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depend on the clinical circumstances, the patient's body habitus, previous abdominal surgery, and the surgeon's preference. A loop colostomy is usually performed as a temporary procedure in acute obstruction or to protect a distal anastomosis from the fecal stream. It is considered easier to construct than the other types of colostomy, although complete diversion of the fecal stream may not be achieved with this technique. A loop of colon is brought to the anterior abdominal wall, sutured on the outside, and then opened. This creates an afferent and efferent stoma with the posterior wall of the colon in continuity. In a double-barreled (end loop) colostomy, the colon is divided completely and the limbs are placed side by side. In a divided (end) colostomy with a mucous fistula, two separate colostomies are formed, so that no fecal stream enters the distal colon and only mucous is carried to the rectum.

Prior to closure of the colostomy, it may be necessary to study the distal limb to assess for leakage at the anastomotic site. The afferent limb may be studied as well, especially if it has not been examined pre-operatively, to identify concurrent lesions such as polyps or carcinoma, and to assess anatomy.

The utility of contrast studies before colostomy closure has been questioned, however, particularly in trauma patients. Some research has shown that preoperative studies did not alter operative plans or yield unexpected findings and concluded that such studies were unnecessary in many instances [40,41]. Examination of the distal limb via the rectum is feasible in some cases. If there is a low rectal anastomosis, however, it may be dangerous to insert a rectal catheter. Examination of the colon via the colostomy may be performed by a variety of methods. A Foley catheter can be employed with the balloon inflated outside the stoma, although there may be leakage of contrast medium onto the abdominal wall with this technique. Inflation of the balloon inside the colon can lead to bowel perforation and generally is not recommended [42]. Special catheters with nipples or cones that create seals at the colostomy site, allow passage of a catheter into the colon, and prevent leakage onto the abdominal wall have been devised [43-45].

The type of contrast to employ to study the distal limb to evaluate for a leak before colostomy closure is somewhat controversial. In the asymptomatic patient being examined weeks or months after surgery, it is generally considered safe to use barium, since if a leak is present, it will have been sealed off, preventing the entrance of free barium into the peritoneal cavity [46]. Barium is denser than water-soluble contrast medium and is therefore a better contrast agent for visualizing and identifying leaks. Water-soluble agents are less dense, may be diluted in a tract or collection, and are also rapidly resorbed.

Figure 6.29. Prolapsed colostomy. Plain films of the abdomen reveal a large soft tissue density extending from the colostomy as a result of prolapsed bowel.

Complications of stoma surgery include ischemic necrosis, retraction, peristomal abscess, stenosis, prolapse (Fig. 6.29), parastomal hernia (Fig. 6.30), peristomal fistula, opening the wrong (distal) end of a divided loop (Fig. 6.31), small-bowel obstruction, diversion colitis, and cancer at the stoma site. Prolapse is more common with loop colostomy than with end colostomy. Although prolapse is generally not of any clinical significance, occasionally it may lead to incarceration and strangulation. Parastomal hernias may contain large or small bowel and may remain in the subcutaneous tissues or herniate completely externally adjacent to the stoma. These hernias are readily demonstrated on CT imaging. Large parastomal hernias may require

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