A CLINICAL DIAGNOSIS: Headache which appears in the upright position and subsides in the reclining position is suggestive of intracranial hypotension Brain magnetic resonance imaging can eliminate an intracranial tumoral process. In most cases, contrast images after gadolinium injection show a diffuse hypersignal of all the meninges including the falx cerebri and the tentorium cerebelli.This clinical presentation is sufficient for diagnosis. Occurring after a recent neurosurgical procedure, the intracranial hypotension is termed secondary. Inversely, is no known cause can be identified, the condition is termed spontaneous.If the clinical manifestations are somewhat doubtful, a spinal tap can reveal the very low pressure of the cerebrospinal fluid (CSF) although it is advisable to avoid further loss of fluid.It is generally accepted that intracranial hypotension results from leakages of CSF through a breach in the dura mater caused by untreated trauma to a particularly fragile area due to a meningocele or an arachnoid cyst for example. Occasionally, the CSF leak can be evidenced with isotopic labeling used to visualize the breach and guide therapy.By analogy with the spinal tap syndrome, a blood-patch with autologous blood is usually proposed as first line medical treatment. Prognosis is generally good.