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Four stages of the thrombus evolution could be observed.The acute thrombosis(days 1 to 5)appeared strongly hypointense in T-weighted images and isointense in spin density-and T-weighted images.In the subacute stage (up to day 15)the thrombus signal was strongly hyperintense in T1-and T2- weighted images.The third stage began in the third week after clinical onset.The thrombus signal was decreased in all sequences and showed an increasing in homogeneity.The fourth(late)stage was characterized by either the restitution of blood flow or the persistence of a residual thrombus.Each stage requires a different diagnostic approach.With the combined use of spin-echo and gradient-echo sequences,it is possible to make the diagnosis of acute thrombosis,in the second stage,multiplantar spin-echo sequences are sufficient.Diagnosis of dural sinus thrombosis can be established accurately with magnetic resonance imaging in the first two stages.However,the diagnosis of the later stages is difficult because of inhomogeneous signs of recanalization and flow phenomena.Therefore,a suspected older dural sinus thrombus still requires intra-arterial angiography as the primary diagnostic tool. |
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