Medulloblastoma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Haytham Allaham, M.D. [2]

Pathogenesis

• Medulloblastoma arises from cerebellar stem cells, which are normally involved in the anatomical development of the cerebellum and other posterior fossa structures.
• Medulloblastoma is usually located at the infratentorial region, where it forms a mass between the brain stem and the cerebellum in the vicinity of the fourth ventricle.
• Medulloblastoma is an invasive and rapidly growing tumor.
• Unlike most brain tumors, medulloblastoma may spread through the cerebrospinal fluid (CSF) and frequently metastasize to different organs of the body.
• Medulloblastoma is often associated with gorlin syndrome and turcot syndrome.

Genetics

• Development of medulloblastoma is the result of multiple genetic mutations.
• Genes involved in the pathogenesis of medulloblastoma include:

• CTNNB1 gene on chromosomes 3
• PTCH1 gene located on chromosome 9
• MLL2 gene located on chromosome 12
• SMARCA4 gene located on chromosome 19
• DDX3X gene located on X chromosome
• CTDNEP1 gene located on chromosome 17
• KDM6A gene located on X chromosome
• TBR1 gene located on chromosome 2

• The progression to medulloblastoma usually involves the P53 molecular pathway.

Gross Pathology

Histologically, the tumor is solid, pink-gray in color, and is well circumscribed.

Mircoscopic Pathology

• The tumor is very cellular, many mitoses, little cytoplasm, and has the tendency to form clusters and rosettes.

• Small round cell tumour, Homer-Wright rosettes: , Rosette with a meshwork of fibers (neuropil) at the centre.

• Shown below is a series of microscopic images observed in medulloblastoma:

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  Medulloblastoma smear

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  Medulloblastoma smear

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  Medulloblastoma smear demonstrating Homer-Wright rosettes

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  Medulloblastoma smear demonstrating cerebellar infiltrative growth

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  Medullloblastoma smear demonstrating demsomplastic nodular growth

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  Anaplastic large cell medulloblastoma smear

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  Medulloblastoma smear

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  Desmoplastic medulloblastoma smear on reticulin stain demonstrating "pale islands"

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  Desmoplastic medulloblastoma on MIB-1 immunostaining

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  Medulloblastoma smear demonstrating areas of geographic necrosis

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  Medulloblastoma smear demonstrating epitheloid ribboning and nuclear moulding of tumor cells

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  Medulloblastoma smear demonstrating partial MAP2 immunoreactivity

References

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