Methemoglobin clot is visualized medially within a focal aneurysmal dilatation of the basilar artery on axial and coronal T1-weighted scans. Evaluation of axial T2-weighted and DWI scans reveals a small acute infarct, located within the brainstem just medial to the clot, and presumed to be secondary to occlusion of small paramedian penetrating branches from the basilar artery.

Part of the on-line supplement to Neuroradiology – The Essentials with MR and CT (© 2015)