CORRELATION OF MICROANATOMICAL LOCALIZATION WITH POSTOPERATIVE SURVIVAL IN POSTERIOR-FOSSA EPENDYMOMAS

TWENTY-TWO SURGICALLY TREATED infratentorial ependymomas were analyzed according to their anatomical origins and characteristics of extension in conjunction with the microsurgical anatomy of the fourth ventricle. The correlation between tumor origin and postoperative survival of the patients was also assessed. The tumors were classified into three types according to their origins and extensions: 1) midfloor-type: tumors originating from the caudal half of the fourth ventricular floor beneath the striae medullares. After occupying the fourth ventricular cavity, they extended downward through the foramen Magendie to the upper cervical level. 2) Lateral type: tumors arising from the vestibular area and/or the lateral recess. They grew not only inferiorly but also laterally to the cerebellomedullary cistern through the cerebellomedullary fissure and the foramen of Luschka. 3) Roof type: tumors originating from the roof of the ventricle. The overall cumulative survival rates at 2, 5, and 10 years were 84, 62, and 47%, respectively. Interestingly, the lateral-type tumors showed a significantly lower 5-year cumulative survival rate and mean survival time (21% and 40 months) when compared with midfloor-type tumors (73% and 170 months). Because the tumor originates near the vital neural structures and because each type has characteristics of extension, a clear knowledge of the microanatomical relationship between the tumor and the surrounding structures would be of great benefit for improving the operative outcome of posterior fossa ependymomas.