Large Bowel Obstruction

Introduction

A large bowel obstruction results from a narrowing of the colorectal lumen that restricts passage of gas and stool. It is a relatively common surgical emergency. Because the condition may be the result of many combinations of causes, locations, and settings, each case is unique, making the choice of treatment challenging.

The most common cause of large bowel obstruction is colorectal adenocarcinoma, which accounts for more than 50% of cases. Most obstructions occur on the left side of the colon because the lumen is more narrow there and the stool is more solid. The age at presentation parallels that of colorectal cancer, with most patients in the seventh decade of life. Other causes of large bowel obstruction include carcinoma of noncolorectal origin, diverticulitis, volvulus, and inflammatory bowel disease ( Box 51-1 ). Iatrogenic causes of obstruction are the ischemia that may follow surgery, an anastomotic stricture, and radiation. A number of attempts have been made to classify large bowel obstruction, but the aim of treatment in each patient is to safely relieve the obstruction while attempting to preserve normal bowel function. Urgent surgery is often performed under suboptimal conditions and includes a bowel resection and then creation of either a temporary or permanent stoma. Newer techniques, including temporary placement of an endoluminal stent, have permitted conversion of an emergency procedure into an elective operation, lowering risks and enhancing recovery. This delay or bridge may be critical for patient stabilization and optimization, delivery of neoadjuvant therapies, and minimizing the need for a stoma.

Clinical and Diagnostic Evaluation

Symptoms of a large bowel obstruction range from mild to severe depending on the degree of obstruction and the length of time it has been present. Most patients first note a change in caliber or a decrease in the volume of stool. They may report constipation. Abdominal distension, associated with bloating and cramping abdominal pain, is a sign of progressive obstruction. As the obstruction worsens, patients become reluctant to eat or drink and are prone to dehydration. In extreme cases, patients may present with peritonitis and/or hemodynamic collapse from colonic ischemia or perforation. Patients presenting with a more chronic obstruction often have weight loss and experience malnutrition.

The goal of the initial evaluation should be to differentiate a complete obstruction with possible ischemia and impending perforation from a stable, partial obstruction. A complete history and physical examination should be performed, including a review of prior radiographic studies and endoscopic procedures, including water-soluble or barium enema studies, computed tomography (CT) scans of the abdomen and pelvis, flexible sigmoidoscopy, and colonoscopy.

The history can identify any potential precipitating factors, such as abdominal surgery, constipation, bowel obstruction, or specific conditions such as colorectal neoplasia, diverticulitis, and inflammatory bowel disease. A detailed history of changing bowel habits helps assess the acuity of the presentation, and the ability to pass gas means that the presentation is likely not urgent. Rectal bleeding is an important clue that may indicate cancer. A physical examination should focus on vital signs, the general appearance of the patient, and a careful abdominal examination. Inspection may reveal distension, and percussion confirms tympani. Distal colonic obstruction causes the transverse colon to distend, which is obvious in slim patients. Volvulus can produce massive distension, and tenderness over the colon is concerning. A thorough rectal examination is performed. In the absence of peritonitis, abdominal imaging should be performed, and in some cases, more than one imaging study may be required. In reality, many patients presenting via the emergency department have already had a CT scan of the abdomen and pelvis, but a plain abdominal radiograph can be performed quickly, is inexpensive, can usually differentiate large bowel from small bowel obstruction, may demonstrate free air, and can suggest a specific diagnosis such as volvulus. It will show the diameter of the cecum, which is important because a large cecal diameter is associated with preferentially increased wall tension for a given intraluminal pressure. Cecal dilatation above 9 cm carries an increased risk of perforation and death. Although such information will assist in triaging and expediting care, plain films may not confirm a specific diagnosis, and thus more testing may be required. A water-soluble contrast enema study, which can be performed relatively quickly and is inexpensive, is effective in locating the site and cause of obstruction, especially distal obstruction. It also can exclude nonanatomic obstructions such as colonic pseudo-obstruction. In fact, only 60% to 63% of mechanical obstructions suggested by plain radiographs are confirmed by a water-soluble enema. Limitations of water-soluble contrast enemas are that they miss small nonobstructing lesions and provide limited or no information about the bowel proximal to the level of obstruction ( Fig. 51-1 ).

In stable patients, a CT scan can provide more information than either plain films or a contrast enema. CT scans can confirm the diagnosis of large bowel obstruction and pseudo-obstruction in more than 90% of patients. Furthermore, a CT scan may identify the location and length of the stricture, as well as evidence of inflammation/abscess, local visceral invasion, and the potential cause. CT also excludes or confirms the presence or absence of metastases and carcinomatosis, and it provides information about the more proximal large and small bowel. CT colonography could also play a role in evaluating patients whose preoperative colonoscopy was incomplete by assisting in the detection of proximal synchronous colon cancers. This information could alter surgical management. However, CT colonography is most accurate after full colonic preparation, and thus its application is often limited in these cases.

Endoscopy is risky in patients with an obstruction because air insufflation during the procedure can result in worsening colonic distension above the blockage. For a distal obstruction, endoscopy can provide an accurate and histologic diagnosis. It should be performed with gentle carbon dioxide insufflation instead of air to reduce the risk of barotrauma.