Childhood medulloblastomas, which form primarily in the cerebellum, are the most common type of malignant brain tumor among children. The standard treatment for children with medulloblastoma usually involves a combination of craniotomy, tumor removal, radiation therapy and/or chemotherapy. For children who also have hydrocephalus, treatment can also include ventriculostomy or shunt placement.
The World Health Organization grades tumors on a scale of one to four, with Grade 1 being the least aggressive and Grade 4 the most. Childhood medulloblastomas, known for growing quickly and having the potential to metastasize to other areas, are Grade 4.
Childhood medulloblastomas are located in the cerebellum, and as they grow, they can expand into one of the ventricles. There, circulating cerebrospinal fluid can pick up malignant tumor cells from the medulloblastoma and transport them to other areas in the brain and spinal cord. Medulloblastomas rarely metastasize to parts of the body other than the brain or spinal cord, but if they do, bone is the most likely destination.
Childhood medulloblastomas develop from embryonal cells that accidentally remained in the brain beyond early development. Normally, embryonal cells mature into specialized cells and tissue, but rarely, they can become trapped in a certain part of the body—for instance, the brain—and develop into a tumor. Researchers continue to investigate the exact type, or types, of embryonal cells from which medulloblastomas arise.
Originally believed to be one disease, childhood medulloblastomas are now known to be a complex set of diseases composed of several subtypes. This knowledge has refined the treatment approaches and improved prognosis for children with medulloblastomas.
Childhood medulloblastomas were initially categorized according to histology characteristics, which can be identified in tissue samples under a microscope. There are seven histologic types:
The latest research has gone one step past histologic types to identify four genetic subgroups: WNT, SHH, Group 3 and Group 4. WNT and SHH are named after cell pathways WNT and SHH, in which the respective mutations occur. Groups 3 and 4 have not been named according to which genes are mutated; research is still establishing the full genetic basis of these subtypes. Group 3 and Group 4 differ by the aggressiveness of the disease and age of occurrence. Research continues into these four subgroups and how the genetic characteristics of each overlap with the histologic types.
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