Transmural passage of subarachnoid metrizamide into a cystic acoustic schwannoma of the cerebellopontine angle: a diagnostic dilemma.

CT metrizamide cisternography performed in a patient with a non-enhancing cerebellopontine angle tumour demonstrated an increase in attenuation within the cystic area between the immediate scan and that undertaken 4 h later indicating delayed inward diffusion of the contrast. At operation the tumour was found to be a cystic acoustic schwannoma of the cerebellopontine angle. Diffusion of metrizamide was not previously been reported across the wall of a cystic tumour.