Teaching NeuroImages: High-resolution MRI before and during a sentinel headache demonstrates aneurysm wall hemorrhage.

A 3T brain MRI, performed in a 48-year-old woman presenting with progressive headaches, demonstrated a 20-mm unruptured saccular basilar artery aneurysm. High-resolution vessel-wall MRI showed a chronic mural thrombus and a circumferential aneurysm wall enhancement (figure), an imaging marker of aneurysm instability.1 Two days later, she had a transient thunderclap headache, considered the worst headache she had ever reported. Repeated 3T MRI demonstrated acute mural hemorrhage without subarachnoid hemorrhage. Sentinel headaches, reported in every fourth patient preceding aneurysm rupture,2 have been interpreted as reflecting a warning for subarachnoid leak or, alternatively, structural wall changes, such as stretching or acute mural hemorrhage.