between february 1997 and may 2000 , seven patients in whom tubular foreign bodies were present underwent removal procedures involving the coaxial snare technique ( table 1 ) .
the foreign bodies were either stents which were malpositioned or had migrated from their correct position in the vascular system ( n=2 ) , a fragmented venous introducer sheath ( n=1 ) , or fragmented external drainage catheters in the biliary tree ( n=2 ) or urinary tract ( n=2 ) .
all procedures were performed with the loop snare coaxially oriented in relation to the guidewire , dilator , or catheter , and to describe them , we use the term ' coaxial snare technique ' .
the devices used for the procedure were a nitinol gooseneck snare ( amplatz gooseneck ; microvena , vadnais heights , minn .
, u.s.a . ) , an angiographic catheter , and a 0.035-inch superelastic guidewire ( glidewire ; terumo , tokyo , japan ) . to facilitate smooth engagement and withdrawal of the foreign bodies ,
a vascular sheath dilator was used in five patients . in cases involving malpositioned or misplaced vascular stents ,
the guidewire remained within the lumen of the stent , and the loop snare was carefully advanced coaxially over the guidewire until it was positioned around the stent 's proximal end .
the loop was then tightened and the stent was withdrawn . in the case involving a rigid broken sheath in the right atrium ,
a loop snare was used to capture the broken fragment , which was then pulled back into the inferior vena cava .
the femoral vein was punctured a second time , and using an angiographic catheter and guidewire , the lumen of the broken fragment was located . a vascular sheath dilator was then advanced over the guidewire , and after tight engagement of the dilator with the sheath fragment , the whole system was withdrawn simultaneously . in the other cases , involving the biliary or urinary systems , direct snaring either failed or was not attempted . instead , a guidewire was passed through the central lumen of each fragmented external drainage catheter ; a loop snare was then introduced coaxially over the extracorporeal end of the guidewire or catheter , which had already been passed through the fragmented catheter .
after the barrel of the object was snared , the loop was closed around it and a vascular sheath dilator was introduced over the guidewire , facilitating tight engagement with the end of the catheter fragment .
, we conducted an ex - vivo experiment to demonstrate how the coaxial snare technique works .
three items retrieved in our clinical cases , namely a vascular stent ( 10 mm in diameter , 8 cm in length ) , a small - bore catheter fragment ( 5-f ) , and a large - bore sheath fragment ( 8-f in internal diameter and 10-f in outer diameter ) , were used , together with a nitinol gooseneck snare ( 20 mm in loop diameter ) , two angiographic catheters ( 4-f and 5-f ) , a 0.035-inch guidewire , a 12-f dilator , and two vascular introducer sheaths ( 10 and 12-f ) .
the retrieval or repositioning of various items present in the vascular , biliary , or urinary system was successful in all cases .
in the two cases involving a misplaced vascular stent retrieval or repositioning was possible without changing the vascular sheath or additional vascular access . the fractured rigid venous sheath was retrieved using a minimum - sized vascular sheath ( 12-f ) , without folding . in the remaining four cases involving fractured catheters in the biliary or urinary system , the coaxial snare technique succeeded with the help of a coaxially engaged dilator . in no case were surgical procedures required , and no procedure - related complications were encountered .
simple snaring of a stent and catheter fragment resulted in the formation of a right angle between them and the snare axis ( figs .
owing to this angulation problem , it was necessary to fold the foreign objects prior to their retrieval by means of a simple snare technique ; consequently , a much larger sheath was required for their extraction .
in contrast , the coaxial snare technique greatly reduced the angle between the foreign objects and the snare axis , and allowed safe and smooth engagement between them and the sheath ( figs .
1b , 2b , 2c ) . where a larger - bore venous sheath fragment was used , however , the extent to which the angle was reduced was insufficient to permit retrieval through the sheath ( fig .
although a larger - bore sheath can solve the problem , it carries the risk of vascular injury . as a variant of the coaxial snare technique
, we used two access routes , the shorter one for a loop snare and the longer one for the retrieval of the sheath fragment . after capturing the fragment with a loop snare ,
3b ) . in order to eliminate the shoulder between the guidewire and the fragment , and to facilitate smooth extraction , a dilator
was then introduced through the sheath over the guidewire , and was tightly engaged with the end of the fragment ( fig .
case 1 . a 48-year - old man with liver cirrhosis which led to massive variceal bleeding
was referred to us for a transjugular intrahepatic portosystemic shunt ( tips ) procedure . after accessing the portal venous system via the right internal jugular route using a colapinto transjugular cholangiography / liver biopsy set ( cook , bloomington , ind .
, we dilated the parenchymal tract between the middle hepatic and left portal vein using a 10 mm - diameter ultrathin diamond balloon catheter ( medi - tech / boston scientific , watertown , mass .
we tried to place a 10 mm - diameter , 8 cm - long niti - s stent ( taewoong , seoul , korea ) in the tract , but during deployment it migrated caudad to the main portal vein ( fig .
a guidewire was inserted into the stent 's central lumen , and an amplatz gooseneck snare , its loop 25 mm in diameter , was introduced over it and positioned around the stent ( fig .
4b ) . after capturing and pulling the far proximal end of the stent by tightening the loop ( fig .
4c ) , we were able to relocate the stent to its appropriate position ( figs . 4c , 4d ) .
case 3 . a 42-year - old man with chronic renal failure underwent internal jugular venous catheterization at the bedside .
during the procedure , the tip of the 8-f internal diameter venous introducer sheath fractured and migrated to the right atrium . because the fragment moved vigorously in accordance with the patient 's heartbeat , it was necessary to prevent its migration to the right ventricle or pulmonary circulation . under fluoroscopic guidance , we inserted a 10-mm gooseneck snare through the right common femoral vein , successfully grasping the fragment and carefully pulling it back into the inferior vena cava ( fig .
5a ) . because the fragment was very stiff and its outer diameter was 10-f , it had to be removed without folding . to this end
, we used the modified coaxial technique illustrated in the ex - vivo study ( figs .
3b , 3c ) , inserting another 12-f vascular sheath ( 13 cm in length ) .
the puncture site was more cranial to the previous one , used for insertion of the loop snare ; the central lumen of the fragment was carefully located using an angiographic catheter and guidewire , and the dilator for the vascular sheath
after the dilator and the end of the sheath fragment were tightly engaged , the whole system was pulled back until the end of the fragment appeared at the femoral access site .
it was grasped with forceps and successfully extracted after release of the loop snare and careful compression of the puncture site ( fig .
a 51-year - old man with renal tuberculosis underwent periodic tube change under fluoroscopic guidance .
the external part of the nephrostomy catheter was resected close to the point at which it entered the body , and during the procedure , the remaining catheter fragment was inadvertently dislodged , entering the nephrostomy tract .
several attempts to capture it caused its further migration into the pelvocalyceal system . we used a homemade loop snare and amplatz gooseneck snare , also employing the ' in - situ loop snare ' technique , as described by savader et al . (
18 ) , but because the fragment was tightly wedged against the wall , were unable to withdraw any part of it ( fig .
, we managed to pass the guidewire through the central lumen of the catheter fragment , inserting the amplatz loop snare over the guidewire and easily capturing the proximal tip of the catheter fragment coaxially ( fig .
a dilator was introduced over the guidewire to eliminate the shoulder between it and the cut catheter end and to allow smooth extraction with minimal injury to the access route .
the entire system was successfully extracted by simultaneously withdrawing the snare and dilator through the tract ( fig .
simple snaring of a stent and catheter fragment resulted in the formation of a right angle between them and the snare axis ( figs .
owing to this angulation problem , it was necessary to fold the foreign objects prior to their retrieval by means of a simple snare technique ; consequently , a much larger sheath was required for their extraction .
in contrast , the coaxial snare technique greatly reduced the angle between the foreign objects and the snare axis , and allowed safe and smooth engagement between them and the sheath ( figs . 1b , 2b , 2c ) . where a larger - bore venous sheath fragment was used , however , the extent to which the angle was reduced was insufficient to permit retrieval through the sheath ( fig .
although a larger - bore sheath can solve the problem , it carries the risk of vascular injury . as a variant of the coaxial snare technique , we used two access routes , the shorter one for a loop snare and the longer one for the retrieval of the sheath fragment . after capturing the fragment with a loop snare ,
3b ) . in order to eliminate the shoulder between the guidewire and the fragment , and to facilitate smooth extraction , a dilator
was then introduced through the sheath over the guidewire , and was tightly engaged with the end of the fragment ( fig .
case 1 . a 48-year - old man with liver cirrhosis which led to massive variceal bleeding
was referred to us for a transjugular intrahepatic portosystemic shunt ( tips ) procedure . after accessing the portal venous system via the right internal jugular route using a colapinto transjugular cholangiography / liver biopsy set ( cook , bloomington , ind .
, we dilated the parenchymal tract between the middle hepatic and left portal vein using a 10 mm - diameter ultrathin diamond balloon catheter ( medi - tech / boston scientific , watertown , mass .
we tried to place a 10 mm - diameter , 8 cm - long niti - s stent ( taewoong , seoul , korea ) in the tract , but during deployment it migrated caudad to the main portal vein ( fig .
a guidewire was inserted into the stent 's central lumen , and an amplatz gooseneck snare , its loop 25 mm in diameter , was introduced over it and positioned around the stent ( fig .
4b ) . after capturing and pulling the far proximal end of the stent by tightening the loop ( fig .
4c ) , we were able to relocate the stent to its appropriate position ( figs . 4c , 4d ) .
case 3 . a 42-year - old man with chronic renal failure underwent internal jugular venous catheterization at the bedside .
during the procedure , the tip of the 8-f internal diameter venous introducer sheath fractured and migrated to the right atrium . because the fragment moved vigorously in accordance with the patient 's heartbeat , it was necessary to prevent its migration to the right ventricle or pulmonary circulation . under fluoroscopic guidance , we inserted a 10-mm gooseneck snare through the right common femoral vein , successfully grasping the fragment and carefully pulling it back into the inferior vena cava ( fig .
because the fragment was very stiff and its outer diameter was 10-f , it had to be removed without folding .
to this end , we used the modified coaxial technique illustrated in the ex - vivo study ( figs .
3b , 3c ) , inserting another 12-f vascular sheath ( 13 cm in length ) .
the puncture site was more cranial to the previous one , used for insertion of the loop snare ; the central lumen of the fragment was carefully located using an angiographic catheter and guidewire , and the dilator for the vascular sheath was then introduced over the guidewire ( fig .
after the dilator and the end of the sheath fragment were tightly engaged , the whole system was pulled back until the end of the fragment appeared at the femoral access site .
it was grasped with forceps and successfully extracted after release of the loop snare and careful compression of the puncture site ( fig .
a 51-year - old man with renal tuberculosis underwent periodic tube change under fluoroscopic guidance .
the external part of the nephrostomy catheter was resected close to the point at which it entered the body , and during the procedure , the remaining catheter fragment was inadvertently dislodged , entering the nephrostomy tract .
we used a homemade loop snare and amplatz gooseneck snare , also employing the ' in - situ loop snare ' technique , as described by savader et al . ( 18 ) , but because the fragment was tightly wedged against the wall , were unable to withdraw any part of it ( fig .
, we managed to pass the guidewire through the central lumen of the catheter fragment , inserting the amplatz loop snare over the guidewire and easily capturing the proximal tip of the catheter fragment coaxially ( fig . 6b ) .
a dilator was introduced over the guidewire to eliminate the shoulder between it and the cut catheter end and to allow smooth extraction with minimal injury to the access route .
the entire system was successfully extracted by simultaneously withdrawing the snare and dilator through the tract ( fig .
with the increasing use of indwelling catheters and interventional devices , the percutaneous retrieval of iatrogenic foreign bodies has become more common .
various techniques for retrieving unwanted objects from various systems have been reported : the devices used include the wire loop snare , retrieval basket , grasping forceps , tip - deflecting wire , pincher device , oversize sheath or catheter , and balloon catheter ( 1 , 3 , 4 , 8 , 14 - 17 ) .
since each technique has its own advantages and limitations , the decision as to which one to use in a particular case is reached only after extremely careful consideration .
retrieval baskets have proved useful in foreign body removal ( 1 , 8) , though there must be a free end or doubled - over segment , and they can not be guided .
many types of grasping forceps have been tried ( 4 , 19 ) , a major advantage of these over a snare or basket being their ability to seize a foreign body at its mid portion as well as its free ends .
any part of the fragment is caught by alligator jaws and pulled out through a catheter or sheath . however , their large size and rigidity , as well as the potential for damage to the vessel wall , have limited their popular use .
oversize sheaths or catheters can be used for the retrieval of foreign bodies such as iatrogenically placed guidewires or their fragments , but their applications are more limited than those of other devices ( 16 , 20 ) . the large number of reports on a variety of retrieval instruments and devices indicate that no particular technique has proven superior in all cases . however , loop snares are the devices most commonly used in retrieving foreign bodies , in part because they are inexpensive and simple , and can be assembled in any angiographic laboratory ( 1 , 2 ) . the snaring technique combines a high degree of success with very little risk of damage , but suffers certain limitations . to ensure a quick retrieval , experience and skill are required , and the outcome is successful only when the foreign body has a free - floating end or doubled - over segment that can be surrounded by the wire loop . because the nature , location and shape of a foreign body varies , so too does the snaring technique applied in a particular case ( 1 , 16 , 18 , 21 - 23 )
. when snaring of the free tip of a foreign body has failed , preliminary manipulation may be able to reorient or move the object by rotating and pulling it to a more easily accessible position ( 3 , 24 ) .
successful preliminary manipulation may involve the use of a catheter , a steerable wire , or grasping forceps .
the coaxial snare technique , as used in our cases , is a variant of the loop snare technique , and a number of reports have described its use ( 8 , 9 , 25 , 26 ) . in most of those cases , however , the guidewires used for deployment were still in place within the lumina of the misplaced stents or catheters . in five of our seven cases , we had no safety guidewire within the lumina of the objects involved , so actively located the central lumen of each object using an angiographic catheter and guidewire .
according to our clinical experience and the results of the ex - vivo experimental study , the placement of a guidewire through the center of the objects not only allowed their rapid capture with a loop snare but also greatly reduced the angle between them and the snare axis .
not only the use of the coaxial snare technique , but also the engagement of a dilator with the end of a fragmented catheter , eliminated the shoulder between the guidewire and the catheter and allowed its safe and smooth extraction without injury to the access route .
however , it is sometimes very difficult to locate the lumen of a free - floating fragment within a greater patulous space ; where patency is impaired , as with a chronically indwelling catheter fragment , it may be impossible . for retrieval of an intravascular foreign body using the coaxial snare technique ,
the minimum inner diameter of the vascular sheath should be greater than the sum of the outer diameter of the foreign body and the catheter used with the loop snare . in order to minimize the profile of the retrieval system for large - bore intravascular foreign objects ,
the use of a coaxial system using dual vascular access , as in our case 3 , should be considered . using this modified technique , it was possible -although an extra vascular access site
was required for the loop snare- to retrieve a large - bore rigid intravascular foreign body without folding it . in this system , since the engaged dilator permits smooth extraction of the fragment through the access site , complete engagement between the fragment and the sheath is not mandatory .
the profile of an introducer sheath can thus be minimized : one which is only slightly larger than the outer diameter of the foreign body is suitable .
metallic stents are important as remedial components of the vascular , biliary , bronchial , urinary , and gastrointestinal systems . as with any procedure , however , there are potential complications , one of which is stent misplacement or migration .
the literature includes cases of stent migration involving the biliary tree ( 12 , 13 ) and the arterial system ( 9 , 28 ) , and of those which occur during tips procedures ( 25 - 27 ) , and we have described the use of a loop snare to relocate or retrieve stents misplaced during a tips or pta procedure .
the ability to retrieve or relocate misplaced stents improves the safety and efficacy of stenting procedures , and it is important , in case misplacement occurs , to keep the guidewire in place within the stent .
technically , snaring and removing a stent by means of the coaxial snare technique is quite simple . to prevent the stent escaping completely , and in order to facilitate passage of the snare loop around it , it is essential that the guidewire remains within the stent throughout the procedure . after snaring its barrel ,
the stent can be either relocated to the desired position or removed . in some instances ,
the snare can not be positioned around the leading margin of the stent , a problem which is usually solved by inflating a balloon at its mouth , thus allowing the snare to pass more easily over the margin . broken diagnostic or indwelling catheter is a not uncommon problem , and one which may well arise if a catheter is reused , or stored for a long time . where catheters are broken , or foreign bodies with lumina are present , the coaxial snare technique can be safely used for retrieval . if direct snaring is possible and there is no chance of traumatic injury , the coaxial technique is not necessary . if , however , the lumina of the objects to be retrieved by the guidewire can be located , placement of the loop snare over the objects
will be easier , and removal will be safer and smoother , as shown in our ex - vivo study and clinical cases . in conclusion , the coaxial snare technique , an application of the loop snare technique , allowed the safe and effective percutaneous retrieval of tubular foreign bodies or stents , without folding , and traumatic injury to the patient during the procedure was minimized .
 objectiveto evaluate the utility and advantages of the coaxial snare technique in the retrieval of tubular foreign bodies.materials and methodsusing the coaxial snare technique , we attempted to retrieve tubular foreign bodies present in seven patients . 
 the bodies were either stents which were malpositioned or had migrated from their correct position in the vascular system ( n=2 ) , a fragmented venous introducer sheath ( n=1 ) , fragmented drainage catheters in the biliary tree ( n=2 ) , or fractured external drainage catheters in the urinary tract ( n=2 ) . after passing a guidewire and/or a dilator through the lumina of these foreign bodies , we introduced a loop snare over the guidewire or dilator , thus capturing and retrieving them.resultsin all cases , it was possible to retrieve or reposition the various items , using a minimum - sized introducer sheath or a tract . 
 no folding was involved . in no case 
 were surgical procedures required , and no complications were encountered.conclusionthe coaxial snare technique , an application of the loop snare technique , is a useful and safe method for the retrieval of tubular foreign bodies , and one which involves minimal injury to the patient . 
MATERIALS AND METHODS
RESULTS
Ex-vivo manipulations
Illustrative cases
DISCUSSION