Hyperdensity of cerebral vasculature and venous sinuses may be associated with Polycythemia. Polycythemia may mimic as well as cause venous thrombosis, confounding non-enhanced computer tomography findings. One should meticulously rule out the cause of hyperdense vasculature by MR venogram, CT venography or catheter venography.

From the manuscript

Non-Enhanced CT Mimicking Contrast Enhanced CT - A Case Report on Polycythemia

Abstract
Diffuse hyperdense cerebral vasculature is sometimes encountered on non-enhanced computed tomography, and polycythemia is one of the conditions which appears the same. The current case report is of a case of 37-year-old female patient arrived with a complaint of feeling severe headache for the past 3 days which was insidious in onset, diffuse in nature and it did not respond to any medication. NECT brain study showed the hyperdense circle of Willis and cerebral venous sinuses. Contrast was not administered for computed tomography study of the brain. On blood investigations, the patient had raised hematocrit level (74%). The hyperdense vessel was due to raised hematocrit (Polycythemia Vera).