The most common cause of SBO is adhesions following abdominal surgery.12 and 3 Although in most cases several months to years have passed from the time of the previous surgery, SBO may occur within the first few weeks following surgery.3 The second most common cause of small intestinal obstruction is incarceration of a groin hernia12 (see Chap.^76). This can occur in infants as well as adults and should be suspected anytime there is a complaint of a "knot" or growth in the inguinal region that fails to reduce with manipulation. Other sites that are occasionally responsible for SBO secondary to hernia include the umbilicus, femoral canal, and, rarely, the obturator foramen. Umbilical hernias are more readily apparent and occur in any age group. Obturator or femoral hernias are much less common and may present with femoral or medial thigh pain. Elderly females are particularly susceptible to these defects, and one needs to consider them as a possible cause of SBO in these patients. Finally, a defect in the mesentery itself may cause intestinal obstruction.
Other causes of SBO are much less common and are generally due to intraluminal or intramural processes. Primary small bowel lesions include polyps, lymphoma, or adenocarcinoma. An unusual cause of intraluminal obstruction is gallstone ileus. In this situation, a gallstone has eroded from the gallbladder through the bowel wall and can cause obstruction at the ileocecal valve. Besides the findings of bowel obstruction, one may note air in the biliary tree on abdominal radiographs. Lymphomas may be the leading point of intussusception and present as SBO.
Bezoars are most commonly composed of vegetable matter or pulp from persimmons. Patients who have undergone gastrointestinal pyloroplasty or pyloric resection are most susceptible to intraluminal obstruction by bezoars.
Inflammatory bowel disease may also affect the small bowel at various sites. Likewise, infectious processes including abscesses may obstruct the bowel. Radiation enteritis is also a possible cause of SBO in patients who have undergone radiation therapy.
Colonic obstruction is almost never caused by hernia or surgical adhesions. Neoplasms are by far the most common cause of large bowel obstruction. 45 Therefore, anyone who has symptoms of colonic obstruction should be evaluated for a neoplasm. Diverticulitis may create significant secondary obstruction and mesenteric edema. Stricture formation may occur with chronic inflammation and scarring. Fecal impaction is a common problem in elderly, debilitated patients and may present with symptoms of colonic obstruction.
The next most frequent cause of large bowel obstruction after cancer and diverticulitis is sigmoid volvulus. Elderly, bedridden, or psychiatric patients who are taking anticholinergic medication are most often subject to this mechanical problem. A history of constipation may precede the volvulus and presenting symptoms. Radiographic appearance is usually classic ( F,i,g,.,,,,,,7,,5,:,,l). Finally, although much less common, cecal volvulus may also cause large bowel obstruction.
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