Spontaneous intracranial hypotension.

Spontaneous intracranial hypotension is a rare benign and usually self-limited condition of unknown aetiology. Four cases are presented that illustrate how the MRI features may support a diagnosis suggested on clinical grounds. The MRI findings include diffuse symmetric smooth dural thickening and enhancement, not only at the cranial level, but also involving the cervical spinal dura, subdural effusions and downward displacement of the cerebellar tonsils.