Increasing headaches and unsteadiness.
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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 edema.
Supratentorial brain is normal.
Posterior fossa tumor centered upon the 4th ventricle, without hydrocephalus. Origin from roof and lateral wall rather than floor would favor medulloblastoma over ependymoma.
The patient went on to have a resection.
MICROSCOPIC DESCRIPTION: Paraffin sections show fragments of a densely hypercellular tumor. Tumor is seen to expand cerebellar white matter and extend through cerebellar cortex in specimen 2. Prominence of an external granular layer containing atypical cells is also noted. Tumor cells have overlapping and moulded pleomorphic hyperchromatic nuclei and delicate processes. Moderately well-formed Homer-Wright rosettes are identified in many areas. There are frequent mitotic figures. No necrosis is seen.
Immunohistochemistry shows strong diffuse staining in tumor cells for synaptophysin and beta-tubulin. No staining for GFAP or epithelial membrane antigen (EMA) is seen in tumor cells. The topoisomerase labeling index is approximately 60%. Patchy moderate nuclear staining in tumor cells for YAP-1, moderate cytoplasmic staining for GAB1 and strong perinuclear and membrane staining for beta-Catenin. No nuclear staining for beta-Catenin is seen. Nuclear staining for INI-1 is preserved.
This immunophenotype is most consistent with Group 2 (Sonic Hedgehog; SHH) medulloblastoma.
FINAL DIAGNOSIS: Medulloblastoma (WHO Grade IV) Group 2 (Sonic Hedgehog; SHH)