as biliary stents are used frequently and for long periods of time , stent - related complications are increasing.1,2 among biliary stent - related intestinal complications , the choledochoduodenal fistula resulting from metallic biliary stent - induced perforation is a very rare complication . to our knowledge , this is the first report of a spontaneous choledochoduodenal fistula as a delayed complication after biliary metallic stent placement in a patient with an ampulla of vater ( aov ) carcinoma . a 76-year - old woman presented with a severe pain in the right upper quadrant of the abdomen and with jaundice that had started to worsen four days before . an uncovered biliary stent ( niti - s , biliary uncovered stent ; taewoong , seoul , korea ) that was 5 cm in length had been inserted 40 days earlier for palliative management of an aov carcinoma due to refusal of a curative surgical or endoscopic resection , despite the t1-stage tumor . laboratory tests revealed the following : white blood cell count , 14.38010/l ( 4.0 - 10.810/l ) ; total bilirubin , 15.2 mg / dl ( 0.2 - 1.2 mg / dl ) ; ast , 75 iu / l ( 0 - 40 iu / l ) ; alt , 72 iu / l ( 0 - 40 iu / l ) ; and alkaline phosphatase , 225 iu / l ( 39 - 117 abdomen computed tomography ( ct ) showed an approximately 2 cm diameter cystic lesion between the duodenum and the mid - portion of the metallic stent , as well as upstream bile duct dilation ( fig . the following day , the patient 's abdominal pain spontaneously improved , and total bilirubin decreased from 15.2 mg / dl to 10.8 mg / dl . a subsequent endoscopy demonstrated that the bile had drained through a small fistula on the medial wall of the proximal second portion of the duodenum ( fig . the endoscopy also showed that the stent was impacted with food materials and stones ( fig . however , there was no stent migration or deformation on the end of the stent . when a mixture of indigo carmine and contrast was injected into the common bile duct , the contrast mixture was passed out the duodenum via the same fistula opening ( fig . as the dye was injected through an endoscopic nasobiliary drainage ( enbd ) tube , fluoroscopy showed a linear track of the fistula from the mid - portion of the metallic stent to the duodenum , which was dissimilar to the ct finding . seven days later , after placement of an enbd tube and conservative management , including antibiotics , there was no fistula found from follow - up cholangiography ( fig . 3b ) . there was no evidence of tumor invasion on the fistula opening upon pathological examination . following the removal of several impacted stones , a covered biliary stent ( niti - s , biliary covered stent ; taewoong ) that was 6 cm in length was reinserted for palliative management of the tumor ingrowth and fistula . biliary stent - related enteric perforations are very rare complications , with an incidence below 1% . intestinal perforations are usually caused by the sharp end of a metallic stent or stent migration.1 - 3 choledochoduodenal fistula caused by tumor invasion or spontaneous perforation of the bile duct have rarely been reported.4 - 6 spontaneous biliary - enteric fistulas have an incidence rate of 3 - 5% among cases ; they are usually caused by calculi in the inflamed gallbladder or biliary tract , peptic ulcers , trauma , crohn 's disease , or malignant invasion by an aov carcinoma or cholangiocarcinoma.4 - 11 among these causes , a choledochoduodenal fistula associated with an aov carcinoma is an extremely rare complication , and metallic biliary stent - related spontaneous choledochoduodenal fistulas without tumor invasion have not yet been reported . this unusual complication developed spontaneously in a patient with an aov carcinoma as a delayed complication after metallic biliary stent placement . however , there was no evidence of tumor invasion at the fistula site , and no evidence of metal stent migration or deformation of the stent end at endoscopic or radiologic findings . the cystic formation between the cbd and duodenum appeared to have been precipitated by a rise in intraductal pressure , following obstruction by distal bile duct stones and tumor ingrowth in the uncovered biliary stent . subsequently , cystic rupture in the duodenum created a choledochoduodenal fistula . the spontaneous symptomatic and laboratory improvement , along with the linear track formation of the fistula from the mid - portion of the metallic stent to the duodenum , which was dissimilar to the ct finding of a round cystic lesion , were suspected to have resulted from the rupture of an inflammatory cystic lesion in the duodenum . by excluding the possibilities of tumor metastasis , direct stent migration and deformation , we differentiated those causes and suggested the pathological explanation that rising intraductal pressure induced necrosis of the duct wall due to direct erosion and inflammation by stones or an uncovered stent . management of choledochoduodenal fistulas depends on their type and etiology . in fistulas with complicating duodenal ulcers , medical management or surgery can be used . endoscopic management and the extraction of a bile duct stone ( if present ) , may be needed.5,7,8,12,13 there is a justified trend towards conservative management of iatrogenic bile duct perforations.2 the current case was also managed conservatively , by reducing the pressure gradient with nasobiliary drainage and antibiotics . in summary , we have been successful in conservatively managing a spontaneous choledochoduodenal fistula that was precipitated by a rise in intraductal pressure following obstruction by distal bile duct stones and tumor ingrowth in the uncovered biliary stent .
biliary stent - related enteric perforations are very rare complications that are caused by the sharp end of a metallic stent , stent migration , or tumor invasion . 
 moreover , the choledochoduodenal fistula resulting from metallic biliary stent - induced perforation is extremely rare . here 
 , we report a case in which a spontaneous choledochoduodenal fistula occurred after biliary metallic stent placement in a patient with an ampulla of vater carcinoma but was successfully managed by supportive treatments , including nasobiliary drainage . 
 this case might have occurred as the result of a rupture of the bile duct following pressure necrosis and inflammation caused by impacted calculi and food materials over the tumor ingrowth in the uncovered biliary stent .