Cerebrospinal fluid volume depletion and its emerging clinical/imaging syndromes.

Cerebrospinal fluid (CSF) volume depletion, due to CSF leakage or CSF shunt overdrainage, is typically indicated when patients present with orthostatic headaches, with or without several other symptoms: neck or interscapular pain, nausea, emesis, diplopia, changes in hearing, visual blurring, facial numbness or weakness, and radicular upper-limb symptoms. Cerebrospinal fluid pressures typically are quite low and head magnetic resonance images typically reveal diffuse pachymeningeal gadolinium enhancement, with or without evidence of sagging of the brain and less frequently with subdural fluid collections, enlarged cerebral venous sinuses or pituitary gland or decreased ventricular size. Magnetic resonance imaging has revolutionized detection of spontaneous CSF leaks, leading to identification of far more cases and recognition of several clinical/imaging forms of presentation of the disorder. These forms, which are different from the "typical" presentation, include a group with consistently normal CSF pressures (normal pressure), another group without abnormal meningeal enhancement (normal meninges), and a group without headache (acephalic). Each of these forms can be seen in a setting of documented and ongoing CSF volume depletion. Awareness of CSF volume depletion is increasing, and its clinical and imaging spectrum is broadening.