Venous sinuses in brain. Coloured three- dimensional computed tomography (CT) scan of the venous sinuses (white) on the surface of the brain. The front of the brain is at top. The venous sinuses are wide channels that drain deoxygenated blood from the brain. They are found in the dura mater, the tough membrane that lies between the brain and the skull. The sinuses have been injected with a contrast medium to allow them to be seen on this scan. CT scans use X-rays to construct images of parts of the body.