Head CT > Stroke > Subarachnoid Hemorrhage

Subarachnoid Hemorrhage

In the absence of trauma, the most common cause of subarachnoid hemorrhage is a ruptured cerebral aneurysm. Cerebral aneurysms tend to occur at branch points of intracranial vessels and thus are frequently located around the Circle of Willis. Common aneurysm locations include the anterior and posterior communicating arteries, the middle cerebral artery bifurcation and the tip of the basilar artery. Subarachnoid hemorrhage typically presents as the "worst headache of life" for the patient. Detection of a subarachnoid hemorrhage is crucial because the rehemorrhage rate of ruptured aneurysms is high and rehemorrhage is often fatal.
CT is currently the imaging modality of choice because of its high sensitivity for the detection of subarachnoid hemorrhage. CT is most sensitive for acute subarachnoid hemorrhage. After a period of days to weeks CT becomes much less sensitive as blood is resorbed from the CSF. If there is a strong clinical indication, LP may be warranted despite a negative CT since small bleeds can be unapparent on imaging.
On CT, a subarachnoid hemorrhage appears as high density within sulci and cisterns. The insular regions and basilar cisterns should be carefully scrutinized for subtle signs of subarachnoid hemorrhage. Subarachnoid hemorrhage may have associated intraventricular hemorrhage and hydrocephalus.

High density blood fills the cisterns (arrowheads) in
this patient with hemorrhage from the left middle cerebral
artery. Note the middle cerebral artery aneurysm (arrows).

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