Extra-axial tumours of the posterior fossa in children

The posterior fossa is the most common site of CNS tumours in children. Although extra-axial tumours in the posterior cranial fossa predominate over intra-axial neoplasms in adults, only 13 (5.6%) out of 231 children observed at our institution, presented tumours in an extra-axial location. The tumours most frequently encountered were dysontogenetic masses (dermoid, lipoma, teratoma) in six children (40%), chordoma in the clivus, neurinoma (extremely rare as an isolated lesion, more frequent in children with neurofibromatosis II, in itself rare in childhood), cavernous angioma, meningeal sarcoma, desmoplastic medulloblastoma and the highly aggressive atypical teratoid/rhabdoid tumour, only recently characterised as a separate entity. The main neuroradiological features of these tumours are described with a view to identifying reliable hallmarks for differential diagnosis.