Abnormal spinal meningeal morphology Empty delta sign 2019-01-27T20:21:18Z The use of multislice contrast-enhanced CT scan, with reconstructions into thinner slices in different planes, markedly improves the yield. The sign may not be seen in the early stage (less than 5 days) of thrombosis, as the fresh clot is hyperdense, or in the late stage (after more than 2 months), as numerous channels of recanalization develop in the thrombus after 2 months. See figure 5 in PMID:29089832. This sign is created by a nonenhancing thrombus in the dural sinus surrounded by triangular enhancing dura as seen on cross-section. The sign, seen on contrast-enhanced CT scan images, suggests dural sinovenous thrombosis. It is best seen on wider window settings. It is a reliable sign of sinus thrombosis but is seen only in 25-30% of these cases.