The malpositioned Greenfield filter: lessons learned.

It is essential that a malpositioned Greenfield filter be recognized as such immediately. Three of the 21 Greenfield filters inserted in the current study were malpositioned. One was placed in the right renal vein, one in the right common iliac vein, and another in the right inferior vena cava in a patient with caval duplication and left ileofemoral thrombosis. A review of the postprocedure radiographs was performed. It was found that two of the three malpositioned filters were at an appropriate vertebral level, and, therefore, this single criteria was inadequate to judge proper filter positioning. A more reliable parameter was the maximal diameter of the open legs of the filter. The mean diameter of the legs in the correctly positioned filters was 29.9 mm compared with 19.0 mm for the malpositioned filters. The authors recommend that the diameter of the filter legs be measured on all postprocedure radiographs. If this diameter is not 30 +/- 4 mm (two standard deviations), then malposition of the filter should be suspected, regardless of the vertebral level at which the filter lies.