According to a comprehensive review the overall incidence of cerebellar mutism (CM) in children with posterior fossa tumors is 11-29% , but numbers vary considerably depending on definitions used and tumor types studied . In a large multicenter study the incidence ofCMS (old definition of CM, ataxia, hypotonia and irritability) for children with medulloblastoma only was 24% . According to a recent, prospective study of 148 pediatric posterior fossa tumor patients the overall incidence of the PFS was 28% (note the broad definition). Sub-divided by tumor pathology it was 40% for medulloblastoma, 16% for pilocytic astrocytoma and 4% for ependymoma .
Generally speaking, narrow definitions (e.g. CM or TCM) and retrospective studies render lower incidence figures than broader definitions (e.g. CMS or PFS) and prospective studies . Until recently, there existed no international consensus on these matters; thus the results of previous studies cannot easily be compared. The new definition of post-operative pediatric CMS has not been implemented yet.
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