INTRODUCTION

Small bowel obstruction (SBO) occurs when the normal flow of intestinal contents is interrupted. Postoperative adhesions are the most common cause of mechanical SBO, which cause extrinsic compression of the intestine. Malignant tumors or strictures of the small bowel can cause intrinsic blockage and are the second leading cause of SBO. Hernias cause extrinsic compression and are the third most common cause of SBO [1]. Intussusception, volvulus, Crohn's disease, and gallstones (gallstone ileus) account for only a small percentage of cases (table 1).

This topic review will focus on the causes and treatment of SBO. The clinical manifestations and diagnosis of SBO are presented separately. (See "Small bowel obstruction: Clinical manifestations and diagnosis".)

CAUSES OF OBSTRUCTION

Adhesions — Postoperative adhesions cause the majority of small bowel obstructions. The risk of developing an obstruction after surgery from postoperative adhesions is estimated to be 9 percent within the first year after abdominal surgery, 19 percent by 4 years, and 35 percent by 10 years [2-5]. Population based studies have shown that 24 percent of patients undergo surgery for SBO during their index admission [6]. Of those who underwent surgery, 38 percent had lysis of adhesions, 18 percent had lysis of adhesions with a small bowel resection, and the remainder had a hernia repair or a small bowel resection with a hernia repair [6].

The risk of SBO due to adhesions depends in part upon the type of surgery being performed and the cause of the SBO [7]. A study comparing open appendectomy to open cholecystectomy in a series of 567 patients showed that obstruction was significantly more common after appendectomy (10.7 versus 6.4 percent) [8]. In a study of 446,331 abdominal operations, ileal pouch–anal anastomosis were associated with the highest incidence of SBO (19 percent), followed by open colectomy (9 percent). The incidence of adhesive SBO was higher in open operations than with laparoscopic surgery (eg, 7 percent in open cholecystectomies versus 0.2 percent in laparoscopic cholecystectomies). The decrease in the frequency of postoperative adhesions with laparoscopic surgery, despite the fact that the procedures and dissection are similar to those done with the open approach, has been documented in other studies as well [9]. The cause for the differences in the rates of postoperative adhesions between open and laparoscopic surgery is not clear, but likely relates to the degree of manipulation and trauma to the intra-abdominal tissues.

Malignancy — Malignant tumors are the second most common cause of SBO, accounting for about 20 percent of cases [1]. SBO has been described in as many as 42 percent of women with ovarian carcinoma and 28 percent of patients with colorectal carcinoma [10]. (See "Surgery for recurrent epithelial ovarian cancer" and "Locoregional methods for management and palliation in patients who present with stage IV colorectal cancer".)