Large-Bowel Obstruction 

Large-bowel obstruction (LBO) is an emergency condition that requires early identification and intervention. The etiology of this condition is age dependent, and it can result from either mechanical interruption of the flow of intestinal contents (see the following image) or by the dilation of the colon in the absence of an anatomic lesion (pseudo-obstruction). Causes include neoplasms or anatomic abnormalities, such as volvulus, incarcerated hernia, stricture, or obstipation.

The challenges in managing this condition are distinguishing colonic obstruction from ileus, ruling out nonsurgical causes, and determining the best surgical management. Distinguishing between a true mechanical obstruction and a pseudo-obstruction is important, as the treatment differs.^[1]

Colonic obstruction is most common in elderly individuals, due to the higher incidence of neoplasms and other causative diseases in this population. In neonates, colonic obstruction may be caused by an imperforate anus or other anatomic abnormalities. Obstruction may also be secondary to meconium ileus. In the pediatric population, Hirschsprung disease can resemble colonic obstruction.

For patient education information, see Digestive Disorders Center as well as Constipation in Adults and Abdominal Pain in Adults.

See also Ogilvie Syndrome, Ileus, Constipation, Small Bowel Obstruction, and Intussusception.

The prevalence of mechanical large-bowel obstruction (LBO) increases with age as does its main causes, colon cancer and diverticulitis. Sigmoid volvulus and cecal volvulus are also potential causes of this disorder.^[2] See the following images.

Mechanical obstruction of the large bowel causes bowel dilatation above the obstruction, which in turn, causes mucosal edema and impaired venous and arterial blood flow to the bowel. Bowel edema and ischemia increase the mucosal permeability of the bowel, which can lead to bacterial translocation, systemic toxicity, dehydration, and electrolyte abnormalities. Bowel ischemia can lead to perforation and fecal soilage of the peritoneal cavity.

The pathophysiology of acute colonic pseudo-obstruction (ACPO), or Ogilvie syndrome, is not clear, but it is thought to result from an autonomic imbalance, which results from decreased parasympathetic tone or excessive sympathetic output.^{[1, 3]} This condition usually occurs in the setting of a wide range of medical or surgical illnesses. If untreated, colonic ischemia or perforation can occur.

Acute colonic pseudo-obstruction is characterized by a loss of peristalsis and results in the accumulation of gas and fluid in the colon. The right colon and cecum are most commonly involved. The risk of perforation for acute colonic pseudo-obstruction ranges from 3%-15%. The mortality rate is 15% with early care; mortality increases to 36% if colonic ischemia or perforation develops.^[4]

Approximately 60% of mechanical large-bowel obstructions (LBOs) are caused by malignancies, 20% are caused by diverticular disease, and 5% are the result of colonic volvulus.^{[1, 5, 6]} The most common causes of adult large-bowel obstruction are as follows:

• Neoplasm (benign or malignant)
• Stricture (diverticular or ischemic)
• Volvulus (eg, colonic, sigmoid, cecal)
• Incarcerated hernia
• Intussusception, usually with an identifiable anatomic abnormality in adults but not in children
• Impaction or obstipation
• Gallstone ileus

Neoplasms and diverticular disease

Obstructions caused by tumors tend to have a gradual onset and result from tumor growth narrowing the colonic lumen.

Diverticulitis is associated with muscular hypertrophy of the colonic wall. Repetitive episodes of inflammation cause the colonic wall to become fibrotic and thickened, leading to luminal narrowing.

Volvuli

A colonic volvulus results when the colon twists on its mesentery, which impairs the venous drainage and arterial inflow. Symptoms of this condition are usually abrupt.

A sigmoid volvulus typically occurs in older, debilitated individuals with a history of chronic constipation, or those living in an institutionalized setting (see the image below).

A cecal volvulus is caused by a congenital defect in the peritoneum, which results in inadequate fixation of the cecum, and increased cecal mobility.^[1] Patients usually present with this disorder in the sixth decade of life.^[7]

Intussusception

Intussusception is primarily a pediatric disease; however, it is estimated that between 5% and 16% of all intussusceptions in the Western world occur in adults, of which approximately two thirds of adult intussusception cases are caused by tumors. Two main types of intussusception affect the large bowel: enterocolic and colocolic.

Enterocolic intussusceptions involve both the small bowel and the large bowel. These are composed of either ileocolic intussusceptions or ileocecal intussusceptions, depending on where the lead point is located.

Colocolic intussusceptions involve only the colon. They are classified as either colocolic or sigmoidorectal intussusceptions.

Acute colonic pseudo-obstruction/Ogilvie syndrome

Acute colonic pseudo-obstruction (ACPO), or Ogilvie syndrome, has many etiologies. This disorder is typically seen in elderly patients who are hospitalized with a severe illness. In a retrospective review of more than 1400 cases of acute colonic pseudo-obstruction, the most common predisposing conditions were operative and nonoperative trauma (11%), infections (10%), and cardiac disease (10-18%).^{[8, 9]}

Large-bowel obstruction (LBO) is a surgical entity.

Before surgical decompression, the patient's overall medical condition and the presence of any comorbidities that define surgical risk determine the prognosis. If large-bowel obstruction is treated early, the outcome is generally good.

After surgical decompression, the prognosis is determined by the underlying disease. If large-bowel obstruction is secondary to carcinoma, the outcome is dependent on the carcinoma prognosis.

Complications

The morbidity and mortality of large-bowel obstruction are often related to the surgical procedure used to relieve the colonic obstruction and, in the long term, to the underlying disease that caused the obstruction. Thus, complications of large-bowel obstruction may include the following:

• Perforation
• Peritonitis from bowel perforation secondary to overstrenuous attempts at reduction of a volvulus or intussusception or injudicious attempts to dilate or stent an unsuitable colonic obstruction
• Sepsis - Misdiagnosis of an ileus secondary to intra-abdominal infection as large-bowel obstruction may occur, with consequent delay in treatment
• Intra-abdominal abscess from anastomotic leakage
• Pneumonia from aspiration during emesis
• Dehydration
• Electrolyte disturbance
• Death