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There is a midline lesion with solid and cystic components is centered upon the 4th ventricle arising from left roof and lateral wall, without extension through foramen of Luschka. The cystic component is seen to the left of the solid component, inferolaterally; its lateral rim does not enhance.
The mass bulges into and effaces the 4th ventricle, without evidence of hydrocephalus. No tonsillar herniation.
The mass is hypointense on T1, hyperintense on T2/FLAIR with pronounced diffusion restriction and vivid if slightly heterogeneous contrast enhancement.
Although no large flow voids are identified, on post contrast imaging there is some curvilinear intralesional enhancement that may be due to prominent vessels.
Spectroscopy shows a large choline peak with essentially absent NAA and no lactate peak.
CBV within the solid component is elevated.
Surrounding the mass is moderate T2 hyperintensity, presumably oedema.
Supratentorial brain is normal.
Posterior fossa tumour centered upon the 4th ventricle, without hydrocephalus. Origin from roof and lateral wall rather than floor would favour medulloblastoma over ependymoma.