Large-bowel obstruction

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Thursday, 29 January 2009 17:33

Large-bowel obstruction (LBO) is an emergency condition that requires early identification and intervention. The etiology of LBO is age dependent. Distinguishing between a true mechanical obstruction and a pseudo-obstruction is important, as the treatment differs. Physical * Abdominal distention may be significant in patients with a large-bowel obstruction. o Bowel sounds may be normal early on but usually become quiet. o Abdomen is hyperresonant to percussion. * Palpation of the abdomen reveals tenderness. Fever, severe tenderness, and abdominal rigidity are ominous signs that suggest peritonitis secondary to perforation. * The cecum is the area most likely to perforate (following the Laplace law). Sigmoid diverticulitis and a perforated sigmoid secondary to carcinoma are clinically difficult to differentiate. * Patients may have guaiac-positive stool if carcinoma is the etiology. * Rectal or lower sigmoidal mass may be palpated on rectal examination. A mass or fullness may be appreciated if a tumor is present in the cecum. Causes * Approximately 60% of mechanical LBOs are caused by malignancies, 20% are caused by diverticular disease, and 5% are the result of colonic volvulus.2 o Obstructions that result from tumors have a gradual onset and result from tumor ingrowth into the colonic lumen. o 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. o Colonic volvulus results when the colon twists on its mesentery. This impairs the venous drainage and arterial inflow. Symptoms are usually abrupt. + Sigmoid volvulus typically occurs in older individuals with a history of constipation and straining. + Cecal volvulus is caused by a congenital defect in the peritoneum, which results in inadequate fixation of the cecum. This type of volvulus generally occurs in a younger population. o Intussusception is primarily a pediatric disease. It is estimated that between 5% and 16% of all intussusceptions in the western world occur in adults. Approximately two thirds of adult intussusception cases are caused by tumors. Two main types of intussusception affect the large bowel. + 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 (ACPO), or Ogilvie syndrome, has many etiologies. This disorder is typically seen in elderly patients who are hospitalized with a severe illness. In a review of more than 400 cases of ACPO, only 6% of cases were idiopathic, 49% of patients had an underlying surgical disorder, and 45% had a precipitating medical disorder.

Last Updated on Thursday, 05 February 2009 16:53