Two cases of epidermoid in the fourth ventricle with characteristic findings of metrizamide CT cisternography

Two cases of epidermoid in the fourth ventricle with characteristic findings of metrizamide CT sisternography (M-CT) were reported. The M-CT findings of the two cases showed a cauliflower-like, irregular, high-density lesion in the low-density area which was not observd in the conventional enhanced CT. In one case, the characteristic finding was observed in the M-CT after the injection of metrizamide through a spinal puncture. In the other case, however, the finding was obtained only when metrizamide was administered in the lateral ventricle through the shunt valve. After the injection of metrizamide into the lateral ventricle through the shunt valve in one case, the concentration of metrizamide in the small irregular cyst of the epidermoid was measured during the operation. A high concentration of metrizamide was observed in the cyst fluid; this proved that metrizamide could enter the cyst through the tumor capsule. The irregular, high-density lesion in the low-density area observed in the M-CT seemed to be a pathognomonic finding with regard to intracranial epidermoids. (author)