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Paper text:

 colonic gallstone ileus is an exceedingly rare cause of mechanical large - bowel obstruction .
it occurs most commonly due to the passage of a solitary large stone or several smaller stones through a cholecystocolonic fistula into the colon .
it is a disease of high morbidity and mortality due to the diagnostic challenge , late presentation , advanced patient age , and comorbid states .
we report a case of gallstone ileus of the sigmoid colon and review the available literature .
a 92-year - old male was admitted to hospital with a 3-day history of intermittent colicky lower abdominal pain associated with absolute constipation and abdominal distension . clinical examination revealed a distended abdomen with left iliac fossa tenderness but no overt peritonism .  
a ct scan at that time demonstrated a 3.8  cm stone in the gallbladder .
biochemical and haematological investigations revealed a crp of 87.6  mg / l and a white cell count of 21.2  10/l .
initial abdominal x - rays showed gaseous distension of the large bowel with no evidence of pneumobilia .
a subsequent contrast - enhanced ct scan of the abdomen demonstrated a 3.8  cm opacity impacted in the midsigmoid colon ( figure 1 ) associated with secondary inflammatory change and multiple diverticulae .
a fistulous connection between a collapsed empty gallbladder and the hepatic flexure of the colon was also identified ( figure 2 ) . at laparotomy
the cholecystocolonic fistula was identified but was not repaired in order to minimise the operative time and hence the risk of perioperative complications .
the diverticulous segment of large bowel at the point of impaction was also not resected for the same reason .
gallstone ileus ( gsi ) of the colon is an extremely rare cause of large - bowel obstruction .
it has been shown to account for 2% to 8% of all cases of gsi [ 1 , 2 ] .
the mechanism of obstruction usually results from a large gallstone greater than 2  cm in diameter entering the colon through a cholecystocolonic fistula .
the fistulous connection usually forms after a preceding episode acute cholecystitis leads to inflammation and adhesions forming between the gallbladder and colon , usually at the hepatic flexure .
the point of impaction is usually a pathological narrowing of the colon which may be a result of diverticular disease [ 3 , 4 ] or prior pelvic irradiation .  
the typical presentation is that of large - bowel obstruction with abdominal pain and distension being the main features .
however , rarer presentations such as diarrhoea or ascending cholangitis can occur . as in gsi of the small bowel ,
the classic x - ray triad of bowel obstruction , pneumobilia , and ectopic gallstones   is sometimes but not always seen .
contrast - enhanced computed tomography allows better visualisation of the point of obstruction and site of fistula [ 8 , 9 ] . about 7% of gsi
have been shown to settle with conservative management . however , in the majority of cases operative management is required . in the main part
this allows relief of the obstruction as well as preventing further stone formation and episodes of cholangitis . for the higher - risk patient such as in our report a single stage enterolithotomy alone may be more appropriate . during either operation the entire length of the small and large bowel
management by colonoscopy and extraction has been successful in few cases [ 11 , 12 ] .
however when the stone is relatively large and the lumen is relatively small , it is less likely to be successful . in conclusion
gsi of the colon is a rare but important cause of large - bowel obstruction .
the diagnosis may be very difficult given the lack of distinguishing clinical features but should be considered if there has been a history of gallstone disease . if plain abdominal films do not reveal the diagnosis , computed tomography will allow visualisation of the fistula and level of obstruction .
treatment depends on the fitness of the patient but should ideally involve relief of the obstruction , cholecystectomy , and repair of the fistula .
gallstone ileus of the colon is an exceedingly rare cause of large - bowel obstruction . 
 it is usually the result of fistula formation between the gallbladder and large bowel facilitating entry of the stone into gastrointestinal tract . 
 contrast enhanced abdominal computed tomography is an important diagnostic aid . 
 surgical management is the treatment of choice to prevent the disastrous complications of large - bowel obstruction . 
 we describe the case of a 92-year - old man who presented with symptoms and signs of large - bowel obstruction . 
 radiological investigation showed a large gallstone impacted in the sigmoid colon . 
 open enterolithotomy was undertaken relieving the obstruction and the patient made a full recovery .