Medulloblastoma
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- Medulloblastoma is the most common malignant brain tumor in children; it is a genetically defined embryonal cell tumor (2016 revised World Health Organization classification)
- 80% occur between ages 1 and 10
- Most arise from the cerebellar vermis and extend into the fourth ventricle; less commonly they can occur in young adults and arise from the cerebellar hemispheres
- Composed of densely packed, small round cells, medulloblastomas have relatively high density on CT studies and show reduced diffusion on MRI compared with other posterior fossa tumors
- On MRI, the tumor can present with variable T1 and T2 intensities and enhancement patterns, cyst formation, areas of hemorrhage or calcification, and leptomeningeal tumor seeding
- The tumors can be well-defined or ill-defined
- Medulloblastomas have a very high tendency to disseminate via the CSF to other parts of the brain, ventricles, and spinal canal; up to one-third of patients have dissemination at presentation
- Medulloblastoma is one of the rare brain tumors that can also have metastases outside of the CNS, although this is rare with current therapies
- Because of the tumor’s tendency for CSF dissemination, contrast-enhanced MRI of the entire spine is integral to the imaging work-up and follow-up
- The key to these tumors is the restricted diffusion with low ADC values, distinguishing them from ependymomas and pilocytic astrocytomas in children
- Koeller KK, Rushing EJ. From the archives of the AFIP: medulloblastoma: a comprehensive review with radiologic-pathologic correlation. RadioGraphics 2003; 23(6):1613-1637
- Yeom KW, Mobley BC, Lober RM, et al. Distinctive MRI features of pediatric medulloblastoma subtypes. American Journal of Radiology 2013; 200:895-903
- Shih RY, Koeller KK. Embryonal Tumors of the Central Nervous System. RadioGraphics 2018; 38:525–541
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