Why is a vena cavogram performed before IVC filter placement?
A vena cavogram is performed to evaluate the size, anatomy, and patency of the IVC. It is important to know the diameter of the IVC because each filter can be safely placed in vessels up to a certain size. Most IVC filters can be placed in a cava up to 28 mm in diameter, whereas a bird’s nest filter can be used in a cava up to 40 mm. Filters can migrate into the heart or pulmonary arteries if they are not sized appropriately. Ideally, the tip of the filter should rest in the infrarenal IVC. A vena cavogram is helpful in identifying the location of the renal veins and variant anatomy that may affect filter placement. The presence of a nonocclusive clot in the cava may change the approach used to place the filter or its location. A jugular approach may be used when there is a large clot low in the IVC to help prevent pushing the clot centrally. To be effective, a filter needs to be placed above any clot in the IVC; this may warrant suprarenal placement.