Discussion of Subarachnoid hemorrhage
- Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space around the brain and spinal cord.
- Common causes of SAH include the following:
- Less frequent etiologies of SAH
- Arteriovenous malformation
- Arterial dissection
- Extension from intracerebral hemorrhage
 Imaging Findings for Subarachnoid hemorrhage
- SAH appears as a high-attenuating, amorphous substance that fills the normally dark CSF-filled subarachnoid spaces.
- These findings are most evident in the largest subarachnoid spaces, such as the suprasellar cistern and Sylvian fissures.
- Acute SAH is typically 50-60 HU.
- When CT scanning is performed several days to weeks after the initial bleed, the findings are more subtle.
- The initial high-attenuation of blood and clot tend to decrease, and these appear as intermediate gray.
- These findings can be isointense relative to normal brain parenchyma.
- In addition to detecting SAH, CT is useful in localizing the source of bleeding.
- Fluid-attenuated inversion recovery (FLAIR) is the most sensitive MRI pulse sequence for the detection of SAH. SAH appears as high-intensity signal in normally low signal CSF spaces.
- T2- and T2*-weighted images can potentially demonstrate SAH as low signal intensity in normally high-signal subarachnoid spaces.
- On T1-weighted images, acute SAH may appear as intermediate- or high-intensity signal in the subarachnoid space.
- MR angiography may be useful in the evaluation of aneurysms and other vascular lesions that cause SAH.
Patient #1: CT images demonstrate diffuse subarachnoid hemorrhage
 See Also
- Perimesencephalic hemorrhage
- Epidural hematoma
- Subdural hematoma
- Intracerebral parenchymal hemorrhage
- Intraventricular hemorrhage
 External Links
 References for Subarachnoid hemorrhage
- Abner Gershon.E-medicine radiology article