Patients with morbid obesity provide a special challenge for the diagnostic radiologist. Large size, decreased mobility, and variable postoperative anatomy make imaging procedures more difficult to perform and interpret. Tailored protocols and a good knowledge of surgical anatomy and complications are required to achieve optimal results in the bariatric patient.

Indications for surgery

Five percent of males and seven percent of females in the United States are morbidly obese, weighing more than one hundred pounds over ideal body weight.1 Medical complications of severe obesity include coronary artery disease, heart failure, respiratory insufficiency, diabetes, hypertension, venous stasis disease, and degenerative arthritis.2 The mortality rate is 11 times higher in the morbidly obese than in non-obese persons of the same age and sex.3 Medical and dietary treatments fail to achieve a sustained weight loss, making surgery the only viable treatment option in most of these patients.

Bariatric surgery for weight reduction is considered in patients whose body mass index (BMI, kg/m2) exceeds 40 (100 pounds over or 160% of ideal weight). Surgery is also recommended in patients with a BMI of 35 to 40 who have high-risk complications, such as cardiopulmonary disease, sleep apnea, uncontrolled diabetes, and hypertension.2,4 The goal of surgery is to produce sufficient weight loss to reduce medical complications, not necessarily to achieve an ideal body weight.5 Psychological and dietary counseling are an integral part of bariatric treatment.

Overview of surgical techniques

Surgical approaches to weight reduction have evolved over the last 30 years based on three concepts: 1) malabsorption of nutrients due to bypass of a portion of intestine, as in jejunoileal bypass (JIB); 2) mechanical restriction of caloric intake, exemplified by vertical banded gastroplasty (VBG); and 3) a combination of mechanical restriction and malabsorption, typified by the Roux-en-Y gastric bypass (RYGB).6

A variety of other bariatric techniques exist, including those that have been discontinued (gastric wrapping, intragastric balloons, horizontal gastroplasty)5 and others which are preferred by fewer surgeons (pancreaticobiliary bypass,7 long limb gastric bypass,8 or combined VBG/RYGB).6 The newest methods use laparoscopic techniques, including placement of a restrictive gastric band, which is adjustable, using fluoroscopic guidance.9 It is best to become familiar with the techniques used by the surgeons who refer to your radiology practice.

This review will focus on JIB, VBG, and RYGB because they account for the majority of bariatric surgeries performed to date and are most likely to be encountered in a general radiology practice.

Jejunoileal bypass (JIB)

JIB was the first popular bariatric surgery, performed in over 100,000 patients from 1954 until the mid-1970s.1 In this procedure, the proximal jejunum was divided 30 cm from the ligament of Treitz and anastomosed to the distal ileum 10 cm from the ileocecal valve.10 The long, defunctionalized segment of jejunum and ileum was left as a blind limb or anastomosed to the colon. Weight loss from malabsorption after JIB was dramatic, but late metabolic complications occurred in 50 to 80% of patients, necessitating takedown surgery in one-third.1 Although JIB surgery has been abandoned, a large number of patients still have an intact bypass and may be referred for imaging of complications or prior to JIB takedown.

Fluoroscopy in JIB shows rapid transit of contrast from the proximal jejunum to the anastomosis with the distal ileum (figure lA). The functional bowel segment may be dilated with thickened folds to compensate for malabsorption (figure lB). When the blind limb is anastomosed to the colon, it may be opacified during a barium enema. CT can be used to image the bypassed bowel segments.

Roux-en-Y gastric bypass (RYGB)

Gastric bypass replaced JIB and has a number of technical variations. Staple lines are placed obliquely in the proximal stomach to separate a 10- to 15-cc proximal gastric pouch from the bypassed distal stomach. This is achieved by stapling alone (gastric bypass in continuity, figure 2A) or by stapling and transection of the stomach (divided or isolated gastric bypass, figure 2B).11 The proximal pouch is drained by a gastrojejunostomy with Roux-en-Y jejunal anastomosis to reduce bile reflux gastritis. The small proximal gastric pouch and 10- to 11-mm outflow channel restrict food intake, and malabsorption occurs due to bypass of the stomach, duodenum, and a variable length of jejunum.6 Dumping syndrome leads to avoidance of dairy products and sweets, including ice cream.12 RYGB produces better sustained weight reduction than VBG and is currently preferred by many surgeons.5,6,12

Scout films will show oblique or mixed gastric staple lines and a staple line at the Roux-en-Y anastomosis in the left mid-abdomen. At fluoroscopy, oral contrast traverses the esophagus into a small proximal gastric pouch and exits the gastrojejunostomy (figure 2C). The distal stomach does not opacify when the staple line is intact (figure 2D). Retrograde filling of the Roux-en-Y limb can occur later in the examination, opacifying the Roux limb and duodenum and refluxing into the bypassed distal stomach, though the latter is rare.

CT after RYGB shows the proximal gastric pouch superomedially and gastrojejunostomy anteriorly, with no oral contrast in the bypassed distal stomach (figure 2E).

Vertical banded gastroplasty (VBG)

VBG was introduced in 1980 and has been the most widely used gastric restrictive surgery.12 Vertical staples are placed along the lesser curvature of the stomach to create a 10- to 15-cc proximal gastric pouch with a 10- to 11-mm outflow tract. The outflow channel is reinforced by non-opaque marlex mesh through a gastric window2 or an opaque silastic ring13 (figure 3A). Intake of a small volume of food into the proximal pouch triggers early satiety, and weight loss is due to decreased caloric intake. VBG is proposed as a simpler bariatric procedure with a lower complication rate than gastric bypass,2 but it is less successful at producing sustained weight loss.5,12

Scout films show a vertical staple line, with or without an opaque ring. In fluoroscopy, contrast traverses the small proximal pouch along the lesser curvature and exits through a single outflow channel to opacify the distal stomach (figures 3B, 3C). CT shows a staple line with oral contrast in both the proximal pouch and distal stomach (figure 3D).

Practical tips for imaging the bariatric patient

Fluoroscopy/radiography-Fluoroscopy is the best way to define surgical anatomy, leaks, staple line dehiscence, and pouch obstruction.1,14 Contrast studies complement endoscopy, which has greater sensitivity for diagnosis of gastritis and ulcers.1 The following tips are suggested for fluoroscopic examinations:

1) Obtain a good patient history. Date and type of surgery and current patient complaints influence how the study is performed (table 1).

2) Evaluate staple lines with a plain radiograph before giving oral contrast. The configuration of the staple line determines the optimal patient position for demonstrating anatomy:15 (a) Vertical staples = VBG, best shown in the right posterior oblique position, (b) horizontal or mixed staple line = horizontal gastroplasty or gastric bypass, best shown in the left posterior oblique (LPO) position.

3) Study the stomach first! The first swallow of contrast is often key to defining anatomy, presence of staple line dehiscence, and size of the gastric outlet.14 Take immediate spot images to document the proximal pouch and outflow channel. The esophagus can be evaluated after gastric anatomy is defined.

4) For early complications (e.g., postoperative leak, obstruction) use water soluble contrast and videofluoroscopy.

5) For late complications (e.g., weight gain, dehiscence, pouch enlargement, ulcer), use high density barium for initial swallows to establish anatomy. If there is no outlet obstruction, a half-dose of effervescent granules and high-density barium will provide distension and mucosal detail. A double-contrast esophagram should be performed before recumbent views are taken. An esophagram in the RAO position using low-density barium will demonstrate esophageal motility, herniation of the gastric pouch, and the diameter of the outflow channel post gastric bypass.

6) A final overhead radiograph will demonstrate global postoperative ana-

tomy, Roux-en-Y anastomosis, distal small bowel loops, and presence of contrast in surgical drains when a leak is suspected.

7) In patients who are too large for the fluoroscopy equipment, a limited contrast study can be obtained by properly positioning the patient and taking overhead films of the upper abdomen while oral contrast is given.

Computed tomography (CT)-When patient size permits, CT is used to investigate postoperative abscess, hematoma, bowel obstruction, bypassed bowel segments, and to guide interventional procedures.14,16 CT supplements fluoroscopy in localizing the extent of gastrointestinal leaks. To optimize CT diagnosis, the following tips are recommended:

1) Obtain an adequate surgical and clinical history. As the radiologist is less likely to see the patient in the CT suite, this must be done by the technical staff.

2) Use abundant oral contrast (2% iodinated contrast), including a dose while the patient is being positioned on the table.

3) Identify the staple lines and

configuration of the stomach and jejunum on CT images to verify that they match expected operative anatomy. Correlate fluoroscopic studies with CT examination.

4) Evaluate bypassed stomach and small bowel loops for obstruction, inflammation, intussusception, or other complications.

Complications of bariatric surgery

Surgery in morbidly obese patients is difficult, having higher complication rates than in patients at a normal weight. Operative mortality for VBG and RYGB is less than 1%.2 Infection due to gastrointestinal leak is the most common cause of perioperative mortality after bariatric surgery. Pulmonary embolism is the second most common cause, occurring with an incidence of nearly 1% in the morbidly obese population.1 Perioperative antibiotics and low dose heparin therapy are used routinely to reduce risk of infection and thromboembolism.

Gastrointestinal leak

Gastrointestinal leak occurs in 0.6% of patients after VBG2 and in 1 to 2% of patients after RYGB.5 Tachycardia is the first sign of leak and may be accompanied by fever, abdominal pain, or referred shoulder pain. Fluoroscopy is performed with water soluble contrast to localize the leak (figures 4A, 5A). CT with dilute iodinated contrast also can be used to further localize leaks and abscesses (figures 5B, 5C). Gastric perforation is most often due to ischemia from the stapling procedure,4 but can be secondary to trauma from nasogastric or gastrostomy tubes, hyperacidity,14 or interventional procedures (figure 6).

Perioperative hemorrhage

Hemorrhage due to bleeding vessels at staple lines or anastomoses is an uncommon complication in the perioperative period. When imaging is required in patients with a decreasing hematocrit and suspected hemorrhage, CT is the best modality (figure 7).

Outlet obstruction

Stomal stenosis after gastric restrictive surgery causes vomiting, gastroesophageal reflux, and enlargement of the proximal pouch.17 It occurs in 12% of patients following gastric bypass, usually within the first two months after surgery.17 Early outlet obstruction is due to edema and will resolve without intervention. Stomal stenosis developing after six weeks is due to fibrosis. Treatment with balloon dilatation, performed endoscopically or with fluoroscopic guidance, is successful in about two-thirds of patients. Those who do not respond to initial dilatation usually require surgical revision.17,18

Staple line dehiscence, VBG

Dehiscence of the staple line after VBG increases outflow from the proximal pouch, reducing the effect of early satiety and allowing increased food intake. Unsatisfactory weight loss or weight gain results.1 Staple dehiscence develops in 30 to 48% of patients who undergo VBG, and revision surgery may be required.6,19 To detect VBG dehiscence at fluoroscopy, it is essential to image the stomach first, with the patient in RPO position to document the proximal gastric pouch, outflow channel, and exit of contrast through areas of staple line dehiscence before the distal stomach opacifies (figure 8).15

Staple dehiscence and ulcer, RYGB

Staple line dehiscence after RYGB causes both weight gain and ulcer formation. Ulcers occur because dehiscence creates a gastrogastric fistula, allowing acid from the distal stomach to enter the proximal pouch and jejunostomy. Stomal ulceration occurs on the jejunal side of the anastomosis (figure 10) and generally responds to medical therapy with H2 blockers.11 Revision surgery to correct the gastrogastric fistula is required in patients with recurrent ulcers.

The surgical anatomy influences the incidence of ulcers. When RYGB is performed in continuity, the incidence of staple line disruption is 29%, with stomal ulceration occurring in 16%. When the stomach is stapled and transected in divided gastric bypass, the incidence of gastrogastric fistula and stomal ulcer is 3%.11 Interposing the jejunal limb between the proximal pouch and distal stomach further reduces the risk of gastrogastric fistula.6

Complications in bypassed bowel segments

After the performance of RYGB there is a 0.3% incidence of significant bleeding from the bypassed distal stomach or duodenum which frequently does not respond to H2 blockers, necessitating distal gastrectomy.20,21 Gastritis also is relatively common in the distal stomach, perhaps due to altered motility and bile reflux.22 Acute gastric dilatation after RYGB causes a closed loop obstruction2 (figure 10) which can be prevented by placing a temporary gastrostomy tube at the time of surgery. However, after the gastrostomy tube is removed, access to the distal stomach in the symptomatic patient is difficult, requiring either endoscopy using a long pediatric colonoscope22 or percutaneous access to the distal stomach by fluoroscopic23 or CT guidance.24

Intussusception, adhesive obstruction, and internal herniation may occur in bypassed loops post-JIB or RYGB.1,10 Internal herniation of the small bowel post-RYGB predisposes the patient to closed loop obstruction and bowel infarction (figure 11). Plain radiography and CT are most useful for detecting these complications in bypassed bowel segments.16

Metabolic complications

Gallstones occur in up to 33% of bariatric patients due to mobilization of cholesterol during weight loss. Protein calorie malnutrition develops in 20% of patients who undergo gastric restrictive surgery because of avoidance of meats.1

By far, the most severe metabolic disturbances result from malabsorptive procedures. After JIB, late complications include diarrhea (58%), nephrolithiasis (21%) (figure 1A), cholelithiasis (20%), liver dysfunction (29%), liver cirrhosis (7%), and malnutrition.10 After RYGB, metabolic effects include anemia and vitamin deficiencies.1

Conclusion

Radiology is essential in the management of the bariatric patient. Fluoroscopy is the best examination available for defining operative anatomy, gastrointestinal leak, and staple line dehiscence, and it can supplement endoscopy in the evaluation of ulcer disease. CT is an excellent tool for diagnosing extraluminal pathology, imaging bypassed bowel segments, and guiding interventional procedures. Successful imaging of the bariatric patient is achievable when steps are taken to correctly document the surgical anatomy and to recognize the variety of postoperative complications that can occur. AR

References

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Dr. Burton is with the Department of Radiology at the University of Florida College of Medicine in Gainesville, FL.