Cervical MRI of eight patients with severe orthostatic headache showed a convex-shaped, prominent, dilated anterior, internal vertebral venous plexus with a flow-void signal in all patients and in seven also extra arachnoid fluid collection. Follow-up MRI showed resolution of the abnormalities in all patients. The authors hypothesize that these findings reflect disturbed compensatory vascular mechanisms by which autoregulation of the CSF pressure tries to compensate for the reduced CSF volume.