Applied Radiology

Dr. Behr is a Clinical Fellow, Abdominal Imaging/Nuclear Medicine, and Dr. Westphalen is an Assistant Professor of Radiology, Department of Radiology, University of California, San Francisco, CA; and Dr. Campos is the Associate Professor of Surgery, Department of Surgery, University of Wisconsin, Madison, WI.

Americans are facing a health crisis: obesity. More than 100 million people in the United States are defined as obese, 12 million of whom have extreme (formerly morbid) obesity.¹ Obesity is defined as a body mass index (BMI, calculated as weight in kilograms divided by height in square meters) >30, and extreme (morbid) obesity as a BMI >40 or BMI >35 with a significant obesity-associated comorbidity. Common serious comorbidities associated with obesity include type 2 diabetes mellitus and hypertension. These patients also have a higher risk for some types of cancer and early mortality. It is estimated that the direct and indirect costs of treating obesity and its complications exceed $75 billion per year.²

Obesity treatments, such as medications, exercise, and diet modifications, do not usually provide longstanding results; thus, bariatric surgery has become a well-accepted treatment option. The exponential increase in the number of bariatric operations performed is the result of 4 factors: the obesity epidemic, recognition of obesity as a public health problem, poor results of nonsurgical methods, and reproducible good results with surgery, including laparoscopic surgical techniques. However, bariatric surgery should be offered only after careful preoperative evaluation and counseling; it is often reserved for patients with extreme obesity and a high risk for physical disability that severely impairs quality of life.

Surgeries achieve weight loss by physically changing the patient’s upper gastrointestinal anatomy and physiology. The most common procedures used in the United States are laparoscopic gastric banding (LB, a restrictive procedure) and laparoscopic Roux-en-Y gastric bypass (RYGB, a combination of restrictive and malabsorptive procedures). In a very few centers, a procedure called the biliopancreatic diversion with duodenal switch (BPD-DS, a malabsorptive procedure) is still used. Despite the high safety profile of these procedures, with complication rates on par with laparoscopic cholecystectomy, the radiologist must be familiar with the typical postoperative appearances and be aware of potential complications.

Each procedure is prone to different complications. The most common complications of RYGB are wound infection (6% to 13% of cases) and gastrojejunal anastomotic stricture (3% to 8%). However, patients are also at risk for postoperative bleeding (1% to 4%), readmission for dehydration (1%), small-bowel obstruction (1%), enteric leak (0.3% to 5%), pulmonary embolism (0.3% to 1%), and death (0.1% to 1%).^3-8 Patients who undergo LB may develop device-related complications (10%), esophageal or gastric pouch dilation (2% to 5%), band erosion into the stomach (2%), gastric slippage (4% to 6%), pulmonary embolism (0.1%), and death (0.1% to 0.4%).⁵ While most experts consider RYGB to be a more complex procedure, the procedure has complication rates as low as LB when performed by properly trained surgeons in high-volume institutions on properly selected patients.^4,5,9-14

This article focuses on the imaging of normal postsurgical anatomy and procedure-specific complications. However, complications inherent to any surgery, such as pulmonary embolism, infection, and hemorrhage, should always be considered when evaluating these patients.

Roux-en-Y gastric bypass

Anatomy

The Roux-en-Y (RYGB) gastric bypass is the most common bariatric procedure (70%) and among the most successful (Figure 1). It is mostly a restrictive procedure, but it also has a malabsorption component, as it bypasses most of the stomach, duodenum and proximal jejunum. The procedure uses linear staplers to create a small, 20- to 30-cc gastric pouch just past the gastroesophageal junction. The gastric pouch should be completely isolated from the larger excluded stomach. The jejunum is then divided approximately 30 to 50 cm beyond the ligament of Treitz, and the distal segment of jejunum (alimentary limb) is brought up in either an antecolic (most common nowadays) or retrocolic fashion and reattached to the small gastric pouch (gastrojejunostomy). There are many techniques for the gastrojejunostomy (handsewn, linear, or circular stapler), but it is usually a small, 1- to 2-cm, end-to-side anastomosis. The excluded stomach and duodenum, along with the 50 cm length from the proximal jejunum after the ligament of Treitz (bilio-pancreatic limb), are then reattached to the gastrointestinal tract about 75 to 150 cm from the gastro-jejunostomy by a side-to-side jejunojejunal anastanomosis.

Perioperative evaluation

Although some have questioned the value of routine imaging, in many institutions an upper-gastrointestinal (UGI) fluoroscopic exam is performed 1 or 2 days postoperatively (Figure 2). The goal of this study is to assess leakage, pouch size, stoma size, pouch emptying, gastro-gastric communication, and jejunojejunal anastomosis patency. Contrast should be seen passing through both the proximal and distal anastomoses; however, it is not unusual for the pouch not to empty readily due to edema and/or a hematoma at the gastrojejunostomy. Computed tomography (CT) can also be utilized to verify proper functioning of the RYGB bypass (Figure 3). Contrast should not be identified in the excluded stomach and duodenum. Reflux of contrast into the bilio-pancreatic limb may reflect postoperative ileus or obstruction distal to the jejunojejunal anastomosis.

Although most surgeons agree that a small gastric pouch is essential for long-term success, the exact size is controversial. Nishie et al¹⁵ stated that different pouch sizes did not have any short-term effects on weight loss. However, Campos et al reviewed 361 patients and found that larger pouch size is an independent predictor of poor weight loss.¹⁶ Pouch size is difficult to quantify during the UGI examination, but a good rule of thumb is for the pouch to be no bigger than the adjacent vertebral body.

Potential complications specific to RYGB

Anastomotic or staple leaks—The perioperative mortality of RYGB should not be more than 0.3%.¹⁷ The major risk factors are anastomotic leaks with peritonitis (75%) and pulmonary embolism (25%).¹⁷ Extraluminal leak occurs in approximately 1% of cases^18-22 and can be seen anywhere along the divided GI tract, but also in the distal esophagus (Figure 4). It is important to recognize these leaks, as fever and abdominal pain may result from myriad postoperative etiologies.

Gastrogastric communication—A gastrogastric fistula is a communication between the proximal gastric pouch and the excluded stomach, anywhere along the divided segment of the stomach wall, but usually on the most superior aspect to the gastric pouch (Figure 5). It occurs in approximately 6% of cases.²³ Patients may present with epigastric pain from ulcerations along the anastomotic site. Conservative management with proton-pump inhibitors can be used, as long as symptoms resolve and weight loss is not affected; otherwise the fistula should be corrected by nonemergent surgery.

Anastomotic stricture—The surgically created gastrojejunostomy stoma usually has a diameter of approximately 1 to 2 cm, yet stenosis can occur. Patients usually present with the inability to advance diet and/or persistent vomiting. Anastomotic strictures can be divided into acute and subacute/chronic types. Early postoperative stricture is in the vast majority of cases the result of hematoma and/or edema; and it usually subsides within a week or 2. The subacute type usually presents at 3 to 4 weeks after surgery and is associated with ischemia, stomal ulcers, and fibrosis at the gastro-jejunostomy. Rarely, strictures may have a later onset, sometimes many months after surgery. Stomal stenosis occurs in about 5% of cases. Treatment with balloon dilatation by endoscopy is successful in most cases.

Other known complications—Small-bowel obstruction (SBO) occurs in approximately 1% to 4 % of cases after RYGB.^19,21,24 It can be seen early in the postoperative period, but more frequently it is seen later, once the patient has lost a significant amount of weight. Early obstructions are usually of the biliary or alimentary limb and related to postoperative edema, intra-luminal or intramural hematoma, adhesions or “kinking” at the jejunojejunal anastomosis (Figure 6). Obstruction late in the postoperative period differs in the frequency of etiology, depending on whether the patient has had open or laparoscopic RYGB. Adhesions are more often related to open RYGB and internal hernias to a laparoscopic RYGB. Internal hernias seem to occur more frequently if the alimentary limb was connected to the gastric pouch using a retrocolic route instead of an antecolic route. In a retrocolic approach, the surgeon has to create an opening in the transverse mesocolon to bring the alimentary jejunal limb to the upper abdomen. In the antecolic approach, though there is no opening in the transverse mesocolon, there is a space in between the alimentary jejunal limb and the transverse colon itself that is a potential site for an internal hernia called Petersen’s Hernia. A common site for internal hernias in both the retrocolic and antecolic approaches is the jejunojejunostomy defect.²⁵ Internal hernias should be expeditiously treated with surgery as they are commonly associated with mesenteric torsion and bowel ischemia. Other infrequent complications are intussusception,²⁶ portal and mesenteric vein thrombosis²⁷ (Figure 7), and bowel ischemia²⁸ (Figure 8), among others.

Adjustable gastric banding

Banding is one of the least invasive of the bariatric procedures; it is performed in 27% of cases. An inflatable and adjustable band is laparoscopically placed around the proximal stomach, about 4 to 5 cm below the gastroesophageal junction (Figure 9). The location of the band and size of the gastric pouch above the band can be determined intraoperatively by using a balloon placed orally and inflated just past the GE junction. The inner size of the band “stoma” is adjusted via a subcutaneous port connected to the band by tubing and located in the subcutaneous tissues. Unlike the case in RYGB, imaging is not routinely performed postoperatively in banding. It is reserved instead for patients with symptoms of obstruction or poor weight loss. Initial fluoroscopic images look at the position of the band’s opening, which should be at 45 to 90 degrees toward the right shoulder (Figure 10). The band is examined in the right posterior oblique and anterior-posterior views to assess the pouch and stoma size. The usual stomal diameter should be between 5 and 10 mm and show adequate emptying.

Complications

The 2 most common complications related to gastric banding include pouch enlargement and band/gastric slippage. The literature reports the incidence of band/gastric slippage to be 1% and 22%.^29-34 The position of the band in relation to the gastric pouch is an important determinant of the cause of pouch dilation, as there may be either an anterior or posterior gastric wall migration through the band. Patients usually present with acute symptoms and require emergent surgical intervention.

Conversely, pouch enlargement is considered when there is nonobstructive dilation of the pouch with or without changes in the angle of the band (Figure 11). This is considered a chronic complication and surgery is reserved when conservative measures fail.

Other complications include band overinflation, band erosion into the stomach, and port- and device-related infection/malfunction, among others. Overinflation of the band can result in obstructive symptoms with pseudoachalasia seen on UGI series (Figure 12). The reported incidence of band erosion varies between 0% and 11% and may be related to gastric wall injury during band placement or tight anterior fixation.³⁵ On a UGI fluoroscopic exam, band erosion is evident by the presence of 2 channels of oral contrast, one through the band and another around it.

Port- and device-related complications include infection and device breakdown. Infection can occur anywhere along the device or intra-abdominally and is best evaluated by computed tomography (CT). Port breakdown can be seen as discontinuous tubing on plain radiograph.

Sleeve gastrectomy

Anatomy

Sleeve gastrectomy, performed in only 3% of cases, involves surgical resection of the greater curvature of the body and fundus of the stomach to leave only about 15% of the original gastric volume (60 to 100 cc), thus creating a restrictive physiology (Figures 13 and 14). It is often performed on extremely obese patients where the risks of a RGYB or duodenal switch (described below) are felt to be too high. While in many centers it is used as a stand-alone technique, it may be an element of a 2-part procedure in which patients first undergo sleeve gastrectomy and later convert to an RYGB or duodenal switch if the desired weight loss is not achieved.

Complications

Major complications associated with sleeve gastrectomy include leak, hemorrhage, infection, and sleeve stricture/hematoma. Since sleeve gastrectomy is a less common procedure, there is limited data concerning complication rates. In a retrospective study by The Cleveland Clinic Florida,³⁶ there was only one instance of each major complication out of 137 cases.

On the fluoroscopic UGI exam, close attention should be paid to the gastric cut line for leak. Leak can occur anywhere along the surgical line and may be seen in more than one location (Figure 15). Sleeve stricture is seen in the chronic setting and is usually treated with balloon dilation (Figure 16). Sleeve hematoma/edema is seen immediately after surgery and is characterized on the fluoroscopic study as obstruction of contrast through the stomach.

Biliopancreatic diversion with duodenal switch

Anatomy

This procedure involves creation of both restrictive (sleeve gastrectomy) and malabsorption (duodenal switch) physiologies (Figure 17). The duodenal switch consists of the division of the small bowel at 2 points: (1) the duodenum, just distal to the pylorus, and (2) the midjejunum (Figure 18). The most distal jejunum and ileal loop are brought up to reconnect to the stomach and duodenum, thus bypassing the biliary and pancreatic drainage. The excluded aspect of the duodenum and jejunum is reattached to the distal portion of the small bowel loop about 150 cm from the ileocecal valve to allow drainage of biliary and pancreatic fluid. Unlike the classic RYGB, the pylorus and first portion of the duodenum are preserved.

Complications

Similar to the RYGB, both the proximal and distal aspects of the anastomoses should be evaluated for leaks and passage of oral contrast during a postoperative fluoroscopic exam. Careful evaluation of sleeve gastrectomy and the duodenojejunal anastomoses should be performed for anastomotic leak or delayed passage, which may be related to edema and/or hematoma. Bowel obstruction is the most common complication, seen in approximately 16% of the cases in one series.³⁷ It is most commonly seen at the proximal anastomosis and often resolves spontaneously with bowel rest. Persistent or worsening symptoms should trigger further evaluation for assessment of possible distal high-grade small-bowel obstructions that may require surgical intervention (Figure 19). Anastomotic leak is the second most common complication, reported to occur in approximately 5% of patients.^37,38 In one series, the leak was reported to occur along the gastrectomy line in 70% of cases.³⁷

Conclusion

Obesity is a significant public health problem that is on the rise; as more obese children become obese adults, the diseases associated with it will increase and more patients are likely to pursue bariatric surgery. It is important that radiologists become active members of the multidisciplinary team that manages these patients. And, for adequate treatment and improved outcomes, it is crucial to have an understanding of the normal postsurgical anatomy and procedure-specific complications.

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