Spontaneous cerebrospinal fluid leaks: from intracranial hypotension to cerebrospinal fluid hypovolemia--evolution of a concept.

Intracranial hypotension causes orthostatic headaches and diffuse pachymeningeal gadolinium enhancement on magnetic resonance imaging with or without subdural fluid collections or imaging evidence of descent of the brain. A review of the literature and my experience and investigations in the past decade reveal a broadening clinical and imaging spectrum of the syndrome. Besides the classic clinical-imaging syndrome of orthostatic headaches, diffuse pachymeningeal gadolinium enhancement, and low cerebrospinal fluid (CSF) pressure, several modes of presentation are recognized, including (1) the typical clinical-imaging syndrome with CSF pressures consistently within normal limits, (2) absence of diffuse pachymeningeal gadolinium enhancement with presence of low CSF pressures and typical clinical manifestations, and (3) absence of headaches despite low CSF pressures and presence of diffuse pachymeningeal gadolinium enhancement. Furthermore, in some patients with headaches, the orthostatic headaches may evolve into lingering chronic daily headaches, although they may be more prominent in upright positions. What determines the various clinical and imaging features of this syndrome seems to be the loss of CSF volume as the independent variable, while other manifestations, including clinical features, CSF pressures, and imaging abnormalities, are variables dependent on the CSF volume. The term CSF hypovolemia is proposed for this syndrome because the term intracranial hypotension no longer seems adequate to embrace all the variations that have emerged.