Patient Data
Large hyperdense posterior fossa mass, with significant positive mass effect on the brain stem and fourth ventricle resulting in lateral and third ventricular dilatation with periventricular low density, in keeping with transependymal spread of CSF.
Case Discussion
The patient went on to have a resection.
Histology
Several tissue fragments that are diffusely infiltrated by a densely cellular neoplasm consisting of closely packed tumor cells with increased nuclear/cytoplasmic ratio, oval, round or carrot-shaped hyperchromatic nuclei and scant cytoplasm. The tumor cells form diffuse sheets with no pattern differentiation. There are numerous apoptotic nuclei. In some areas, the tumor cells tend to display clear cytoplasm around central round nuclei. The mitotic activity varies, being frequent in some parts of the tumor and less conspicuous in others. Most tumor cells are strongly immunoreactive for synaptophysin and there are frequent areas of intense immunoreactivity for neuron-specific enolase (NSE). Staining for neurofilament protein is negative. A few GFAP-positive reactive astrocytes are seen scattered in the tumor. The MIB-1 stain shows many cells in the mitotic cycle.
Final Diagnosis: medulloblastoma.