***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVE To assess and compare the quality of nonstructured and structured abstract s  of original research articles in three medical journals . DESIGN Blind , criterion-based observational study . SAMPLE R and om sample of 300 abstract s ( 25 abstract s per journal each year ) of articles published in the British Medical Journal ( BMJ ) , the Canadian Medical Association Journal and the Journal of the American Medical Association ( JAMA ) in 1988 and 1989 ( nonstructured abstract s )  and in 1991 and 1992  ( structured abstract s ) . MAIN OUTCOME MEASURES The quality of abstract s  was measured against 33 objective criteria , which were divided into eight categories ( purpose , research design , setting , subjects , intervention , measurement of variables , results and conclusions ) . The quality score was determined by dividing the number of criteria present by the number applicable ; the score varied from 0 to 1 . RESULTS The overall mean quality scores for nonstructured and structured abstract s were 0.57 and 0.74 respectively ( p < 0.001 ) . The frequency in meeting the specific criteria was generally higher for the structured abstract s than for the nonstructured ones . The mean quality score was higher for nonstructured abstract s in JAMA than for those in BMJ ( 0.60 v. 0.54 , p < 0.05 ) . The scores for structured abstract s  did not differ significantly between the three journals . CONCLUSIONS The findings support recommendations that promote the use of structured abstract s. Further studies should be performed to assess the effect of time on the quality of abstract s and the extent to which abstract s reflect the content of the articles BACKGROUND Although endoscopic bilateral metal stenting using a " stent-in-stent " method is currently used to treat patients with unresectable hilar cholangiocarcinoma , this method has limited application in cases of tight strictures or endoscopic revision in case of tumor recurrence , especially on the first stent ( initial Y stent placed ) side . OBJECTIVE To evaluate the clinical efficacy of bilateral metal stenting with the use of a slimmer ( 7F ) , open-cell- design stent . DESIGN Prospect i ve , uncontrolled , single center . SETTING Tertiary referral university hospital . PATIENTS This study involved 34 patients with unresectable hilar cholangiocarcinoma ( Bismuth type II-IV ) . INTERVENTION Endoscopic bilateral metal stenting using a stent-in-stent method was performed . First , a Y stent with a central , wide-open mesh was inserted , then a Zilver stent , with a preloaded delivery system that is slimmer ( 7F ) than those ( 7.5 - 8.5F ) of conventional stents , was placed into the contralateral hepatic duct through the central portion of the Y stent . The Zilver stent has an open-cell design , and it can be dilated easily . Thus , revision with bilateral plastic stents was tried in cases of stent obstruction . MAIN OUTCOME MEASUREMENTS Technical success , functional success , complications , and revision method . RESULTS Technical success ( bilateral stenting using Y and Zilver stents ) was achieved in 29 of 34 ( 85.3 % ) patients . Functional success was noted in 29 of the 29 ( 100.0 % ) patients who received bilateral stenting . Early complications such as pancreatitis and cholecystitis occurred in 3 ( 10.3 % ) patients . Late complications occurred in 11 ( 37.9 % ) patients . Cholecystitis , which occurred in 2 patients , was managed by percutaneous transhepatic gallbladder drainage . Stent obstruction by tumor ingrowth or overgrowth occurred in 9 of 29 ( 31.0 % ) patients . These patients were managed by placement of bilateral plastic stents ( 4 of 9 ) , percutaneous transhepatic biliary drainage ( 4 of 9 ) , and a combined method ( 1 of 9 ) . Of the 5 patients in whom endoscopic revision was attempted , 4 ( 80 % ) were managed endoscopically with bilateral plastic stents . LIMITATIONS Small number of patients , uncontrolled study . CONCLUSION A slimmer ( 7F ) , open-cell- design stent is effective in endoscopic bilateral stenting for advanced hilar cholangiocarcinoma and endoscopic revision in case of tumor recurrence Patients with biliary obstruction due to malignant disease , and judged unfit for open operation , were r and omised to have a biliary stent inserted either endoscopically via the papilla of Vater or percutaneously . Analysis after 75 patients had been entered showed that the endoscopic method had a significantly higher success rate for relief of jaundice ( 81 % versus 61 % , p = 0.017 ) and a significantly lower 30-day mortality ( 15 % versus 33 % , p = 0.016 ) . The higher mortality after percutaneous stents was due to complications associated with liver puncture ( haemorrhage and bile leaks ) . When stenting is indicated in elderly and frail patients the endoscopic method should be tried first BACKGROUND Bilateral endoscopic drainage is difficult in malignant hilar biliary obstruction . Recently , unilateral drainage in malignant hilar biliary obstruction has been shown to be equally effective . However , contrast injection leads to cholangitis . There have been no reported studies on contrast-free metal stenting in malignant hilar biliary obstruction . The present study was undertaken to evaluate the results of contrast-free unilateral metal stenting in type II malignant hilar biliary obstruction . METHODS We prospect ively studied the results of  unilateral metal stenting in type II malignant hilar biliary obstruction without contrast injection in 18 patients . RESULTS A successful endoscopic drainage was achieved in 100 % ( 18/18 ) of patients with hilar strictures .  Cholangitis and 30-day mortality occurred in none . CONCLUSIONS Unilateral endoscopic metal stenting without contrast in type II malignant hilar biliary obstruction is a safe and effective method of palliation BACKGROUND The necessity for drainage of both liver lobes in tumors arising at the biliary bifurcation is controversial . The aim of this study was to compare the outcome of unilateral versus bilateral drainage in patients with biliary obstruction at the hilum . METHODS One hundred fifty-seven consecutive patients with primary cholangiocarcinoma , gallbladder cancer , or periportal lymph node metastases were r and omly allocated to unilateral ( group A ) or bilateral ( group B ) hepatic duct drainage . RESULTS In intention-to treat analysis , group A had a significantly higher rate of successful endoscopic stent insertion  than group B ( 88.6 % vs. 76.9 % , p = 0.041 ) . Group B had a significantly higher rate of complications than group A ( 26.9 % vs. 18.9 % , p = 0.026 ) because of the higher rate of early cholangitis ( 16.6 % vs. 8.8 % , p = 0.013 ) . In per- protocol analysis the rate of successful drainage , complications , and mortality did not differ between the two groups . Median survival did not differ between the two groups but was significantly different for patients with cholangiocarcinoma and those with gallbladder cancer versus patients with metastatic tumors ( p = 0.0247 ) . CONCLUSION The insertion of more than one stent would not appear justified as a routine procedure in patients with biliary bifurcation tumors Background / Aims Although endoscopic bilateral stent-in-stent placement is challenging , many recent studies have reported promising outcomes regarding technical success and endoscopic re-intervention . This study aim ed to evaluate the technical accessibility of stent-in-stent placement using large cell-type stents in patients with inoperable malignant hilar biliary obstruction . Methods Forty-three patients with inoperable malignant hilar biliary obstruction from four academic centers were prospect ively enrolled from March 2013 to June 2015 . Results Bilateral stent-in-stent placement using two large cell-type stents was successfully performed in 88.4 % of the patients ( 38/43 ) . In four of the five cases with technical failure , the delivery sheath of the second stent became caught in the hook-cross-type vertex of the large cell of the first stent , and subsequent attempts to pass a guidewire and stent assembly through the mesh failed . Functional success was achieved in all cases of technical success . Stent occlusion occurred in 63.2 % of the patients ( 24/38 ) , with a median patient survival of 300 days . The median stent patency was 198 days . The stent patency rate was 82.9 % , 63.1 % , and 32.1 % at 3 , 6 , and 12 months postoperatively , respectively . Endoscopic re-intervention was performed in 14 patients , whereas 10 underwent percutaneous drainage . Conclusions Large cell-type stents for endoscopic bilateral stent-in-stent placement had acceptable functional success and stent patency when technically successful . However , the technical difficulty associated with the entanglement of the second stent delivery sheath in the hook-cross-type vertex of the first stent may preclude large cell-type stents from being considered as a dedicated st and ard tool for stent-in-stent placement 
    Output:
    
Conclusion In patients with unresectable malignant hilar obstruction , unilateral and bilateral metallic stenting techniques are comparable in terms of efficacy and safety