Spontaneous intracranial hypotension.

Since the introduction of magnetic resonance imaging (MRI), spontaneous intracranial hypotension has been diagnosed much more frequently. The aim of this review is to discuss the symptoms and signs of the condition, in particular the characteristics of the associated headache, with sudden onset after sitting or standing, so that it can be included under the rubric of 'thunderclap headache'. This type of headache, like post lumbar puncture headaches, may be caused by cerebral vasodilatation and exacerbated by lowered pressure of the cerebrospinal fluid (CSF). Other symptoms include neck stiffness, nausea, vomiting, vertigo, tinnitus, deafness, and cognitive abnormalities. The clinical picture can sometimes mimic frontotemporal dementia, and the behaviour of some patients can sometimes be described as hypoactive-hypoalert, with somnolence, impaired attention, and stereotyped motor activity. Sagging of the brain, caused by leakeage of the CSF, can cause lesions in the brainstem with stupor, gaze palsies, and cranial nerve palsies. The condition can be a risk factor for cerebral venous thrombosis because of slowing of the blood flow and distortion of the blood vessels. The clinical picture may well suggest the diagnosis, but the headache may possibly indicate a subarachnoid haemorrhage. However, MRI will help to confirm the diagnosis and to localize the site of the CSF leak. MRI myelograms are of particular value, but if they are equivocal a computed tomography myelogram should be performed. The leakage of CSF is due to a tear in the dura, most frequently where the spinal roots leave the subarachnoid space. If this does not heal with bedrest, an epidural blood patch or a percutaneous injection of fibrin glue may be needed. More information is required on long-term follow-up.