Specific Imaging Findings

Increased density in the occluded sinus leading to a “cord sign” is the classic imaging finding of dural venous sinus thrombosis (DVST) on unenhanced CT images. However, a high variability in the degree of thrombus density is responsible for a low sensitivity of this sign. Thus, evaluation with CT angiogram, MR and MRV may be required to confirm the diagnosis. The “empty delta” sign consisting of a triangular area of enhancement with a relatively low-density center is seen in 25-30% of cases on contrast-enhanced CT scans. On MRI, acute thrombus is T1 isointense, T2 and T2* hypoin-tense. Of note, this T2 hypointensity may mimic normal flow-void. Peripheral enhancement is seen around the acute hypointense clot corresponding to the empty delta CT sign. Subacute thrombus becomes T1 and T2 hyperintense. Chronic thrombus is most commonly T1 isointense and T2 hyperin-tense. DWI/ADC signal of the thrombus is variable, as is the degree of enhancement in organized thrombus. Visible serpiginous intrathrombus flow-voids on T2WI, corresponding areas of flow signal on TOF-MRV, and brightly enhancing channels on post-contrast MRV are present in most cases of chronic partial recanalization. Thrombosis shows no flow-related signal on phase contrast MRV, and absent to diminished enhancement on post contrast MRV and CTV. Engorged collateral veins may be present, primarily in the chronic phase. TOF-MRV of a subacute T1 bright clot may potentially misrepresent sinus patency.