Sara E. Clark
Lillian G. Dawes
Presentation
A 78-year-old man with a history of hypertension, diabetes, and coronary artery disease presents with a 2-day history of diffuse abdominal pain, nausea, and several episodes of emesis. He has not been able to tolerate any oral intake. His bowel movements have been normal up until the previous day when he had a liquid bowel movement. He has not had any flatus for at least 2 days. On physical exam, his abdomen is distended and tympanitic, and he has diffuse abdominal tenderness without guarding. He has a midline abdominal scar and a right subcostal scar. He has had multiple abdominal surgeries including an open aortic aneurysm repair, a cholecystectomy, and a right hemicolectomy for colon cancer.
Differential Diagnosis
The constellation of abdominal pain, nausea, vomiting, and decreased flatus/bowel movements is nonspecific but may represent a small bowel obstruction. A mechanical small bowel obstruction results when there is blockage of the lumen of the small bowel. Neurogenic causes of bowel dilatation such as a paralytic ileus can cause distention due to a lack of bowel motility. In this patient with a history of multiple abdominal surgeries, a mechanical bowel obstruction is a concern.
Adhesions from prior surgery are the most common cause of a mechanical small bowel obstruction, accounting for up to two-thirds of all bowel obstructions. Incarcerated hernias and neoplasms are the next most common cause. Crohn’s disease or inflammatory bowel disease can cause a mechanical obstruction in diseased segments of bowel. Less common causes of a small bowel obstruction include volvulus, bezoar, gallstone ileus, or intussusception (Table 1).
TABLE 1. Causes of Small Bowel Obstruction
Small bowel neoplasms can progressively occlude the lumen or serve as a leading point for intussusception. Symptoms may be intermittent as the onset is slow, and patients usually have chronic anemia. Extrinsic neoplasms may entrap loops or cause external compression. Comprehensive physical exam looking for a hernia is a must—patients with incarcerated hernias can present with small bowel obstruction and bowel compromise. Internal hernias, which may not be apparent on physical examination, can occur through the obturator foramen, acquired adhesive defects or lateral to surgical defects (e.g., parastomal hernias). Volvulus results from rotation of bowel loops from a fixed point due to congenital anomalies or acquired adhesions. Patients with volvulus will usually have acute onset of symptoms and strangulation often occurs rapidly. Malrotation of the intestine is a cause of volvulus in children but is very rare in adults. Other rare causes of obstruction include foreign bodies (bezoar, ingested), gallstone ileus (passage of large stone through cholecystenteric fistula), and inflammatory bowel disease (secondary to inflammation and fibrosis of small bowel wall).
Workup
The patient undergoes further evaluation with laboratory workup significant for a mild leukocytosis, hypokalemia and hypochloremia. He has no evidence of acidosis on his initial labs and his creatinine is normal. His acute abdominal series shows air-fluid levels and dilated loops of small bowel with no evidence of free air. He undergoes computed tomography (CT) scan of the abdomen and pelvis showing large fluid filled stomach, dilated loops of small bowel with possible transition point in the pelvis. His distal ileum and colon are decompressed (Figure 1).
FIGURE 1 • Dilated small bowel is evident as is a collapsed colon. A transition point was found to be in the pelvis.
When presented with this clinical scenario, several things need to be considered.
1. Is this a mechanical small bowel obstruction or is this an ileus?
2. If a mechanical bowel obstruction, is the blockage partial or complete?
3. Is this a simple or strangulating obstruction?
Workup for small bowel obstruction to help answer these questions should include a combination of radiographic and laboratory investigations. Initially an acute abdominal series should be performed to look for free air, dilated small bowel or stomach, air-fluid levels in small bowel, and presence or absence of air/fluid in colon. A CT scan is often performed as a second evaluation to look at integrity of small bowel, and assess for the presence or absence of signs of bowel ischemia including pneumatosis, complete obstruction with a transition point, presence of small bowel volvulus, intussusception, hernias, or neoplasm.
Laboratory evaluation may reveal leukocytosis, anemia if there is a bleeding mass or elevated hematocrit if the patient is volume contracted. Electrolyte abnormalities may be present because of gastric losses and creatinine may be elevated if the patient is dehydrated. If there is significant bowel compromise, the lactic acid may be elevated.
An ileus can at times mimic a small bowel obstruction. Conditions that may cause an ileus are listed in Table 2. An ileus tends to affect the entire gastrointestinal tract and there should not be a transition point on CT scan. With an ileus, the large bowel is usually dilated as well as the small bowel.
TABLE 2. Causes of Lleus
Diagnosis and Treatment
In the patient from our scenario, a nasogastric tube (NGT) is placed and 1 L of bilious material is immediately drained. He has partial resolution of his abdominal pain following placement. Conservative treatment is elected and he is placed on intravenous fluids and kept NPO.
Typically, if the patient is thought to have a partial small bowel obstruction secondary to adhesions, a trial of conservative (nonsurgical) management is pursued initially. This includes NGT decompression, bowel rest, intravenous fluid resuscitation, and correction of electrolyte abnormalities. If the patient fails to improve clinically over 48 hours, it is likely that the patient requires an operation.
The challenge with treating a small bowel obstruction is deciding when to operate. Sixty-five to eighty-five percent of partial small bowel obstructions will resolve with conservative management. The old dictum of “never let the sun rise nor set on a bowel obstruction” is still true for complete small bowel obstruction, large bowel obstruction, or when there is concern of strangulation or bowel compromise. Delay in surgical therapy in these cases can lead to irreversible bowel ischemia. However, proceeding with immediate operation in patients with a partial small bowel obstruction may lead to an unnecessary intervention.
Indications for immediate operation include peritonitis, sepsis, hemodynamic instability, acidosis, or radiographic evidence of small bowel compromise, such as pneumatosis, perforation, signs of bowel ischemia, internal hernia, or volvulus. Physical findings suggesting the need for early operation are fever, tachycardia, and pain out of proportion to physical findings. CT scanning provides additional useful information. Although the presence of a transition point on CT scan has failed to reliably predict the need for operation, there are some findings that should alert the surgeon that earlier surgery is warranted. Bowel compromise is associated with intraperitoneal fluid and decreased enhancement of the bowel wall. Pneumatosis and portal venous air can also be seen with bowel ischemia. The presence of a “whirl sign” is concerning for a volvulus or internal hernia (Figure 2).
FIGURE 2 • In the center of this CT scan image, there are mesenteric vessels that move in a circular pattern to the left. This is known as a “swirl sign” and is concerning for a potential volvulus. At operation, a loop of bowel twisted around an internal hernia was found. Untwisting of the mesentery restored blood flow and relieved the obstruction.
One special case worth mentioning is postbariatric surgery patients presenting with bowel obstruction. Because of the mesenteric defects from the gastrojejunostomy (often antecolic) and the jejunojejunostomy, bariatric surgery patients are at very high risk for internal hernias. If a large amount of small bowel is involved, these patients can have catastrophic midgut volvulus, even leading to short gut syndrome. In these patients, the surgeon should look carefully for evidence of internal hernia or volvulus (e.g., mesenteric “swirl” sign on CT scan) and promptly explore patients with any suggestion of an internal hernia.
Small bowel obstruction due to intussusception in adults is often due to a tumor of the small bowel that serves as a lead point. The hallmark of intussusception on CT scan is the presence of a “target sign.” A target sign on CT scan may at times be seen with normal peristalsis. However, when evidence of intussusceptions on CT scan is associated with a bowel obstruction or a mass (Figure 3), operative intervention and small bowel resection with removal of the abnormal segment are indicated.
FIGURE 3 • Small bowel intussusception is demonstrated here with a mass as the lead point. A spindle cell tumor was found at operation causing the intussusception and bowel obstruction.
Surgical Approach
The usual approach to patients with bowel obstruction is through a midline incision (Table 3). Entering the abdomen away from a prior incision may be beneficial if possible (e.g., entering the midline just above or below a prior laparotomy site). The abdomen is entered carefully with sharp dissection in order to avoid bowel injury. The bowel is freed from the anterior abdominal wall and is carefully inspected. All adhesions that could possibly cause obstruction are taken down and the small bowel is inspected in its entirety. It is important to try and identify the point of obstruction, or “transition point” where the bowel goes from dilated to decompressed. It is much more satisfying when the causative adhesions are lysed. However, oftentimes the transition point will not be obvious. For very dense adhesions, dissection with a scalpel is often useful. Any areas of enterotomy can be repaired if the bowel is viable. If it is not viable or the damage is extensive, a small bowel resection must be performed. In order to determine viability you must assess the vascular supply of the small bowel. This can be done by standard clinical judgment (i.e., color and appearance), Doppler ultrasound of mesentery, and, in rare cases, fluorescein dye evaluation.
TABLE 3. Key Technical Steps and Potential Pitfalls
The less common causes of small bowel obstruction are usually apparent on inspection of the small bowel. When the small bowel is inspected, any volvulus will be reduced. Intussusception can be reduced by gentle traction, and any masses/neoplasms can be resected. With all circumstances, bowel viability must be assessed. Hernias can be approached through an incision over the hernia (umbilical, inguinal) with low threshold for conversion to open laparotomy if there is concern for bowel strangulation to assess intra-abdominal bowel. For hernias where incarcerated and strangulated bowel is suspected, one should not attempt reduction of the hernia until operative intervention to allow inspection of the involved loop of bowel.
During the operation, it is essential to be aware of any enterotomies and spillage from small bowel. Missed enterotomies and spillage can lead to postoperative intra-abdominal abscess, sepsis, and other morbidities.
Special Intraoperative Considerations
During exploration for small bowel resection, it is important to be aware of findings of Crohn’s disease. Findings of Crohn’s disease at laparotomy include fibrotic strictures, usually short and multiple with “skip” areas of normal interposed bowel. There is often “creeping fat” onto the small bowel. Strictures from Crohn’s disease can cause obstruction and abdominal pain and often are managed with strictureplasty rather than resection to avoid excessive loss of small bowel and the development of short bowel syndrome.
If an obstructing stone is found in the ileum just proximal to the ileocecal valve, a “gallstone ileus” is likely the cause. Inspection of the gallbladder is warranted to investigate the possibility of a cholecystoenteric fistula. Often this is diagnosed preoperatively due to the presence of air in the bile ducts without any history of iatrogenic or surgical intervention. Inspection of the entire small bowel for multiple stones should be performed as there can be more than one stone present. Relieving the obstruction by performing an enterotomy with removal of the stone is all that is usually required for treatment. Repair of the cholecystoenteric fistula is usually not necessary but can be considered in a low-risk patient.
Postoperative Management
Postoperatively, the NGT should be continued until there is return of bowel function with flatus. Care should be taken to maintain the patient’s volume status and all electrolyte abnormalities should be aggressively corrected. If the patient has been in a fasted state for a long period of time, consideration should be given to starting parenteral nutrition. Patients with chronic obstructive problems may have prolonged ileus following lysis of adhesions. Nutritional status is important to prevent complications including wound infection and dehiscence.
Case Conclusion
Two days after admission, our patient still has output from his NGT of 600 mL per shift and he has not passed any flatus. He is taken to surgery where he is found to have dense adhesions with a transition point in the ileum. The adhesions are taken down and postoperatively he has an uneventful course.
TAKE HOME POINTS
· Complete bowel obstructions or when bowel ischemia is suspected requires early surgical intervention
· Partial bowel obstructions can be initially conservatively managed with NGT decompression, intravenous fluids, and close observation.
· CT scanning can be helpful in distinguishing between ileus and obstruction (i.e., determining the presence of a “transition point” and identifying complications that require immediate operative intervention, e.g., internal hernia, volvulus, or ischemic bowel).
· Careful inspection for potential enterotomy will help avoid the serious complication of postoperative small bowel fistula.
· Evaluation of the bowel’s blood supply is important. Resect if ischemic, or if in doubt, consider a “second look” operation.
· Preserve as much small bowel as possible and if significant amount of small bowel needs to be resected, measure the amount of remaining small bowel.
SUGGESTED READINGS
Colon MJ, Telem DA, Wong D, et al. The relevance of transition zones on computed tomography in the management of small bowel obstruction. Surgery. 2010;147(3):373–377.
Diaz JJ Jr, Bokhari F, Mowery NT, et al. Guidelines for management of small bowel obstruction. J Trauma. 2008;64(6):1651–1664.
Kendrick ML. Partial small bowel obstruction: clinical issues and recent technical advances. Abdom Imaging. 2009; 34:329–334.
O’Day BJ, Ridgway PF, Keenan N, et al. Detected peritoneal fluid in small bowel obstruction is associated with the need for surgical intervention. Can J Surg. 2009;52(3):201–206.
Olasky J, Moazzez A, Barrera K, et al. In the era of routine use of CT scan for acute abdominal pain, should all adults with small bowel intussusceptions undergo surgery? Am Surg. 2009;75(10):958–961.
Zielinski MD, Eiken PW, Bannon MP, et al. Small bowel obstruction-who needs an operation? A multivariate prediction model. World J Surg. 2010;34(5):910–929.