A 32-year-old man with a fourth ventricular mass.

Lipoastrocytomas are rare and only four cases have been reported previously. Our case is in the fourth ventricle of a 32 year-old man.Many areas showed tumor cells with a signet-ring appearance and focally formed perivascular arrangements. Eosinophilic granular bodies were frequent. There was strong positive immunoreactivity to GFAP and S-100 protein, even in those vacuolated tumor cells.The proliferation index was less than 10%. Ultrastructural studies showed that the signet-ring cells had large lipid droplets as well as intermediate filaments. Ultrastructural features characteristic of ependymomas were not seen. These findings confirm that the vacuoles were lipid droplets in astrocytic tumor cells. The features noted are suggestive of a probable better prognosis in this variant of low-grade astrocytoma.