CSF hypovolemia vs intracranial hypotension in “spontaneous intracranial hypotension syndrome”

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Abstract
Objectives: To investigate the role of CSF hypovolemia in spontaneous intracranial hypotension (SIH) syndrome because so-called SIH syndrome sometimes lacks intracranial hypotension. Methods: Ten women (aged from 28 to 49 years) with characteristic orthostatic headache without a previous history of dural tear were investigated. In addition to gadolinium (Gd)–enhanced brain MRI, spinal MRI with and without Gd enhancement was performed. Results: Gd-enhanced brain MRI demonstrated diffuse pachymeningeal enhancement in all patients. Sagittal T2-weighted spinal MRI revealed a variable amount of CSF in the extradural space in all patients. Sagittal T2-weighted MRI or axial Gd-enhanced T1-weighted MRI showed dilated epidural veins located in the high cervical portion in each patient. The intensity of dilatation of the epidural veins correlated significantly with the amount of CSF in the epidural space. This suggested that the Monro–Kellie doctrine was applicable in this circumstance. Conclusions: Since some patients with SIH syndrome have normal CSF pressure and since a downward displacement of the brain due to a reduction of the buoyant action of CSF may induce symptoms, CSF hypovolemia, not intracranial hypotension, may be the cause. Based on the Monro–Kellie doctrine, detecting leaked CSF and venous engorgement (epidural vein dilatation and pachymeningeal enhancement) is an important clue to diagnose so-called SIH syndrome. Dilatation of epidural veins suggests CSF hypovolemia in appropriate conditions.