Adhesions

In discussing small-bowel obstruction, one must take into account that adhesions are either the first [1,2] or second [3] most common cause. One study states that up to 70% of small-bowel obstructions in the United States are secondary to adhesions [4], while other studies showed that the rate may vary between 49 [5,6] and 80% [7]. A prospective study showed that at surgery, 93% of patients with prior abdominal surgery had evidence of adhesions even if they were not obstructed [8]. In patients with previous abdominal surgery there is a 33% rate of readmission within a 10-year period for a possibly adhesion-related problem [9]. Among patients with one episode of small-bowel obstruction secondary to adhesions, 15 to 30% will develop a recurrence of that problem [10-12]. More significantly, the National Center for Health Statistics estimated that 344,000 operations were performed for the lysis of adhesions in 1992 [13]. Other adhesion-related problems cause between 3 and 5% of all laparotomies [8,9,14]. Patients who had had an appendectomy had an 11% rate of adhesive small-bowel obstruction during a 5-year follow-up period [15]. This compares with a 5% rate of the same period for patients with prior cholecystectomies. Total colec-tomy with ileal anal reservoir creation resulted in a rate of adhesive small-bowel obstruction slightly greater than 25% [16].

Intraperitoneal adhesions are formed by the transudation of serosan-guinous fluid that is rich in protein [2]. This fluid coagulates during the first several postoperative hours [2]. Aiding in the production of adhesions is a reduction in fibrinolytic activity within the peritoneal cavity [17]. These two factors combine to allow the formation of fibrinous bands between adjacent intraperitoneal organs [18]. Collagen deposition and fibroblast proliferation is noted in these adhesions within 5 days [19].

The struggle to prevent adhesions is an ongoing one. As the preceding statistics demonstrate, even a small decrease in the rate of adhesions and subsequent small-bowel obstruction would have a major impact on health care and the course of providing it. Three different tactics have been or are being used to possibly prevent lesions. These are fibrinolytic therapy, anti-inflammatory medication, and physical separation of tissues [2].

Formerly, hyperosmolar solutions of dextran were used to help prevent lesions. Complications including occasional anaphylaxis as well as doubts of its efficacy have led to the abandonment of this technique [20,21]. Another older technique that led to serious and unexpected complications was the instillation into the peritoneum of mineral oil or other lipoid substances [22]. In 1908 Bake instilled sterile olive oil [23], and eventually mineral oil, Vaseline, animal fat, and paraffin were also tried [22]. By 1934, it had been noted that lipids not only failed to prevent adhesions but also caused an increase in them [24]. The oil resulted in the formation of dense adhesions, and the droplets were encapsulated by fibrous tissue containing foreign body giant cells, as well [22]. Calcification occurred within the fibrous stroma and in the periphery of these nodules. This could occur as early as 4 months after instillation [24] or as late as 30 years postoperatively [22].

On conventional radiography, calcified plaques may be seen outlining the serosal surfaces of the intraperitoneal organs. When actual lipid droplets are surrounded by fibrous tissues that calcify, ringlike calcifications, either incomplete or continuous, are noted (Figs. 5.1 and 5.2A). These may reach up to 3.5 cm in diameter. On computerized tomography (CT), the low density lipid center is easily demonstrated (Fig. 5.2B,C) and helps to differentiate this entity from pseudomyxoma peri-tonei, in which ringlike intraperitoneal calcifications may also be noted [22].

Current research centers on absorbable and nonabsorbable barriers [25-28]. Gore-Tex (polytetrafluoroethylene) is sutured in place and acts as a nonabsorbable barrier preventing adhesions from bridging from one organ to adjacent viscera [25,26]. Another approach, combining fib-rinolytic therapy with a barrier mechanism, is the infusion of methyl-cellulose mixed with hyaluronidase, has proven effective in decreasing the rate of adhesions seen at second-look procedures or at the time of stomal closures [27,28]. Sodium carboxymethylcellulose instillation has shown no deleterious effects on wound or anastomosis healing in an animal model [2].

The role of the conventional or plain film of the abdomen in small-bowel obstruction is still a controversial one. Sensitivities of 50 to 60% in cases of complete small-bowel obstruction and even lower in partial obstruction have been reported [29,30]. Other studies report sensitivities and accuracy similar to that seen with computerized tomography [31,32].

Baker and Cho have written extensively on the plain film findings of small-bowel obstruction [3]. These signs may include abnormal dilatation of the small bowel (>2.5cm), disproportionate dilatation compared with the colon, and the "stretch" sign in which air is caught between the valvulae conniventes, creating thin lucencies perpendicular to the long axis of the small-bowel loop. Radiographs utilizing a horizontal beam, either upright or decubitus films, transformed the stretch sign into the "string of pearls" sign in which small bubbles of air are caught between the valvulae at the top of fluid-filled small-bowel loops.

The upright film may also demonstrate differential air fluid levels in the small bowel. This sign of small-bowel obstruction was championed by Frimman-Dahl in his groundbreaking work [33]. However, Frimman-Dahl was commenting on dynamic fluoroscopic evaluation of the small bowel, not a single static image of the abdomen. More recent work on plain film analysis shows that differential air fluid levels do not help differentiate a small-bowel obstruction from an ileus [34,35].

Another, and very significant problem with the interpretation of the plain film of the abdomen is the reporting of the results. Many referring physicians and radiologists use the term "nonspecific bowel gas pattern" [36]. Emergency room physicians often interpret this as meaning a normal-appearing abdomen [37]. Yet radiologists attach various meanings to the term, which is used by 70% of a group of radiologists who were polled in the past decade [36]. Of these, 65% meant that the bowel gas pattern is normal or probably normal, 22% meant that at the bowel gas pattern is abnormal or normal, while only 13% meant that although the bowel gas pattern was abnormal the respondents could not determine whether an ileus or obstruction was present. Because of the

Hernia Discal
Figure 5.1. Mineral oil globulosis. Supine film of the abdomen shows small ringlike calcific densities throughout the abdomen. These represent small globules of mineral oil and their encapsulation.

Figure 5.2. Mineral oil globulosis. (A) Supine film of the abdomen of another patient reveals large masses with cyst wall calcifications in the upper abdomen. (B) CT scan on the same patient shows the thick calcified wall encompassing a mixed attenuation center. (C) Magnified view on one of these lesions demonstrates some of the low density lipid material within the pseudocyst. (Courtesy of S.R. Baker, MD, Newark, NJ)

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