Filters surgical placement

Clinical
                                        From initial open surgical placement, insertion of inferior vena cava filters has evolved into a percutaneous technique using an introducer sheath. Indications for inserting inferior vena cava filters have expanded from patients who had a pulmonary embolus and could not be anticoagulated to those at risk for emboli. Ease of filter insertion and reduced associated morbidity have expanded the indications further, although in a setting of a pulmonary embolus anticoagulation is generally the first step.Recurrent emboli in the face of adequate anticoagulation or a complication of anticoagulation, such as bleeding, indicates the need for filter insertion. Contraindications to anticoagulation include a recent hemorrhage, with other contraindications often relative and at times subjective.
A number of vena cava filters are available. They differ in their appearance, such as cone, basket,or net; in their construction material and thus radiodensity; and in whether they are readily removable. In broad terms, all filters trap most clots, but some pulmonary emboli are unavoidable. At times vena caval filters are inserted temporarily, such as in the presence of iliac vein or caval thrombi and or in the risk of embolization during thrombolysis. Carbon dioxide is an alternate contrast agent for vena cavography during filter insertion when iodinated contrast agents are contraindicated or in those patients with renal insufficiency.
Complications
Complication rates for radiologic and surgical placement of inferior vena cava filters appear comparable although in one institution radiologists achieved a higher success rate and fewer
complications; part of the reason may be that radiologists tended to perform cavography prior to filter placement and surgeons did not. A review of over 1700 implanted filters at one institution (up to 1998) found a 6% prevalence of observed postfilter pulmonary emboli, fatal in 4% of patients, with most fatal pulmonary emboli occurring a median of 4 days after filter insertion; the prevalence of observed postfilter caval thrombosis was 3%. Intrafilter clots are not uncommon. Benefit must be balanced against risk. Other filter complications include malposition,
filter tilting, and insufficient opening. Ideally, a filter is positioned between the ileal vein confluence and renal veins. A filter cephalad to the renal veins risks renal vein thrombosis. Mild filter tilting is common, but the ability to trap clots is reduced with excessive tilting. Likewise, insufficient filter opening reduces a filter’s clot trapping ability. A filter is designed to prevent pulmonary emboli, and the evidence of such an embolus after filter placement represents filter failure. In such a situation the filter should be investigated for migration, strut failure, or inferior vena cava thrombosis. Filter migration occurs either caudal or cranial.Vena caval thrombosis is a recognized filter complication, regardless of filter design. Some caval thrombi are asymptomatic. Even without a thrombus, extremity venous stasis tends to accentuate after filter placement. Rare complications include myocardial infarction due to filter migration and pericardial tamponade.
Filter perforation is rare. Anecdotal reports describe caval penetration resulting in pancreatitis and even biliary obstructive. Filter struts can fracture and migrate, including to the kidneys. Rare reports describe penetration of a
vertebral body and caval perforation leading to small bowel volvulus.
Caval filters are recognized on contrastenhanced SGE MRI because of their symmetry and magnetic artifacts. Incidentally, J-tipped guidewires should be
used with care around filters; these guidewires are at risk for entrapment.
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