Figure 7d. Medulloblastoma in a 4-year-old boy with a 2-week history of headaches and vomiting. (a) Axial CT image shows a heterogeneous mass in the posterior fossa midline. Soft-tissue portions are hyperattenuated whereas more cystlike areas are hypoattenuated. (b) On an axial T1-weighted MR image, the mass has similar heterogeneity. (c) Axial T2-weighted MR image demonstrates mild hyperintensity of the soft-tissue section and marked hyperintensity of the cystlike compartment. Note that the signal intensity of the cystlike portion (arrows) is even more intense than that of CSF, indicating that it is not simple fluid. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement within the soft-tissue segment.