Subarachnoid hemorrhage CT

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Template:Saram

CT

The diagnosis of subarachnoid hemorrhage cannot be made on clinical grounds alone. Medical imaging is usually required to confirm or exclude bleeding. The modality of choice is computed tomography (CT/CAT) of the brain. This has a high sensitivity (it will correctly identify >95% of the cases), especially on the first day after the onset of bleeding.

• Subarachnoid hemorrhage 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 Subarachnoid hemorrhage 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 Subarachnoid hemorrhage, CT is useful in localizing the source of bleeding.

Images courtesy of RadsWiki

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  CT: Diffuse subarachnoid hemorrhage
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  CT: Diffuse subarachnoid hemorrhage
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  CT: Diffuse subarachnoid hemorrhage
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  CT: Diffuse subarachnoid hemorrhage

Once a subarachnoid hemorrhage is confirmed, the next question is about its origin. CT angiography (using radiocontrast) to identify aneurysms is generally the first step, as invasive angiography (injecting radiocontrast through a catheter advanced to the brain arteries) has a small rate of complications but is useful if there are plans to obliterate the source of bleeding, such as an aneurysm, at the same time.