49 ACUTE LARGE BOWEL OBSTRUCTION
Elizabeth C. Brew M.D.

1. What are the mechanical causes of large bowel obstruction?

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The three most common mechanical causes are carcinoma (50%), volvulus (15%), and diverticular disease (10%). Extrinsic compression from metastatic carcinoma is another cause of obstruction. Less frequent causes include stricture, hernia, intussusception, benign tumor, and fecal impaction.

2. How is the diagnosis made?

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1. The patient complains of crampy abdominal pain and bloating. Nausea and vomiting occur later in large bowel obstruction and may be feculent. An acute onset of symptoms is more consistent with volvulus compared with the gradual development of obstructive complaints from patients with colon carcinoma.
2. Physical examination reveals abdominal distention and high-pitched bowel sounds. Rectal examination may reveal an obstructing rectal cancer or evidence of fecal impaction. Absence of bowel sounds and localized tenderness may be signs of peritonitis. Progression of symptoms accompanied by a high fever or tachycardia requires immediate operative attention.
3. Flat and upright abdominal radiographs reveal dilated colon proximal to the obstruction. An upright chest radiograph may show free air under the diaphragm if a perforation has occurred.

3. How is the diagnosis confirmed?

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A contrast enema (barium or water-soluble contrast) is necessary to delineate the level and nature of an obstruction. A volvulus can be identified by a “bird’s beak” narrowing at the neck of the volvulus. Sigmoidoscopy or colonoscopy is an essential part of the evaluation; it allows visualization of the colon and may be therapeutic in the case of a sigmoid volvulus.

4. What is the role of computed tomography (CT) scanning in the diagnosis of large bowel obstruction?

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CT scans may be valuable in distinguishing between mechanical obstruction or pseudo-obstruction. It can help with the diagnosis of diverticulitis or colon carcinoma. However, plain radiographs, colonoscopy, and physical examination exceed the benefits of CT scanning in the evaluation of large bowel obstruction.

5. Why is tenderness in the right lower quadrant (RLQ) important?

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The cecum is the area that is most likely to perforate. When the cecum reaches 15 cm at its widest diameter, the tension on the wall is so great that decompression is essential to prevent perforation. The larger diameter of the cecum causes more tension of the cecal wall at the same intraluminal pressure (law of Laplace). The other area at risk for perforation is the site of a primary colon cancer.

6. Where is the obstructing cancer usually located?

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Most obstructing colorectal carcinomas occur in the splenic flexure, descending colon, or hepatic flexure. In contrast, lesions of the right colon usually present with occult bleeding. Cecal and rectal cancers are uncommon causes of obstruction.

KEY POINTS: CAUSES OF LARGE BOWEL OBSTRUCTION

1. Carcinoma: most common cause: 50%
2. Volvulus: 15%
3. Diverticular disease: 10%
4. Stricture, hernia, intussusception, fecal impaction: 25%

7. What is a volvulus? Where is it located?

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A volvulus is an abnormal rotation of the colon on an axis formed by its mesentery and occurs either in the sigmoid colon (75%) or cecum (25%). Sigmoid volvulus occurs in an older population when chronic constipation causes the sigmoid colon to elongate and become redundant. Cecal volvulus requires a hypermobile cecum as a result of incomplete embryologic fixation of the ascending colon.

8. When is surgery indicated?

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Surgery is performed early in colon obstruction. Urgent laparotomy is necessary in patients with suspected perforation or ischemia. Danger signs are quiet abdomen, RLQ tenderness, and increasing pain. The patient’s cardiopulmonary status should be assessed and optimized preoperatively. It is essential to correct dehydration and administer perioperative antibiotics. Marking of possible stoma sites and deep venous thrombosis prophylaxis are other important preoperative considerations.

9. Which operation should be performed for a large bowel obstruction?

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The traditional procedure for a large bowel obstruction has been a decompressing colostomy. However, careful assessment of the patient’s condition, viability of the bowel, location of the obstruction, and absence of intra-abdominal contamination often allow resection with or without a primary anastomosis. In fact, an initial diverting colostomy has not been shown to have any survival advantage and incurs the risk of further surgeries.
An obstructing carcinoma may be resected satisfactorily under emergency conditions in 90% of patients. Carcinomas of the right and transverse colon (proximal to the splenic flexure) are routinely treated with resection and primary anastomosis. Recently, obstructing cancers of the descending colon have been treated either with resection and colostomy or intraoperative lavage followed by resection and primary anastomosis. Techniques for nonoperative decompression of the colon, such as balloon dilation, laser therapy, and stent placement, are under investigation. Theoretically, these techniques will allow palliation, bowel preparation, and elective colon resection.
A volvulus should be reduced and resected. Reduction of a sigmoid volvulus can be achieved nonoperatively by sigmoidoscopy or hydrostatic decompression with a contrast enema. The recurrence rate of volvulus after simple nonoperative reduction is 75%. Surgical therapy includes detorsion with colopexy or sigmoid colectomy. Cecal volvulus can be treated similarly with nonoperative decompression, cecopexy, or surgical resection.
The optimal treatment of diverticular disease is initial bowel rest; intravenous antibiotics; and percutaneous abscess drainage, if necessary. Colon resection and primary anastomosis can be performed after adequate bowel preparation.

10. What are the nonmechanical causes of large bowel obstruction?

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Paralytic ileus (i.e., colonic pseudoobstruction) or toxic megacolon.

11. What is Ogilvie’s syndrome?

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Ogilvie’s syndrome is an acute paralytic (adynamic) ileus or pseudoobstruction (i.e., enormous dilation of the colon without a mechanical distal obstructing lesion). Patients present with a massively dilated abdomen and a small amount of pain. Nonoperative management, including bowel rest, intravenous fluids, and gentle enemas, is the therapy of choice. Gastrografin enema or colonoscopy is diagnostic and therapeutic. Neostigmine is another treatment modality in patients with colons > 10 cm in diameter.

12. What is toxic megacolon?

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Toxic megacolon is dilatation of the entire colon secondary to acute inflammatory bowel disease. The disease is manifested by acute onset of abdominal pain, distention, and sepsis. Initial therapy includes intravenous fluid resuscitation, nasogastric decompression, and broad-spectrum antibiotics. If symptoms do not resolve within a few hours, the patient requires an operation to avoid perforation. Surgical therapy most often consists of an emergency abdominal colectomy with formation of an ileostomy.

References
WEB SITE
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BIBLIOGRAPHY
1. Adler DG, Baron TH: Endoscopic palliation of colorectal cancer. Hematol Oncol Clin North Am 16:1015-1029, 2002. Medline Similar articles
2. Dauphine CE, Tan P, Beart RW Jr, et al: Placement of self-expanding metal stents for acute malignant large-bowel obstruction: A collective review. Ann Surg Oncol 9:574-579, 2002. Medline Similar articles Full article
3. Frager D: Intestional obstruction: Role of CT. Gastroenterol Clin North Am 31:777-799, 2002. Medline Similar articles
4. Lopez-Kostner F, Hool GR, Lavery IC: Management and causes of acute large-bowel obstruction. Surg Clin North Am 77:1265-1290, 1997. Medline Similar articles
5. Murray JJ, Schoetz DJ, Coller JA, et al: Intraoperative colonic lavage and primary anastomosis in nonelective colon resection. Dis Colon Rectum 34:527-531, 1991.
6. Paran H, Silverberg D, Mayo A: Treatment of acute colonic pseudo-obstruction with neostigmine. J Am Coll Surg 190(3):315-318, 2000.
7. Tan SG, Nambiar R, Rauff A, et al: Primary resection and anastomosis in obstructed descending colon due to cancer. Arch Surg 126:748-751, 1991.