In suspected subarachnoid hemorrhage with a negative CT, which imaging test can identify an aneurysm?

• A. MRI without contrast.
• B. CT angiography can identify aneurysm.
• C. Ultrasound of the head.
• D. Electroencephalography can identify aneurysm.

Answer: (B)

When subarachnoid hemorrhage is suspected but the noncontrast CT is negative, the priority is to visualize the brain’s arteries to look for an aneurysm. CT angiography uses intravenous contrast with CT imaging to render the cerebral vessels, so an aneurysmal dilation or irregularity stands out clearly. It’s fast, widely available, and has high sensitivity for detecting intracranial aneurysms, making it the best choice in this scenario.

MRI without contrast doesn’t reliably visualize vessels without contrast enhancement, so it’s not ideal for identifying an aneurysm. Ultrasound of the head (transcranial Doppler) assesses blood flow patterns and can help monitor vasospasm, but it doesn’t reliably detect aneurysm anatomy. Electroencephalography records electrical activity and provides no information about vascular structures or aneurysms.