''Bull's-eye'' sign on gadolinium-enhanced magnetic resonance venography determines thrombus presence and age: A preliminary study

Purpose: Venous thrombosis is associated with a significant inflammatory response, which can be visualized by gadolinium magnetic resonance venography (MRV). Gadolinium extravasates into tissue during inflammation, producing perithrombus enhancement on magnetic resonance scanning. This study determines (1) whether gadolinium enhancement occurs during deep venous thrombosis (DVT); and (2) whether this enhancement changes with time and can therefore establish the age of thrombus. Methods: Patients with a diagnosis of iliofemoral DVT by duplex ultrasound who were referred for MRV to document central thrombus extent were studied. T1 weighted images were obtained before and after gadolinium injection (0.1 mmol/kg); repeat scans were obtained up to 3 months thereafter. At the level of maximum thrombus, measurements of signal intensity were made at the periphery (rim), and the center of the thrombosed vein, as well as the contralateral normal vein, on images after gadolinium enhancement. Rim-center vein signal intensity ratios were then calculated and followed. Results: A total of 39 scans were obtained in 14 patients (eight men, six women). The thrombosed veins were enlarged, with a peripheral rim of enhancement (''bull's-eye'' sign). The rim-center ratio for thrombosed veins (2.16 +/- 0.18) was different from that of normal veins (0.66 +/- 0.10; n = 39; p < 0.001). For all acute studies (less than or equal to 14 days) the rim-center ratio was 2.38 +/- 0.17 (n = 31), whereas for all chronic studies (>14 days) the rim-center ratio was 1.29 +/- 0.44 (n = 8; p = 0.001). Among patients who underwent both early and late studies, the rim-center ratio dropped significantly, from 2.33 +/- 0.20 acutely to 1.29 +/- 0.44 in chronic studies (n = 8; p = 0.03). One patient with active malignancy had a paradoxic increase in rim-center ratio over time and a clinical recurrence of symptoms, suggesting active thrombosis. Conclusions: We conclude that (1) a pattern of peripheral gadolinium enhancement (bull's-eye sign) is seen around acutely thrombosed veins on gadolinium-enhanced MRV, facilitating DVT diagnosis; and (2) the ratio of signal intensity at the rim versus the center of the thrombosed vein may be a good discriminator of acute compared with chronic DVT, which may help direct therapy.