Traditional classification of bariatric procedures

Historically, bariatric operations have been classified into 1 of 3 categories: restrictive, malabsorptive, or combined. The restrictive category has traditionally included operations such as vertical banded gastroplasty (VBG) that served to limit the functional volume of the stomach and induce weight loss by restricting oral intake. Malabsorptive operations were considered to be those that limited digestion and absorption by rerouting the intestinal path taken by food and digestive enzymes, such as the no longer performed jejunoileal bypass. Combined operations were considered to be those that had elements of both restriction and malabsorption, such as the Roux-en-Y gastric bypass and biliopancreatic diversion with duodenal switch (BPD-DS).

These distinctions are becoming less relevant as more about the endocrine and metabolic effects of bariatric procedures is learned. For example, it is commonly noted that gastric bypass patients have an early reduction in appetite starting in the immediate postoperative phase that is unrelated to mechanical filling of the gastric pouch. In addition, patients with type 2 diabetes mellitus undergoing gastric bypass experience an immediate improvement in their glucose metabolism that appears to be unrelated to weight loss. These and other findings suggest that mechanical restriction and malabsorption may be less relevant than the substantial endocrine and metabolic effects that occur after surgery. Thus, the historically useful categorization of procedures as restrictive or malabsorptive is becoming less relevant.

Today, the most commonly performed bariatric operations in the United States include the Roux-en-Y gastric bypass, the laparoscopic adjustable gastric band, the vertical sleeve gastrectomy, and BPD-DS. In this review of bariatric anatomy and mechanisms of action, the authors focus individually on each of these procedures.

Historical gastric bypass (Billroth II loop technique)

Gastric bypass was first used to treat severe obesity in the 1960s. Initially, the operation involved the creation of a gastric pouch by firing a multirow surgical stapler horizontally across the mid-upper stomach. This horizontally oriented pouch included the entire gastric fundus along its upper edge and was bound inferiorly by the horizontal staple line ( Fig. 1 ). The pouch was anastomosed in an end-to-side manner to a loop of jejunum in manner of a Billroth type II anastomosis. With this early configuration, as with current operations, the lower stomach—generally referred to as the gastric remnant, or bypassed stomach—was completely excluded from the food path. The gastric remnant emptied its mucus and gastric secretions into the duodenum, where it intermixed with bile and pancreatic secretions before passing into the proximal jejunum, also referred to as the afferent limb.

Loop (Billroth II type) gastric bypass. Of historical relevance, this procedure is no longer performed. The gastric pouch is horizontally oriented, and remains in continuity with the gastric remnant. The jejunum proximal to the gastrojejunostomy is referred to as the afferent limb whereas the distal jejunum is the efferent limb. This terminology is not used when referring to a Roux-en-Y gastric bypass.

( Courtesy of Daniel M. Herron, © 2010; with permission.)

In the Billroth II type anatomy there is a single anastomosis, the gastrojejunostomy. Ingested food leaving the gastric pouch joins with the bile and pancreatic secretions immediately after passing through this anastomosis. The food continues into the efferent limb of the jejunum toward the ileum. It should be emphasized that the terms “afferent limb” and “efferent limb” refer expressly to the loop gastric bypass; these terms should be strictly avoided when describing the anatomy of the Roux-en-Y gastric bypass.

In the early days of bariatric surgery, loop gastric bypass anatomy was preferred because it required only one anastomosis rather than the two required in Roux-en-Y gastric bypass and was felt to be technically easier to perform. However, this anatomy brings the flow of bile and pancreatic juice into contact with the gastric pouch. Without the protective valve action of the pylorus, the pouch is exposed to bile and the patient is at risk for bile reflux gastritis or esophagitis, which can be challenging to treat. In addition, it may in fact be more technically difficult to bring a loop of small intestine to the very uppermost portion of the obese abdomen rather than the single limb of a Roux. For these reasons, the loop gastric bypass has been nearly universally abandoned in favor of the Roux-en-Y gastric bypass.

Historical gastric bypass (Billroth II loop technique)

Gastric bypass was first used to treat severe obesity in the 1960s. Initially, the operation involved the creation of a gastric pouch by firing a multirow surgical stapler horizontally across the mid-upper stomach. This horizontally oriented pouch included the entire gastric fundus along its upper edge and was bound inferiorly by the horizontal staple line ( Fig. 1 ). The pouch was anastomosed in an end-to-side manner to a loop of jejunum in manner of a Billroth type II anastomosis. With this early configuration, as with current operations, the lower stomach—generally referred to as the gastric remnant, or bypassed stomach—was completely excluded from the food path. The gastric remnant emptied its mucus and gastric secretions into the duodenum, where it intermixed with bile and pancreatic secretions before passing into the proximal jejunum, also referred to as the afferent limb.

Loop (Billroth II type) gastric bypass. Of historical relevance, this procedure is no longer performed. The gastric pouch is horizontally oriented, and remains in continuity with the gastric remnant. The jejunum proximal to the gastrojejunostomy is referred to as the afferent limb whereas the distal jejunum is the efferent limb. This terminology is not used when referring to a Roux-en-Y gastric bypass.

( Courtesy of Daniel M. Herron, © 2010; with permission.)

In the Billroth II type anatomy there is a single anastomosis, the gastrojejunostomy. Ingested food leaving the gastric pouch joins with the bile and pancreatic secretions immediately after passing through this anastomosis. The food continues into the efferent limb of the jejunum toward the ileum. It should be emphasized that the terms “afferent limb” and “efferent limb” refer expressly to the loop gastric bypass; these terms should be strictly avoided when describing the anatomy of the Roux-en-Y gastric bypass.

In the early days of bariatric surgery, loop gastric bypass anatomy was preferred because it required only one anastomosis rather than the two required in Roux-en-Y gastric bypass and was felt to be technically easier to perform. However, this anatomy brings the flow of bile and pancreatic juice into contact with the gastric pouch. Without the protective valve action of the pylorus, the pouch is exposed to bile and the patient is at risk for bile reflux gastritis or esophagitis, which can be challenging to treat. In addition, it may in fact be more technically difficult to bring a loop of small intestine to the very uppermost portion of the obese abdomen rather than the single limb of a Roux. For these reasons, the loop gastric bypass has been nearly universally abandoned in favor of the Roux-en-Y gastric bypass.

Roux-en-Y gastric bypass

The Roux-en-Y operation is named after César Roux, a Swiss surgeon who developed a Y-shaped intestinal reconstruction to decompress an obstructed stomach in 1892. This procedure was first applied to the gastric bypass operation in the 1970s in hopes of eliminating the risk of bile reflux and minimizing tension on the gastrojejunostomy. Over the past two decades, the Roux-en-Y gastric bypass has become the most commonly performed bariatric procedure in the United States ( Fig. 2 ).

Roux-en-Y gastric bypass. Typically performed laparoscopically, this is the most common bariatric operation in the United States at present. The gastric pouch is small, vertically oriented, and completely divided from the gastric remnant. Gastric secretions, bile and pancreatic juice flows through the biliopancreatic limb, while ingested food passes through the Roux limb. The bowel distal to the lower anastomosis is referred to as the common channel.

( Courtesy of Daniel M. Herron, © 2010; with permission.)

In the Roux-en-Y gastric bypass the jejunum is typically divided approximately 40 to 100 cm distal to the ligament of Treitz. The distal end is brought up to the stomach pouch and is referred to as the Roux limb, or the alimentary limb, because food but no gastric, bile, or pancreatic secretions passes through this segment. The proximal divided side of the small bowel transmits gastric secretions along with the bile and pancreatic juice, and is thus referred to as the biliopancreatic limb.

The current Roux-en-Y gastric bypass is different from the operations of the 1960s and 1970s in several significant ways. The gastric pouch has evolved to become very small, generally 30 mL in volume or less. Care is taken to completely exclude the fundus from the pouch, to minimize both its volume and the amount of acid-secreting mucosa contained within.

Variation in the technique of pouch formation exists. Some surgeons create a tall, narrow pouch based on the lesser curvature. To accomplish this, the linear surgical stapler is fired transversely across the lesser curvature, approximately 4 to 6 cm distal to the gastroesophageal junction. After this transverse firing, several additional firings are run vertically, parallel to lesser curvature, completely excluding the fundus and forming the left side of the pouch. Other surgeons create a more transversely oriented pouch by firing the stapler several times just underneath the gastroesophageal junction. Still others create a pouch so small as to be referred to as a “virtual pouch,” functionally similar to an esophagojejunostomy.

Another significant difference in the modern gastric bypass is a direct result of the newer staplers. Surgeons of the 1970s and 1980s used a linear stapler that formed a double row of staggered titanium staples (Covidien TA-90; Covidien, Mansfield, MA, USA). While this created a compartmentalized stomach, the pouch and gastric remnant remained in direct continuity. Because of unacceptably high rates of gastric pouch-to-gastric remnant fistula formation across the staple line (gastrogastric fistula), the stapler was modified to lay down 2 additional rows of staggered staples, for a total of 4 rows (TA-90B; Covidien). Some surgeons applied this stapler to the tissue twice, effectively placing 8 rows of superimposed staples. Current staplers function quite differently in that they form 2 triple rows of staples, then divide the tissue down the middle with a cutting blade, creating a “divided pouch” that is fully separated from the gastric remnant. Although there was initial concern that this might lead to an increased staple line leak rate, this has not occurred.

Laparoscopic approach

In 2010, the majority of Roux-en-Y gastric bypass operations are performed through a laparoscopic approach. The use of 5 to 7 small incisions rather than a single 15- to 30-cm vertical midline incision generally results in fewer wound-related complications, less postoperative pain, and a shorter convalescence. Regardless of whether the surgical approach is laparoscopic or open, the resultant internal visceral anatomy is the same.

The overwhelming majority of laparoscopic linear staplers in current use divide the tissue after it has been stapled. In a laparoscopic gastric bypass, the pouch is most commonly created using a surgical stapler that fires 3 rows of staples on the proximal side and another 3 rows of staples on the distal side, then cuts the intervening tissue. This action creates a fully divided gastric pouch, in contradistinction to earlier approaches in which staples were applied but the stomach tissue was not divided. The use of a fully divided pouch has resulted in a decreased risk of fistula formation between pouch and remnant.

The gastric pouch created in a laparoscopic procedure is quite small, generally 15 to 30 mL in volume. On endoscopy, the pouch is entered immediately distal to the gastroesophageal junction. The pouch may have several different configurations, and may be long and narrow or short and wide. Regardless of the configuration of the pouch, the gastrojejunostomy anastomosis should be easily visible within several centimeters of the gastroesophageal junction.

The gastrojejunostomy may be formed using any number of different surgical techniques. Many surgeons prefer using a circular stapler in which 2 concentric rows of titanium staples are fired to connect the end of the pouch to the side of the Roux limb. If this method has been used then it is expected that some staples may be visible internally on endoscopy. Some surgeons prefer the use of a linear cutting stapler to anastomose the side of the stomach pouch to the side of the Roux limb. The remaining enterotomy through which the linear stapler has been inserted is then closed, generally using absorbable suture material. Other surgeons prefer a more traditional surgical technique in which 2 layers of absorbable or permanent sutures are placed using a standard hand-suturing technique.

Regardless of technique, most anastomotic approaches result in and end-to-side type connection, whereby the distal end of the gastric pouch is connected to the side of the Roux limb. On endoscopy, 2 passages into small bowel should be clearly visible immediately beyond the gastrojejunostomy. One limb of bowel will end blindly within several centimeters, while the other will pass down toward the distal anastomosis (jejunojejunostomy). The distance from the gastrojejunostomy to the distal anastomosis is variable but is typically between 40 and 100 cm, generally beyond the reach of a typical upper endoscope.

Alternative types of gastric bypass

Although the vast majority of gastric bypasses are performed using the generally accepted techniques described thus far, some surgeons prefer alternative operations. One such example is the so-called mini-gastric bypass, which is a laparoscopic version of the Billroth II loop-type gastric bypasses. Proponents of this approach suggest that it is technically easier to perform because there is only a single gastrointestinal anastomosis to create. Although acceptable weight loss results have been reported with this operation, surgeons’ concern regarding the potential for bile reflux gastritis or esophagitis has kept this technique from becoming widespread.

Laparoscopic adjustable gastric band

The laparoscopic adjustable gastric band (LAGB) has been available outside the United States since the 1990s and has been performed in the United States since 2001 ( Fig. 3 ). At present the Food and Drug Administration (FDA) has approved two different brands; the LAP-BAND device is manufactured by Allergan Inc (Irvine, CA, USA) while the Realize band is made by Ethicon Inc (Somerville, NJ, USA). Although there are minor differences in design between the two brands, they function very similarly within the human body. Weight loss after LAGB placement is variable, but has been reported to range from 40% up to 70% of initial excess body weight.

Laparoscopic adjustable gastric band. A rigid band with an inflatable balloon lining the inner aspect is placed around the upper stomach. The band can be tightened by injecting saline into the subcutaneous access port. Most surgeons in the United States secure the band anteriorly by using 2 to 5 sutures to imbricate the stomach over the band, not shown in this diagram.

( Courtesy of Daniel M. Herron, © 2010; with permission.)

The bands are placed via laparoscopic surgical approach, around the stomach immediately beneath the gastroesophageal junction, and locked in place using a buckle-type fastener. Anteriorly, the band is fixed in position by imbricating the body of the stomach upward over the band and suturing the fold back to the upper stomach. Some surgeons believe that anterior fixation is unnecessary and omit this step. Posteriorly, the band is held in position by retroperitoneal tissue because the band is placed above the peritoneal reflection of the lesser sac.

The inner surface of the band consists of a saline-filled silicone balloon that is connected, via internal silicone tubing, to a subcutaneous access port. The port, generally located on the anterior abdominal wall near the subcostal, subxiphoid, or periumbilical area, is accessed percutaneously with a noncoring Huber needle. Injecting saline inflates the band and increases restriction whereas removing saline does the opposite.

The band and access port are radio-opaque and are clearly visualized on a plain radiograph of the upper abdomen. A normal band will appear immediately below the gastroesophageal junction, and will be oriented horizontally or with the left side slightly higher than the right (up to about 30° from the horizontal). If the band appears vertical, or with the left side lower than the right, this may suggest that the band has slipped down on the stomach or that part of the stomach has abnormally prolapsed up through the band, commonly referred to as a “band slip.”

Because the band is placed around the serosal surface of the stomach, it should not be directly visible on endoscopy. Located immediately beyond the gastroesophageal junction, the band may be appreciated as an extraluminal constriction. Although it is generally possible to pass the endoscope through the lumen of the band into the main stomach compartment, this may be difficult or impossible depending on the tightness of the band, the caliber of the endoscope, and the presence of inflammation or edema in the gastric tissue. Once past the band, the endoscope can be retroflexed to provide a clear view of the band’s position.

If any plastic or rubber portion of the band is visible on endoscopy, this represents a highly abnormal finding that necessarily implies that the device has eroded through the full thickness of the esophagus or stomach. Erosion may occur because of surgical trauma at the time of initial operation or as a result of infection or abscess formation immediately adjacent to the band, resulting in inflammation and breakdown of the gastric wall. In general, erosion begins in one small area of the band and gradually enlarges. Erosion may progress to the point where the entire gastric portion of the band becomes intraluminal. Eroded bands are typically removed via a laparoscopic surgical approach. Several reports describe removal of such eroded bands through an endoscopic approach, although a surgical procedure is still required to remove the access port component.

Whereas erosion is fairly straightforward to diagnose on endoscopy, band slippage may be a more difficult assessment. If the mucosa is intact but the pouch seems excessively large or the constricted area particularly low on the stomach, this may represent a gastric prolapse or band slip.

Adjustable gastric bands should not be confused with nonadjustable gastric bands, which were used in the 1970s and 1980s and have since fallen into disfavor. These bands were strips of polypropylene mesh that were surgically wrapped around the mid-portion of the stomach and sutured in place. Similarly, the adjustable gastric band is distinct from the VBG, referred to by many laypeople as a “stomach stapling.” In the VBG a surgical stapler is fired parallel to the lesser curvature to create a narrow pouch similar to that of a gastric bypass. The distal portion of the pouch is constricted by a nonadjustable ring of either polypropylene mesh or silastic tubing. Although popular in the 1980s, the VBG has also fallen out of use because of the difficulty in performing it laparoscopically and its poor long-term weight loss results. Most VBGs were performed using staplers that did not divide the gastric tissue after stapling; as a result, gastric pouch-to-remnant fistula formation is a not uncommon finding.