Sixty-eight cases of metastases affecting 34 patients were studied by computerized tomography (CT) before and after the injection of an iodinated contrast medium. CT data provided a diagnosis in most cases. After injection of the contrast medium, a ring aspect was found in half the cases. This morphological feature is a sign of blood-brain barrier impairment crossed by the contrast medium. The low density area inside the ring is not caused by central necrosis, nor is it caused by too little contrast medium. The increase in density is a sign of extra-vascular loss of iodinated molecules in the peritumoral cerebral tissue. Performance of CT should be improved using specific tracers of the tumoral cells.