A patient is presented in whom iophendylate (Pantopaque) within the ba
sal cisterns closely resembled the appearance on MRI of thrombosed ane
urysms of the middle cerebral arteries. The sometimes subtle differenc
es between the appearances on MRI of Pantopaque and aneurysmal clot ar
e discussed to permit accurate diagnosis without resorting to more inv
asive diagnostic tests, such as cerebral angiography.