Lesions within the dural sinuses (e.g., superior sagittal sinus, transverse sinus…) and not external compression of the sinus by a mass.
1. dural sinus thrombus: acute thrombus is hyperdense on CT, and hyperintense on T1 MRI
2. tumor: especially parasagittal meningiomas (up to 50% invade the superior sagittal sinus)
3. focal sinus stenosis: e.g., transverse sinus stenosis is common in pseudotumor cerebri (bilateral stenosis was seen in 93%). This may be causative in some cases of pseudotumor, but it may be a result of increased CSF pressure in some. Transverse sinuses are normally asymmetric, with the right usually larger/dominant
4. giant arachnoid granulation: most common in the transverse sinus in the middle or lateral third with a slight left-sided prevalence, the superior sagittal sinus is the next most common location
Typically > 1 cm diameter. May erode into the inner table of the skull. The arachnoid granulation does not enhance (but there is often a linear central enhancing vessel, presumably a vein) and does not show diffusion restriction on DWI MRI