Diagnosis and differential diagnosis of non-traumatic subarachnoid hemorrhage

Non-traumatic subarachnoid haemorrhage (SAH) is by far most frequently caused by a rupture of an intracranial aneurysm. Apart from that, the differential diagnosis consists of a heterogeneous group of diseases. Clinical presentation and patterns of SAH which differ from the "typical" aneurysmal SAH are described in this review. Characteristic findings in vascular and parenchymal neuroimaging are reported. MRI is of great importance in detecting focal and subacute subarachnoid bleeding which is negative on CT. Intra-arterial angiography is still mandatory and obligatory for exact classification of arteriovenous malformation and fistula, especially prior to treatment by a multidisciplinary team. Finally, the radiologist should keep in mind that various artifacts on CT or MRI, such as pseudo-SAH, might simulate an SAH.