Improved localization of infratentorial ependymoma by magnetic resonance imaging: implications for radiation treatment planning.

Ependymomas of the posterior fossa extend into the upper cervical spinal cord in approximately one-third of cases. Unfortunately, the posterior fossa and upper cervical cord region is often poorly seen on computed tomography (CT), making radiotherapy planning difficult. We report five cases of posterior fossa ependymoma with extension into the cervical cord where magnetic resonance imaging (MRI) demonstrated the caudal extent of tumor more clearly than CT. The extent of tumor depicted by MRI in each case correlated well with the operative findings. Higher doses of radiotherapy to the entire tumor volume are associated with improved survival in infratentorial ependymoma; however, the radiation tolerance of the cervical spinal cord is close to the dose necessary to control posterior fossa ependymoma, making limitation of radiation field volumes important. MRI may provide a method of precisely defining caudal tumor extent of posterior fossa ependymomas so that limited volume, high dose radiotherapy can be more safely administered to these patients.