Gallstone ileus is a rare complication of cholelithiasis and is one of the rarest forms of all mechanical bowel obstructions. It is, however, a more common cause of non-strangulating mechanical small bowel obstruction, accounting for 1% to 4% in all patients and up to 25% in the elderly. The diagnosis is often delayed since symptoms may be intermittent and investigations may fail to identify the cause of the obstruction. As a result, gallstone ileus continues to be associated with relatively high rates of morbidity and mortality. 
It was first described in 1654 by Dr. Erasmus Bartholin and is thought to be caused by impaction of a gallstone in the gastrointestinal (GI) tract after passing through a biliary-enteric fistula. Gallstone ileus is more common in women (the ratio being 3.5 females to 1 male) and older patients, particularly those older than 60 years. Other factors that contribute to gallstone ileus are a long history of cholelithiasis, repeated episodes of acute cholecystitis, and stones greater than 2 cm. According to literature, approximately 40% to 50% of patients eventually diagnosed with gallstone ileus have a history of recent biliary colic bouts, jaundice, or acute cholecystitis.
Gallstone ileus occurs in 0.3% to 0.5% of all patients with gallstones, and one of the rarest causes of gallstone ileus, occurring in about less than 0.1% of all mechanical obstruction cases and 1% to 4% of non-strangulating mechanical small bowel obstructions. Despite 350 years of medical advances, mortality remains high, ranging from 12% to 27%, partially because of non-specific symptoms, unremarkable biochemical investigations, high misdiagnosis rate, and delayed discovery.
The etiology of gallstone ileus results from adhesions forming between an inflamed gallbladder and an adjacent GI tract followed by gallstones causing pressure necrosis or inflammation between the two tissues. The inflammation or necrosis results in erosion and formation of a cholecyst-enteric fistula. Gallstones can move from the gallbladder to the GI tract through this direct access. Fistulas can form within any part of the GI tract, with approximately 60% occurring in the duodenum due to the proximity. Less commonly, a gallstone may enter the duodenum through the common bile duct, a dilated papilla of Vater, or after an endoscopic sphincterotomy. Spillage of gallstones during laparoscopic cholecystectomy may also result in an intraabdominal abscess that can ulcerate the intestinal wall and lead to an entryway into the bowel lumen. The site of fistula formation, size of gallstone, and size of bowel lumen will determine the location of impaction. Gallstones most commonly impact at the terminal ileum and ileocecal valve due to their narrow lumen and potentially less active peristalsis. The majority of gallstones smaller than 2 cm may pass spontaneously while those larger are more likely to become impacted. The presence of diverticula, strictures or neoplasms can also serve as impaction sites.
Unfortunately, the diagnosis is often delayed since symptoms may be non-specific, intermittent or investigations fail to identify the cause of the obstruction due to the “tumbling phenomenon” as the stone tumbles through the variable portions of the GI tract. Patients typically present 4 to 8 days after symptoms start. The signs and symptoms are usually non-specific, including crampy, intermittent abdominal pain, variable abdominal distention, nausea, vomiting, and constipation intermittently as the stone travels through the GI tract. The degree of obstruction will vary based on the location of the gallstone, and occasionally the gallstone passes through the rectum without notice. The physical examination may be non-specific, but a provider may appreciate abdominal distension, abdominal tenderness, high-pitched bowel sounds, and obstructive jaundice. Importantly, the intensity of the pain often does not correlate with the underlying anatomic alteration.
The diagnosis is usually made three to eight days after symptoms, and a correct preoperative diagnosis is reported in 30% to 70% of cases. As a result, a high index of suspicion is necessary. Laboratory studies are usually non-specific, as only one-third of patients present with jaundice and/or alteration of hepatic enzymes. Ultrasound can be used to demonstrate fistulas, pneumobilia, impacted gallstones and residual cholelithiasis or choledocholithiasis, but difficulties of locating stones and distortion by bowel gas make ultrasound suboptimal. Plain abdominal radiographs can also be used for diagnosis, with Rigler’s triad being present and in some cases partial or complete intestinal obstruction, pneumobilia or contrast in the biliary tree, a gallstone, and gallstone position changes on serial films, but sensitivity range from 40% to 70%. CT scanning is a better entity and has a sensitivity of 93%. Balthazar et al. described a fifth sign: two air-fluid levels in the right upper quadrant on abdominal radiograph corresponding to the duodenum and the lateral to the gallbladder, yet this sign is only present in approximately 24% of patients at the time of admission. Therefore, if you have a clinical suspicion but negative x-ray findings, a CT scan should be performed. Findings consistent with gallstone ileus include gallbladder wall thickening, pneumobilia, intestinal obstruction, and obstructing gallstones. Pneumobilia, a non-specific findings, is found in approximately 30% to 60% of patients. HIDA scan, MRCP, and EGD may be performed if there is still a question after CT scanning. However, gallstone ileus is more typically diagnosed intra-operatively when a patient is undergoing laparotomy for small bowel obstruction of unknown origin. 
Although the treatment and management of gallstone ileus are still under controversy, the main therapeutic goal is the extraction of the offending stone after resuscitation. Gallstone ileus involves three key elements: cholelithiasis, biliary-enteric fistula, and intestinal obstruction. Cholelithiasis and fistula are typically addressed by stone removal and fistula closure. Stone removal typically addresses intestinal obstruction. The current surgical options are 1) simple entero-lithotomy; 2) entero-lithotomy, cholecystectomy and fistula closure (one-stage procedure); and 3) entero-lithotomy with cholecystectomy performed later (two-stage procedure). Most conclude that entero-lithotomy alone is the best option for most patients. Some have advocated that one-stage procedure (cholecystectomy and fistula repair) should be considered in low-risk patients in good general condition and adequately stabilized preoperatively. A two-stage surgery is usually an option for those with persistent symptoms despite entero-lithotomy surgery. Whether interval biliary surgery should be performed at the same time as the obstruction relief (one-stage procedure), performed later, or not at all remains unanswered. 
An open procedure is the "gold standard" to treat this condition. It is difficult to examine the distended bowel and find the exact location of the gallstone during laparoscopy. Plus, laparoscopy does take a longer time to perform and needs more experienced surgeons. Some reports do indicate that that the laparoscopic enterolithotomy and classic surgery can produce good results and may help with diagnosis and also be therapeutic.
Gallstone ileus is usually managed by several different healthcare specialists which includes a radiologist, a gastroenterologist, and a general surgeon. Since most of these patients are frail seniors, a critical care specialist should be involved in their care before and after surgery.
The nurse plays a vital role in the education patients with symptoms of biliary colic and acute pancreatitis. The patient should be educated about the symptoms of gallstone ileus and when to seek medical help. Further, when the patient is admitted with bowel obstruction, the nurse should closely monitor the abdominal girth, urine output, and Nasogastric residuals. These patients are elderly and are also at risk for DVT and aspiration pneumonia- hence appropriate precautions should be taken. Finally, since obesity is a risk factor for gallstones, patients should be urged to lose weight, eat a healthy diet and exercise regularly.  (Level V)
Only anecdotal reports and small case series exist on the management of gallstone ileus. If the diagnosis is delayed, it carries a mortality rate of 15-30%. Further, these patients have a prolonged stay in the hospital and develop a wide range of complications such as a prolonged ileus, recurrent bowel obstruction, aspiration pneumonia, and fistulas. (Level III)