Bouveret syndrome is caused by a large stone passing through a bilioduodenal fistula causing gastric outlet obstruction. Morbidity and mortality rates have decreased in recent years but remain high, estimated at 60% and 12% to 30%, respectively. Unfortunately, the chance of misdiagnosis is still high due to non-specific symptoms and laboratory findings.
Bouveret syndrome is the most infrequent variant of gallstone ileus, with a little over 300 cases in literature since its first description in 1654 through 2008. It results from a gallstone entering the intestinal lumen and causing obstruction at the gastric outlet and occasionally in other portions of the intestine as well. The entry point is typically a fistula between the gallbladder and a portion of the stomach or intestine.
The risk factors for Bouveret syndrome are similar to the risk factors of gallstones since gallstones play an integral role in the etiology of Bouveret syndrome. These risk factors for gallstones can be remembered using the 5-F rule mnemonic: fair (more prevalent in Caucasians), fat (body mass index (BMI) greater than 30kg/m2), female gender, fertile (one or more children) and forty (generally older age around 40). The well-studied risk factors for Bouveret Syndrome include a history of cholelithiasis, stones greater than 2 cm to 8 cm, female gender, and age older than 60 years. It has been reported that approximately 43% to 68% of patients have a history of recurrent biliary colic, jaundice, or acute cholecystitis. Unfortunately, mortality ranges from 12% to 27% in part due to delay in diagnosis, misdiagnosis and non-specific symptoms at presentation and laboratory investigations.
Bouveret syndrome typically occurs secondary to recurrent inflammation of the gallbladder as it abuts a portion of the gastrointestinal (GI) resulting in inflammatory adhesions between the two systems. Usually, a large biliary stone results in gallbladder wall necrosis, which can eventually form a fistula between the biliary and the enteric system. In 60% of the cases, the fistula is cholecystoduodenal, but less common variants are cholecystocolic (17%), cholecystogastric (5%), and choledochoduodenal (5%). The biliodigestive fistula allows the passage a large gallstone from the biliary tree to the enteric system. Not commonly, this results in the impaction of the gallstone in the pylorus or proximal duodenum resulting in gastric outlet obstruction. The size of the gallstones that cause obstruction are usually more than 2.5 cm, as those smaller than 2.5 cm usually do not lodge and pass spontaneously .
The presentation of Bouveret syndrome is typically non-specific, and often with waxing and waning symptoms of nausea and vomiting (present in 85% of patients), abdominal distension and pain (present in 70% of patients) due to the varying locations of the gallstone. The patient may also exhibit epigastric and right hypochondrium pain, along with signs of dehydration and weight loss. Less frequently, Bouveret syndrome may present with hematemesis secondary to duodenal and celiac artery erosions or with the expulsion of stones in the vomitus. Usually, the symptoms begin 5 to 7 days before patients seek medical consultation. Importantly, the intensity of the pain often does not correlate with the underlying anatomic alteration.
A physical exam is also non-specific, although one may appreciate dry mucous membranes, abdominal distension, abdominal tenderness, high-pitched bowel sounds, and obstructive jaundice. 
Unfortunately, laboratory studies are typically non-specific. Labs may show jaundice and hepatic enzyme alterations, but this is only seen in about one-third of the patients with Bouveret syndrome. Leucocytosis, electrolyte abnormalities, acid-base alterations, and renal failure may also be present, but the grade depends on the comorbidity, the intensity of the inflammatory response and the compensatory mechanisms of the individual. As far as imaging is concerned, the constellation of pneumobilia, bowel obstruction, and an aberrant gallstone referred to as Rigler's triad is highly suggestive of Bouveret syndrome but is only found in 40% to 50% of cases. Ultrasound may be useful, showing possible cholecystitis, dilated stomach, pneumobilia, and ectopic location of gallstone, yet bowel gas makes it suboptimal. If the gallbladder is contracted, it may be difficult to detect the exact location of the stone (orthotopic or ectopic) using ultrasound.
Abdominal radiographs, though nonspecific, may help identify bouveret syndrome. The subtle cues include pneumobilia, intestinal obstruction, an aberrantly located gallstone, air-fluid levels in the right upper quadrant due to air in the gallbladder, gastric distention, and a change in the location of a previously observed stone. However, abdominal radiographs are only diagnostic in 21% of Bouveret’s syndrome cases. CT is the imaging modality of choice, with an overall 93% sensitivity, 100% specificity, and a 99% diagnostic accuracy. In addition to its higher accuracy compared to plain radiograph or ultrasound, it can also provide important information about the presence of a fistula, presence of an abscess, inflammatory state of the surrounding lumen and tissue, size of gallstone, and the number of gallstones. In patients unable to tolerate oral contrast or with intense emesis, as well as in cases with isoattenuating stones, magnetic resonance cholangiopancreatography (MRCP) can be utilized, as it distinguishes stones from fluid, visualizes the fistula with good precision, and does not require the use of oral contrast material. Esophagogastroduodenoscopy (EGD) is another option, with diagnostic and therapeutic advantages. Simultaneous removal of the stone is however only successful in a minority of cases and can be associated with further complications. In about 20% to 40% of cases, the final diagnosis is established intra-operatively when a patient is undergoing laparotomy for small bowel obstruction of unknown cause. This applies in particular to the 15% to 25% of gallstones that are isoattenuating and not visible on CT scan. 
Given the advanced age and extensive comorbidities of the typical patient with bouveret syndrome, many have advocated for endoscopic or percutaneous approaches such as laser or extracorporeal shockwave lithotripsy initially.  Approximately 91% of patients fail this procedure and require surgical treatment. The surgical options are a one-stage procedure (enterolithotomy to relieve bowel obstruction, cholecystectomy, and repair of chole-enteric fistula), the two-stage procedure (enterolithotomy and interval cholecystectomy) and enterolithotomy alone. Depending on the experience of the center and the surgeon, the laparoscopic approach typically fails in approximately 50% of cases. Although the best method is still controversial, surgical management with enterolithotomy is the most common treatment, with only 5% of patients developing biliary symptoms and 10% requiring an unplanned reoperation. Supporters of this method believe that the spontaneous fistula closure occurs in more than 50% of cases, and that enterolithotomy alone has fewer complications. 
Bouveret syndrome generally carries a good prognosis provided timely diagnosis and management.
The complications of untreated bouveret syndrome include ongoing gastric outlet obstruction resulting in anorexia, dehydration, nutritional deficiencies, and electrolyte abnormalities. The most feared complication is intestinal perforation which can lead to major morbidities.
Specific complications are related to the mode of treatment strategy employed. Incomplete lithotripsy may lead to recurrent gallstone ileus. Shock wave dispersion may lead to damage to surrounding structures. If a fistula is not excised, there is a risk for recurrent bouveret syndrome as well. Surgery in itself carries the inherent risks of bleeding and infection. in addition, cholecystectomy may result in inadvertent injury to the biliary tree especially in the presence of inflammation. 
Despite the fact that a large gallstone is the cause of the gastric outlet obstruction, a history of prior gallstone disease is only present in a few patients. Nevertheless, the condition should be considered in elderly patients who have a history of chronic cholecystitis and who present with repeated episodes of hematemesis or vomiting.
Bouveret syndrome is a very rare cause of gastric outlet obstruction. Both the diagnosis and management are complex and the disorder carries high morbidity and mortality. These patients are best managed by a multidisciplinary team that includes an emergency department physician, general surgeon, radiologist, gastroenterologist, and specialty nurses. The best method of managing these patients still has not been determined but the patients need close monitoring in an ICU setting. Wound infections, fistula formation, and multiorgan failure have all been reported. The nurse has to ensure that the patients have DVT prophylaxis as many patients remain bedridden for a prolonged time.
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