CHAPTER 17 Bowel Obstruction

Ashley Steinberg, MD • Evangelia Davanos, PharmD, BCNSP, CNSC

Bowel obstruction refers to a blockage in either the small or the large bowel. When a patient presents with symptoms suggestive of bowel obstruction, it is important to determine the location of the obstruction. Based on the location, certain etiologies may be more likely. Both the history and the physical examination play essential roles in helping to determine both the location and the cause of a bowel obstruction.

ANATOMY, PHYSIOLOGY, AND PATHOLOGY

The anatomy, physiology, and pathology of a bowel obstruction depend primarily on the site of origin, namely small versus large bowel. The simplest way to determine the cause of an obstruction is to first determine—almost always radiologically—whether the obstruction originated in the small or large intestine.

Small Bowel Obstruction

The number one cause of small bowel obstructions (SBO) is adhesions. Adhesions may develop as a result of previous surgery and can form anywhere from days to years after abdominal surgery. Adhesions are fibrous bands of tissue that are usually reactive, and are developed by manipulation or inflammation of the bowel. They are akin to the “scar tissue” of the abdomen. They occasionally occur in the “virgin” abdomen (no previous history of surgery) secondary to peritonitis. Adhesions may cause obstruction if two external walls of bowel adhere to each other, and a loop of bowel wraps around or becomes lodged between the adhesion(s). There is compromised blood supply to that segment of the intestine, with resultant ischemia and necrosis. An adhesion may also act as a constrictive band on its own, limiting blood supply.

Hernias are the second most common cause of SBO and less commonly colonic obstruction. Common examples of external hernias are inguinal, paraumbilical, and ventral. Internal herniation is rare by comparison, but is an increasingly common cause of SBO, especially with the rise in bariatric surgical procedures utilizing a Roux-en-Y anastomotic technique (Blachar & Federle, 2002; Gunabushanam, Shankar, Czerniach, Kelly, & Perugini, 2009). These occur within the abdominal cavity, are usually intramesenteric, and are often symptomatically intermittent, obstructing and reducing spontaneously, making diagnosis difficult. Incarceration of a hernia is caused when the bowel becomes trapped in a hole in the muscle wall or in a natural or iatrogenic foramen. Delay in diagnosing the obstruction leads to strangulation of the bowel, which often precedes ischemic changes in the bowel wall. Necrosis of the small bowel secondary to either external or internal hernias will result if the ischemic changes are not reversed. The mortality rate associated with necrosis of the bowel and/or mesentery is very high and increases in patients with multiple medical problems (Tendler, 2003).

The inflammatory bowel diseases (IBDs), Crohn’s disease and ulcerative colitis, can also cause bowel obstruction. SBOs caused by IBD are more prevalent in younger individuals owing to the nature of these diseases. The most common site of obstruction in Crohn’s disease is the ileocecal region, because it is the narrowest segment in the entire gastrointestinal tract. The mechanism for obstruction with IBD initially involves inflammation with resultant stricture formation. In ulcerative colitis, which involves only the large bowel, chronic inflammation can lead to stricture formation with resultant obstruction (see Chapter 23, “Inflammatory Bowel Disease”).

Other less-prevalent causes of SBO include neoplasia (if malignant it is usually metastatic, as primary small bowel malignancies are rare), radiation, and mechanical obstruction secondary to a foreign body (bezoars, other ingested materials).

Large Bowel Obstruction

A volvulus, which is a twist in the colon, much like a twist in a pretzel, results in a compromise in the blood flow and ischemia. It occurs most often in the large bowel and is associated with a redundant portion of bowel, most often in the sigmoid colon and much less often in the cecum (Halabi et al., 2014). Chronic constipation and laxative abuse have been suggested as causes of the redundant sigmoid colon. Patients usually present with abdominal distention and inability to pass flatus or to have a bowel movement; they may or may not have abdominal pain. This is usually easily diagnosed by the classic “bent inner tube” or “coffee bean” sign on an abdominal x-ray, where imaging shows a distended loop of bowel folded onto itself resembling a coffee bean or inner tube on the x-ray image.

Malignant causes of intestinal obstruction are mechanical obstruction secondary to the bulkiness of a tumor within the lumen of the intestine. Larger tumors may cause obstruction in the cecum and other areas with a larger diameter. The descending colon has a narrower lumen, and malignancy in this part of the colon may present as an obstruction (see Chapter 21, “Gastroenterologic Cancers”). In a patient with no prior abdominal surgeries, malignancy/tumor should be very high on the differential diagnosis list. Treatment of the obstruction is very different in these patients. Conservative management is not the first choice, as this is usually a surgical diagnosis.

Ogilvie’s syndrome, or colonic pseudo-obstruction, is often seen in seriously ill patients, patients with neurological or psychiatric disorders, or nursing home patients who are sedentary much of the time. It lacks the mechanical aspect of a true large bowel obstruction and is therefore labeled a “pseudo-obstruction.” These patients are often managed conservatively with colon decompression.

Occasionally, a tumor can cause an obstruction by initiating an intussusception. This is most commonly seen in the small bowel and can be caused by both malignant and benign lesions. At the site of intussusception, the tumor acts as an initiator, and one portion of bowel “telescopes” over the adjacent piece of intestine. This causes edema and obstruction as well as a decrease in blood flow to the loops of intestine involved, with resultant ischemia. There are few reports in medical literature of idiopathic intussusception, in which the large bowel telescopes into itself and no pathological diagnosis is revealed postoperatively (Amoruso, D’Abbicco, Praino, Conversano, & Margari, 2013).

Less common causes of large bowel obstruction include diverticulitis with peridiverticular abscess, radiation, and IBD (namely ulcerative colitis).

Paralytic Ileus

Paralytic ileus mimics the signs and symptoms of obstruction and should always be considered when a patient presents with such symptoms. With paralytic ileus, the peristaltic function of the small and large bowel is disrupted, and the intestine dilates. Patients who present with signs and symptoms suggestive of sepsis are more than likely to have a paralytic ileus rather than an obstructive process. Other causes of a paralytic ileus include perforation, peritonitis, electrolyte abnormalities, and increased use of narcotics. Peptic ulcer disease, blunt trauma to the abdomen, and cancers with resultant perforations can all result in the development of a paralytic ileus. Another common cause for a paralytic ileus is abdominal surgery. All patients undergoing a laparotomy may have a postoperative ileus for a short period of time. This is expected and should not cause alarm. The bowel function usually returns to normal quickly, with the small intestine having return of function within 24 hours, the stomach within 48 hours, and the colon within 3 to 5 days (Colaizzo-Anas, 2007).

EPIDEMIOLOGY

Bowel obstruction is a very common etiology for a surgery admission, and specifically SBO accounts for about 12% to 16% of surgical admissions (Maung et al., 2012). SBO accounts for more than 300,000 operations annually in the United States, which translates to more than $2.3 billion in health care expenditures (Maung et al., 2012). The most common cause of bowel obstruction is the development of adhesions postoperatively. Other frequent causes are external and internal hernias, strangulation, and tumors (Gümüstas, Gümüstas, Yalçin, Savci, & Soylu, 2008). Adhesions can occur in anyone who has ever had abdominopelvic surgery. A volvulus is a less common cause of large bowel obstruction, occurring mostly in the elderly or hospitalized patients. Intussusception is an uncommon cause of obstruction in adults, accounting for approximately 1% of all obstructions (Gümüstas et al., 2008). In adults, an underlying pathology can be found in up to 80% to 90% of cases of intussusception (Gümüstas et al., 2008).

Malignant causes of bowel obstruction usually occur in the colorectal region and are most commonly secondary to adenocarcinomas. Less common causes of malignant obstruction include carcinoid tumors in the distal ileum, lymphoma (more commonly in the distal small bowel), and adenocarcinoma in the proximal small bowel.

DIAGNOSTIC CRITERIA