[Acute headache: limitations of cerebral computed tomography and analysis of cerebrospinal fluid in the diagnosis of subarachnoid haemorrhage].

Subarachnoid haemorrhage constitutes a neurological emergency. In most cases the diagnosis is easy to establish by cerebral computed tomography or cerebrospinal fluid tap. However, in rare cases verification of the diagnosis is more difficult and a residual uncertainty remains. We describe three patients supposed to have a subarachnoid haemorrhage without pathological findings in both cerebral computed tomography and cerebrospinal fluid. In these cases vasospasm or cerebral aneurysm were detected by means of transcranial Doppler sonography and/or conventional angiography. We comment on the special features of this rare presentation of a severe acute neurological emergency, and we discuss diagnostic work-up and differential diagnoses.