Richard I. Farb
Gadolinium-enhanced MR venography has provided neuroradiologists with the ability to visualize the effect that altered intracranial pressure (ICP) has on the appearance of the dural venous sinuses. Specifically, the dural sinuses appear mildly compressed when ICP is elevated and will distend when ICP is abnormally low. This changing contour of the dural sinuses has been shown to be a dynamic phenomenon, and is displayed nicely by the transverse sinuses. Narrowing of the distal transverse sinus associated with elevated ICP is best visualized with gadolinium-enhanced MR venography and typically seen in idiopathic intracranial hypertension as well as other pathologic states associated with elevated ICP. Enlargement of the dural venous sinuses is one of the well-recognized stigmata of intracranial hypotension. Clearly, in imaging patients with headache, it would be beneficial to be able to comment on the presence or absence of intracranial hypotension without the use of gadolinium.
After reviewing several patients with this clinical syndrome it became evident that by applying the criteria of the “venous distension sign” (VDS)—a convex undersurface of the middle third of the dominant transverse sinus—we could determine, in a binary fashion, whether there was presence or absence of intracranial hypotension. We have found the VDS particularly useful when evaluating patients with subdural hemorrhage or hygroma. A positive VDS in a patient with subdural collections indicates that intracranial hypotension is present and is likely the primary abnormality. Conversely, it is worth checking for the VDS in patients suspected of having Chiari type I malformations. The greatest challenge in imaging intracranial hypotension is not in the diagnosis but in identifying the cause.