Clinical significance of free-floating venous thrombi.

To evaluate the fate of free-floating venous thrombi, venous duplex scans of 5238 consecutive lower extremities over a 2 1/2 year period were reviewed. Acute deep venous thrombosis was found in 732 cases. Eighty-two free-floating deep venous thrombi were diagnosed in 73 of these patients. Nine of 72 patients (13%) had pulmonary emboli as diagnosed by ventilation perfusion scanning or pulmonary angiography or both. Seven of these patients (78%) had a pulmonary embolus before the initial duplex scan. Two (22%) had a pulmonary embolus after the diagnosis of free-floating thrombus. Thirty-three of 73 patients (45%) had follow-up of free-floating thrombi by duplex scanning performed in the acute period (less than 30 days): 18 (55%) showed attachment of the free-floating thrombus, three (9%) showed progression in size of the free-floating tail, and eight (24%) showed decrease in size or resolution of the free-floating thrombus. Four (12%) showed persistent thrombus without evidence of resolution, propagation, or attachment. In conclusion, free-floating venous thrombi occurred in 10% of cases of acute deep venous thrombosis. Only 13% of free-floating thrombi were associated with clinically significant pulmonary emboli, confirmed by ventilation perfusion scanning. Usually the embolus occurred before diagnosis of free-floating thrombus. Most free-floating thrombi followed noninvasively by duplex scanning do not embolize, but rather they become attached to the vein wall or resolve.