[Acute headache--diagnostic considerations].

Acute headache may be the presenting symptom of several conditions. Sometimes, a headache with an abrupt onset and unusual severity may occur, experienced by the patient as the worst headache ever. The diagnostic evaluation primarily aims at ruling out subarachnoid haemorrhage (SAH), as well as other serious causes of acute headache, such as meningitis or stroke. The clinical examination should immediately be followed by cerebral computed tomography (CT). A CT scan will reveal 95% of SAHs, provided that it is performed within the first 24 hours after headache onset. If the CT scan is normal, a lumbar puncture should follow, preferably 12 hours after the onset of headache, unless infectious meningitis is suspected. If infectious meningitis is strongly suspected, lumbar puncture should be performed without delay. The spinal fluid should be investigated by spectrophotometry, in order to obtain optimal diagnostic accuracy for SAH. This article briefly reviews the various conditions that may present with an acute headache.