Cerebral venous thrombosis is a rare (but dangerous) cause of headaches and strokes in patients below the age of 50. It includes thrombosis of the cerebral veins and major dural sinuses.
A d-dimer can NOT be used to rule it out, as it would be falsely negative in up to 40% of patients. A dry head CT is completely normal in 30% of patients, with nonspecific changes present in another 30%.
Take home: If you are considering the diagnosis, obtain a CT venography (95% sensitive) and don’t rely on a negative dimer or dry head CT.
Long B, Koyfman A, Runyon MS. Cerebral Venous Thrombosis: A Challenging Neurologic Diagnosis. Emerg Med Clin N Am 35 (2017) 869–878