AnswerThe patient had a myelogram performed in 1970. At that time, myelograms were performed using Pantopaque contrast agent, a mixture of iodinated esters with an oily consistency. Small droplets of the contrast agent would frequently linger in the subarachnoid space and remain visible even decades after injection. Intracranial Pantopaque may be observed on head CT as hyperdense droplets along the subarachnoid space. Pantopaque has a higher attenuation coefficient than thrombus, allowing it to be distinguished from thrombosed aneurysms. The MRI appearance of Pantopaque may be particularly confusing, but fat saturation pulses may help differentiate Pantopaque from intraluminal clots. Reference 1. Milov MW, Silvers AR, Mosesson RE, et al. Pantopaque simulating thrombosed intracranial aneurysms on MRI.