A particular form of hemorrhagic stroke is subarachnoid hemorrhage. Cerebral aneurysms are in general responsible for it. In the acute phase CT is the best method for the evaluation of the hemorrhagic stroke. MR is superior in the subacute-chronic phase. Cerebral angiography is not needed in hypertensive haemorrhage, but should be performed in the majority of other cases, in particular if we suspect a vascular malformation.
Ischemia is the most frequent cause of stroke.
It is due to a critical local diminished blood flow to brain parenchyma. Another cause is a thromboembolism in cardiac diseases. In the very acute phase CT is frequentely negative. However this finding can be useful in final diagnosis. MR is certainly more sensitive in the detection of ischemic lesions, in particular using diffusion-weighted images.