The cord sign refers to cordlike hyperattenuation within a dural venous sinus on non-contrast enhanced CT of the brain due to dural venous sinus thrombosis. The sign is most commonly seen in the transverse sinus because along the origin of the tentorium it runs approximately in the axial plane such that it is visible on one image.
It is important to appreciate that normal blood within the dural sinuses is usually of slightly increased density relative to brain parenchyma and that true hyperdensity is the key to recognizing thrombosis. A false positive cord sign may also be seen in the setting of generalized cerebral edema when it is actually the brain which is of reduced density rather than the sinus being hyperdense.
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