due to high bacterial load and thin wall.